WO2016153155A1

WO2016153155A1 - Biomimetic based pressure sensor manufacturing method and pressure sensor manufactured thereby

Info

Publication number: WO2016153155A1
Application number: PCT/KR2015/014384
Authority: WO
Inventors: 고현협; 하민정
Original assignee: 울산과학기술원
Priority date: 2015-03-23
Filing date: 2015-12-29
Publication date: 2016-09-29

Abstract

A biomimetic-based pressure sensor manufacturing method according to the present invention comprises: (a) a step of forming a plurality of micropillars on each of a pair of PDMS substrates from a silicon microhole pattern; (b) a step of growing nanowire in a plurality of micropillars formed on the pair of PDMS substrates; (c) a step of partially coating any one of the pair of PDMS substrates, in which the nanowire has grown in the micropillars, with a metal film; and (d) a step of engaging the PDMS substrates in which the nanowire has grown, among the pair of PDMS substrates, with the PDMS substrate which has been partially coated with the metal film in step (c). The method is effective in improving the performance as a pressure sensor by maximizing the surface area and enabling effective pressure transmission.

Description

Bio simulation based pressure sensor manufacturing method and pressure sensor manufactured by the manufacturing method

The present invention relates to a bio-simulating pressure sensor, and more particularly, hierarchical by fusing the microstructure patterning of organic materials and the nanostructure of inorganic materials. The present invention relates to a method for manufacturing a bio simulation-based pressure sensor which improves performance as a pressure sensor by maximizing surface area by interlocking the fabricated structure.

The development of electronic skin (or pressure sensors) is gaining much attention in many applications such as robots, prostheses, health monitoring, wearable electronics, and medical diagnostics. However, conventional electronic skin is still far from performing flexibility, high sensitivity, and quick response like human skin.

Large sensory organs in human skin can experience real touch, vibration, texture, and hardness through several types of tactile receptors. Human skin, in particular, can distinguish between static and dynamic mechanical stimuli due to different types of mechanical receptors, such as Ruffini Organs and Pancinian blood cells.

Slow-adapted lupine organs are suitable for static sensing, such as gripping objects at constant pressure, while fast-adapted Pacinian blood cells are usually suitable for detecting dynamic stimuli of high-frequency vibrations.

Typical sensing materials used in electronic skin are polymer conductive polymers with high dielectric constants (k) (poly (3-hexylthiophene), polypyrrole, polyaniline), or semiconductors (silicon, zinc oxide, cadmium selenide) and elastomers. conductive materials such as nanomaterial metals (CNTs, graphene, gold, and silver) contained in (elastomers).

However, elastomers with viscoelastic behavior lead to slow response time (˜10 seconds) and large hysteresis, and also large thermal expansion of conductive polymers has the problem of changing inherent electrical properties.

In particular, the conductive polymer and the composite pressure sensor has a viscoelastic (viscoelastic), there is a problem that the reaction rate is slow and the sensor performance changes with respect to the external temperature also frequently.

In addition, it is a piezoresistive method that can be detected by changing the resistance as the contact area changes with the pressure recently, and the capacitance that can be detected by changing the capacitance as the thickness of the dielectric layer changes according to the external pressure. Capacitive, piezoelectric, which reacts to external pressure using piezoelectric materials, and triboelectirc electronic skin that senses the movement of objects using electrostatic properties commonly seen in everyday life. Etc. are being developed.

However, the above-described prior art has a problem in that due to the pressure sensing in a single manner, unlike the human skin, the static and dynamic pressure cannot be simultaneously recognized.

(Prior art document)

(Patent literature)

Republic of Korea Patent Publication No. 10-1308104 (2013. 09. 06)

In order to solve the above problems, the present invention is to fuse the microstructure patterning (organic) material of the organic material (nanostructure) and the nanostructure (organic structure) of the inorganic material (inorganic) to produce a hierarchical structure It is an object of the present invention to provide a method for manufacturing a bio simulation-based pressure sensor that improves the performance as a pressure sensor by maximizing the surface area by interlocking.

In addition, in order to solve the above problems, the present invention is to provide a pressure sensor capable of recognizing both static and dynamic pressure, such as human skin using a nano-material capable of both resistance / piezoelectric signal transmission. It is done.

According to an aspect of the present invention, there is provided a method of manufacturing a bio simulation-based pressure sensor, comprising: (a) forming a plurality of microfillers on each of a pair of PDMS substrates from a silicon microhole pattern; (b) growing nanowires on a plurality of microfillers formed on the pair of PDMS substrates; (c) coating any one of the pair of PDMS substrates with a metal film on the microfiller on which the nanowires are grown; And (d) engaging the PDMS substrate on which the nanowires are grown with the PDMS substrate partially coated with the metal film in step (c) of the pair of PDMS substrates, wherein (b) The nanowire of the PDMS substrate of step) and the nanowire of the step (c) are connected to each other so that the pressure sensor of the piezoresistive method, the nanowire of the PDMS substrate of the step (b) and the metal film of the step (c) The coated nanowires are interlocked to simultaneously implement a piezoelectric pressure sensor.

In the method of manufacturing a bio simulation-based pressure sensor according to the present invention, a hierarchical structure is manufactured by fusing a microstructure patterning of an organic material and a nanostructure of an inorganic material. By interlocking with each other, the surface area is maximized, and effective pressure transmission is possible, thereby improving performance as a pressure sensor.

In addition, the bio simulation-based pressure sensor manufacturing method according to the present invention by using an inorganic material of non-viscoelastic properties is very fast reaction speed compared to the conventional pressure sensor, and has an excellent stability against external temperature changes.

In addition, unlike the conventional pressure sensor, the method for manufacturing a bio simulation-based pressure sensor according to the present invention can detect both static and dynamic external pressure by using the structural and material-specific piezolectic properties of zinc oxide (ZnO). It has an effect.

1 illustrates a biobased hierarchical ZnO nanowire array;

2 is a diagram comparing the static pressure sensing capability of the electronic skin based on the interlocking structure of the hierarchical ZnO nanowire array;

3 is a view for explaining the dynamic pressure sensing capability of the electronic skin based on the engagement structure of the hierarchical ZnO nanowire array;

4 is a view for explaining a change in contact resistance according to the applied pressure,

5 is a view for explaining a piezoelectric pressure sensor, and

6 is a graph illustrating the relationship between the frequency and the current of the piezoresistive and piezoelectric methods.

Hereinafter, with reference to the accompanying drawings will be described in detail an embodiment of the present invention. Prior to this, terms or words used in the present specification and claims should not be construed as being limited to the ordinary or dictionary meanings, and the inventors should properly explain the concept of terms in order to best explain their own inventions. Based on the principle that it can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention.

Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

1 is a diagram illustrating a manufacturing process of a bio simulation-based pressure sensor according to the present invention.

As shown in FIG. 1, a microfiller is formed on a PDMS (polydimethylsiloxane) substrate through a soft lithography method from a silicon microhole pattern (S100).

Although FIG. 1 illustrates the formation of a micropillar on one PDMS (polydimethylsiloxane) substrate, the microfiller is substantially formed on a pair of PDMS (polydimethylsiloxane) substrates in step S100. .

Thereafter, a hierarchical zinc oxide layer on the pair of PDMS micropillar arrays is formed through hydrothermal synthesis to fabricate a hierarchical micro and nanostructured interlocking structure for flexible electronic skin (or pressure sensor). ZnO) performing a step of forming a nanowire (NW) (S200).

The zinc oxide nanowire array according to the hydrothermal synthesis method can be fixed at low cost, large area and low temperature, and can be grown on a flexible substrate with high aspect ratio according to optimized experimental conditions.

In this process, the PDMS microarray was formed from the original microphone-hole patterned silicon micromold. At this time, ZnO nanowires are formed on the top of the PDMS micropillar array by hydrothermal method.

As a next step, the hierarchical zinc oxide nanowires are coated with a thin metal film to reduce electrical conductivity and resistance (S300).

That is, in the step S300, a metal film is partially coated on the plurality of microfillers in which the nanowires are grown on any one PDMS substrate among the pair of PDMS substrates.

The electron micrograph in FIG. 1D shows that the ZnO nanowires were uniformly grown on the top of the PDMS microfiller array by the hydrothermal method.

As shown in FIG. 2A, the zinc oxide nanowires are grown through hydrothermal synthesis using zinc oxide nanocrystals uniformly coated on a PDMS micropillar array as a nucleus by a dip-coating method.

At this time, the PDMS substrate is suspended on the surface of the growth solution in a state in which the lower side of the microfiller is in contact with the solution so that the zinc oxide nanowires can be uniformly grown without any zinc oxide deposit.

During the growth of the zinc oxide nanowires, zinc cations (Zn ²⁺ ) from zinc nitrate hydrate (Zn (NO ₃ ) ₂ xH ₂ O) and oxygen anions from distilled water (DI) water follow the C axis of the ZnO nanowires. Alternately stacked

As shown in FIG. 2B, X-ray diffraction analysis showed that the grown zinc oxide nanowires had the highest planar peak (002) with respect to the C-axis crystal growth direction and a few planar peaks for hexagonal symmetry. 102) shows a hexagonal urzite structure.

Since semiconducting ZnO nanowires with large direct band gaps ((~ 3.3 eV) have high electrical resistance (~ 10 ⁹ Ω), the thin metal film coated on top of the ZnO nanowire array is 10 times higher than the pure resistance of ZnO nanowires. ^The electrical resistance can be reduced by more than ^-3 times to facilitate the current flow between ZnO nanowires.

In contrast to conventional conductive composite films, in electronic skin design based on interlocked hierarchical micro and nanostructures, the resistive method is primarily responsible for the stress (or stress) -induced change in contact area between interlocked hierarchical structures. Affected by

Thus, the dimensions of the zinc oxide nanowires and PDMS microfillers have a significant impact on the strain-induced contact area change and thus on the overall performance of the electronic skin.

In the present invention, the aspect ratio (AR) of ZnO nanowires (Fig. 2C, d) and the pitch of PDMS microfiller arrays (Fig. 3 and Table 1) are systematically investigated to investigate the detection performance of the electronic skin. , 30, 40um).

Table 1

Pattern information	Micropillar
Pitch size (um)	20	30	40
Diameter / Width (um)	10
Height (um)	8.3 ± 0.2

Figure 3a shows a hierarchical micro and nano structure interlock device configuration for highly sensitive resistive electronic skin.

The electron microscopy image in FIG. 3b clearly shows that the top and bottom of the ZnO nanowires are interlocked with each other on the PDMS microfiller array. As shown in FIG. 4, the pressure applied in this interlocked structure induces a change in contact surface between the interlocked nanowires and a change in contact resistance.

In particular, the hierarchical structure of ZnO nanowires on PDMS micropillar arrays provides a large surface area that can lead to large changes in contact resistance.

In addition, the hierarchical structure allows for minimal contact between nanowires at an early stage without any pressure, and allows for a continuous increase of the contact area under pressure, resulting in very sensitive resistance changes in the electronic skin. Cause.

In order to confirm the relationship between the structural shape and the pressure sensitivity of the hierarchical nanowire array, in the present invention, microfiller arrays of different pitch sizes and planar nanowire arrays were introduced to compare resistance changes with pressure.

3c shows that the relative resistance of the electronic skin decreases rapidly with increasing contact area at low pressure (below 2 kPa) and slowly decreases at high pressure (more than 2 kpa).

Due to the difference in contact area with different pitch sizes of the micropillar array, the largest reduction in resistance is observed in the smallest pitch size (20um) sensor, 3.7 times higher than the planar array at pressures below 0.3 kPa. This can be seen in Table 2 below.

TABLE 2

Pattern types	Linear pressure-sensitivities (\| kPa ^-1 \|)
Pattern types	Low pressure range (0 -0.33 kPa)	Middle pressure range (0.33-4.57 kPa)	High pressure range (4.57 -13.07 kPa)
Planar	1.86	0.015	0.0016
Micropillar	6.82	0.010	6.78 × 10 ^-5

Resistance change is nonlinear depending on pressure change. That is, the pressure change may be due to the nonlinear relationship between the applied pressure and the contact area between the nanowires.

The gradual decrease in sensitivity as a function of nonlinear exponential law is advantageous for increasing the dynamic range of the pressure sensor to detect stimuli over a wide pressure range.

The nonlinear dependence of resistance on pressure depends on the exponential law function y = ax ^-b It can be defined by (Fig. 3c). As can be seen in Figure 3d, the index b with a 0.64 value for the 20um pitch sensor decreases with an increase in the microfiller pitch and finally reaches 0.17, corresponding to planar zinc oxide nanowires with infinite pitch size.

Because of the typical elastic deformation of the contact surface, the index b is known to be proportional to the surface roughness and the surface area.

As described above, among the pair of PDMS substrates, the PDMS substrate on which the zinc oxide nanowires are formed in step S200 and the other PDMS substrate partially coated with a metal film in step S300 are engaged with each other. As shown in FIG. 1e, a step of configuring a pressure sensor of a piezoresistive type and a piezoelectric type is performed (S400).

In the piezoresistive method, the contact resistance is changed depending on the pressure, and thus the static pressure may be mainly detected.

At this time, the piezoelectric pressure sensor is a pressure sensor formed by engaging a hierarchical structure without any metal coating according to S300 among the pair of PDMS substrates being engaged.

In particular, the metal-coated ZnO nanowire hierarchy and the non-metal-coated ZnO nanowire contacts are in Schottky contact.

The piezoelectric pressure sensor may sense dynamic pressure by generating an instantaneous electrical potential difference in the piezoelectric material due to pressure.

In more detail, the piezoelectric pressure sensor will be described with reference to FIG. 5.

As shown in FIG. 5A, when pressure is applied to a pressure sensor composed of a top layer coated with a nickel film and a bottom layer of zinc oxide nanowires as shown in FIG. 5A, the interlocked zinc oxide nanowires are stressed and are not coated. A positive electrical potential difference occurs in the stretching portion of the nanowire, and a negative electrical potential difference occurs in the compression portion.

This results in a Schottky contact in the form of reverse-bias at the contact between the nanowire and the metal having a positive electrical potential difference, and in the forward-bias form at the contact between the nanowire and the metal having a negative electrical potential difference. Key contacts appear to allow electrons to flow from the nanowires with negative electrical potential differences towards the metal coated nanowires.

As shown in FIGS. 5B and 5C, as the pressure applied to the hierarchical structure is greater than that of the planar structure, the change in output voltage and current density is larger.

In addition, it can be seen from FIG. 5D that the piezoelectric electronic skin can detect high frequency stimulation of 3 Hz or higher, and FIG. 5E shows that the hierarchical nanowire array has a high signal-to-noise ratio at the output voltage. It can be seen that (2.1m / s) can be detected.

That is, due to the increase in the number of nanowires that are stressed according to the strength of the pressure, the piezoelectric current and the voltage signal are increased, so that the external pressure can be detected. The high frequency of 250Hz was also detected according to the possible characteristics, and when compared with the piezoresisitive method that can recognize static pressure, it can be seen that it transmits the accurate signal even at the high frequency.The piezoelectric method When referring to the formula related to the current, the current is related to the strain rate of the nanowire, which increases as the frequency increases, resulting in an increase in the strain rate. I can see that

As described above, although the present invention has been described by means of a limited embodiment and drawings, the present invention is not limited thereto and by those skilled in the art to which the present invention pertains, Of course, various modifications and variations are possible within the scope of equivalents of the claims to be described.

Claims

(a) forming a plurality of microfillers in each of the pair of PDMS substrates from the silicon microhole pattern;

(b) growing nanowires on a plurality of microfillers formed on the pair of PDMS substrates;

(c) coating any one of the pair of PDMS substrates with a metal film on the microfiller on which the nanowires are grown; And

(D) of the pair of the PDMS substrate, the nanowire-grown PDMS substrate and the step of engaging the PDMS substrate partially coated with a metal film in the step (c); Pressure sensor manufacturing method.
The method of claim 1,

In the step (d),

The nanowires of the PDMS substrate of step (b) and the nanowires of step (c) are coupled to each other so that the pressure sensor of the piezoresistive type, the nanowires of the PDMS substrate of step (b) and the nanowires of step (c) Biofilm-based pressure sensor manufacturing method characterized in that the metal film coated nanowires are engaged to simultaneously implement a piezoelectric pressure sensor.
The method of claim 1,

In step (a),

And the micropillar array is formed on the PDMS substrate through a soft lithography method.
The method of claim 1,

In step (b),

The nanowires are bio simulation-based pressure sensor manufacturing method characterized in that formed on the micro-pillar through hydrothermal synthesis.
The method of claim 1,

In step (a)

And a pitch size representing a distance between the micropillars formed on the PDMS substrate is 20 um.
The method of claim 2,

When the piezoelectric pressure sensor is implemented,

The nanowire structure coated with the metal film and the nanowires not coated with the metal are Schottky contact, characterized in that the bio-simulating method of manufacturing a pressure sensor.
The method of claim 2,

When implementing the piezoelectric pressure sensor

When pressure is applied while the nanowires coated with the metal film and the nanowires not coated with the metal film are engaged, positive charges are generated in the nanowires coated with the metal film, and the nanowires not coated with the metal film are applied. Bio-simulation-based pressure sensor manufacturing method characterized in that the negative charge is generated in the potential difference occurs.
The method according to any one of claims 1 to 7,

The nanowires are zinc oxide (ZnO) nanowires characterized in that the manufacturing method of the bio-simulating pressure sensor.
The bio simulation-based pressure sensor, characterized in that produced by the method of any one of claims 1 to 7.