A high-sensitivity two-dimensional heterojunction flexible pressure sensor and a preparation method thereof

Abstract

The application belongs to the technical field of flexible sensing electronic preparation, and particularly relates to a high-sensitivity two-dimensional heterojunction flexible pressure sensor and a preparation method thereof. The flexible pressure sensor is composed of a flexible substrate, a transition metal sulfide, a two-dimensional semiconductor material with piezoelectric properties, and a source electrode and a drain electrode; the two-dimensional piezoelectric material is arranged on the top layer of the TMD to form a heterojunction contact; the source electrode and the drain electrode form an ohmic contact with the WSe2 layer. The preparation method comprises the following steps: combining the two-dimensional semiconductor material with piezoelectric properties and the WSe2 material through a dry transfer technology, and transferring to a flexible substrate; preparing a metal electrode on a SiO2 / Si substrate through a photolithography technology, and transferring to the flexible substrate, so that the flexible pressure sensor with high sensitivity and good durability is realized. The piezoelectric effect of the two-dimensional piezoelectric material and the high mobility characteristics of the TMD material are effectively combined, and the device still has high sensitivity after being bent for many times.

Description

Technical Field

[0001] This invention belongs to the field of flexible sensing electronics fabrication technology, specifically relating to a two-dimensional heterojunction flexible pressure sensor and its fabrication method. Background Technology

[0002] Traditional piezoelectric materials mainly include inorganic piezoelectric crystals, piezoelectric ceramics, and organic piezoelectric polymers. With the development of electronics, piezoelectric materials are frequently used in various sensors and energy converters. However, for some important applications, such as artificial intelligence interface electronics, flexible wearable devices, and bio-implantable electronics, piezoelectric materials are required to be ultrathin, flexible, chemically stable, and biocompatible. Traditional piezoelectric ceramics, lacking mechanical flexibility, struggle to meet these requirements and also lack chemical stability in biological environments, potentially containing toxic components. This dilemma can be addressed by using ultrathin two-dimensional (2D) layered piezoelectric materials that possess excellent electrical and mechanical properties.

[0003] Two-dimensional piezoelectric materials are two-dimensional materials based on the piezoelectric effect and semiconductor coupling. They can be used in various micro- and nano-scale piezoelectric devices, such as highly sensitive flexible sensors, high-output-power nanogenerators, actuators, and energy harvesters. Furthermore, two-dimensional materials are easily integrated with state-of-the-art semiconductor processes and traditional electronic technologies. Combining the piezoelectric effect with other unusual properties of two-dimensional materials, such as ferromagnetism or topological insulators, may create new device design concepts and lead to superior device performance.

[0004] This invention proposes a highly sensitive two-dimensional heterojunction flexible pressure sensor. By constructing a van der Waals heterostructure on a flexible substrate, it effectively combines two-dimensional piezoelectric materials with TMD materials, overcoming the shortcomings of traditional piezoelectric devices, such as complex structures, low sensitivity, and inability to meet flexible functional requirements. Furthermore, the device maintains high pressure sensing sensitivity even after repeated bending, enabling innovative applications in flexible wearable devices and self-powered sensors. Summary of the Invention

[0005] Based on the problems and development needs of traditional piezoelectric devices mentioned above, the purpose of this invention is to propose a highly sensitive two-dimensional heterojunction flexible pressure sensor and its fabrication method.

[0006] The two-dimensional heterojunction flexible pressure sensor provided by the present invention comprises a flexible substrate (1), a two-dimensional WSe2 layer (2), a two-dimensional piezoelectric semiconductor material (3), and a source electrode and a drain electrode (4) stacked sequentially; wherein, the two-dimensional piezoelectric semiconductor material (3) and the two-dimensional WSe2 (2) form a van der Waals heterojunction; the source electrode and the drain electrode (4) form an ohmic contact with the two-dimensional WSe2 (2), and its cross-sectional view is shown in the figure. Figure 1 As shown.

[0007] The method for fabricating a high-sensitivity two-dimensional heterojunction flexible pressure sensor proposed in this invention, such as... Figure 2 The specific steps are as follows:

[0008] (1) Use a flexible material as the substrate and cut it to a suitable size;

[0009] (2) Transfer of two-dimensional WSe2 layer: A few layers (usually 5-10 layers) of WSe2 are prepared by mechanical exfoliation, and the exfoliated WSe2 is transferred to the flexible substrate by dry transfer technology using PDMS;

[0010] (3) Transfer of two-dimensional piezoelectric material: A two-dimensional piezoelectric material of appropriate thickness was prepared by mechanical exfoliation and then transferred to the WSe2 layer using PDMS;

[0011] (4) Clean the SiO2 / Si substrate step by step using acetone, ethanol and deionized water;

[0012] (5) On a clean SiO2 / Si substrate, spin-coat photoresist and pattern the spin-coated photoresist using photolithography.

[0013] (6) Deposit source and drain electrodes on a patterned SiO2 / Si substrate using a thermal evaporation process;

[0014] (7) Use PMMA as a support layer transfer electrode, and etch away the SiO2 layer with NaOH solution; transfer the source and drain electrodes on PMMA to both ends of the WSe2 layer, and remove PMMA with acetone.

[0015] Preferably, in step (1), the flexible material is selected from polyethylene terephthalate (PET) and polyethylene terephthalate (PEN), with a thickness of 100μm-500μm, which allows the device to be bent and folded at will, and the device can still achieve high-sensitivity pressure sensing after multiple bends.

[0016] Preferably, in step (3), the two-dimensional piezoelectric semiconductor material is selected from SnS2 or ZnBrI, and has a thickness of 30-50 layers. The two-dimensional piezoelectric material in the heterostructure can be used as the gate voltage applied to the WSe2 layer, and the magnitude of the external force determines the degree of electrostatic doping.

[0017] Preferably, in step (3), the two-dimensional piezoelectric semiconductor material and WSe2 are subjected to high-vacuum annealing at 100-120°C for 2-3 hours after forming a heterojunction to improve contact and enhance van der Waals interaction.

[0018] Preferably, in step (5), the photoresist is a LOR / S1818 double-layer photoresist, which has better quality.

[0019] Preferably, in step (6), the deposited metal source / drain electrodes are Cr / Au of appropriate thickness, such as Cr of 4nm-20nm and Au of 40nm-80nm, so that the metal electrodes have good ohmic contact with the WSe2 layer.

[0020] Preferably, in step (6), the vacuum degree of the thermal evaporation process is 5×10⁻⁶. -4 With a current of 100A, good electrode quality can be achieved.

[0021] The two-dimensional heterojunction flexible pressure sensor prepared in this invention operates on the following principle: The TMD material generates source-drain current under source-drain voltage. By coating its surface with a novel two-dimensional piezoelectric semiconductor material, it can function as an analog gate voltage regulator. This is mainly because the two-dimensional piezoelectric material exhibits polarization under pressure, resulting in opposite charges on its upper and lower surfaces, with the amount of charge proportional to the pressure. Therefore, the charge generated on the lower surface of the two-dimensional piezoelectric material electrostatically dops the TMD material, causing a change in the concentration of conductive carriers within the TMD material. Thus, by monitoring the change in source-drain current, the magnitude of the force acting on the two-dimensional piezoelectric material can be identified.

[0022] This invention fully leverages the nanoscale advantages of two-dimensional materials in the vertical direction by constructing a two-dimensional material heterostructure, effectively combining the piezoelectric effect of two-dimensional piezoelectric materials with the high mobility characteristics of TMD materials; at the same time, the device can still achieve highly sensitive pressure sensing after multiple bends, making it possible to innovate the application of pressure sensors in flexible wearable devices.

[0023] The advantages of this invention are:

[0024] A. This novel high-sensitivity flexible pressure sensor relies on two-dimensional piezoelectric materials, which combine piezoelectric properties with unique low-dimensional advantages. By constructing a heterostructure with it and traditional two-dimensional TMD materials, a novel high-sensitivity, high-response-speed flexible pressure sensor was fabricated.

[0025] B. This novel flexible pressure sensor uses a two-dimensional piezoelectric semiconductor material selected from SnS2 and ZnBrI, with a thickness of several tens of layers. Under the action of an external force in a vertical plane, the two-dimensional piezoelectric material can generate opposite charges on its upper and lower surfaces, and the magnitude of the external force determines the amount of charge generated. Therefore, the two-dimensional piezoelectric material in the heterostructure can be used as a gate voltage applied to the WSe2 layer, enabling controllable electrostatic doping of the TMD material. Thus, pressure can be sensed by monitoring the changes in charge carriers inside the TMD material.

[0026] C. This novel flexible pressure sensor uses a flexible material as a substrate, enabling the sensor to achieve high sensitivity even under bending conditions. This novel sensor has broad application prospects in the fields of flexible electronics and wearable devices. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the cross-sectional structure of the high-sensitivity two-dimensional flexible pressure sensor of the present invention.

[0028] Figure 2 This is a flowchart illustrating the fabrication process of the high-sensitivity two-dimensional flexible pressure sensor of the present invention.

[0029] In the figure, the numbers are: 1 is the flexible substrate, 2 is the WSe2 layer, 3 is the two-dimensional piezoelectric semiconductor material, and 4 is the source electrode and the drain electrode. Detailed Implementation

[0030] The specific implementation method of the present invention will be described in detail below with reference to the accompanying drawings. Figure 2 As shown. Clearly, the described examples are only a portion of the embodiments of the present invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0031] Example 1, the specific preparation process is as follows:

[0032] ① Cut 100μm thick PET into 10mm×15mm pieces to serve as flexible substrate 1;

[0033] ② Transfer of WSe2 layer: Using PDMS and adhesive tape, WSe2 layer 2 with a thickness of more than ten atomic layers was prepared by mechanical peeling. The peeled WSe2 was then transferred to the flexible substrate by dry transfer method.

[0034] ③ Transfer piezoelectric semiconductor SnS2: SnS2 within a specific thickness range is prepared by mechanical peeling using PDMS and tape, and the peeled two-dimensional piezoelectric semiconductor material 3 is transferred to the surface of WSe2 layer 2 by dry transfer method;

[0035] ④ Spin-coat a double layer of LOR / S1818 photoresist onto a clean SiO2 / Si substrate. First, spin-coat the LOR photoresist at 3000 rpm for 1 min, then dry at 180°C for 10 min. Next, spin-coat the S1818 photoresist at 3000 rpm for 1 min, and dry at 120°C for 1 min. Pattern the photoresist using laser direct writing. Then, immerse the substrate in S1818 developer for 28-30 s, remove the developer from the surface with deionized water, and finally dry the surface with a nitrogen air gun.

[0036] ⑤ The source electrode and drain electrode 4 are deposited by thermal evaporation process, with a vacuum degree of 5×10⁻⁶. -4 Pa, operating current is 100A, in the processed electrode, Cr thickness is 5nm and Au thickness is 50nm;

[0037] ⑥ Using PMMA as a support layer, the SiO2 sacrificial layer is etched away using NaOH solution;

[0038] ⑦ Transfer the source and drain electrodes on the PMMA to the WSe2 layer (2) and clean the PMMA with acetone;

[0039] ⑧ The prepared device was connected to the probe station, and the electrical performance of the device was tested using a semiconductor analyzer. The test results showed that the sensitivity of the device could still be maintained above 90% after 50 bends, which met the requirements of a high-sensitivity flexible pressure sensor.

[0040] Example 2, the specific preparation process is as follows:

[0041] ① Cut a 200μm thick PEN into 10mm×15mm pieces to serve as flexible substrate 1;

[0042] ② Transfer of WSe2 layer: WSe2 with a thickness of more than ten atomic layers was prepared by mechanical peeling using PDMS and tape. The peeled WSe2 was then transferred to the flexible substrate 1 by dry transfer method.

[0043] ③ Transfer of piezoelectric semiconductor ZnBrI: ZnBrI within a specific thickness range is prepared by mechanical exfoliation using PDMS and tape, and the exfoliated two-dimensional piezoelectric semiconductor material is transferred to the surface of WSe2 layer by dry transfer method;

[0044] ④ Spin-coat a double layer of LOR / S1818 photoresist onto a clean SiO2 / Si substrate. First, spin-coat the LOR photoresist at 3000 rpm for 1 min, then dry at 180°C for 10 min. Next, spin-coat the S1818 photoresist at 3000 rpm for 1 min, and then dry at 120°C for 1 min. Pattern the photoresist using laser direct writing. Afterward, immerse the substrate in S1818 developer for 28-30 s, remove the developer from the surface with deionized water, and finally dry the surface with a nitrogen gas gun.

[0045] ⑤ The source electrode and drain electrode 4 are deposited by thermal evaporation process, with a vacuum degree of 5×10⁻⁶. -4 Pa, operating current is 100A, in the processed electrode, Cr thickness is 5nm and Au thickness is 50nm;

[0046] ⑥ Using PMMA as a support layer, the SiO2 sacrificial layer is etched away using NaOH solution;

[0047] ⑦ Transfer the source and drain electrodes on the PMMA to the WSe2 layer 2, and clean the PMMA with acetone;

[0048] ⑧ The prepared device was connected to the probe station, and the electrical performance of the device was tested using a semiconductor analyzer. The test results showed that the sensitivity of the device could still be maintained above 90% after 50 bends, which met the requirements of a high-sensitivity flexible pressure sensor.

Claims

1. A method for fabricating a highly sensitive two-dimensional heterojunction flexible pressure sensor, characterized in that, The specific steps are as follows: (1) Use a flexible material as the substrate and cut it to a suitable size; (2) Transfer of two-dimensional WSe2 layer: a few-layer WSe2 was prepared by mechanical exfoliation, and the exfoliated WSe2 layer was transferred to a flexible substrate by dry transfer technology using PDMS; (3) Transfer of two-dimensional piezoelectric material: Two-dimensional piezoelectric material is prepared by mechanical exfoliation and transferred to WSe2 using PDMS; the two-dimensional piezoelectric semiconductor material is selected from SnS2 and ZnBrI. (4) Clean the SiO2 / Si substrate step by step using acetone, ethanol and deionized water; (5) On a clean SiO2 / Si substrate, spin-coat photoresist and pattern the spin-coated photoresist using photolithography. (6) Deposit source and drain electrodes on a patterned SiO2 / Si substrate using a thermal evaporation process; (7) Using PMMA as a support layer transfer electrode, the SiO2 layer is etched away with NaOH solution; the source and drain electrodes on PMMA are transferred to both ends of WSe2, and PMMA is removed with acetone; When subjected to pressure, two-dimensional piezoelectric materials exhibit polarization, resulting in opposite charges appearing on their upper and lower surfaces. The amount of charge generated is proportional to the magnitude of the pressure. The charge generated on the lower surface of the two-dimensional piezoelectric material electrostatically dops the TMD material, causing a change in the concentration of conductive carriers inside the TMD material. By monitoring the changes in source and leakage current, the magnitude of the force acting on the two-dimensional piezoelectric material can be identified.

2. The preparation method according to claim 1, characterized in that, The heterojunction of WSe2 and two-dimensional piezoelectric semiconductor material described in step (3) is subjected to high vacuum annealing at 100-120 ℃ for 2-3 h after the transfer is completed.

3. The preparation method according to claim 1, characterized in that, The photoresist mentioned in step (5) is LOR / S1818 double-layer photoresist, and the photolithography technology is laser direct writing.

4. The preparation method according to claim 1, characterized in that, The vacuum degree of the thermal evaporation process described in step (6) is 5×10⁻⁶. -4 Pa, current is 100 A-120 A.

5. The two-dimensional heterojunction flexible pressure sensor prepared by the preparation method according to any one of claims 1 to 4, characterized in that, It consists of a flexible substrate, a two-dimensional WSe2 layer, a two-dimensional piezoelectric semiconductor material, and source and drain electrodes stacked sequentially; wherein, the two-dimensional piezoelectric semiconductor material and the two-dimensional WSe2 layer form a van der Waals heterojunction; the source and drain electrodes form ohmic contacts with the two-dimensional WSe2.

6. The two-dimensional heterojunction flexible pressure sensor according to claim 5, characterized in that, The flexible substrate is selected from polyethylene terephthalate and polyethylene terephthalate, with a thickness of 100 mm to 500 mm.

7. The two-dimensional heterojunction flexible pressure sensor according to claim 5, characterized in that, The electrodes and source / drain electrodes (4) are Cr / Au electrodes, wherein the thickness of Cr is 4 nm-20 nm and the thickness of Au is 40 nm-80 nm.

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