Active pressure sensing unit, preparation method and pressure sensor

Abstract

The invention discloses an active pressure sensing unit, which comprises a TFT (Thin Film Transistor) base structure and a piezoresistive film covering the TFT base structure, and is characterized in that the TFT base structure comprises a substrate, a grid electrode, a dielectric layer, a source electrode and a drain electrode which are arranged from bottom to top; the piezoresistive film is used for piezoresistive conversion and serves as an active conductive channel of the TFT base structure. According to the scheme, the micro-structure piezoresistive thin film is adopted and has the functions of a TFT conducting channel and piezoresistive sensing, and the processing technology of the TFT micro-structure is simplified; the size of the TFT base structure array is reduced to 0.5 mm, the sensing resolution can be increased to 100 DP I or even higher, and the resolution of 1 mm is achieved.

Description

Technical Field

[0001] The present application belongs to the field of sensors, and in particular relates to an active pressure sensing unit, a preparation method and a pressure sensor. Background Art

[0002] Human-computer interaction has become one of the most important technologies in the 21st century and has been developed in important fields such as robotics, electronics, and industry. Among them, tactile perception, as a supplement to visual and auditory perception, plays an important role in human-computer interaction.

[0003] The most important signal in tactile perception is pressure. Traditional pressure sensors include resistive, capacitive or piezoelectric sensors. Among them, capacitive sensors are easily affected by external electromagnetic interference, and piezoelectric sensors can only detect dynamic signals, so their application is restricted. Piezoresistive sensors have been widely studied due to their simple structure, good stability, and ability to detect static pressure.

[0004] The current mainstream active piezoresistive sensors are constructed using piezoresistive films and thin-film transistor (TFT) matrices. Piezoresistive films are usually prepared by doping conductive materials such as carbon nanotubes and carbon powder with polydimethylsiloxane (PDMS), etc., which can realize the conversion of pressure and resistance; TFTs are usually prepared using materials such as carbon nanotubes, indium gallium zinc oxide (IGZO), or semiconductor oxides as active channels, which can control the sampling of sensing points and reduce crosstalk between adjacent sensors.

[0005] However, there are still two problems with current pressure sensors: First, in terms of manufacturing, all pressure sensors of this type are prepared by independently and completely manufacturing two parts, and then synthesizing and packaging them. Therefore, the complete TFT micro-machining process, including the five-layer process of gate metal layer-dielectric layer-carbon tube conductive channel-source and drain metal layer-organic protective layer, is cumbersome, which greatly increases the uncertainty of device processing performance and reduces the device yield;

[0006] Secondly, in terms of sensor pixel density, the resolution of human fingertips is 1mm, while the previous TFT active sensor matrix unit size is 1mm, corresponding to a pixel density of 50DPI. According to the Nyquist sampling theorem, only a resolution of 2mm can be achieved, which is lower than the fingertip resolution of human fingers and it is difficult to achieve the required resolution.

[0007] Therefore, there is an urgent need for a new type of active pressure sensor that can solve the above problems. Summary of the invention

[0008] In order to address the deficiencies of the prior art, the present application provides an active pressure sensing unit, a preparation method and a pressure sensor, which optimize the device processing technology while improving the sensing resolution, and can be better applied in the field of human-computer interaction.

[0009] The technical effects to be achieved by this application are achieved through the following solutions:

[0010] According to a first aspect of the present application, an active pressure sensing unit is provided, comprising a TFT base structure and a piezoresistive film covering the TFT base structure, wherein:

[0011] The TFT basic structure includes a substrate, a gate, a dielectric layer, and a source and drain arranged from bottom to top;

[0012] The piezoresistive film is used for piezoresistive switching and serves as an active conductive channel of a TFT infrastructure.

[0013] Preferably, the piezoresistive film comprises a flexible film and a conductive layer, wherein the conductive layer covers the bottom layer of the flexible film and is used for conducting the source and the drain in the source-drain electrode.

[0014] Preferably, the conductive layer forms an inverted pyramid-shaped microstructure on the surface of the flexible film.

[0015] Preferably, the flexible film is a PDMS film, and the conductive layer is a semiconductor carbon nanotube layer spin-coated onto the PDMS film.

[0016] According to a second aspect of the present application, a method for preparing an active pressure sensing unit is provided, comprising the following steps:

[0017] Step 1: Apply photoresist on the substrate and expose to form a gate shape, and remove the remaining photoresist after sputtering to form the gate;

[0018] Step 2: After depositing a dielectric layer on the gate, applying photoresist on the dielectric layer and exposing to form source and drain shapes, sputtering to form source and drain electrodes, and removing the photoresist to complete the TFT basic structure;

[0019] Step 3: Lay the prepared piezoresistive film onto the TFT base structure to complete the preparation of the active pressure sensing unit.

[0020] Preferably, in step 3, the piezoresistive film is manufactured in an inverted pyramid-shaped microstructured silicon mold.

[0021] Preferably, in step 3, the method for preparing the piezoresistive film is:

[0022] Step 31: preparing a carbon nanotube suspension and a PDMS dilution respectively, wherein the carbon nanotube suspension is prepared by mixing carbon nanotubes and chloroform at a ratio of 10 mg / mL; and the PDMS dilution is prepared by mixing PDMS prepolymer and chloroform at a ratio of 500 mg / mL;

[0023] Step 32: Mixing the carbon nanotube suspension and the PDMS dilution to obtain a dispersion;

[0024] Step 33: After the chloroform in the dispersion is completely volatilized, a PDMS curing agent is added at a mass ratio of 10:1 of PDMS prepolymer to curing agent, and the bubbles in the solution are removed to obtain a PDMS solution;

[0025] Step 34: After spraying a stripping agent on the silicon mold with the inverted pyramid-shaped microstructure, the PDMS solution is spin-coated, and after the spin coating is completed, it is placed on a hot plate for drying, and the piezoresistive film is prepared by stripping.

[0026] Preferably, in step 3, the method for preparing the piezoresistive film is:

[0027] Step 41: Mixing PDMS prepolymer and chloroform at a ratio of 500 mg / mL to obtain a PDMS dilution solution;

[0028] Step 42: adding PDMS curing agent to the PDMS dilution solution at a mass ratio of PDMS prepolymer to curing agent of 10:1, and removing bubbles in the solution to obtain a PDMS solution;

[0029] Step 43: After the chloroform in the PDMS solution is completely volatilized, the solution is spin-coated onto a silicon mold having an inverted pyramid microstructure coated with a stripping agent, and then dried and stripped to obtain a microstructured PDMS film without a piezoresistive effect;

[0030] Step 44: On the surface of the microstructured PDMS film, carbon nanotubes are pulled by a solution method, and the piezoresistive film is prepared after drying.

[0031] According to the third aspect of the present application, a pressure sensor using the above-mentioned active pressure sensing unit is provided, comprising a structural array composed of a TFT basic structure, the size of the TFT basic structure is not greater than 0.5mm×0.5mm, the structural array is connected to a back-end driving circuit, and a piezoresistive film is laid on the surface of the structural array.

[0032] Preferably, the pattern of the source and drain electrodes in the TFT infrastructure is one or more of a flat pattern, a finger pattern, a diamond pattern and a ring pattern.

[0033] According to an embodiment of the present application, the beneficial effect of using the present active pressure sensing unit is that: a semiconductor carbon nanotube layer is directly spin-coated on the surface of PDMS, or PDMS is directly mixed with carbon nanotubes to produce a microstructured piezoresistive film, which has both the functions of TFT conductive channel and piezoresistive sensing, thereby simplifying the processing technology of TFT microstructure;

[0034] The size of the TFT infrastructure array is reduced to 0.5mm, and the sensing resolution can be increased to 100DPI or even higher, achieving a resolution of 1mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present application or the existing technical solutions, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0036] Figure 1 This is a structural schematic diagram of an active pressure sensing unit in one embodiment of the present application;

[0037] Figure 2 for Figure 1 A schematic diagram of the structure of the active pressure sensing unit when it is under pressure;

[0038] Figure 3 This is a schematic diagram of a structure array in an active pressure sensor in one embodiment of the present application;

[0039] Figure 4 Schematic diagram of the pattern of source and drain electrodes in the TFT basic structure in one embodiment of the present application. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the present application clearer, the technical solution of the present application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0041] like Figure 1 As shown, the active pressure sensing unit in one embodiment of the present application includes a TFT basic structure 10 and a piezoresistive film 20 covering the TFT basic structure 10, wherein:

[0042] The TFT basic structure 10 includes a substrate 11, a gate 12, a dielectric layer 13 and a source and drain electrode 14 arranged from bottom to top; specifically: a three-layer structure of a gate 12 metal layer-dielectric layer-source and drain metal layer is formed on a glass substrate or a silicon substrate;

[0043] The typical material of the metal layer is titanium aluminum gold, which can be expanded to other metal materials. The typical material of the dielectric layer is hafnium dioxide, which can be expanded to other dielectric materials such as yttrium oxide. The shape of the source and drain 14 can be designed to be various shapes such as interdigital, diamond, and plane. The metal layer preparation process includes but is not limited to magnetron sputtering, chemical vapor deposition, evaporation, etc., and the dielectric layer preparation process includes but is not limited to positive photolithography, negative photolithography, laser direct writing, etc.

[0044] The substrate 11 may be a glass substrate 11 , a silicon substrate 11 , or a polyimide flexible film 21 substrate 11 .

[0045] The piezoresistive film 20 is used for piezoresistive conversion and serves as an active conductive channel of the TFT infrastructure 10. The piezoresistive film 20 includes a flexible film 21 and a conductive layer 22. The conductive layer 22 covers the bottom layer of the flexible film 21 and is used for conducting the source electrode 141 and the drain electrode 142 in the source and drain electrode 14. The flexible film 21 is a PDMS film, and the conductive layer 22 is a semiconductor carbon nanotube layer spin-coated on the PDMS film.

[0046] PDMS film has excellent performance. In terms of physical properties, it has excellent elasticity and resilience. The Young's modulus of PDMS material is low, which makes the film made from it soft and easy to fit various surfaces, providing good touch comfort. In addition, PDMS film has high optical transparency, with a transmittance of more than 93% and a color refraction factor of 1.41. It is suitable for use in various working environments, such as display screens, robot grippers, etc.

[0047] In terms of chemical properties, PDMS film has excellent chemical stability, can withstand corrosion from a variety of chemicals, and is suitable for complex chemical environments. PDMS film is harmless to the human body and is a safe and environmentally friendly product. It can pass cytotoxicity, skin irritation and subcutaneous reactivity tests and is suitable for medical devices and other fields.

[0048] During the preparation, polydimethylsiloxane polymer (PDMS) is poured into a silicon mold with an inverted pyramid-shaped microstructure to make a microstructure film, and a semiconductor carbon nanotube layer is directly spin-coated on the surface to form a conductive channel of the TFT.

[0049] Accordingly, the film only forms a conductive thin layer, acting as a conductive channel of the TFT, and can be expanded into a form without a microstructure or with other materials (such as other organic matter combined with carbon tubes / carbon powder / carbon tube solution / metal powder / ion solution, etc.) as the substrate. It can also be constructed in a mixed doping manner without being limited to the spin coating method.

[0050] The pyramid-shaped microstructure can produce a large deformation under a small force, causing a large change in the contact area between the piezoresistive film and the electrode, and a large resistance change rate. Compared with the conductive layer without a microstructure contact area, it can greatly improve the sensitivity.

[0051] The above active pressure sensing unit includes two situations in the pressure sensing process: whether there is a gate voltage and whether there is pressure applied.

[0052] In the case of whether the gate voltage is applied: the piezoresistive film is covered on the surface of the source and drain. When no voltage is applied to the gate, regardless of whether pressure is applied or not, there is a higher voltage value between the source and drain, and the current signal of the source is very small;

[0053] By applying a negative voltage to the gate G, the piezoresistive film is attracted to form a conductive channel, the TFT is turned on, and the current signal of the source s is detected, thereby realizing active sensing of pressure.

[0054] In the case of whether pressure is applied, when there is no pressure, the contact resistance between the source S and the drain D is very high and almost non-conductive, such as Figure 2 As shown in a: When pressure is applied to the film, the microstructure of the piezoresistive film is deformed, the contact area between the source S and the drain D increases, and the resistance decreases, but the resistance at this time still maintains a high value; Figure 2 bWhen the gate voltage is applied and a conductive channel is formed on the surface of the film, the resistance between the source and the drain is greatly reduced, realizing active pressure sensing.

[0055] In one embodiment of the present application, the preparation method of the active pressure sensing unit comprises the following steps:

[0056] Step 1: Apply photoresist on the substrate and expose to form a gate shape, and remove the remaining photoresist after sputtering to form the gate;

[0057] In this step, taking a rigid glass substrate as an example, a photoresist is applied on the substrate and then a gate pattern is formed by a photolithography process, 20nm titanium and 90nm gold or other metals are sputtered or evaporated onto the glass surface, and then the remaining photoresist is removed from the glass to form a gate;

[0058] Step 2: After depositing a dielectric layer on the gate, apply photoresist on the dielectric layer and expose to form the source and drain shapes. After sputtering to form the source and drain, remove the photoresist to complete the TFT basic structure.

[0059] In this step, a dielectric layer with a thickness of 15 nm is deposited on the gate. The material of the dielectric layer is HfO2, which can also be replaced by other inorganic substances. Finally, the source and drain patterns are formed by photolithography, and the source and drain metal layers are sputtered or evaporated. The materials of the source and drain are palladium and gold, which can also be replaced by other metals.

[0060] The TFT basic structure is manufactured based on traditional micro-machining technology, which does not limit the type of process. Compared with other TFTs, its advancedness lies in the omission of the active conductive layer and the top protective layer, which greatly simplifies the processing technology.

[0061] Step 3: Lay the prepared piezoresistive film onto the TFT base structure to complete the preparation of the active pressure sensing unit.

[0062] In this step, the piezoresistive film can be directly laid on the TFT infrastructure to simplify the process flow; in order to ensure the robustness of the device, an additional layer of film such as silicone or polyimide can also be encapsulated to ensure safety and reliability during use.

[0063] There are two methods for preparing piezoresistive films, namely, the mixed solution piezoresistive film production process and the carbon tube pulling piezoresistive film production process. The specific method of the mixed solution piezoresistive film production process is as follows:

[0064] Step 31: preparing a carbon nanotube suspension and a PDMS dilution respectively, wherein the carbon nanotube suspension is prepared by mixing carbon nanotubes and chloroform at a ratio of 10 mg / mL; and the PDMS dilution is prepared by mixing PDMS prepolymer and chloroform at a ratio of 500 mg / mL;

[0065] In this step, taking the preparation of a 4% concentration carbon nanotube piezoresistive film as an example, 4 g of carbon nanotube powder is prepared into a mixed solution of carbon nanotubes and chloroform at a ratio of 10 mg / mL, and ultrasonicated at a power of 180 W for 1 h to obtain a carbon nanotube suspension;

[0066] 174 g of PDMS prepolymer was prepared into a mixed solution of PDMS prepolymer and chloroform at a ratio of 500 mg / mL, and magnetically stirred at 500 r / min for 15 min to obtain a PDMS dilution solution;

[0067] Step 32: Mixing the carbon nanotube suspension and the PDMS dilution to obtain a dispersion;

[0068] In this step, the carbon nanotube suspension and the PDMS dilution solution are mixed and then dispersed by 180W ultrasonic wave for 1 hour to obtain a dispersion.

[0069] Step 33: After the chloroform in the dispersion is completely volatilized, a PDMS curing agent is added at a mass ratio of 10:1 of PDMS prepolymer to curing agent, and the bubbles in the solution are removed to obtain a PDMS solution;

[0070] In this step, the dispersion was placed on a hot plate and magnetically stirred to evaporate the chloroform. The temperature was set to 61.2°C, the boiling point of chloroform, and the heating time was 1 h.

[0071] After adding the PDMS curing agent, the mixture was fully stirred and then vacuumed at room temperature for about 30 minutes to remove bubbles in the solution to obtain a PDMS solution.

[0072] Step 34: After spraying a stripping agent on the silicon mold with the inverted pyramid-shaped microstructure, the PDMS solution is spin-coated, and after the spin coating is completed, it is placed on a hot plate for drying, and the piezoresistive film is prepared by stripping.

[0073] In this step, a stripping agent is sprayed on the surface of the silicon mold with a microstructure, and PDMS is spin-coated on the surface of the silicon mold at a certain rotation speed. The rotation speed can be adjusted according to the required thickness of the PDMS. The film and the silicon plate are then placed on a hot plate and dried at 85°C for 2 hours to further remove excess chloroform and moisture, and the preparation of the mixed solution piezoresistive film is completed by stripping.

[0074] The preparation method of the carbon tube pulling piezoresistive film manufacturing process is as follows:

[0075] Step 41: Mixing PDMS prepolymer and chloroform at a ratio of 500 mg / mL to obtain a PDMS dilution solution; in this step, 174 g of PDMS prepolymer is taken to prepare a PDMS prepolymer and chloroform mixed solution at a ratio of 500 mg / mL, and magnetically stirred at 500 r / min for 15 minutes to obtain a PDMS dilution solution;

[0076] Step 42: adding PDMS curing agent to the PDMS dilution solution at a mass ratio of PDMS prepolymer to curing agent of 10:1, and removing bubbles in the solution to obtain a PDMS solution;

[0077] In this step, after adding the PDMS curing agent, the mixture is fully stirred and then vacuumed at room temperature for about 30 minutes to remove bubbles in the solution to obtain a PDMS solution;

[0078] Step 43: After the chloroform in the PDMS solution is completely volatilized, the solution is spin-coated onto a silicon mold with an inverted pyramid microstructure coated with a stripping agent, and then dried and stripped to obtain a microstructured PDMS film without a piezoresistive effect;

[0079] In this step, the PDMS solution was placed on a hot plate and magnetically stirred to evaporate the chloroform. The temperature was set to 61.2°C, the boiling point of chloroform, and the heating time was 1 h until the chloroform was completely evaporated.

[0080] Spray the stripping agent on the surface of the silicon mold with microstructures, spin-coat the PDMS solution on the surface of the silicon mold at a certain speed, which can be adjusted according to the required thickness of the PDMS, and then place the film and silicon plate on a hot plate and bake at 85°C for 2 hours to further remove excess chloroform and moisture, and peel off to form a microstructured PDMS film without piezoresistive effect. At this time, the film surface has an inverted pyramid-shaped microstructure.

[0081] Step 44: On the surface of the microstructured PDMS film, carbon nanotubes are pulled by a solution method, and the piezoresistive film is prepared after drying.

[0082] In this step, carbon nanotubes are pulled on the surface of the microstructured PDMS film, i.e., the side containing the inverted pyramid-shaped microstructure, by using a solution method, and then dried at 85° C. for 2 hours to complete the preparation of the carbon nanotube pulled piezoresistive film.

[0083] like Figure 3 As shown, a pressure sensor using the above-mentioned active pressure sensing unit includes a structural array composed of a TFT basic structure, the size of the TFT basic structure is not greater than 0.5mm×0.5mm, the structural array is connected to a back-end driving circuit, and a piezoresistive film is laid on the surface of the structural array.

[0084] In this embodiment, a glass substrate or silicon substrate is covered with a PI flexible film, a three-layer structure of an array gate metal layer-dielectric layer-source and drain metal layer is formed on the PI flexible film, and a piezoresistive film is matched to form a TFT active sensing matrix, and a laser lift-off method is used for flexible lift-off. The array structure can also be directly formed on silicon, glass, or other rigid substrates to make a rigid pressure sensor.

[0085] The TFT basic structure size in this embodiment is designed to be 0.5mm×0.5mm, and is matched with a piezoresistive film and a back-end driving circuit to form a surface array sensor with a sensing density of 100DPI. According to the Nyquist sampling theorem, a sensing unit with a spacing of 0.5mm can achieve a sensing resolution of 1mm, which is comparable to the fingertip resolution of a human finger. At the same time, by designing the back-end circuit to perform row and column scanning of the signal, active sensing of the entire surface array sensor is realized.

[0086] like Figure 4 As shown, the pattern of the source and drain electrodes in the TFT basic structure can be arbitrarily extended, and can be a flat pattern corresponding to a typical source and drain electrode structure (such as Figure 4 a), or a cross-finger pattern (as shown in Figure 4 b), one of the diamond patterns and the circular ring patterns, or a combination of multiple patterns, can effectively increase the overlapping area between the source and drain electrodes and enhance the conduction ability of the TFT.

[0087] The beneficial effects of using the active pressure sensing unit are: directly spin coating a semiconductor carbon nanotube layer on the surface of PDMS, or directly mixing PDMS with carbon nanotubes to make a microstructured piezoresistive film, which has the functions of TFT conductive channel and piezoresistive sensing, and simplifies the processing technology of TFT microstructure;

[0088] The size of the TFT infrastructure array is reduced to 0.5mm, and the sensing resolution can be increased to 100DPI or even higher, achieving a resolution of 1mm.

[0089] It should be noted that the above detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present application belongs.

[0090] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should also be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0091] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein.

[0092] In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or inherent to these processes, methods, products, or apparatuses.

[0093] For ease of description, spatially relative terms, such as "above", "above", "on the upper surface of", "above", etc., may be used herein to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" may include both "above" and "below". The device may also be positioned in other different ways, such as rotated 90 degrees or in other orientations, and the spatially relative descriptions used herein are interpreted accordingly.

[0094] In the above detailed description, reference is made to the accompanying drawings, which form a part of this document. In the accompanying drawings, similar symbols typically identify similar components unless the context indicates otherwise. The illustrated embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be used, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein.

[0095] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An active pressure sensing unit, characterized in that: The invention comprises a TFT basic structure and a piezoresistive film covering the TFT basic structure, wherein: The TFT basic structure includes a substrate, a gate, a dielectric layer, and a source and drain arranged from bottom to top; The piezoresistive film is used for piezoresistive switching and serves as an active conductive channel of a TFT infrastructure.

2. The active pressure sensing unit according to claim 1, characterized in that: The piezoresistive film comprises a flexible film and a conductive layer. The conductive layer covers the bottom layer of the flexible film and is used for conducting the source and the drain in the source and drain electrodes.

3. The active pressure sensing unit according to claim 2, characterized in that: The conductive layer forms an inverted pyramid-shaped microstructure on the surface of the flexible film.

4. The active pressure sensing unit according to claim 2, characterized in that: The flexible film is a PDMS film, and the conductive layer is a semiconductor carbon nanotube layer spin-coated on the PDMS film.

5. A method for preparing an active pressure sensing unit according to any one of claims 1 to 4, characterized in that: The steps include: Step 1: Apply photoresist on the substrate and expose to form a gate shape, and remove the remaining photoresist after sputtering to form the gate; Step 2: After depositing a dielectric layer on the gate, applying photoresist on the dielectric layer and exposing to form source and drain shapes, sputtering to form source and drain electrodes, and removing the photoresist to complete the TFT basic structure; Step 3: Lay the prepared piezoresistive film onto the TFT base structure to complete the preparation of the active pressure sensing unit.

6. The preparation method according to claim 5, characterized in that: In step 3, the piezoresistive film is fabricated in an inverted pyramid-shaped microstructured silicon mold.

7. The preparation method according to claim 6, characterized in that: In step 3, the preparation method of the piezoresistive film is: Step 31: preparing a carbon nanotube suspension and a PDMS dilution respectively, wherein the carbon nanotube suspension is prepared by mixing carbon nanotubes and chloroform at a ratio of 10 mg / mL; and the PDMS dilution is prepared by mixing PDMS prepolymer and chloroform at a ratio of 500 mg / mL; Step 32: Mixing the carbon nanotube suspension and the PDMS dilution to obtain a dispersion; Step 33: After the chloroform in the dispersion is completely volatilized, a PDMS curing agent is added at a mass ratio of 10:1 of PDMS prepolymer to curing agent, and the bubbles in the solution are removed to obtain a PDMS solution; Step 34: After spraying a stripping agent on the silicon mold with the inverted pyramid-shaped microstructure, the PDMS solution is spin-coated, and after the spin coating is completed, it is placed on a hot plate for drying, and the piezoresistive film is prepared by stripping.

8. The preparation method according to claim 6, characterized in that: In step 3, the preparation method of the piezoresistive film is: Step 41: Mixing PDMS prepolymer and chloroform at a ratio of 500 mg / mL to obtain a PDMS dilution solution; Step 42: adding PDMS curing agent to the PDMS dilution solution at a mass ratio of PDMS prepolymer to curing agent of 10:1, and removing bubbles in the solution to obtain a PDMS solution; Step 43: After the chloroform in the PDMS solution is completely volatilized, the solution is spin-coated onto a silicon mold having an inverted pyramid microstructure coated with a stripping agent, and then dried and stripped to obtain a microstructured PDMS film without a piezoresistive effect; Step 44: On the surface of the microstructured PDMS film, carbon nanotubes are pulled by a solution method, and the piezoresistive film is prepared after drying.

9. A pressure sensor using the active pressure sensing unit according to any one of claims 1 to 4, characterized in that: The invention comprises a structural array composed of a TFT basic structure, wherein the size of the TFT basic structure is not greater than 0.5mm×0.5mm, the structural array is connected with a back-end driving circuit, and a piezoresistive film is laid on the surface of the structural array.

10. The pressure sensor according to claim 9, characterized in that: The pattern of the source and drain electrodes in the TFT infrastructure is one or more of a flat pattern, a finger pattern, a diamond pattern and a ring pattern.

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