KR100753801B1 - Humidity Sensor and Fabricating Method of the Same - Google Patents

Abstract

The present invention relates to a humidity sensor having a high stability and sensitivity so as to predict and control the performance of a high frequency system according to a change in humidity, and capable of being integrated into a high frequency system without causing structural complexity and a manufacturing method thereof. The present invention provides a strip patch antenna comprising a glass substrate, a wavelength converter formed on the glass substrate, a strip feeding line connected to one side of the wavelength converter, a meander patch formed on the wavelength converter, and the Provided is a humidity sensor formed on the meander patch, including a humidity sensing layer made of polyimide containing no hydrophobic elements. Therefore, the sensor's stability and sensitivity are excellent, and additional circuits such as impedance matching are not required, so it can be easily integrated without causing structural complexity, and it can be implemented through a simple manufacturing process, so that mass production is possible at a low production cost. Do.

Humidity Sensor, Polyimide, High Frequency Resonator, CPW-to-slotline Ring Resonator, Microstrip Patch Antenna

Description

Humidity Sensor and Fabricating Method of the Same

1A and 1B are perspective views showing a CPW-to-slotline ring resonator and a micro strip patch antenna structure according to the present invention;

2 is a view showing the synthesis process of the moisture-sensitive material according to the present invention,

3 is a perspective view of a humidity sensor using a CPW-to-slotline ring resonator structure according to the present invention;

4 is a process flowchart showing a manufacturing process of a humidity sensor using a CPW-to-slotline ring resonator structure according to the present invention;

5 is an optical photograph of a humidity sensor using a CPW-to-slotline ring resonator structure manufactured in FIG. 4;

6a to 6d is a graph showing the characteristics of the humidity sensor using a CPW-to-slotline ring resonator structure according to the present invention,

7 is a perspective view of a humidity sensor using a microstrip patch-type antenna structure according to the present invention;

8 is a process flowchart showing a manufacturing process of a humidity sensor using a microstrip patch-type antenna structure according to the present invention;

9 is an optical photograph of a humidity sensor using a microstrip patch-type antenna structure manufactured in FIG. 8;

10A and 10B are graphs illustrating sensitivity characteristics of a humidity sensor using a microstrip patch antenna structure according to the present invention.

<Description of the symbols for the main parts of the drawings>

1: glass substrate 2: metal film

3: CPW feeder 4: ring

5: slot line 6: moisture layer

7: mask 11: 1/4 wavelength converter

12: strip feeder 13: meander patch

The present invention relates to a humidity sensor and a manufacturing method thereof, and more particularly, to a humidity sensor using two types of high frequency resonator structure and a polyimide excluding hydrophobic elements, and a manufacturing method thereof.

Due to the advanced micro machining technology, SOC (system-on-a-chip) research is actively being conducted to implement various functional systems on a single chip. In order to effectively process information in a high density chip or system, the operating frequency is continuously increasing and the minimum line width is continuously decreasing. As long as this trend persists, parasitic effects, signal delays and thermal problems inevitably increase. Among these negative effects, parasitic capacitance is a major source of loss in high frequency systems, which is highly dependent on humidity because the relative dielectric constant of water is about 80, whereas the relative dielectric constant of water is about 80. Thus, sensing of humidity is required to predict and control the performance of high frequency systems.

Conventional humidity sensors are largely classified into three types: capacitive type using polymer, conductive type using ceramic, and type using surface acoustic wave device. Most of these humidity sensors operate in the quasi-DC region. Therefore, in order to integrate the humidity sensor into the high frequency system, an additional circuit such as an impedance matching circuit is required, which causes a problem of increasing the structural complexity and the production cost of the system. Although the humidity sensor using surface acoustic waves has recently approached about 2 GHz, it also has a problem of requiring ultra-precision micromachining of about 0.5 μm.

In addition, polyimide, which is frequently used as a moisture-sensitive material for capacitive humidity sensors, has been widely used as an interlayer and packaging material in the microelectronic industry. These applications required low dielectric constants and moisture insensitive properties. Factors affecting the characteristics and dielectric constant of polyimide with respect to humidity include chemical affinity, glass transition temperature, fluorine contents, and free volume. Among these methods, a method of incorporating a Group 7 element such as fluorine into the monomer of polyamide has been widely used as a method of securing low dielectric constant and insensitivity to humidity. However, as described above, polyimide having insensitivity to humidity through component adjustment is inappropriate as a moisture sensitive material for a high-sensitivity humidity sensor.

The present invention has been made to solve the above problems and has a high stability and sensitivity to predict and control the performance of the high frequency system according to the change in humidity, humidity that can be integrated in the high frequency system without causing structural complexity It is to provide a sensor and a method of manufacturing the same.

Humidity sensor according to the first embodiment of the present invention is formed on a glass substrate, the glass substrate, a ring in the center, a slot line to form a predetermined distance along the outer ring, the opposite direction in the slot line A damper layer covering the resonator comprising a resonator composed of a pair of coplanar waveguide (CPW) feed lines extending to the shortest region, and a polyimide containing no hydrophobic elements; humidity sensing layer).

In the manufacturing method of the humidity sensor according to the first embodiment of the present invention, depositing a metal film on a glass substrate, forming a ring in the center of the metal film, and forming a slot line to have a predetermined distance along the outer edge of the ring. And manufacturing a resonator by forming a pair of coplanar waveguide (CPW) feed lines extending from the slot line to the shortest region of the metal film in opposite directions. Coating a moisture sensitive material on the substrate; forming a mask in a region corresponding to the resonator of the coated moisture absorbent material region; and removing the mask after removing the moisture sensitive material in the remaining regions except for the mask region. It is characterized by.

A humidity sensor according to a second embodiment of the present invention includes a glass substrate, a wavelength converter formed on the glass substrate, a strip feeding line connected to one side of the wavelength converter, and a meander patch formed on the wavelength converter. And a strip patch type antenna formed of a), and a humidity sensing layer formed on the meander patch and made of polyimide containing no hydrophobic elements.

According to a second aspect of the present invention, there is provided a method of manufacturing a humidity sensor, comprising depositing a metal film on a glass substrate, a wavelength converter on the metal film, a strip feeding line on one side of the wavelength converter, and an upper portion of the wavelength converter. Manufacturing a strip patch antenna by forming a meander patch, coating a moisture sensitive material on the entire surface of the metal film including the strip patch antenna, and a region corresponding to the strip patch antenna in the coated moisture absorbing material region Forming a mask in the mask, and removing the mask after removing the moisture absorbent material in the remaining regions except for the mask region.

Therefore, the sensor has excellent stability and sensitivity, no additional circuits such as impedance matching are required, so it can be easily integrated without causing structural complexity, and it can be implemented through a simple manufacturing process. It is possible.

Advantages and features of the present invention having the above characteristics will become more apparent from the embodiments and the accompanying drawings.

Hereinafter, the first and second embodiments of the humidity sensor and its manufacturing method according to the present invention with reference to the accompanying drawings in detail as follows.

First, the structures of the CPW-to-slotline ring resonator used in the first embodiment and the microstrip patch antenna used in the second embodiment are as shown in FIGS. 1A and 1B, respectively.

The CPW-to-slotline ring resonator is designed to resonate at 3.375 GHz and as shown in FIG. 1A, a metal film (aluminum or copper) is formed on the Pyrex glass substrate 1 by vacuum deposition. By using a photo lithography method, by defining a CPW feeding structure 3 and a central ring 4, a slotline 5 which is an interval between the CPW feeding structure 3 and the ring 4 Is formed.

The microstrip patch-type antenna is designed to resonate at 5.0 GHz, and as shown in FIG. 1B, a metal film (aluminum or copper) is formed on the Pyrex glass substrate 1 by vacuum deposition, and photo lithography is performed on it. It is formed by defining a quarter wavelength converter 11, a 50 ohm class strip feed line 12, and a meander patch 13 using the scheme.

At this time, by using Pyrex glass as a substrate instead of a material such as silicon, it is possible to satisfy the functions of the insulating layer and the substrate such as silicon oxide film (SiO ₂ ), silicon nitride film (Si ₃ N ₄ ).

In addition, the manufacturing of the humidity sensor is completed by forming a moisture sensitive material on the CPW-to-slotline ring resonator and the micro strip patch antenna.

At this time, polyamic acid obtained by dissolving oxidianiline (ODA) and m-pyromellitic dianhydride (PMDA), which are hydrophobic elements-excluded monomers, for high stability and sensitivity in polar solvent N-methly-2-pyrolidone (NMP) A polyimide film obtained by thermally polymerizing (polyamic acid) was used.

Detailed synthesis process of the polyimide film used in the present invention is shown in FIG. 6.00 g of ODA was dissolved in 75 ml of polar solvent NMP to prepare a mixed solution (S10), and then 6.54 g of PMDA was added slowly (S20) to stir at a constant temperature and rotational speed to prepare a polyamic acid (S30). ). The coated polyamic acid is rotated on a substrate and thermally polymerized to prepare a polyimide film, which is a moisture sensitive material (S40).

Looking at the humidity sensor and the manufacturing method according to the first and second embodiments of the present invention described above in detail.

First Embodiment

As shown in FIG. 3, the humidity sensor using the CPW-to-slotline ring resonator structure according to the present invention includes a Pyrex glass substrate 1, a metal film 2 formed on the glass substrate 1, and the metal film. A ring resonator, defined in (2), comprising a ring in the center, a slot line forming a gap outside the ring, a coplanar waveguide (CPW) feed line (3) for transmitting a resonant frequency, It comprises a humidity sensing layer 6 made of polyimide containing no hydrophobic elements and covering the resonator.

At this time, the ring and the slot line are invisible by the moisture sensitive layer 6 in the drawing.

The mean circumference of the ring resonator occurs at an integer multiple of the guided wave length. This is represented by equation (1). In addition, the guided wavelength is expressed as Equation 2, and the resonance frequency is calculated by Equation 3.

here,

n: number of modes

λ _g : guided wavelength

r: average radius of the ring

f: resonant frequency

c: speed of light

ε _eff : Effective relative dielectric constant of the substrate

Next, a manufacturing process of the humidity sensor using the above-described ring resonator will be described with reference to FIG. 4.

First, a 3 μm thick metal film 2, that is, aluminum (or copper) is vacuum deposited on a Pyrex glass substrate 1 having a thickness of 500 μm (a).

Subsequently, the shape of the ring resonator (ring, slot line, CPW feed line) is defined through the photolithography process of the deposited aluminum (b).

In addition, after forming the polyimide, which is the moisture-sensitive layer 6, by rotating coating, an aluminum mask 7 for dry etching is formed (c).

Finally, dry etching of the polyimide is performed, and the aluminum mask is removed to manufacture a ring resonator type humidity sensor (d).

An optical photograph of the manufactured humidity sensor is shown in FIG. 5.

Referring to the operation of the humidity sensor according to the invention produced as described above are as follows.

First, the relative dielectric constant of the moisture sensitive layer 6, that is, the polyimide, changes according to the absorbed humidity.

Subsequently, the resonance frequency of the ring resonator in contact with the moisture sensitive layer 6 is also changed by changing the dielectric constant of the moisture sensitive layer 6.

Therefore, the external system recognizes the change of the resonant frequency through the CPW feeder line and eventually detects the humidity.

Characterization of sensitivity, hysteresis and stability of the ring resonator type humidity sensor according to the present invention described above was performed using an environmental chamber and a network analyzer with precise temperature and humidity control.

Sensitivity and hysteresis were measured at a temperature of 30 ° C with a relative humidity of 20% from 30% to 90%, and stability measurements were taken every 30 minutes for 240 minutes while maintaining a temperature of 30 ° C and a relative humidity of 40%. Recorded.

6a to 6d show the characteristics of the ring resonator type humidity sensor thus measured. 6A shows the sensitivity of the sensor in the form of a change in resonant frequency according to the change in relative humidity, -181 kHz /% RH, and FIG. 6B shows the sensitivity of the sensor in the form of a change in insertion loss according to the change in relative humidity. 4.95 mdB /% RH.

6c is a hysteresis measured while increasing the relative humidity from 30% to 90% and again from 90% to 30%, and FIG. 6d shows a 0.002% grapher for stability, thus showing the conventional capacitance. It can be seen that the hysteresis of the humidity sensor of the type, the conduction type using the ceramic and the surface acoustic wave device is about 1%, and the stability is about 0.1%, whereas the hysteresis is excellent (the lower the hysteresis and the better the stability).

Second Embodiment

As shown in FIG. 7, the humidity sensor using the microstrip patch type antenna structure according to the present invention has a microstrip feed line 12, a quarter-wavelength converter 11, and a meander patch 13 on a Pyrex glass substrate 1. ) And an polyimide, which is a material of the moisture sensitive layer 6.

Next, a manufacturing process of the humidity sensor using the aforementioned micro strip patch antenna will be described with reference to FIG. 8.

First, a 3 탆 thick metal film 2, that is, aluminum (or copper) is vacuum deposited on a Pyrex glass substrate 1 having a thickness of 500 탆 (a ').

Subsequently, the shape of the microstrip patch antenna is defined through the photolithography process of the deposited aluminum (b ').

In addition, the polyimide, which is the material of the moisture sensitive layer 6, is rotated to form an aluminum mask 7 for a dry etching process (c ′).

Finally, the dry etching of the polyimide is performed, and the aluminum mask is removed to manufacture a humidity sensor using a patch antenna structure (d ').

An optical photograph of the manufactured humidity sensor is shown in FIG. 9.

Briefly describing the operation of the humidity sensor according to the present invention produced as follows.

First, the relative dielectric constant of the moisture sensitive layer 6, that is, the polyimide, changes according to the absorbed humidity.

Subsequently, the resonant frequency of the strip patch antenna in contact with the moisture sensitive layer 6 is also changed by changing the dielectric constant of the moisture sensitive layer 6.

Therefore, the external system recognizes the change of the resonant frequency through the strip feed line, and eventually the humidity can be detected.

The sensitivity of the humidity sensor of the strip patch-type antenna structure according to the present invention was measured in the form of resonance frequency and return loss according to relative humidity change using an environmental chamber and a network analyzer in which temperature and humidity are precisely controlled. . 10A and 10B show the sensitivity of the humidity sensor measured in the form of resonant frequency and return loss according to the change of relative humidity, respectively.

At this time, it can be seen that the resonance frequency of the humidity sensor according to the present invention is -108 kHz /% RH as shown in FIG. 10A. And it can be seen that the sensitivity shown in the form of the return loss of the humidity sensor according to the present invention is -5.50 mdB /% RH.

As such, those skilled in the art will appreciate that the present invention can be implemented in other specific forms without changing the technical spirit or essential features thereof. Therefore, the above-described embodiments are to be understood as illustrative in all respects and not as restrictive. The scope of the present invention is shown by the following claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be construed as being included in the scope of the present invention. do.

Referring to the effects of the humidity sensor and a method of manufacturing the same according to the present invention described above are as follows.

First, by using a polyimide excluding hydrophobic elements as a moisture sensitive material, the stability and sensitivity of the sensor are superior to that of ceramic or commercial polyimide, respectively.

Second, the existing humidity sensor operating in the quasi-DC region requires an additional circuit such as impedance matching to integrate into a high frequency system, but in the present invention, a simple design parameter is modified to operate at a high frequency operating at the same operating frequency as the high frequency system. The use of resonators allows the integration of humidity sensors, which provide basic data for predicting and controlling the performance of high frequency systems, without incurring the structural complexity of the system.

Third, it can be implemented through a much simpler manufacturing process than the existing humidity sensor, so mass production is possible at a low production cost.

Claims (7)

Glass substrates; A strip patch antenna including a wavelength converter formed on the glass substrate, a strip feeding line connected to one side of the wavelength converter, and a meander patch formed on the other side corresponding to one side of the wavelength converter; And The humidity sensor is formed on the meander patch, and comprises a humidity sensing layer (humidity sensing layer) made of polyimide (polyimide) containing no hydrophobic elements. The method of claim 1, The strip patch-type antenna is a humidity sensor, characterized in that formed by processing a metal film made of at least one of aluminum or copper. Depositing a metal film on the glass substrate; Manufacturing a strip patch type antenna by forming a wavelength converter on the metal film, a strip feeding line on one side of the wavelength converter, and a meander patch on the other side corresponding to one side of the wavelength converter; Coating a moisture sensitive material on an entire surface of the metal film including the strip patch antenna; Forming a mask in a region of the coated moisture sensitive material corresponding to the strip patch antenna; And And removing the mask after removing the moisture absorbent material of the remaining area except for the mask area. The method of claim 3, wherein The metal film is a humidity sensor manufacturing method characterized in that made by vacuum deposition of one of aluminum or copper. The method of claim 3, wherein Forming a strip patch antenna on the metal film is a humidity sensor manufacturing method characterized in that it is made through a photo lithography process. The method of claim 3, wherein The humidity sensitive material is a humidity sensor manufacturing method characterized in that the polyimide (polyimide) does not contain a hydrophobic element. The method of claim 6, The polyimide thermally dissolves polyamic acid obtained by dissolving ODA (oxidianiline) and PMDA (m-pyromellitic dianhydride), which are monomers that do not contain hydrophobic elements, in NMP (N-methly-2-pyrolidone), a polar solvent. Humidity sensor manufacturing method characterized in that the polymerized.

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