Method for proximity and contact signal discrimination of piezoelectric transistor dual mode sensor

Abstract

The application belongs to the technical field of electronic technology information sensing, and particularly relates to a proximity and contact signal identification method of a piezoelectric transistor dual-mode sensor. A piezoelectric capacitor is combined with a transistor to construct a piezoelectric transistor device to realize the integration of proximity sensing and contact sensing. However, the piezoelectric transistor cannot effectively distinguish the source of the sensing signal when working. The application proposes a dual-gate piezoelectric transistor proximity / contact dual-mode sensing device with an expanded gate structure, which is constructed by combining a dual-gate transistor with a piezoelectric capacitor. The piezoelectric capacitor serves as a sensing end of proximity and contact signals. The top electrode of the piezoelectric capacitor device is electrically connected with the gate electrode of the dual-gate transistor, and both are connected with the ground through a switching circuit. The other electrode of the piezoelectric capacitor device is connected with the other gate electrode of the transistor. Through the difference between the source-drain current signal response rules of proximity sensing and contact sensing in the periodic on / off process of the switching circuit, the effective distinction of the proximity sensing and contact sensing signals is realized.

Description

A method for proximity and contact signal recognition using a piezoelectric transistor dual-mode sensor Technical Field

[0001] This invention belongs to the field of electronic technology and information sensing technology, specifically relating to a method for identifying proximity and contact signals during the operation of a piezoelectric transistor proximity / contact dual-mode sensor. Background Technology

[0002] Proximity sensing and contact sensing have broad application prospects in fields such as the Internet of Things (IoT), wearable devices, and robotics. Taking human-computer interaction environments as an example, based on proximity sensors, robots can detect and track the approach of objects, thereby taking possible countermeasures to avoid unnecessary collisions. Theoretically, any long-range interaction, such as magnetic fields, electrostatics, ultrasound, and light, can be applied to the design of proximity sensor devices. Contact sensing, on the other hand, can quantify the force between the object and the robot, facilitating various operations performed by the robot on the object. Common contact sensing principles include piezoelectric, piezoresistive, and capacitive sensing. In recent years, researchers have been committed to developing multi-mode sensor devices that integrate multiple sensing functions, such as integrating proximity sensing and contact sensing functions into a single device, greatly simplifying device fabrication processes and improving device integration. The applicant's previous work integrated piezoelectric devices and thin-film transistor devices to construct a piezoelectric-transistor dual-mode sensor device. The proximity sensing function is achieved by utilizing the threshold voltage drift of the transistor caused by electrostatic induction between the charged object and the transistor; while the piezoelectric component can convert the contact signal into a voltage signal, thereby inducing the threshold voltage drift of the transistor to achieve force sensing. For details, please refer to the research papers "A Multi-Functional Flexible Ferroelectric Transistor Sensor for ElectronicSkin," *Advanced Materials Interfaces*, 8(2021)2101166 and "Ferroelectric Polarization Enhancement of Proximity Sensing Performance in Oxide Semiconductor Field-Effect Transistors," *ACS Applied Electronic Materials*, 2(2020)3443, etc. However, in piezoelectric transistor dual-mode sensors, since both proximity and contact sensing signals are fed back from the transistor source-drain current, the proximity and contact sensing signals cannot be effectively distinguished. That is, although the dual-mode device can sense the approach and contact of a charged object, it cannot distinguish whether the detected signal originates from the contact or the proximity process. This greatly limits the application of piezoelectric transistor dual-mode sensors.

[0003] Based on the above reasons, the applicant proposes a method for identifying proximity and contact signals in a piezoelectric transistor proximity / contact dual-mode sensor. Specifically, a piezoelectric capacitor with upper and lower electrodes is integrated with a dual-gate transistor to form an extended-gate transistor structure. The piezoelectric capacitor serves as the sensing end for both proximity and contact signals. The top electrode of the piezoelectric capacitor is electrically connected to the gate of the dual-gate transistor, and both are connected to ground via a switching circuit. The difference in the leakage current signal response patterns of the proximity and contact sensing sources during the periodic on / off switching of the circuit enables effective differentiation between the proximity and contact sensing signals. Summary of the Invention

[0004] The purpose of this invention is to provide a method for identifying proximity and contact signals using a piezoelectric transistor dual-mode sensor, in order to solve the problem of how to effectively distinguish between proximity and contact signals in a piezoelectric transistor proximity / contact dual-mode sensor.

[0005] The present invention provides a method for identifying proximity and contact signals during the operation of a piezoelectric transistor proximity / contact dual-mode sensor. First, a dual-gate piezoelectric transistor proximity / contact dual-mode sensor with an extended gate structure is constructed. Specifically, a dual-gate piezoelectric transistor is combined with a piezoelectric capacitor, with the piezoelectric capacitor serving as the sensing end for proximity and contact signals. Then, proximity and contact signals are identified during the operation of the dual-mode sensor. Wherein:

[0006] The dual-gate piezoelectric transistor is composed of a first gate 1, a second gate 2, a source, a drain, a first gate dielectric 1, a second gate dielectric 2, and a semiconductor.

[0007] The piezoelectric capacitor, serving as the sensing end of the dual-mode sensor, is composed of a first electrode 1, a piezoelectric element, and a second electrode 2, wherein the electrode closest to the charged target in the piezoelectric capacitor is defined as the first electrode 1.

[0008] The first electrode 1 of the piezoelectric capacitor is electrically connected to the first gate 1 of the dual-gate transistor, and both are connected to ground via a switching circuit; the second electrode 2 of the piezoelectric capacitor is connected to the second gate 2 of the dual-gate transistor; the source of the dual-gate transistor is grounded, and the drain is connected to a DC bias voltage; the source-drain current is measured and recorded by a current measuring device; see Figure 1.

[0009] The switching circuit refers to any circuit system capable of periodically connecting the first gate 1 and the first electrode 1 to ground, including relays or other circuit systems that can perform this function; the on state of the switching circuit is defined as the first gate 1 and the first electrode 1 not being connected to ground, while the off state of the switching circuit means that the first gate 1 and the first electrode 1 are electrically connected to ground.

[0010] The area of ​​the first electrode 1 of the piezoelectric capacitor should be greater than or equal to the area of ​​the second electrode 2, so as to ensure that the first electrode 1 can completely shield the electrostatic effect of the target object on the second electrode 2 after being grounded.

[0011] The target object is a charged object, which can be an insulator with a certain surface potential or a conductor to which a voltage is applied. Many common insulators in daily life and industrial production have surface potentials, such as polytetrafluoroethylene, rubber, and plastics. Even electrically neutral insulators can be charged artificially, such as through friction. Therefore, the target objects monitored here are universal and widespread.

[0012] The method for identifying proximity and contact signals during the operation of the piezoelectric transistor proximity / contact dual-mode sensor provided by the present invention is shown in Figures 2-6; the specific steps are as follows.

[0013] (1) In the first stage, there is no target object, and the source and drain current of the dual-gate transistor is at the ground state current value.

[0014] (2) In the second stage, the charged target approaches the sensing end from a distance;

[0015] (2.1) When the switching circuit is in the on state, under the electrostatic effect of the target object, equal amounts of opposite charges are induced on the first electrode 1 and capacitor 2 of the piezoelectric capacitor. The first gate 1 and second gate 2 of the dual-gate transistor, which are connected to the first electrode 1 and the second electrode 2 respectively, are induced with charges opposite to those on the first electrode 1 and the second electrode 2 respectively. The charges induced on the first gate 1 and the second gate 2 regulate the threshold voltage of the dual-gate transistor, which strengthens or inhibits the formation of conductive channels at the semiconductor / gate dielectric interface, resulting in a change in the source and drain current, thereby realizing the detection of the approach of the target object. As the distance between the target object and the sensing end decreases, the source and drain current deviates further from the ground state current. Whether the induced charges on the first gate 1 and the second gate 2 strengthen or inhibit the formation of conductive channels at the semiconductor / gate dielectric interface depends on the amount and polarity of the induced charges on the first gate 1 and the second gate 2 as well as the semiconductor type. Figure 3 shows the case when the n-type semiconductor is used, the surface potential of the target object is positive, and the switch is in the on state. Positive and negative charges are induced on the first gate 1 and the second gate 2 respectively, attracting majority carriers (electrons) in the n-type semiconductor to form channels at the semiconductor / gate dielectric 1 interface, resulting in an increase in the source and drain current.

[0016] (2.2) When the switching circuit is in the off state, the first electrode 1 and the first gate 1 are grounded, and no induced charge appears on them; and due to the shielding effect of the first electrode 1 on the second electrode 2, no induced charge appears on the second electrode 2 and the second gate 2 either; at this time, the dual-gate transistor does not respond to the approach of the target object, and the source and drain current of the transistor returns to the ground state current value; Figure 4 shows the induced charge on the first electrode 1, the second electrode 2, the first gate 1 and the second gate 2 and the channel formation when the n-type semiconductor, the surface potential of the target object is positive and the switch is in the off state; at this time, the dual-gate transistor does not sense the electrostatic effect of the target object, and the source and drain current returns to the ground state current value;

[0017] During the approach of the target object, the switching circuit is repeatedly turned on and off, and the periodic change of the source leakage current is observed in the second stage.

[0018] (3) In the third stage, the target object comes into contact with the sensing end and a force is applied;

[0019] (3.1) When the switching circuit is in the on state, due to the force acting on the piezoelectric body, equal amounts of opposite charges are induced on the first electrode 1 and the second electrode 2, and the polarity of the induced charges on the first electrode 1 and the second electrode 2 depends on the polarization state orientation of the piezoelectric body; the first gate 1 and the second gate 2 connected to the first electrode 1 and the second electrode 2 are induced with charges opposite to those on the first electrode 1 and the second electrode 2; the induced charges on the first gate 1 and the second gate 2 cause the threshold voltage of the dual-gate transistor to drift, and promote or inhibit the formation of a conductive channel at the semiconductor / gate dielectric interface, thereby causing an increase in the source drain current (corresponding to channel formation and enhancement) or a decrease in the source drain current (corresponding to channel inhibition or even destruction); the channel enhancement or inhibition depends on the amount and polarity of the induced charges on the first gate 1 and the second gate 2 and the semiconductor type; the degree to which the source drain current deviates from the ground state current value is controlled by the magnitude of the force; Figure 5 shows the case when an n-type semiconductor and a piezoelectric body are pressed and induced with negative charges on electrode 1 and positive charges on electrode 2; the induced charges on the first gate 1 and the second gate 2 promote the formation of a conductive channel at the semiconductor / gate dielectric 1 interface, thereby increasing the source drain current;

[0020] (3.2) When the switching circuit is in the off state, since the first gate 1 and the first electrode 1 are grounded, the piezoelectric material cannot generate induced charges on the first gate 1 and the first electrode 1 due to force deformation. However, unlike the situation when the switching circuit is in the off state in the second stage, the piezoelectric material still generates induced charges on the second electrode 2 and the second gate 2 due to force deformation. The induced charges on the second electrode 2 and the second gate 2 have opposite polarities, and their specific polarities depend on the polarization state in the piezoelectric material. The presence of induced charges on the second gate 2 will also cause the transistor threshold voltage to drift, thereby causing the source-drain current to deviate from the ground state current value. Moreover, when the switching circuit is in the off state, only the induced charges on the second gate 2 regulate the threshold voltage drift, while when the switching circuit is in the on state, both the second gate 2 and the first gate 1 have induced charges that regulate the transistor threshold voltage drift. Therefore, the degree of transistor threshold voltage drift in the on state is greater than that in the off state. In the off-state, i.e., the on-state, the source-drain current deviates more from the ground-state current. Therefore, under contact conditions, the on / off operation of the switching circuit still causes a change in the source-drain current of the transistor, but the source-drain current will not return to the ground-state current value in the off-state. This is different from the proximity sensing case, where the source-drain current returns to the ground-state current value when the switching circuit is off. Therefore, the difference between proximity and contact sensing can be made based on whether the source-drain current returns to the ground-state current when the switching circuit is off. Figure 6 shows the case where an n-type semiconductor and a piezoelectric body are pressed onto the second electrode 2 to induce positive charges. The negative induced charges on the second gate 2 tend to form a conductive channel at the semiconductor / gate dielectric 1 interface, resulting in a source-drain current greater than the ground-state current. However, compared with the source-drain current value when the switching circuit is on as shown in Figure 5, the source-drain current of the transistor in Figure 6 is slightly smaller than that in Figure 5.

[0021] During the process of the target object contacting the sensing end, the switching circuit is repeatedly turned on and off, and the periodic change of the source leakage current in the third stage of Figure 2 is observed.

[0022] (4) In the fourth stage, the target object is far away from the sensing end, and its effect on the regulation of the source and drain current of the dual gate transistor can be ignored. At this time, the source and drain current returns to the ground state current value.

[0023] Using the same analytical method, we can analyze cases where the surface potential of the target object is negative and the piezoelectric polarization states are oriented differently.

[0024] As can be seen from the above analysis, based on the criterion that the source-drain current returns to the ground state current value when the switching circuit is in the off state, it is possible to determine whether the piezoelectric dual-gate transistor combined sensor is working in proximity sensing or contact sensing state; while the change of current with distance and force when the switching circuit is in the on state can be used to quantify the proximity sensing and contact sensing processes.

[0025] The surface potential of the target object that can be sensed by this invention depends on the performance of the dual-gate transistor and the distance between the target object and the sensing end. The applicable absolute value of the surface potential is between 0V and 10kV, and can be 0.1V-10kV. The distance between the target object and the sensing end that can be detected depends on the surface potential of the target object and the performance of the transistor. The applicable distance is between 0-1m, and can be 10μm-1m.

[0026] The switching frequency of the switching circuit depends on the response frequency of the switching circuit system, the approach speed of the target object, and the contact time between the target object and the sensing end, and is typically 0-1kHz. During the approach of the target object to the sensing end, the switching circuit should be able to guarantee at least one cycle of on / off operation. During the contact between the target object and the sensing end, the switching circuit should also be able to guarantee at least one cycle of on / off operation.

[0027] In a dual-gate transistor structure, the semiconductor can be various silicon, oxide, organic and two-dimensional semiconductor materials, the gate dielectric can be various organic and inorganic dielectric layer materials, and the source drain gate electrodes can be various metals, conductive oxides and conductive polymer materials, etc.

[0028] In the construction of a piezoelectric capacitor, the piezoelectric body can be various piezoelectric materials that exhibit piezoelectric properties, such as inorganic crystals, ceramics, polymers, and small molecules, while the piezoelectric electrode can be various conductive materials such as metals, polymers, and oxides. Attached Figure Description

[0029] Figure 1 shows the structure of a piezoelectric dual-gate transistor proximity / contact sensor with an extended gate structure.

[0030] Figure 2 is a schematic diagram showing the variation of the source leakage current with the on / off state of the switching circuit as the target object gradually approaches and eventually contacts the sensing end.

[0031] Figure 3 shows the induced charge and channel formation on the first electrode 1, the second electrode 2, the first gate 1, and the second gate 2 when a surface-positive potential object is close to the sensing end and the switching circuit is in the on state.

[0032] Figure 4 shows the induced charge and channel formation on the first electrode 1, the second electrode 2, the first gate 1, and the second gate 2 when a surface-positive potential object is close to the sensing end and the switching circuit is in the off state.

[0033] Figure 5 shows the induced charge and channel formation on the first electrode 1, the second electrode 2, the first gate 1, and the second gate 2 when a surface-positive potential object is in contact with the sensing end and the switching circuit is in the on state.

[0034] Figure 6 shows the induced charge and channel formation on the first electrode 1, the second electrode 2, the first gate 1, and the second gate 2 when a surface-positive potential object is in contact with the sensing end and the switching circuit is in the off state.

[0035] Figure 7 shows a typical current response curve of a dual-mode sensor device based on a dual-gate oxide thin-film transistor and a piezoelectric polymer capacitor. Detailed Implementation

[0036] To enable those skilled in the art to better understand the present invention, the technical solutions in this embodiment will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. The embodiments described below are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0037] Example 1: A proximity / contact dual-mode sensor device based on a dual-gate oxide thin-film transistor and a piezoelectric polymer P(VDF-TrFE) capacitor.

[0038] Fabrication and structure of dual-gate oxide transistor: Using n-type heavily doped silicon (second gate 2) with a 300nm thick SiO2 layer (second gate dielectric 2) as a substrate, a 20nm thick indium tungsten oxide (IWO) semiconductor layer is prepared on it by magnetron sputtering. Then, indium zinc oxide (ITO) is deposited on the IWO as source and drain electrodes by magnetron sputtering and with the aid of a mask. After that, a 300nm thick polymethyl methacrylate (PMMA) is deposited on it by spin coating as the first gate dielectric 1. Finally, a 50nm thick aluminum electrode is deposited on the PMMA by vacuum thermal evaporation as the first gate 1.

[0039] Fabrication and structure of the piezoelectric capacitor: A 50 nm thick aluminum electrode (electrode 2) was deposited on a clean glass slide using a vacuum thermal evaporation process. Subsequently, a 10 μm thick P(VDF-TrFE) (vinylidene fluoride-trifluoroethylene copolymer) was spin-coated onto it as a piezoelectric body. Finally, a 50 nm thick aluminum electrode (electrode 1) was deposited on it using a vacuum thermal evaporation process. The polarization direction of the piezoelectric body was from the second electrode 2 to the first electrode 1.

[0040] The wiring connection of the extended-gate piezoelectric dual-gate transistor is consistent with that in Figure 1. A relay is used to implement the switching circuit, with a switching frequency of approximately 0.25Hz. A 2902A precision source meter is used to apply a 1V bias voltage to the transistor drain, and the source-drain current values ​​are recorded.

[0041] The target object is biased at +200V and has an area of ​​1cm². 2The copper film was used. The target object gradually approached the piezoelectric capacitor sensing end from a distance of 10 cm. After contacting the sensing end, it remained at a near-constant pressure for a period of time before finally being removed from the sensing end. The changes in source-drain current recorded during this process are shown in Figure 7. It can be seen that the transistor's ground-state current value is approximately 0.5 μA. During the approach sensing process, when the relay is open, the source-drain current increases with time (i.e., as the distance between the target object and the sensing end decreases); while when the relay is in the off state, the source-drain current returns to the ground-state current value. After the target object contacts the sensing end, if the relay is in the open state, P(VDF-TrFE) is subjected to force, generating induced charges, resulting in a source-drain current value of 0.74 μA; while when the relay is in the off state, the induced charges only appear on electrode 2 and gate 2, with limited control over the transistor threshold voltage, causing the source-drain current to decrease slightly to 0.72 μA. After the target object moves away from the sensing end, the source-drain current returns to the ground-state current value. By comparing whether the source-drain current returns to the ground-state current value when in the off state, the approach and contact processes can be clearly distinguished.

Claims

1. A method for recognizing proximity and contact signals using a piezoelectric transistor dual-mode sensor, characterized in that, First, a dual-mode proximity and contact sensor with an extended gate structure is constructed using a dual-gate piezoelectric transistor. Specifically, the dual-gate transistor is combined with a piezoelectric capacitor, which serves as the sensing end for proximity and contact signals. Then, the proximity and contact signals are identified during the operation of the dual-mode sensor. Specifically: the dual-gate transistor consists of a first gate, a second gate, a source, a drain, a first gate dielectric, a second gate dielectric, and a semiconductor; the piezoelectric capacitor consists of a first electrode, a piezoelectric element, and a second electrode, wherein the electrode closest to the charged target is defined as the first electrode; the first electrode of the piezoelectric capacitor is electrically connected to the first gate of the dual-gate transistor, and both are connected to ground via a switching circuit; the second electrode of the piezoelectric capacitor is connected to the second gate of the dual-gate transistor; the source of the dual-gate transistor is grounded, and the drain is connected to a DC bias voltage, with the source-drain current measured and recorded by a current measuring device; the on state of the switching circuit is defined as the first gate and the first electrode not being connected to ground, and the off state of the switching circuit is defined as the first gate and the first electrode being connected to ground.

2. The identification method according to claim 1, characterized in that, The area of ​​the first electrode of the piezoelectric capacitor is greater than or equal to the area of ​​the second electrode, so as to ensure that the first electrode can completely shield the electrostatic effect of the target object on the second electrode after being grounded.

3. The identification method according to claim 1, characterized in that, The target object is a charged object, which is an insulator with surface potential or a conductor to which a voltage is applied.

4. The identification method according to claim 1, characterized in that, In the dual-gate transistor, the semiconductor is various types of silicon, oxide, or organic and two-dimensional semiconductor materials, the gate dielectric is various types of organic or inorganic dielectric layer materials, and the source, drain, and gate electrodes are various types of metal, conductive oxide, or conductive polymer materials.

5. The identification method according to claim 1, characterized in that, In the piezoelectric capacitor, the piezoelectric element is an inorganic crystal, ceramic, or polymer material exhibiting piezoelectric properties, and the piezoelectric electrode is a conductive metal, polymer, or oxide material.

6. The identification method according to any one of claims 1-5, characterized in that, The identification of proximity and contact signals during the operation of the dual-mode sensor includes the following four stages: (1) Stage 1: There is no target object, and the source-drain current of the dual-gate transistor is at the ground state current value; (2) Stage 2: A charged target object approaches the sensing end from a distance; (2.1) When the switching circuit is in the open state, under the electrostatic action of the target object, equal amounts of opposite charges are induced on the first and second electrodes of the piezoelectric capacitor, and the first gate of the dual-gate transistor connected to the first electrode and the second gate of the dual-gate transistor connected to the second electrode are respectively induced with charges opposite to those of the first and second electrodes. The charge induced on the first and second gates modulates the threshold voltage of the dual-gate transistor, which can enhance or suppress the formation of conductive channels at the interface between the semiconductor and the gate dielectric, resulting in changes in the source and drain current, thereby enabling the detection of the approach of the target object. As the distance between the target and the sensing end decreases, the source drain current deviates further from the ground state current; whether the induced charge on the first gate and the second gate strengthens or inhibits the formation of the conductive channel at the interface between the semiconductor and the gate dielectric depends on the amount and polarity of the induced charge on the first gate and the second gate and the semiconductor type; positive and negative charges are induced on the first gate and the second gate respectively, attracting majority carriers in the n-type semiconductor to form a channel at the interface between the semiconductor and the gate dielectric, resulting in an increase in the source drain current; (2.2) When the switching circuit is in the off state, the first electrode and the first gate are grounded, and no induced charge appears on them; and due to the shielding effect of the first electrode on the second electrode, no induced charge will appear on the second electrode and the second gate; at this time, the dual-gate transistor does not feel the electrostatic effect of the target, and the source drain current of the dual-gate transistor returns to the ground state current value; during the approach of the target, the switching circuit is repeatedly turned on and off, and the periodic change of the source drain current in the second stage is observed; (3) In the third stage, the target comes into contact with the sensing end and applies force; (3.1) When the switching circuit is in the open state, due to the force acting on the piezoelectric body, equal amounts of opposite charges are induced on the first electrode and the second electrode, and the polarity of the induced charges on the first electrode and the second electrode depends on the polarization state orientation of the piezoelectric body; the first gate and the second gate connected to the first electrode and the second electrode are induced with charges opposite to those on the first electrode and the second electrode. The induced charges on the first and second gates cause the threshold voltage of the dual-gate transistor to drift and promote or inhibit the formation of a conductive channel at the interface between the semiconductor and the gate dielectric, thereby causing an increase or decrease in the source-drain current. Channel enhancement or suppression depends on the amount and polarity of the induced charge on the first and second gates, as well as the semiconductor type; The degree to which the source-drain current deviates from the ground state current value is controlled by the magnitude of the force; (3.2) When the switching circuit is in the off state, since the first gate and the first electrode are grounded, the piezoelectric body cannot generate induced charges on the first gate and the first electrode due to the force deformation; however, unlike the situation when the switching circuit is in the off state in the second stage, the piezoelectric body still generates induced charges on the second electrode and the second gate due to the force deformation; the polarity of the induced charges on the second electrode and the second gate is opposite, and its specific polarity depends on the polarization state in the piezoelectric body; the presence of induced charges on the second gate will also cause the transistor threshold voltage to drift, thereby causing the source-drain current to deviate from the ground state current value; Furthermore, when the switching circuit is in the off state, only the induced charge on the second gate regulates the threshold voltage drift. However, when the switching circuit is in the on state, induced charges on both the second and first gates regulate the transistor threshold voltage drift. Therefore, the degree of threshold voltage drift in the on state is greater than that in the off state, meaning that the source-drain current deviates more from the ground state current in the on state. Under contact conditions, the on and off operations of the switching circuit still cause changes in the transistor source-drain current, but the source-drain current does not return to the ground state current value when the switching circuit is off. This is different from proximity sensing, where the source-drain current returns to the ground state current value when the switching circuit is off. Therefore, the difference between proximity and contact sensing processes can be made based on whether the source-drain current returns to the ground state current when the switching circuit is off. During the process of the target object contacting the sensing end, the switching circuit is repeatedly turned on and off, and the periodic change of the source leakage current in the third stage is observed. (4) In the fourth stage, the target object is far away from the sensing end, and its effect on the regulation of the source and drain current of the dual gate transistor is negligible. At this time, the source and drain current returns to the ground state current value.

7. The identification method according to claim 6, characterized in that, The surface potential of the target object that can be sensed depends on the performance of the dual-gate transistor and the distance between the target object and the sensing end. The applicable absolute value of the surface potential is between 0V and 10kV. The distance between the target object and the sensing end that can be detected depends on the surface potential of the target object and the performance of the transistor. The applicable distance is 0-1m.

8. The identification method according to claim 6, characterized in that, The switching frequency of the switching circuit depends on the response frequency of the switching circuit system, the approach speed of the target object, and the contact time between the target object and the sensing end, specifically 0-1kHz; during the process of the target object approaching the sensing end, the switching circuit completes at least one cycle of opening and closing operations; during the process of the target object contacting the sensing end, the switching circuit completes at least one cycle of opening and closing operations.

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