WO2016061410A1 - Three-port piezoelectric ultrasonic transducer - Google Patents
Three-port piezoelectric ultrasonic transducer Download PDFInfo
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- WO2016061410A1 WO2016061410A1 PCT/US2015/055825 US2015055825W WO2016061410A1 WO 2016061410 A1 WO2016061410 A1 WO 2016061410A1 US 2015055825 W US2015055825 W US 2015055825W WO 2016061410 A1 WO2016061410 A1 WO 2016061410A1
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
- B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
- B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
- B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
- B06B1/06—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction
- B06B1/0607—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using multiple elements
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
- B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
- B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
- B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
- B06B1/0207—Driving circuits
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06V—IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
- G06V40/00—Recognition of biometric, human-related or animal-related patterns in image or video data
- G06V40/10—Human or animal bodies, e.g. vehicle occupants or pedestrians; Body parts, e.g. hands
- G06V40/12—Fingerprints or palmprints
- G06V40/13—Sensors therefor
- G06V40/1306—Sensors therefor non-optical, e.g. ultrasonic or capacitive sensing
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/18—Methods or devices for transmitting, conducting or directing sound
- G10K11/26—Sound-focusing or directing, e.g. scanning
- G10K11/34—Sound-focusing or directing, e.g. scanning using electrical steering of transducer arrays, e.g. beam steering
- G10K11/341—Circuits therefor
- G10K11/346—Circuits therefor using phase variation
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
- B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
- B06B2201/00—Indexing scheme associated with B06B1/0207 for details covered by B06B1/0207 but not provided for in any of its subgroups
- B06B2201/20—Application to multi-element transducer
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
- B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
- B06B2201/00—Indexing scheme associated with B06B1/0207 for details covered by B06B1/0207 but not provided for in any of its subgroups
- B06B2201/50—Application to a particular transducer type
- B06B2201/55—Piezoelectric transducer
Definitions
- This disclosure relates to piezoelectric transducers and to techniques for fabricating and operating piezoelectric transducers, and more particularly to a piezoelectric ultrasonic transducer suitable for use in an electronic sensor array or interactive display for biometric sensing, imaging, and touch or gesture recognition. DESCRIPTION OF THE RELATED TECHNOLOGY
- Thin film piezoelectric acoustic transducers are attractive candidates for numerous applications including biometric sensors such as fingerprint sensors, gesture detection, microphones and speakers, ultrasonic imaging, and chemical sensors.
- biometric sensors such as fingerprint sensors, gesture detection, microphones and speakers, ultrasonic imaging, and chemical sensors.
- Such transducers may include piezoelectric micromechanical ultrasonic transducers
- PMUTs configured as a multilayer stack that includes a piezoelectric layer stack and a mechanical layer disposed over a cavity.
- the piezoelectric layer stack may include a layer of piezoelectric material.
- a respective upper and lower electrode layer may be disposed on or proximate to each of an upper and a lower surface of the piezoelectric layer.
- the electrode layers may be patterned or unpatterned.
- a piezoelectric ultrasonic transducer 100 may be configured such that it includes a piezoelectric layer stack 110 and a mechanical layer 130 disposed so as to form a diaphragm supported by the anchor structure 170 over a cavity 120.
- the piezoelectric layer stack 110 includes a piezoelectric layer 115 with associated lower electrode 112 and upper electrode 114 disposed, respectively, below and above the piezoelectric layer 115.
- the cavity 120 may be formed in a
- semiconductor substrate 160 such as, for example, a silicon wafer, a silicon-on- insulator (SOI) wafer, or as a glass or polymer substrate with thin film transistor (TFT) circuitry.
- the piezoelectric layer stack 110 and mechanical layer 130 may be caused to vibrate in response to a time-varying excitation voltage applied across lower electrode 112 and upper electrode 114 by transceiver circuitry 1010.
- one or more ultrasonic pressure waves 122 having frequencies in, for example, an ultrasonic frequency band, may be propagated into a propagation medium 124.
- the propagation medium 124 may include air, a platen, a cover glass, a device enclosure, or an acoustic coupling or matching layer.
- the piezoelectric layer stack 110 may likewise receive reflected ultrasonic pressure waves from an object in the propagation medium, and convert the received ultrasonic pressure waves into electrical signals that may be read by transceiver circuitry 1010.
- One innovative aspect of the subject matter described in this disclosure relates to a method that includes: transmitting, during a first time period, responsive to signals from transceiver circuitry, first ultrasonic signals by way of a first electrode of a piezoelectric micromechanical ultrasonic transducer (PMUT), the PMUT including a diaphragm disposed over a cavity, the diaphragm including a piezoelectric layer stack including a piezoelectric layer, the first electrode and a second electrode, each of the first electrode and the second electrode being electrically coupled with the transceiver circuitry; and receiving, during a second time period, second ultrasonic signals by way of the second electrode.
- the first time period and the second time period are at least partially overlapping.
- the PMUT may be configured to simultaneously transmit first ultrasonic signals by way of the first electrode and to receive second
- each of the first electrode and the second electrode is disposed on or proximate to a first surface of the piezoelectric layer, the first surface being opposite from the cavity.
- the first electrode may be disposed in an inner portion of the diaphragm and the second electrode is disposed in an outer portion of the diaphragm, the outer portion being proximal to a wall of the cavity and between the wall and the first electrode.
- a portion of the second electrode may extend beyond the wall of the cavity.
- the diaphragm includes a third electrode, the third electrode being disposed between the piezoelectric layer and the cavity.
- the third electrode may be configured as a reference electrode in common with each of the first electrode and the second electrode.
- a voltage of the reference electrode may be clamped to ground or other reference voltage.
- the diaphragm may be supported by an anchor structure and may extend over the cavity, the diaphragm being configured to undergo one or both of fiexural motion and vibration and operate in a first fiexural mode when the PMUT receives or transmits ultrasonic signals.
- each of the first and second electrodes may experience a respective first and second oscillating load cycle that includes alternating periods of tensile and compressive stress.
- the first and second oscillating load cycles may be approximately in phase.
- the first and second oscillating load cycles may be out of phase.
- the first and second oscillating load cycles may be 180° out of phase.
- the second electrode may be configured to be in a transmit mode during the first time period and in a receive mode during the second time period.
- an apparatus includes a piezoelectric micromechanical ultrasonic transducer (PMUT), the PMUT including: a diaphragm disposed over a cavity, the diaphragm including a piezoelectric layer stack including a piezoelectric layer, a first electrode electrically coupled with transceiver circuitry, and a second electrode electrically coupled with the transceiver circuitry.
- the first electrode is disposed in a first portion of the diaphragm
- the second electrode is disposed in a second portion of the diaphragm, the first portion being separated from the first portion.
- Each of the first electrode and the second electrode is disposed on or proximate to a first surface of the piezoelectric layer, the first surface being opposite from the cavity.
- the PMUT is configured to transmit first ultrasonic signals by way of the first electrode during a first time period and to receive second ultrasonic signals by way of the second electrode during a second time period, the first time period and the second time period being at least partially overlapping.
- the second electrode may be disposed proximal to a wall of the cavity and between the wall and the first electrode. In some examples, a portion of the second electrode may extend beyond the wall of the cavity.
- the PMUT may be configured to simultaneously transmit first ultrasonic signals by way of the first electrode and to receive second ultrasonic signals by way of the second electrode.
- the diaphragm may include a third electrode, the third electrode being disposed between the piezoelectric layer and the cavity.
- the first electrode is a transmit electrode
- the second electrode is a receive electrode
- the third electrode is configured as a reference electrode in common with each of the transmit electrode and the receive electrode.
- the diaphragm may include a mechanical layer, the mechanical layer being positioned between the piezoelectric layer stack and the cavity or positioned on a side of the piezoelectric layer stack opposite the cavity.
- the apparatus may further include an anchor structure disposed over a substrate, wherein the diaphragm is supported by the anchor structure and extends over the cavity, the diaphragm being configured to undergo one or both of flexural motion and vibration when the PMUT receives or transmits ultrasonic signals.
- the diaphragm may be configured as an elongated rectangle having a longitudinal dimension of length L and a width of W, L being at least two times W.
- the anchor structure may support the diaphragm at a first discrete location that is proximal to a proximal end of the longitudinal dimension and at a second discrete location of the diaphragm that is proximal to a distal end of the longitudinal dimension.
- the anchor structure may support the diaphragm in a central portion of the diaphragm.
- the anchor structure may support the diaphragm in a peripheral region of the diaphragm.
- the diaphragm may be substantially circular.
- the anchor structure may support the diaphragm in a central portion of the diaphragm.
- the cavity may be formed by removing a sacrificial material through at least one release hole.
- the release hole may be disposed through the diaphragm.
- the first electrode and the second electrode may be approximately coplanar.
- an apparatus includes an array of piezoelectric micromechanical ultrasonic transducer (PMUT) sensors and an acoustic coupling medium.
- PMUT piezoelectric micromechanical ultrasonic transducer
- At least one PMUT includes a diaphragm disposed over a cavity, the diaphragm including a piezoelectric layer stack including a piezoelectric layer, a first electrode electrically coupled with a transceiver circuitry, and a second electrode electrically coupled with the transceiver circuitry.
- the first electrode is disposed in a first portion of the diaphragm
- the second electrode is disposed in a second portion of the diaphragm, the first portion being separated from the second portion.
- Each of the first electrode and the second electrode is disposed on or proximate to a first surface of the piezoelectric layer, the first surface being opposite from the cavity.
- the PMUT is configured to transmit first ultrasonic signals by way of the first electrode during a first time period and to receive second ultrasonic signals by way of the second electrode during a second time period, the first time period and the second time period being at least partially overlapping.
- the acoustic coupling medium is disposed above the piezoelectric layer stack.
- the PMUT is configured to receive or transmit ultrasonic signals through the acoustic coupling medium.
- the array of PMUT sensors may include a platen, wherein the acoustic coupling medium is disposed between the PMUT sensors and the platen.
- the PMUT may be configured to simultaneously transmit first ultrasonic signals by way of the first electrode and to receive second ultrasonic signals by way of the second electrode.
- the diaphragm may include a third electrode, the third electrode being disposed between the piezoelectric layer and the cavity.
- the first electrode may be a transmit electrode
- the second electrode may be a receive electrode
- the third electrode may be configured as a reference electrode in common with each of the transmit electrode and the receive electrode.
- the array of PMUT sensors may be configured as an ultrasonic fingerprint sensor array.
- a non-transitory computer readable medium has software stored thereon, the software including instructions for causing an apparatus to: transmit, during a first time period, responsive to signals from transceiver circuitry, first ultrasonic signals by way of a first electrode of a piezoelectric micromechanical ultrasonic transducer (PMUT), the PMUT including a diaphragm disposed over a cavity, the diaphragm including a piezoelectric layer stack including a piezoelectric layer, the first electrode and a second electrode, each of the first electrode and the second electrode being electrically coupled with the transceiver circuitry; and receive, during a second time period, second ultrasonic signals by way of the second electrode.
- the first time period and the second time period are at least partially overlapping.
- Figures 1A-1B illustrate an example of a piezoelectric ultrasonic transducer.
- Figures 2A-2C illustrate cross-sectional views of various configurations of PMUT ultrasonic sensor arrays.
- Figure 3 depicts signal waveforms representative of transmitted and received ultrasonic signals as a function of time.
- Figures 4A and 4B illustrate, respectively, a cross-sectional view and a plan view of a three-port PMUT, according to some implementations.
- Figure 5 illustrates an arrangement of a three-port PMUT coupled with transceiver circuitry.
- Figure 6 illustrates a plot of transmit and receive voltage signals as a function of time for a three-port PMUT, according to some implementations.
- Figure 7 illustrates another arrangement of a three-port PMUT, according to some implementations.
- Figure 8 illustrates example configurations of a long rectangular diaphragm for a three-port PMUT, according to some implementations.
- Figure 9 illustrates further example configurations of a long rectangular diaphragm for a three-port PMUT, according to some implementations.
- Figure 10 illustrates yet further example configurations of a long rectangular diaphragm for a three-port PMUT, according to some implementations.
- Figures 1 lA-11C illustrate example configurations of a circular diaphragm for a three-port PMUT, according to various implementations.
- Figure 12 illustrates an example of a method for operating a PMUT sensor, according to some implementations.
- Figures 13A-13D illustrate plan views of a three-port PMUT with a circular diaphragm and various electrode configurations, according to some implementations .
- Figures 14A-14D illustrate plan views of a three-port PMUT with a circular diaphragm having various electrode configurations and a center release hole, according to some implementations.
- Figure 15 illustrates a block diagram of a method for operating a PMUT sensor having at least one dedicated receive electrode, according to some
- Figure 16 illustrates a schematic diagram of transceiver circuitry and various configurations of a three-port PMUT with at least one dedicated receive electrode, according to some implementations.
- Figure 17 illustrates a plot of push-pull transmit signals and illustrative receive signals as a function of time for a three-port PMUT with at least one dedicated receive electrode, according to some implementations.
- Figure 18 illustrates a block diagram of a method for operating a PMUT sensor having at least one switchable transmit/receive electrode, according to some implementations .
- Figure 19 illustrates a schematic diagram of transceiver circuitry and various configurations of a three-port PMUT with at least one switchable
- Figure 20 illustrates a plot of push-pull transmit signals and illustrative receive signals as a function of time for a three-port PMUT with at least one switchable transmit/receive electrode, according to some implementations.
- the described implementations may be included in or associated with a variety of electronic devices such as, but not limited to: mobile telephones, multimedia Internet enabled cellular telephones, mobile television receivers, wireless devices, smartphones, Bluetooth® devices, personal data assistants (PDAs), wireless electronic mail receivers, hand-held or portable computers, netbooks, notebooks, smartbooks, tablets, handwriting digitizers, fingerprint detectors, printers, copiers, scanners, facsimile devices, global positioning system (GPS) receivers/navigators, cameras, digital media players (such as MP3 players), camcorders, game consoles, wrist watches, clocks, calculators, television monitors, flat panel displays, electronic reading devices (e.g., e-readers), mobile health devices, computer monitors, auto displays (including odometer and
- EMS electromechanical systems
- MEMS microelectromechanical systems
- non-EMS applications aesthetic structures (such as display of images on a piece of jewelry or clothing) and a variety of EMS devices.
- teachings herein also may be used in applications such as, but not limited to, electronic switching devices, radio frequency filters, sensors, accelerometers, gyroscopes, motion-sensing devices, fingerprint sensing devices, gesture recognition, magnetometers, inertial components for consumer electronics, parts of consumer electronics products, varactors, liquid crystal devices, electrophoretic devices, drive schemes, manufacturing processes and electronic test equipment.
- electronic switching devices radio frequency filters
- sensors accelerometers
- gyroscopes motion-sensing devices
- fingerprint sensing devices gesture recognition
- magnetometers magnetometers
- inertial components for consumer electronics, parts of consumer electronics products, varactors, liquid crystal devices, electrophoretic devices, drive schemes, manufacturing processes and electronic test equipment.
- the systems, methods and devices of the disclosure each have several innovative aspects, no single one of which is solely responsible for the desirable attributes disclosed herein.
- the subject matter described in this disclosure can be implemented in a piezoelectric micromechanical ultrasonic transducer (PMUT) certain aspects of which have been described in United States Patent Application No. 14/569,280, filed on December 12, 2014 and entitled "MICROMECHANICAL ULTRASONIC TRANSDUCERS AND DISPLAY," and in United States Patent Application No. 14/569,256, filed on December 12, 2014 and entitled
- PIEZOELECTRIC ULTRASONIC TRANSDUCER AND PROCESS each assigned to the assignee of the present invention and hereby incorporated by reference into the present application in its entirety for all purposes.
- a PMUT configured as a multilayer stack that includes a multilayer diaphragm structure that includes a piezoelectric layer stack and three or more electrodes.
- the three electrodes may include a separate electrode for each of transmitting signals to and receiving signals from associated transceiver circuitry, and a common reference or ground electrode.
- the arrangement allows transmit and receive timings to be independent of each other, thereby enabling, for example, simultaneous transmission and reception of ultrasonic waves.
- transmit and receive electrodes may be formed in the same electrode layer.
- each of the transmit electrode and the receive electrode may experience a differing orientation of mechanical stress or strain during bending.
- a first portion of the piezoelectric layer proximate to the first electrode may be under tension at the same time that a second portion of the piezoelectric layer proximate to the second electrode is under compression.
- a boundary or boundary region, that may be referred to as an "inflection zone" may be located between such portions of piezoelectric layer.
- a transmit/receive electrode may be positioned either to cover the tensile strain region of the piezoelectric layer or the compressive strain region of the piezoelectric layer, but not both.
- a portion of the PMUT device diaphragm is not used in typical two-port implementations.
- implementations of the three-port PMUT structure described hereinbelow where a transmit electrode and a separate receive electrode are positioned on opposite sides of the inflection zone, a greater portion of the PMUT device diaphragm is used, thereby improving efficiency of the device.
- the disclosed techniques may provide for electrical separation between the two electrodes such that transmit circuitry may be connected to the transmit electrode and separate receive circuitry may be connected to the receive electrode, removing the need for a time separation between operation in a transmit mode and operation in a receive mode.
- One innovative aspect of the subject matter described in this disclosure can be implemented in an apparatus that includes a one- or two-dimensional array of three-port piezoelectric micromechanical ultrasonic transducer (PMUT) elements positioned below, beside, with, on, or above a backplane of a display or an ultrasonic fingerprint sensor array.
- PMUT piezoelectric micromechanical ultrasonic transducer
- the PMUT array may be configurable to operate in modes corresponding to multiple frequency ranges.
- the PMUT array may be configurable to operate in a low-frequency mode corresponding to a low-frequency range (e.g., 50 kHz to 200 kHz) or in a high- frequency mode corresponding to a high-frequency range (e.g., 1 MHz to 25 MHz).
- a low-frequency mode corresponding to a low-frequency range (e.g., 50 kHz to 200 kHz) or in a high- frequency mode corresponding to a high-frequency range (e.g., 1 MHz to 25 MHz).
- an apparatus may be capable of imaging at relatively higher resolution. Accordingly, the apparatus may be capable of detecting touch, fingerprint, stylus, and biometric information from an object such as a finger placed on the surface of the display or sensor array.
- Such a high-frequency mode may be referred to herein as a fingerprint sensor mode.
- the apparatus When operating in the low- frequency mode, the apparatus may be capable of emitting sound waves that are capable of relatively greater penetration into air than when the apparatus is operating in the high-frequency mode.
- Such lower-frequency sound waves may be transmitted through various overlying layers including a cover glass, a touchscreen, a display array, a backlight, a housing or enclosure, or other layers positioned between an ultrasonic transmitter and a display or sensor surface.
- a port may be opened through one or more of the overlying layers to optimize acoustic coupling from the PMUT array into air.
- the lower- frequency sound waves may be transmitted through the air above the display or sensor surface, reflected from one or more objects near the surface, transmitted through the air and back through the overlying layers, and detected by an ultrasonic receiver. Accordingly, when operating in the low- frequency mode, the apparatus may be capable of operating in a gesture detection mode, wherein free-space gestures near but not necessarily touching the display may be detected.
- the PMUT array may be configurable to operate in a medium- frequency mode corresponding to a frequency range between the low-frequency range and the high-frequency range (e.g., about 200 kHz to about 1 MHz). When operating in the medium- frequency mode, the apparatus may be capable of providing touch sensor functionality, although with somewhat less resolution than the high-frequency mode.
- the PMUT array may be addressable for wavefront beam forming, beam steering, receive-side beam forming, and/or selective readout of returned signals. For example, individual columns, rows, sensor pixels and/or groups of sensor pixels may be separately addressable.
- a control system may control an array of transmitters to produce wavefronts of a particular shape, such as planar, circular or cylindrical wavefronts.
- the control system may control the magnitude and/or phase of the array of transmitters to produce constructive or destructive interference in desired locations.
- the control system may control the magnitude and/or phase of the array of transmitters to produce constructive interference in one or more locations in which a touch or gesture has been detected or is likely to be detected.
- PMUT devices may be co-fabricated with thin- film transistor (TFT) circuitry on the same substrate, which may be silicon, glass or plastic substrate in some examples.
- TFT substrate may include row and column addressing electronics, multiplexers, local amplification stages and control circuitry.
- an interface circuit including a driver stage and a sense stage may be used to excite a PMUT device and detect responses from the same device.
- a first PMUT device may serve as an acoustic or ultrasonic transmitter and a second PMUT device may serve as an acoustic or ultrasonic receiver.
- different PMUT devices may be capable of low- and high-frequency operation (e.g. for gestures and for fingerprint detection).
- the same PMUT device may be used for low- and high- frequency operation.
- the PMUT may be fabricated using a silicon wafer with active silicon circuits fabricated in the silicon wafer.
- the active silicon circuits may include electronics for the functioning of the PMUT or PMUT array.
- the PMUT array may be configured as an ultrasonic sensor array.
- Figures 2A-2C illustrate cross-sectional views of various configurations of PMUT ultrasonic sensor arrays.
- Figure 2 A depicts an ultrasonic sensor array 200a with PMUTs as transmitting and receiving elements that may be used, for example, as an ultrasonic fingerprint sensor, an ultrasonic touchpad, or an ultrasonic imager.
- PMUT sensor elements 262 on a PMUT sensor array substrate 260 may emit and detect ultrasonic waves. As illustrated, an ultrasonic wave 264 may be transmitted from at least one PMUT sensor element 262.
- the ultrasonic wave 264 may travel through an acoustic coupling medium 265 and a platen 290a towards an object 202 such as a finger or a stylus positioned on an outer surface of the platen 290a.
- a portion of the ultrasonic wave 264 may be transmitted through the platen 290a and into the object 202, while a second portion is reflected from the surface of platen 290a back towards the sensor element 262.
- the amplitude of the reflected wave may depend in part on the acoustic properties of the object 202.
- the reflected wave may be detected by the sensor elements 262, from which an image of the object 202 may be acquired.
- An acoustic coupling medium 265 such as an adhesive, gel, a compliant layer or other acoustic coupling material may be provided to improve coupling between an array of PMUT sensor elements 262 disposed on the sensor array substrate 260 and the platen 290a.
- the acoustic coupling medium 265 may aid in the transmission of ultrasonic waves to and from the sensor elements 262.
- the platen 290a may include, for example, a layer of glass, plastic, sapphire, metal, metal alloy, or other platen material.
- An acoustic impedance matching layer (not shown) may be disposed on an outer surface of the platen 290a.
- the platen 290a may include a coating (not shown) on the outer surface.
- Figure 2B depicts an ultrasonic sensor and display array 200b with PMUT sensor elements 262 and display pixels 266 co-fabricated on a sensor and display substrate 260.
- the sensor elements 262 and display pixels 266 may be collocated in each cell of an array of cells.
- the sensor element 262 and the display pixel 266 may be fabricated side-by-side within the same cell.
- part or all of the sensor element 262 may be fabricated above or below the display pixel 266.
- Platen 290b may be positioned over the sensor elements 262 and the display pixels 266 and may function as or include a cover lens or cover glass.
- the cover glass may include one or more layers of materials such as glass, plastic or sapphire, and may include provisions for a capacitive touchscreen.
- An acoustic impedance matching layer or coating (not shown) may be disposed on an outer surface of the platen 290b.
- Ultrasonic waves 264 may be transmitted and received from one or more sensor elements 262 to provide imaging capability for an object 202 such as a stylus or a finger placed on the cover glass 290b.
- the cover glass 290b is substantially transparent to allow optical light from the array of display pixels 266 to be viewed by a user through the cover glass 290b. The user may choose to touch a portion of the cover glass 290b, and that touch may be detected by the ultrasonic sensor array.
- Biometric information such as fingerprint information may be acquired, for example, when a user touches the surface of the cover glass 290b.
- An acoustic coupling medium 265 such as an adhesive, gel, or other acoustic coupling material may be provided to improve acoustic, optical and mechanical coupling between the sensor array substrate 260 and the cover glass.
- the coupling medium 265 may be a liquid crystal material that may serve as part of a liquid crystal display (LCD).
- LCD implementations a backlight (not shown) may be optically coupled to the sensor and display substrate 260.
- the display pixels 266 may be part of an amorphous light-emitting diode (AMOLED) display with light-emitting display pixels.
- AMOLED amorphous light-emitting diode
- the ultrasonic sensor and display array 200b may be used for display purposes and for touch, stylus or fingerprint detection.
- Figure 2C depicts an ultrasonic sensor and display array 200c with a sensor array substrate 260a positioned behind a display array substrate 260b.
- An acoustic coupling medium 265a may be used to acoustically couple the sensor array substrate 260a to the display array substrate 260b.
- An optical and acoustic coupling medium 265b may be used to optically and acoustically couple the sensor array substrate 260a and the display array substrate 260b to a cover lens or cover glass 290c, which may also serve as a platen for the detection of fingerprints.
- An acoustic impedance matching layer (not shown) may be disposed on an outer surface of the platen 290c.
- Ultrasonic waves 264 transmitted from one or more sensor elements 262 may travel through the display array substrate 260b and cover glass 290c, reflect from an outer surface of the cover glass 290c, and travel back towards the sensor array substrate 260a where the reflected ultrasonic waves may be detected and image information acquired.
- the ultrasonic sensor and display array 200c may be used for providing visual information to a user and for touch, stylus or fingerprint detection from the user.
- a PMUT sensor array may be formed on the backside of the display array substrate 260b.
- the sensor array substrate 260a with a PMUT sensor array may be attached to the backside of the display array substrate 260b, with the backside of the sensor array substrate 260a attached directly to the backside of the display array substrate 260b, for example, with an adhesive layer or adhesive material (not shown).
- each PMUT element while having a single diaphragm, functions as both a transmitter and a receiver of ultrasonic signals in order to improve efficiency, speed and resolution as well as to achieve integration and cost benefits.
- Figure 3 depicts examples of signal waveforms representative of transmitted and received ultrasonic signals as a function of time for a PMUT array with an approximately 400 micron thick platen positioned on top of the array.
- Figure 3 depicts a series of five tone burst (TB) cycles applied to a two-port PMUT (see top graph).
- the acoustic transmit power depicted in the second graph shows a build-up in acoustic energy in the sensor stack as additional tone burst cycles are applied.
- Typical ultrasonic transmitter signals may include a series of one or more tone burst (TB) cycles and the echo from the first cycle may arrive back at the receiver prior to completion of the tone burst cycles.
- outputted and returning ultrasonic signals may substantially overlap.
- a time interval between an outputted ultrasonic signal and a returning ultrasonic signal may be very small (less than about 0.2 ⁇ ), depending largely on the acoustic path length through the platen and the speed of sound of material in the acoustic path.
- additional echoes may occur, as depicted in the fourth and fifth graphs.
- the acoustic power from all of the reverberations are combined, illustrating the difficulty in detecting the most suitable peak for imaging an object positioned on the surface of the platen.
- a voltage output from the PMUT to the transceiver circuitry 1010 may be related to the amplitude of the ultrasonic signal at the PMUT.
- a receive signal envelope 310 shown in the bottom graph of Figure 3 depicts the buildup of the acoustic signal and the decay after the tone burst cycles have been discontinued.
- the transceiver circuity may need to switch from a transmit mode to a receive mode. Because a single pair of electrodes (e.g., lower electrode 112 and upper electrode 114 as shown in Figures 1 A-B) may be electrically coupled with transceiver circuitry 1010, a separation in time indicated by a switching interval time t s must be provided between transmitting signals and receiving signals from the electrode pair. The first measurable echo for this arrangement may occur after completion of the switching interval time t s . It will be appreciated that t s and the time for multiple tone burst cycles at least for a PMUT array sized for a fingerprint sensor can substantially exceed the roundtrip travel time of an ultrasonic signal.
- FIGS 4A and 4B illustrate a cross-sectional view and a plan view of a three-port PMUT, according to some implementations.
- PMUT 400 includes a piezoelectric layer stack 410 and a mechanical layer 430, configured to form a diaphragm 440, disposed over a cavity 420.
- the diaphragm 440 is supported by an anchor structure 470 over the cavity 420.
- the PMUT 400 may be configured to operate with the diaphragm 440 experiencing one or more flexural modes wherein the diaphragm 440 may undergo one or both of flexural motion and vibration when the PMUT transmits or receives ultrasonic signals.
- the piezoelectric layer stack 410 includes a piezoelectric layer 415 with an associated lower electrode 412 disposed below the piezoelectric layer 415.
- An inner electrode 413 is disposed above the piezoelectric layer 415 in a central region of the diaphragm 440.
- an outer electrode 414 is also disposed above the piezoelectric layer 415.
- the inner and outer electrodes, disposed on a surface of the piezoelectric layer 415, may be substantially coplanar.
- the outer electrode 414 may be electrically connected together by extending the outer electrode 414 partially or completely around the perimeter of the three-port PMUT 400 in one example.
- segmented outer electrodes 414 on the diaphragm 440 may be interconnected internally with one or more jumpers or externally with one or more electrical interconnects in another example (not shown).
- Contact and via structures may be used to make electrical contact with underlying or external pixel circuitry.
- the cavity 420 may be connected to one or more etch channels 422 and release holes 424 through which sacrificial material (not shown) may be removed by a suitable etchant to form the cavity 420.
- One or more plugs 426 of metal or other suitable material may be used to seal the release holes 424 and retain a controlled pressure (e.g. a vacuum level) inside the cavity 420 during PMUT operation.
- the PMUT shown in Figure 4B and elsewhere may be part of a PMUT array with one or more rows and columns (not shown), the dashed lines at the periphery of the plan view indicating that additional PMUTs formed on a common substrate may be positioned on one or more sides of the PMUT 400 as part of the PMUT array.
- a three-port PMUT may be configured as a PMUT with at least one transmit electrode, at least one receive electrode, and at least one reference electrode. Many of these variants are described below.
- An alternative and sometimes preferred interpretation of a three-port PMUT is a PMUT having an electrical input (Tx) port, an ultrasonic output port (serving also as an ultrasonic input port), and an electrical output (Rx) port.
- the electrical input port and the electrical output port may, respectively, physically and electrically separated and yet may be disposed on the same portion of the PMUT microstructure (e.g., on the diaphragm above the cavity).
- Figure 5 illustrates an arrangement of a three-port PMUT coupled with transceiver circuitry 510.
- the lower electrode 412, inner electrode 413 and outer electrodes 414 may be electrically coupled with transceiver circuitry 510 and may function as separate electrodes providing, respectively, signal transmission, signal reception, and a common reference or ground.
- This arrangement allows timing of transmit (Tx) and receive (Rx) signals to be independent of each other. More particularly, the illustrated arrangement enables substantially simultaneous transmission and reception of signals between piezoelectric ultrasonic transducer 400 and transceiver circuitry 510.
- transmit and receive electrodes may be formed in the same electrode layer during a common fabrication process of deposition, masking and etching, for example.
- one or more piezoelectric layers and associated electrode layers may be included in the piezoelectric stack (not shown).
- transceiver circuitry 510 may be electrically coupled with piezoelectric ultrasonic transducer 400 by way of three input/output terminals or ports associated with the transceiver circuitry 510 and three electrodes 412, 413 and 414 associated with the three-port PMUT. In the illustrated
- a first terminal or port is electrically coupled with the lower
- reference electrode 412 a second terminal or port is electrically coupled with the inner (transmit) electrode 413; and a third terminal or port is electrically coupled with the outer (receive) electrode(s) 414.
- portions of the piezoelectric layer 415 that are proximate to the outer electrodes 414 are in an opposite state of mechanical stress compared to portions of the piezoelectric layer 415 that are proximate to the inner electrode 413 during vibrations of the PMUT diaphragm. More particularly, at the instantaneous moment illustrated in Figure 5, portions of the piezoelectric layer 415 that are proximate to the outer electrode 414 are in compression, whereas portions of the piezoelectric layer 415 that are proximate to the inner electrode 413 are in tension.
- the arrangement may use a difference in the mechanical strain direction on an inside area of the diaphragm compared to an outside area of the diaphragm to improve transmitter and receiver efficiency.
- the PMUT cavity 420 is circular
- the diaphragm 440 disposed over the PMUT cavity 420 the "suspended portion" of diaphragm 440
- an inflection zone exists at about 60-70% of the cavity radius, i.e. the stress direction on the same side (e.g. top or bottom) of the piezoelectric layer stack 410 is of opposite sense on either side of the inflection zone.
- transmitter and receiver efficiencies may be improved by positioning the outer perimeter of the inner electrode 413 and the inner perimeter of the outer electrode 414 close to the inflection zone. For other shapes such as rectangular or square diaphragms, a similar approach may be applied to optimize the electrode shapes.
- An outer edge of the outer electrode 414 may be substantially aligned with a perimeter of the cavity 420 or may (as illustrated) extend beyond the walls of the cavity 420.
- the PMUT diaphragm may be supported by an anchor structure 470 that allows the diaphragm to extend over the cavity 420.
- the diaphragm may undergo fiexural motion when the PMUT receives or transmits ultrasonic signals.
- the PMUT diaphragm may operate in a first fiexural mode when receiving or transmitting ultrasonic signals.
- the inner and outer electrodes when operating in the first flexural mode, may experience a respective first and second oscillating load cycle that includes alternating periods of tensile and compressive stress.
- the first and second oscillating load cycles may be out of phase, that is, one being tensile while the other is compressive on each side of the inflection zone, as shown in Figure 5.
- the first and second oscillating load cycles may be approximately 180° out of phase.
- the first and second oscillating load cycles may be approximately in phase.
- the receive electrode may be operable to receive ultrasonic signals while the transmit electrode is emitting ultrasonic signals.
- Figure 6 illustrates a plot of transmit and receive voltage signals as a function of time for a three-port PMUT, according to some implementations.
- the present invention allows substantially simultaneous reception and transmission of voltage signals.
- a large echo e.g., 1 st echo
- the reflections of ultrasonic waves from an object being imaged such as a finger may significantly overlap with the tone burst signal, allowing a build-up of acoustic energy that varies with the presence of a fingerprint ridge or a fingerprint valley on a surface of a PMUT sensor array, as shown by the receive signal envelope 610.
- a further advantage of the presently disclosed techniques is that, compared to a two-port PMUT, the three-port PMUT transceiver may have a single lower electrode positioned below the transmit and receive electrodes that is connected to a reference voltage such as a ground potential.
- Grounding the lower electrode or otherwise connecting the lower electrode to a low impedance voltage source may reduce electrical crosstalk between transmit and receive portions of the transceiver circuitry and/or reduce crosstalk between adjacent PMUT sensor elements.
- a parasitic capacitance from the transmitter electronics may reduce the received signal strength by a factor of ten or more.
- the presently disclosed three-port PMUT inherently separates the transmitter from the receiver, thereby reducing the need for signal isolation and minimizing losses due to associated parasitic
- a mechanical layer 530 is disposed between the cavity 420 and the piezoelectric layer 415. Such an arrangement may be referred to as a "bottom mech” arrangement.
- Figure 7 illustrates another arrangement of a three-port PMUT according to some implementations.
- the three-port PMUT 700 is configured in a "top mech" arrangement where the piezoelectric layer 415 is disposed between the cavity 420 and a mechanical layer 730.
- Figure 8 illustrates example configurations of a long rectangular diaphragm for a three-port PMUT according to some implementations.
- a long dimension L of the diaphragm 800 is at least two times longer than the width dimension W.
- a "long" rectangular plate or diaphragm may be defined as a diaphragm with a length at least twice the width.
- the shapes of the electrodes may also become rectangular with longer sides, with less concern about the placement and shape of the electrodes along the shorter sides of the diaphragm.
- the diaphragm 800 may be supported by separate anchor structures 870, disposed for example as shown proximate to opposite ends of the long dimension L. As a result, flexural motion of the diaphragm 800, as illustrated in View B-B and View C-C, may occur during transmission and reception of ultrasonic waves or signals.
- Transmit electrodes 813 (Tx) and receive electrodes 814 (Rx) may be disposed on the diaphragm 800 in various arrangements, a few of which are illustrated by way of example in Detail A, Detail B, and Detail C. More particularly, as may be observed in Detail A, in some implementations the transmit electrode 813 and the receive electrode 814 may be approximately equal in size and may be disposed symmetrically with respect to the diaphragm 800.
- the transmit electrode 813 and the receive electrode 814 may be of substantially different size and may be disposed symmetrically with respect to the diaphragm 800.
- an asymmetric arrangement of the transmit electrode 813 and the receive electrode 814 may be contemplated. While the configurations shown in Detail A, B and C have electrodes specifically labeled as Tx or Rx, the electrodes marked Tx may serve as receive electrodes and the electrodes marked Rx may serve as transmit electrodes without loss of generality in Figure 8 and throughout this disclosure.
- the diaphragm geometries shown may also be square or have L:W ratios of less than 2: 1 without loss of generality. Electrical connections (e.g. electrical traces) to the transmit electrodes and receive electrodes and electrical contacts thereto are not shown in the accompanying diagrams for clarity.
- Figure 9 illustrates further example configurations of a rectangular diaphragm for a three-port PMUT according to some implementations.
- the diaphragm 900 may be supported on all four sides by a perimeter anchor structure 970, disposed for example as shown proximate to the peripheral edges of the diaphragm 900.
- a perimeter anchor structure 970 disposed for example as shown proximate to the peripheral edges of the diaphragm 900.
- flexural motion of the diaphragm 900 as illustrated in View D-D and View E-E, may occur during transmission and reception of ultrasonic waves or signals.
- Transmit electrodes 913 (Tx) and receive electrodes 914 (Rx) may be disposed on the diaphragm 900 in various arrangements, a few of which are illustrated by way of example in Detail D, Detail E, and Detail F. More particularly, as may be observed in Detail D, in some implementations the transmit electrode 913 and the receive electrode 914 may be approximately equal in size and may be disposed symmetrically with respect to the diaphragm 900. As may be observed in Detail E, in other implementations the transmit electrode 913 and the receive electrode 914 may be of substantially different size and may be disposed symmetrically with respect to the diaphragm 900. Finally, as may be observed in Detail F, an asymmetric arrangement of the transmit electrode 913 and the receive electrode 914 may be contemplated.
- FIG. 10 illustrates yet further example configurations of a rectangular diaphragm for a three-port PMUT according to some implementations.
- the diaphragm 1000 may be supported by a centrally disposed anchor structure 1070.
- flexural motion of the diaphragm 1000 as illustrated in View F-F and View G-G may occur during transmission and reception of ultrasonic waves.
- Transmit electrodes 1013 (Tx) and receive electrodes 1014 (Rx) may be disposed on the diaphragm 1000 in various arrangements, a few of which are illustrated by way of example in Detail G, Detail H and Detail J. More particularly, as may be observed in Detail G, in some implementations the transmit electrode 1013 and the receive electrode 1014 may be approximately equal in size and may be disposed
- FIG. 11 illustrates further example configurations of a circular diaphragm for a three-port PMUT according to various implementations. In each of the examples of mushroom configurations illustrated in Detail K, Detail L, and Detail M, a circular diaphragm 1100 is supported by a centrally disposed anchor structure 1170.
- Transmit electrodes 1113 (Tx) and receive electrodes 1114 (Rx) may be disposed on the diaphragm 1100 in various arrangements. More particularly, as may be observed in Detail K and Detail L, in some implementations the transmit electrode 1113 and the receive electrode 1114 may be approximately equal in size. As may be observed in Detail M, in other implementations the transmit electrode 1113 and the receive electrode 1114 may be of substantially different size.
- Figure 12 illustrates an example of a method for operating a PMUT sensor, according to some implementations.
- the PMUT sensor may include a diaphragm disposed over a cavity, the diaphragm including a piezoelectric layer stack including a piezoelectric layer, a first electrode, a second electrode and a reference electrode, each of the first electrode, the second electrode and the reference electrode being electrically coupled with transceiver circuitry.
- method 1200 includes a step 1210 for transmitting, during a first time period, responsive to signals from the transceiver circuitry first ultrasonic signals by way of the first electrode.
- the method may proceed, at step 1220, with receiving during a second time period second ultrasonic signals by way of the second electrode.
- the first time period and the second time period are at least partially overlapping.
- the PMUT may be configured to
- FIGS 13A-13D illustrate plan views of a three-port PMUT with a circular diaphragm and various electrode configurations, according to some implementations.
- Three-port PMUT 1300a in Figure 13A has a transmit electrode 1313 (Tx) and a receive electrode 1314 (Rx) positioned in an inner region of the PMUT diaphragm.
- the transmit electrode 1313 and the receive electrode 1314 are both located inside the inflection zone, so both experience the same sign of bending stress (tensile or compressive) when the diaphragm vibrates, either to launch ultrasonic waves or to receive ultrasonic waves.
- a lower reference electrode 1312 is shown along with the upper transmit electrode 1313 and receive electrode 1314 with connective electrical traces and contacts for connections to transceiver circuitry.
- the PMUT diaphragm extends over the cavity 1320.
- Three-port PMUT 1300a shows symmetrical transmit and receive electrodes in an inner region of the PMUT diaphragm (inside the inflection zone), whereas three-port PMUT 1300b in Figure 13B shows asymmetrical transmit and receive electrodes inside the inflection zone with a larger transmit electrode and a smaller receive electrode. Smaller receive electrodes may be useful to allow more area for larger transmit electrodes (e.g., more acoustic transmit power for the same size diaphragm and actuation voltage), while still retaining adequate receive signal levels on the receive side.
- Three-port PMUT 1300c in Figure 13C has a symmetric transmit electrode 1313 (Tx) and receive electrode 1314 (Rx) positioned in an outer region of the PMUT diaphragm, where both transmit and receive electrodes are positioned outside the inflection zone and therefore experience the same sign of bending stress (compressive or tensile) when the diaphragm vibrates.
- Tx transmit electrode 1313
- Rx receive electrode 1314
- Asymmetrical transmit and receive electrode arrangements in the outer portion of the PMUT diaphragm have been contemplated.
- Three-port PMUT 1300d in Figure 13D shows an asymmetrical arrangement of a transmit electrode 1313b (Tx-) and receive electrode 1314 (Rx-) in the outer region of the diaphragm, and an additional transmit electrode 1313a (Tx+) positioned in the inner region of the diaphragm.
- Dual transmit electrodes with one in an inner region and one in an outer region of the PMUT diaphragm, allow for the generation of more acoustic power when driven differentially, as described in more detail below.
- symmetrical or asymmetrical arrangements of transmit and receive electrodes may be applied to transmit and/or receive electrodes that are inside or outside the inflection zone.
- FIGS 14A-14D illustrate plan views of a three-port PMUT with a circular diaphragm having various electrode configurations and a center release hole 1428 disposed through the diaphragm, according to some implementations.
- Center release holes 1428 may be formed through the PMUT diaphragm to allow removal of sacrificial material (not shown) to form cavity 1420 and to suspend the PMUT diaphragm over the cavity region.
- Three-port PMUT 1400a has a symmetric transmit electrode 1413 (Tx+) and receive electrode 1414 (Rx+) along with a reference electrode 1412, with both the transmit electrode and receive electrode positioned in an inner portion of the diaphragm inside the inflection zone.
- Three-port PMUT 1400b has an asymmetric transmit electrode 1413 (Tx+) and receive electrode 1414 (Rx+) located on the same side of the inflection zone.
- Three-port PMUT 1400c shows a symmetric transmit electrode 1413 (Tx-) and receive electrode 1414 (Rx-) positioned in an outer region of the PMUT diaphragm, outside of the inflection zone.
- Three-port PMUT 1400d shows an arrangement with push-pull transmit electrodes 1413a (Tx+) and 1413b (Tx-) and a single receive electrode 1414 (Rx-). Transmit electrode 1413a is inside the inflection zone, while transmit electrode 1413b and receive electrode 1414 are outside the inflection zone.
- FIG. 15 illustrates a block diagram of a method 1500 for operating a PMUT sensor having at least one dedicated receive electrode, according to some implementations. Differential push-pull transmit voltage signals may be applied to PMUT transmit electrodes that are positioned on opposite sides of the inflection zone, as shown in block 1510. Vibrations of the PMUT diaphragm may launch one or more ultrasonic waves, as shown in block 1520.
- Reflected ultrasonic waves from a distant or near object may be detected by one or more dedicated PMUT receive electrodes, as shown in block 1530.
- the received signals may be processed, for example, to generate an ultrasonic image, detect a gesture, determine the position of a stylus tip, or to validate a user when used as a biometric sensor such as an ultrasonic fingerprint sensor, as shown in block 1540.
- FIG. 16 illustrates a schematic diagram of transceiver circuitry 1610 and various configurations of a three-port PMUT with at least one dedicated receive electrode, according to some implementations.
- Transceiver circuitry 1610 may include a control unit 1620 for generating ultrasonic waves and for receiving ultrasonic signals. Signals from the control unit 1620 may be amplified, buffered, or otherwise conditioned with a transmitter drive circuit 1622 to provide push-pull transmit signals that may be applied to the positive transmit electrode (Tx+) and negative transmit electrode (Tx-) of a three-port PMUT as applicable.
- Tx+ positive transmit electrode
- Tx- negative transmit electrode
- a reference electrode of a PMUT may be connected to a reference voltage level (such as ground) via a reference level drive circuit 1628 that may receive reference level signals from the control unit 1620.
- Receive signals from one or more receive electrodes on the PMUT may be amplified, buffered or otherwise conditioned with a receiver circuit 1632 and converted to a digital signal via an analog-to-digital (A/D) converter 1634 before being processed by a signal processing unit 1630.
- the processed signals may be provided on one or more digital output lines 1640 for further processing, such as with an applications processor of a mobile device.
- Detail P shows a cross-sectional view of a three-port PMUT with a center transmit electrode (Tx+) and an outer receive electrode (Rx-) along with a reference electrode (Ref) that may be connected to transceiver circuitry 1610.
- Detail Q shows a three-port PMUT with push-pull transmit electrodes (Tx+ and Tx-) and a single, dedicated receive electrode (Rx-).
- Detail R shows a cross-sectional view of a three-port PMUT with a single transmit electrode (Tx+) and a pair of differential receive electrodes (Rx+ and Rx-).
- the differential receive electrodes may be positioned on opposite sides of the inflection zone to increase the level of the output signals obtainable and to cancel some common-mode effects such as temperature variations or noise signals common to both receive electrodes.
- Detail S shows a cross-sectional view of a three-port PMUT with a differential pair of transmit electrodes (Tx+ and Tx-) and a differential pair of receive electrodes (Rx+ and Rx-).
- Figure 17 illustrates a plot of push-pull transmit signals 1720, 1722 and illustrative receive signals 1730 as a function of time for a three-port PMUT with at least one dedicated receive electrode, according to some implementations.
- a pair of differential transmit signals 1720 and 1722 may be applied to a differential pair of transmit electrodes on a suitably configured three-port PMUT.
- Reflected signals may occur shortly after launch of the ultrasonic waves, and an illustrative receive signal 1730 within a receive signal envelope 1732 may be detected during a receive mode and processed.
- a peak detector (not shown) may be used to acquire ultrasonic signals at a
- the peak detector may acquire signals over a relatively short period of time (e.g., less than a period of an ultrasonic wave) by using a relatively narrow acquisition time window (e.g., range-gate window or RGW). This process may be repeated for each PMUT as desired.
- a fingerprint image may be acquired by launching one or more plane waves from an array of PMUTs operating in a transmit mode, then capturing reflected ultrasonic signals with the array of PMUTs operating in a receive mode for each frame of images.
- FIG. 18 illustrates a block diagram of a method 1800 for operating a PMUT sensor having one or more switchable receive electrodes, according to some implementations.
- Differential push-pull transmit voltage signals may be applied to PMUT transmit electrodes, as shown in block 1810.
- Vibrations of the PMUT diaphragm may launch one or more ultrasonic waves, as shown in block 1820.
- One or more transmit/receive electrodes may be switched from a transmit mode to a receive mode while continuing to launch ultrasonic waves with the aid of at least one transmit electrode, as shown in block 1830.
- Reflected ultrasonic waves from an object may be detected by the switched PMUT transmit/receive electrodes, as shown in block 1840.
- the received signals may be processed, as shown in block 1850.
- Figure 19 illustrates a schematic diagram of transceiver circuitry 1910 and various configurations of a three-port PMUT with at least one switchable
- Transceiver circuitry 1910 may include a control unit 1920 for generating ultrasonic waves and for receiving ultrasonic signals. Signals from the control unit 1920 may be amplified, buffered, or otherwise conditioned by a transmitter drive circuit 1922 to provide push- pull transmit signals that may be applied to the positive transmit electrode (Tx+) and negative transmit electrode (Tx-) of a three-port PMUT as applicable.
- Tx+ positive transmit electrode
- Tx- negative transmit electrode
- signals from the control unit 1920 may be amplified, buffered, or otherwise conditioned with a transmitter drive circuit 1924 with a tri-state buffer 1926 or other suitable switching circuitry to provide push-pull transmit signals to one or more transmit/receive electrodes during a transmit mode and to allow one or more transmit/receive electrodes to serve as a receive electrode when switched to a receive mode.
- a reference electrode of a PMUT may be connected to a reference voltage level (such as ground) via a reference level drive circuit 1928.
- Receive signals may be amplified, buffered or otherwise conditioned with a receiver circuit 1932 and converted to a digital signal via an analog-to-digital converter (A/D) 1934 before being processed by a signal processing unit 1930.
- A/D analog-to-digital converter
- the processed signals may be provided on one or more digital output lines 1940 for further processing, such as with an applications processor of a mobile device.
- Detail T shows a cross-sectional view of a three-port PMUT with a center transmit electrode (Tx+) and a switchable outer transmit/receive electrode (Tx-/Rx-) along with a reference electrode (Ref) that may be connected to transceiver circuitry 1910. Note that either the inner electrode, outer electrode or both may be switchable from a transmit mode to a receive mode.
- Detail U shows a cross-sectional view of a three-port PMUT with a differential pair of transmit electrodes (Tx+ and Tx-) and a differential pair of receive electrodes (Rx+ and Rx-), with one or more of the transmit electrodes or receive electrodes being switchable between a transmit mode and a receive mode.
- Figure 20 illustrates a plot of push-pull transmit signals 2020, 2022 and illustrative receive signals 2030 as a function of time for a three-port PMUT with at least one switchable transmit/receive electrode, according to some implementations.
- a pair of differential transmit signals 2020 and 2022 may be applied to a differential pair of transmit electrodes on a suitably configured three-port PMUT.
- Reflected signals may occur shortly after launch of the ultrasonic waves, and an illustrative receive signal 2030 within a receive signal envelope 2032 may be detected during a receive mode and processed. This process may be repeated for each PMUT, PMUT array or portion of a PMUT array as desired.
- Three-port PMUTs may be configured with one or more dedicated or switched transmit/receive electrodes having symmetrical or asymmetrical arrangements of transmit and receive electrodes that are inside or outside the inflection zone, with or without center release holes, with circular, square, rectangular or long rectangular diaphragms, using a variety of anchor structures.
- a three-port PMUT having a ground (reference) electrode, and configured to simultaneously transmit first ultrasonic signals by way of a first electrode and to receive second ultrasonic signals by way of a second electrode has been disclosed. It will be appreciated that a number of alternative configurations and fabrication techniques may be contemplated. For example, the electrode
- the piezoelectric layer stack may be formed over the anchor structure.
- the piezoelectric layer stack may include a piezoelectric layer such as aluminum nitride (A1N), zinc oxide (ZnO), lead-zirconate titanate (PZT) or other suitable piezoelectric material with one or more electrode layers electrically coupled to the piezoelectric layer.
- the piezoelectric layer stack may be patterned and etched to form vias, release holes and other features.
- the mechanical layer may include Si0 2 , SiON, silicon nitride (SiN), other dielectric material, or a combination of dielectric materials or layers.
- a single A1N or PZT layer may be used as the piezoelectric layer for coupling to both transmit and receive electrodes.
- an A1N layer may be used with the transmit electrode and a PZT layer may be used with the receive electrode in the same diaphragm.
- a PZT layer may be used with the transmit electrode and an A1N layer may be used with the receive electrode in the same diaphragm.
- a piezoelectric layer of PZT and a piezoelectric layer of A1N may be substantially coplanar, that is, formed on or below the same surface of a multi-layer PMUT diaphragm.
- a two- layer stack of piezoelectric layers that are of the same or different piezoelectric material may be used to form the three-port PMUTs described above.
- a first layer of PZT may be used with one or more transmit electrodes
- a second layer of A1N may be used with one or more receive electrodes.
- Transmit and receive piezoelectric layers may be above one or the other in a stacked configuration; in other implementations they may be beside one another on or in the same diaphragm.
- Reference electrodes may be common to one or more associated transmit or receive electrodes.
- One or more mechanical layers and/or electrode layers may be positioned above, below or between the various piezoelectric layers.
- a phrase referring to "at least one of a list of items refers to any combination of those items, including single members.
- "at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c.
- the various illustrative logics, logical blocks, modules, circuits and algorithm processes described in connection with the implementations disclosed herein may be implemented as electronic hardware, computer software, or
- the hardware and data processing apparatus used to implement the various illustrative logics, logical blocks, modules and circuits described in connection with the aspects disclosed herein may be implemented or performed with a general purpose single- or multi-chip processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein.
- a general purpose processor may be a microprocessor or any conventional processor, controller, microcontroller, or state machine.
- a processor also may be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.
- a processor also may be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.
- the functions described may be implemented in hardware, digital electronic circuitry, computer software, firmware, including the structures disclosed in this specification and their structural equivalents thereof, or in any combination thereof. Implementations of the subject matter described in this specification also can be implemented as one or more computer programs, i.e., one or more modules of computer program instructions, encoded on a computer storage media for execution by or to control the operation of data processing apparatus. [0095] If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium, such as a non-transitory medium. The processes of a method or algorithm disclosed herein may be implemented in a processor-executable software module which may reside on a computer-readable medium.
- Computer-readable media include both computer storage media and communication media including any medium that can be enabled to transfer a computer program from one place to another.
- Storage media may be any available media that may be accessed by a computer.
- non-transitory media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that may be used to store desired program code in the form of instructions or data structures and that may be accessed by a computer.
- any connection can be properly termed a computer-readable medium.
- Disk and disc includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and blu-ray disc where disks usually reproduce data
Abstract
Description
Claims
Priority Applications (6)
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CN201580054255.9A CN107107114B (en) | 2014-10-15 | 2015-10-15 | Three port piezoelectric ultrasonic transducers |
BR112017007742-6A BR112017007742B1 (en) | 2014-10-15 | 2015-10-15 | THREE-PORT PIEEZOELECTRIC ULTRASONIC TRANSDUCER |
EP15790345.1A EP3206804B1 (en) | 2014-10-15 | 2015-10-15 | Three-port piezoelectric ultrasonic transducer |
KR1020177010141A KR102004061B1 (en) | 2014-10-15 | 2015-10-15 | Three-port piezoelectric ultrasonic transducer |
JP2017518497A JP2018502467A (en) | 2014-10-15 | 2015-10-15 | 3-port piezoelectric ultrasonic transducer |
CA2961645A CA2961645C (en) | 2014-10-15 | 2015-10-15 | Three-port piezoelectric ultrasonic transducer |
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US14/883,583 US10001552B2 (en) | 2014-10-15 | 2015-10-14 | Three-port piezoelectric ultrasonic transducer |
US14/883,586 US10139479B2 (en) | 2014-10-15 | 2015-10-14 | Superpixel array of piezoelectric ultrasonic transducers for 2-D beamforming |
US14/883,583 | 2015-10-14 | ||
US14/883,585 US9995821B2 (en) | 2014-10-15 | 2015-10-14 | Active beam-forming technique for piezoelectric ultrasonic transducer array |
US62/241,651 | 2015-10-14 | ||
US14/883,585 | 2015-10-14 |
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PCT/US2015/055825 WO2016061410A1 (en) | 2014-10-15 | 2015-10-15 | Three-port piezoelectric ultrasonic transducer |
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PCT/US2015/055821 WO2016061406A1 (en) | 2014-10-15 | 2015-10-15 | Superpixel array of piezoelectric ultrasonic transducers for 2-d beamforming |
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