Microstructure piezoelectric grid-based biological flexible pressure sensor and preparation process

Abstract

The application discloses a kind of biological flexible pressure sensor and preparation process based on microstructure piezoelectric grid, adopt full thin film structure, each functional layer is good, harmless to human body, can be well and biological compatible with good environmental stability.Simultaneously, the active layer of pressure sensitive sensor is polypyrrole film, is prepared using electrochemical synthesis method, and pyrrole raw material cost is low and preparation process is simple, green and environmentally friendly, low in cost.Piezoelectric layer is the mixture film of barium titanate and polydimethylsiloxane, and polydimethylsiloxane is the most commonly used flexible substrate material, and the price is relatively low, and barium titanate is the most widely used material in electronic ceramics, and the price is also very low.The application can be mass integrated with high spatial resolution.The structure of flexible pressure sensitive sensor adopts field effect structure, and can realize the application of scale array structure pressure sensitive sensing electronic skin, with high spatial resolution.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of electronic devices, and further relates to a biological flexible pressure sensor based on a microstructure piezoelectric grid and a preparation process. The present application can be applied to electronic devices in bionic electronic skin and pressure touch imaging technology. BACKGROUND

[0002] The field effect regulated pressure sensor is a sensor that uses an organic semiconductor that is easily stimulated by external stimuli to change the charge carrier density and mobility of the semiconductor, thereby causing a change in the electrical signal to achieve sensing. Compared with current mainstream pressure sensors such as piezoresistive, piezoelectric, and capacitive pressure sensors, the field effect regulated pressure sensor has the advantages of small size, easy-to-design structure, large-scale integration, strong anti-interference ability, and strong sensing ability. However, the field effect regulated pressure sensor has poor biological compatibility and gradually cannot meet the requirements of working in various complex environments. Some key problems such as high spatial resolution need to be solved.

[0003] The Electronic Science and Technology University proposed a flexible pressure sensor based on an organic field effect transistor and a preparation method thereof in its applied patent document “A flexible pressure sensor based on an organic field effect transistor and a preparation method thereof” (Patent Application No. CN 201910810036.9, Publication No. CN 110514327A). The flexible pressure sensor described in the patent is a top gate bottom contact structure, and its structure is a substrate, a biological material semiconductor layer, a plant dielectric layer, a gate electrode, and a packaging layer from bottom to top. The plant dielectric layer is made of plant leaf or petal biological material. The leaves and petals of plants, as a kind of natural biological material, have a three-dimensional cell wall network structure. When they are used in the dielectric layer and work together with the biological material semiconductor layer, the change in pressure will cause changes in the thickness and structure of the dielectric layer, thereby causing a large change in the capacitance, thereby realizing high sensitivity and high response detection of pressure. The flexible pressure sensor effectively eliminates the use of toxic reagents and is helpful for wide application in human electronic devices. However, the sensor and its preparation process still have the following deficiencies: the flexible pressure sensor of the organic field effect transistor has an active gate, which needs an external power supply to work, and under the condition of high integration of flexible electronics, pure biological materials cannot be prepared in large areas, and the device cannot be realized large-scale integration and array.

[0004] In the published paper "Energy-efficient, fully flexible, high-performance tactile sensor based on piezotronic effect: Piezoelectric signal amplified with organic field-effect transistors" (Nano Energy, 2020, 76: 105050.), Liu et al. of Shandong University proposed a gate-independent organic field-effect transistor sensor device, which uses a beta-polyvinylidene fluoride (PVDF) nanorod array with a piezoelectric effect to construct a high-performance, efficient, and fully flexible piezoelectric tactile sensor. The channel material of the sensor is the famous organic small molecule pentacene, and the PVDF nanorod array greatly improves the piezoelectric performance of the material, converting external mechanical force into piezoelectric voltage to drive the transistor sensor device. This structure of field effect transistor completely isolates the gate from the semiconductor layer and does not occur leakage current. The sensitivity of the flexible pressure-sensitive sensor reaches 5.17kPa -1 The leakage current changes under different weights of the weight, and has great development prospect in the field of wearable devices. However, the sensor device and the preparation process still have deficiencies, that is, the process of preparing the nanorod array with high piezoelectric performance is relatively complex, the channel material used is easily affected by environmental factors, resulting in poor sensing performance of the device, and the device structure is difficult to realize large-scale integration. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the prior art, and to provide a microstructure piezoelectric gate-based biological flexible pressure sensor and a preparation process, which are used to solve the problems that the existing pressure-sensitive sensor cannot realize large-area preparation with pure biological materials, the device cannot be large-scale integrated to realize high spatial resolution sensing requirements, and the working mode of the active gate of the organic field-effect transistor pressure sensor is changed.

[0006] To achieve the above objectives, this invention develops a field-effect modulated pressure-sensitive sensor. The organic semiconductor is made of the polymer polypyrrole, which can be fabricated on a large scale through electrochemical synthesis. Polypyrrole has already been used in human medical engineering for skin tissue engineering scaffolds and skin cells, and can be well used in biological systems. The piezoelectric gate of this invention is a thin film of a mixture of barium titanate and polydimethylsiloxane. This functional layer, through the design of a microstructure resembling an inverted pyramid, can enhance the sensitivity of the pressure sensor to low pressure. This invention utilizes the electromechanical conversion characteristics of the piezoelectric gate. Mechanical external force causes deformation of the piezoelectric gate layer to generate a piezoelectric gate voltage. By controlling the pressure change, the migration and transport capabilities of charge carriers in the organic semiconductor are modulated, realizing the change of electrical signal of the passive piezoelectric gate sensor. In addition, the structure of this invention adopts an organic field-effect structure. Through the array of inverted pyramid gates, a large-scale integrated sensor is formed. Each inverted pyramid gate corresponds to a pressure sensing unit, realizing a large-scale array sensor device with high spatial resolution.

[0007] The technical solution for achieving the objective of this invention is as follows:

[0008] The bio-flexible pressure sensor of this invention employs thin-film imprinting to assemble its functional layers, which include: a polysiloxane substrate layer, metal source and drain electrodes, an organic polymer layer, a polyacetamide dielectric layer, a hydrogel fixing layer, a piezoelectric gate layer, and an encapsulation layer. The functional layers are connected using non-noble metals; the organic polymer layer is made of a material possessing both biocompatibility and organic semiconductor properties; the piezoelectric gate layer is made of a material with piezoelectric properties, and its surface has an inverted pyramid-like microstructure; the hydrogel is embedded in the inverted pyramid-like microstructure of the piezoelectric gate layer to fix the interlayer structure.

[0009] The fabrication process of the bio-flexible pressure sensor of this invention includes the following steps:

[0010] Step 1: Spin-coat polysiloxane, dry to form a polysiloxane substrate, peel off and set aside;

[0011] Step 2: Electrochemical polymerization of solutions of pyrrole and sodium p-toluenesulfonate is carried out, and an organic polymer layer of appropriate thickness is prepared by controlling the polymerization current and polymerization time.

[0012] Step 3: Using electrode fabrication technology, prepare metal source and drain electrodes on an organic polymer layer;

[0013] Step 4: Spin-coat polyacetamide adhesive onto the organic polymer layer to form a polyacetamide dielectric layer;

[0014] Step 5: Spin-coating a mixture of barium titanate and polysiloxane with a component ratio of 20%, imprinting with a template, and curing and demolding to form a microstructured piezoelectric gate layer;

[0015] Step 6, the water gel fixing layer is prepared by spin coating, and the piezoelectric gate layer sample is quickly placed on the water gel fixing layer, and the gel is embedded and cured from the substrate after the microstructure is cured;

[0016] Step 7, spin coating and drying PMMA, polyacetamide or other polysiloxane on the cleaned substrate to form an encapsulation layer.

[0017] Compared with the prior art, the present application has the following advantages:

[0018] First, the piezoelectric material with microstructure is used in the biological flexible pressure sensor gate of the present application, which replaces the existing technology of external power supply regulation and control, overcomes the defects of high power consumption and high structural complexity of active gate devices, reduces the structural complexity of the biological flexible pressure sensor of the present application, realizes self-powered sensing function, and better meets the application of small power integrated circuits.

[0019] Second, the raw materials used in the biological flexible pressure sensor of the present application are high molecular silicone polymer, polypyrrole polymer and other non-biologically toxic organic materials, and the full thin film structure is adopted, and non-noble metal is used for internal connection, which overcomes the shortcomings that the existing biological sensor cannot meet the complex biological environment, so that each functional layer of the biological flexible pressure sensor of the present application has the advantages of good environmental stability, low price, no harm to human body and good compatibility with biology.

[0020] Third, the biological flexible sensor of the present application uses electrochemically synthesized polypyrrole organic polymer material, which overcomes the shortcomings that the existing field effect regulated pressure sensor has poor biological compatibility, and the material with biological compatibility and organic semiconductor characteristics cannot be prepared in large area, so that the biological flexible sensor of the present application has excellent flexibility and high stability, and is easy to adapt to biological application environment.

[0021] Fourth, the preparation process of the biological flexible pressure sensor of the present application adopts three-electrode electrochemical preparation process, the three-electrode preparation process is easy to control, the synthesis time is short, and the polypyrrole appears planar conformation semiconductor characteristics, so that the preparation process of the biological flexible sensor device of the present application is simple and the sensing performance is excellent. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a structural schematic diagram of the biological flexible pressure sensor of the present application;

[0023] Fig. 2 is a schematic diagram of an array device of the biological flexible pressure sensor of the present application;

[0024] Figure 3 is a schematic diagram of an array device acquisition system of the biological flexible pressure sensor of the present application. DETAILED DESCRIPTION

[0025] The application will be further described in detail below with reference to the accompanying drawings and examples.

[0026] Referring to Figure 1 The structure of the flexible pressure sensor of the application will be further described in detail.

[0027] The flexible pressure sensor of the application adopts a thin film to assemble each functional layer, which includes a polysiloxane substrate layer 1, a metal source-drain electrode 2, an organic polymer layer 3, a polyamide dielectric layer 4, a hydrogel fixing layer 5, a piezoelectric gate layer 6, and an encapsulation layer 7.

[0028] The metal source-drain electrode 2 adopts a non-biotoxic metal, and the thickness of the source-drain electrode is 500 nm, and the channel length is 20 μm.

[0029] The organic polymer layer 3 adopts a polypyrrole material, and the thickness is 2-20 μm.

[0030] The functional layer adopts a non-noble metal connection, and the organic polymer layer 3 adopts a material with both biocompatibility and organic semiconductor characteristics.

[0031] The piezoelectric gate layer 6 adopts a material with piezoelectric characteristics, and the surface of the piezoelectric gate layer 6 is a microstructure in the shape of a quasi-inverted pyramid. The hydrogel 5 is embedded into the quasi-inverted pyramid microstructure of the piezoelectric gate layer 6 to fix the structure between layers.

[0032] The piezoelectric gate 6 adopts a material with piezoelectric characteristics, which is a barium titanate / polysiloxane mixture, and the component ratio is 10-30%, and the thickness is 100-500 μm.

[0033] The average pyramid height of the quasi-inverted pyramid of the piezoelectric gate 6 is about 15 μm, and the distance between the pyramids is 30 μm.

[0034] The biological flexible pressure sensor of the embodiment of the application is a top-gate bottom-contact structure, and the materials and thicknesses of each layer are as follows: the source electrode and the drain electrode 2 are both zinc metal thin films, and the thickness is 500 nm; the organic channel 3 adopts a polypyrrole polymer layer, and the thickness is 2-20 μm; the substrate 1 material is polysiloxane, and the thickness is 50-100 μm; the piezoelectric gate layer 6 is composed of a barium titanate / polysiloxane mixture, and the component ratio is 10-30%, and the thickness is 100-500 μm, and has an inverted pyramid structure; the hydrogel 5 is an ether-based hydrogel containing oxygen groups, and the insulating layer 4 is composed of polyacetamide, and the thickness is 500 nm-1 μm. The encapsulation layer 7 is polyacetamide or other polysiloxane, and the thickness is 10-100 μm. The structure of the biological flexible pressure sensor of the embodiment of the application can realize a field effect transistor pressure sensor with high sensitivity and high stability.

[0035] The steps of the bio-flexible pressure sensor preparation process of the application include the following:

[0036] Step 1, spin coating polysiloxane, drying to form a substrate 1, and peeling off for standby use.

[0037] Step 2, preparing a solution of pyrrole and sodium p-toluenesulfonate for electrochemical polymerization, and preparing an organic polymer layer 3 with a corresponding thickness by controlling the polymerization current and polymerization time.

[0038] The electrochemical polymerization is an ionic solution electrochemical polymerization method, and a 9.5 cm*5.4 cm stainless steel plate is used as the working electrode and the counter electrode in a three-electrode synthesis system, an Ag / AgCl electrode is used as the reference electrode, an ionic solution of 0.2 M pyrrole and 0.05 M sodium p-toluenesulfonate is prepared, and the current density is set to 0.4 mA / cm 2 A polypyrrole film is polymerized on the stainless steel working electrode.

[0039] Step 3, preparing a source-drain electrode 2 on the organic polymer layer 3 by using an electrode preparation process.

[0040] The electrode preparation process refers to any process of photolithography, laser direct writing and electron beam direct writing to prepare an electrode pattern, and any method of physical vapor deposition of evaporation plating, magnetron sputtering, plasma enhanced chemical vapor deposition, screen printing, printing and spin coating to prepare a metal electrode.

[0041] Step 4, spin coating polyacrylamide glue on the organic polymer layer 3 to form a polyacrylamide dielectric layer 4.

[0042] Step 5, spin coating a mixture of 20% barium titanate and polysiloxane, using a template to press and imprint, and forming a microstructure piezoelectric gate 6 after curing and demolding.

[0043] Step 6, spin coating a hydrogel to prepare a hydrogel fixing layer 5, and quickly placing the piezoelectric gate 6 sample on the hydrogel fixing layer 5, and embedding the gel into the microstructure to be cured and then peeled off from the substrate.

[0044] Step 7, spin coating and drying PMMA, polyacrylamide or other polysiloxane on the cleaned substrate to form a cladding layer 7.

[0045] The organic channel layer 3 in step 2 of the bio-flexible pressure sensor preparation process of the application can also be prepared by mixing, dropping, pressing, printing and spraying using other methods and organic materials with similar properties.

[0046] In step 3 of the fabrication process of the bio-flexible pressure sensor of the present invention, the source and drain electrodes 2 can also be fabricated by laser direct writing, electron beam direct writing to prepare electrode patterns, or by any of the following methods: magnetron sputtering, plasma-enhanced chemical vapor deposition, screen printing, or spin coating to prepare metal electrodes.

[0047] Steps 1 and 4 of the bio-flexible pressure sensor fabrication process of the present invention are not limited to polyacetamide or polysiloxane, but are flexible, non-biotoxic polymer materials.

[0048] To achieve the sensing effect, refer to Figure 2 and below. Figure 3 The arrayed sensor and the pressure-sensitive testing system will be further explained separately.

[0049] The arrayed sensor shown in Figure 2(a) comprises, from top to bottom, a PI coating layer, a piezoelectric gate dielectric with a surface microstructure, a hydrogel immobilization layer, a thin PMMA insulating layer, an organic semiconductor layer of polypyrrole, and arrayed source and drain electrodes. Figure 2(a) shows Zn metal electrodes as the source and drain electrodes, which offer good biocompatibility. The microstructure is inverted pyramid-shaped, with an average cone height of approximately 15 mm. The distance between the cones is 30. Each inverted pyramid piezoelectric gate corresponds to a source-drain electrode, forming a single pressure sensing unit. These units can be connected in series to realize a large-scale array of sensor devices.

[0050] As shown in Figure 2(b), the arrayed sensor bends under pressure. The inverted pyramidal microstructure of the piezoelectric layer deforms due to the contact between the functional layers. The deformation mainly occurs in the pressing area, with the tip undergoing extrusion deformation, thereby generating the piezoelectric voltage of the sensor. This gives the arrayed sensor good flexibility, skin fit, and durability under bending conditions.

[0051] pass Figure 3 The test system uses an XY scan method for addressing and measurement. The device includes a sensor device with upper and lower cross electrode layers, a piezoelectric sensor unit layer, and a fixed encapsulation layer drain, a connector, an analog multiplexer, a pulse power supply unit controller, a preamplifier, an analog-to-digital converter, and a digital control unit. Figure 3 The Y-axis is powered sequentially by the pulse power supply unit controller. The column analog multiplexer is selected by the digital logic unit and supplies power to the column devices. The row analog multiplexer is controlled by the digital logic unit to select the X-ray activation. The analog signals are acquired by the preamplifier and analog-to-digital converter and converted into digital signals for processing by the digital logic unit. The digital logic unit is responsible for switching timing synchronization and signal correction and noise reduction. The digital logic unit initializes the pressure device array signals and stores the correction bias voltage. The entire pressure image of the array devices is acquired through synchronous XY timing scanning.

Claims

1. A microstructured piezoelectric grating-based bioflexible pressure sensor, which assembles each functional layer using thin film imprinting, and whose functional layers include: Polymer substrate layer (1), metal source drain electrode (2), organic polymer layer (3), polyamide dielectric layer (4), hydrogel fixed layer (5), piezoelectric gate layer (6), encapsulation layer (7); characterized in that the functional layer uses non-precious metal connection; the organic polymer layer (3) uses a material with both biocompatibility and organic semiconductor characteristics; the piezoelectric gate layer (6) uses a material with piezoelectric characteristics, and the surface of the piezoelectric gate layer (6) is a microstructure similar to an inverted pyramid; the hydrogel fixed layer (5) is embedded in the fixed layer interstructure of the piezoelectric gate layer (6) inverted pyramid microstructure.

2. The microstructured piezoelectric grating-based bioflexible pressure sensor according to claim 1, wherein, The metal source drain electrode (2) uses a non-biotoxic metal, and the source drain electrode has a thickness of 500 nm and a channel length of 20 μm.

3. The microstructured piezoelectric grating-based bioflexible pressure sensor according to claim 1, wherein, The organic polymer layer (3) uses a polypyrrole material, and has a thickness of 2-20 μm.

4. The microstructured piezoelectric grating-based bioflexible pressure sensor according to claim 1, wherein, The piezoelectric gate layer (6) uses a material with piezoelectric characteristics, which is a barium titanate / polysiloxane mixture, and has a component ratio of 10-30% and a thickness of 100-500 μm.

5. The microstructured piezoelectric grating-based bioflexible pressure sensor according to claim 1, wherein, The average cone height of the piezoelectric gate layer (6) inverted pyramid microstructure is 15 μm, and the distance between the cones is 30 μm.

6. The process for fabricating a microstructured piezoelectric grid based flexible pressure sensor according to claim 1, wherein, The steps of the preparation process include the following: Step 1, spin coating polysiloxane, drying to form a polysiloxane substrate (1), and peeling for standby use; Step 2, preparing a solution of pyrrole and sodium p-toluenesulfonate for electrochemical polymerization, and preparing an organic polymer layer (3) with a corresponding thickness by controlling the polymerization current and polymerization time; Step 3, using an electrode fabrication process to prepare a metal source drain electrode (2) on the organic polymer layer (3); Step 4, spin coating polyacrylamide glue on the organic polymer layer (3) to form a polyacrylamide dielectric layer (4); Step 5, spin coating a barium titanate / polysiloxane mixture with a component ratio of 20%, and using a template to press and form a microstructure piezoelectric gate layer (6) after curing and demolding; Step 6, spin coating hydrogel to prepare a hydrogel fixed layer (5), and quickly placing the piezoelectric gate layer (6) sample on the hydrogel fixed layer (5), and peeling from the substrate after the gel is embedded and cured; Step 7, spin coating and drying PMMA, polyacrylamide or other polysiloxane on a clean substrate to form an encapsulation layer (7).

7. The microstructured piezoelectric grating-based bioflexible pressure sensor fabrication process according to claim 6, wherein, The electrochemical polymerization described in Step 2 is an ionic solution electrochemical polymerization method, in which a 9.5 cm x 5.4 cm stainless steel plate is used as the working electrode and the counter electrode in a three-electrode synthesis system, an Ag / AgCl electrode is used as the reference electrode, an ionic solution of 0.2 M pyrrole and 0.05 M sodium p-toluenesulfonate is prepared, and the current density is set to 0.4 mA / cm 2 A polypyrrole film is formed on the stainless steel working electrode by polymerization.

8. The microstructured piezoelectric grating-based bioflexible pressure sensor fabrication process according to claim 6, wherein, The electrode fabrication process in step 3 refers to any one of photolithography, laser direct writing and electron beam direct writing to prepare an electrode pattern, and any one of physical vapor deposition by evaporation plating, magnetron sputtering, plasma enhanced chemical vapor deposition, screen printing and printing spin coating to prepare a metal electrode.

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