A flexible thermosensitive sensor and its preparation method

Abstract

The present invention discloses a flexible thermal sensor and a preparation method thereof. The flexible thermal sensor includes a flexible substrate, a palladium diselenide (PdSe2) thermal film located on the substrate, metal electrodes, and a polymer encapsulation and passivation film. The specific steps of the preparation method are as follows: directly grow or transfer a layer of palladium diselenide film on the flexible substrate, and the palladium diselenide is prepared by selenization through plasma-enhanced chemical vapor deposition (PECVD). Then, deposit metal electrodes on the palladium diselenide and encapsulate it with a polymer film. The advantages of the present invention are that it is compatible with flexible substrates at low temperatures, the process is simple, it is easy to integrate, and it is convenient for large-scale production of highly sensitive flexible thermal sensors.

Description

Technical Field

[0001] The present invention belongs to the field of thermosensitive temperature sensor devices, and particularly relates to a flexible thermosensitive device and a preparation method thereof. Background Art

[0002] A temperature sensor is a device that converts temperature changes into electrical quantity changes and is widely used in daily production and life. Usually, there are two ways to measure temperature: thermocouples and resistance thermometers, which utilize the thermoelectric effect to generate potential differences and the change of material resistivity to convert into temperature changes respectively. Thermocouples are widely used to measure temperatures in the range of 100 - 1300 °C. Resistance thermometers are widely used in automatic measurement and remote measurement due to their advantages in the low-temperature range (generally -200 °C, and a few can reach -272.15 °C) and high temperature resolution. Traditional resistance thermometer materials include metals or metal alloy materials such as platinum, copper, and nickel, as well as semiconductor materials such as BaTO 3 , vanadium oxide, etc. To measure the sensitivity of resistance to temperature, the temperature coefficient of resistance (TCR) is introduced, and the magnitude of TCR is an important parameter for measuring thermosensitive devices. Since the TCR of metals is relatively low, semiconductor materials (such as vanadium oxide) are often used as the materials for thermistor devices. Summary of the Invention

[0003] The purpose of the present invention is to provide a flexible thermosensitive device and a preparation method thereof, which have the advantages of high negative TCR, good stability, wide working range, and simple preparation process.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0005] Provide a flexible thermosensitive device, including (from bottom to top): a flexible substrate, a palladium diselenide thin film thermosensitive element, a metal electrode, and a polymer encapsulation passivation film.

[0006] The substrate is a flexible substrate including PI, PDMS, PU, PMMA, etc.

[0007] The palladium diselenide thin film layer is prepared by magnetron sputtering or thermal evaporation and deposition of a metal palladium film on the substrate, and then plasma-enhanced chemical vapor deposition seleniumization; the substrate of the palladium film includes a flexible substrate (PI) and a hard substrate (SiO 2 / Si, Al 2 O 3 ); the thickness of the palladium diselenide thin film layer is 2 - 50 nanometers.

[0008] The flexible substrate of the flexible thermosensitive device is PI, PDMS, PU, PET.

[0009] The electrode is a metal electrode, the channel width between the electrodes is 1 - 500 micrometers, and the electrode thickness is 30 - 500 nanometers.

[0010] The encapsulating material is polymethyl methacrylate (PMMA), PI, or parylene film (Parylene-C).

[0011] The preparation method of the flexible thermosensitive device includes the following steps:

[0012] Step 1: Form a palladium thin film on the substrate by using vacuum coating technologies such as magnetron sputtering or thermal evaporation. After the palladium thin film is selenized by plasma-enhanced chemical vapor deposition, a palladium diselenide thin film layer is obtained.

[0013] Step 2: Use photolithography and a metal mask to form a two-terminal electrode structure, and deposit metal electrodes on the palladium diselenide thin film layer by using vacuum coating technology.

[0014] Step 3: Spin-coat a layer of PMMA, PI, or Parylene-C film on the palladium diselenide thin film layer to encapsulate it into a flexible thermosensitive device.

[0015] In the preparation method of the flexible thermosensitive device, the specific process of Step 1 is as follows:

[0016] Step 1-1 Magnetron sputtering method: Place the substrate in the magnetron sputtering chamber, use metallic palladium as the target, control the background vacuum degree of the chamber to be lower than 1×10 -3 Pa, introduce argon gas with a flow rate of 40 - 100 sccm, at a radio frequency power of 10 - 100 watts and a sputtering pressure of 1 - 10 Pa, sputter for 1 - 6 minutes to obtain a palladium thin film sputtered on the substrate with a thickness of 2 - 10 nanometers.

[0017] Thermal evaporation method: Place the substrate in the thermal evaporation chamber, use metallic palladium particles as the evaporation material, control the background vacuum degree of the chamber to be lower than 1×10 -4 Pa, control the thermal evaporation rate to be 0.3 - 2 Å / s, sputter for 1 - 10 minutes to obtain a palladium thin film sputtered on the substrate with a thickness of 2 - 10 nanometers.

[0018] Step 1-2 Plasma-enhanced chemical vapor deposition method: Place the palladium thin film obtained in Step 1-1 in the quartz tube of the tube furnace of the inductively coupled plasma generating device, evacuate the pressure in the quartz tube to a vacuum degree of 1 - 5 Pa, and inject argon gas at the front end of the tube furnace with its flow rate controlled to be 5 - 20 sccm; place selenium powder upstream of the palladium film, heat the central area of the tube furnace from room temperature to 250 °C within 20 minutes, turn on the plasma, with the radio frequency source power of 200 - 400 watts, maintain the temperature for 30 - 60 minutes, and then cool down naturally to obtain a palladium diselenide thin film.

[0019] In Step 1-1 or 1-2, use a hard substrate such as SiO 2If it is / Si, it further includes step 1-3 of transferring the palladium diselenide film to a flexible substrate. The specific process of step 1-3 is as follows:

[0020] Step 1-3(1): Take the palladium diselenide film grown on the SiO 2 / Si substrate, and spin-coat a PMMA anisole solution with a mass fraction of 5% on the surface of the palladium diselenide film;

[0021] 1-3(2): Bake the product processed in step 1-3(1) at 60-100 °C for 5-15 minutes;

[0022] 1-3(3): Place the product baked in step 1-3(2) in a hydrofluoric acid solution with a mass fraction of 5-25% and react for 3-10 minutes; until the PMMA and the palladium diselenide film are peeled off from the substrate and float in the solution;

[0023] 1-3(4): Scoop up the floating PMMA and palladium diselenide film in step 1-3(3) and place it in deionized water for repeated washing 2-4 times;

[0024] 1-3(5): Scoop up the PMMA and palladium diselenide film in step 1-3(4) with a flexible substrate and bake it at 60-80 °C for 5 minutes;

[0025] 1-3(6): Put the product prepared in step 1-3(5) into acetone to wash off the PMMA on the surface, and obtain the palladium diselenide film transferred to the flexible substrate.

[0026] The specific process of step 2 is as follows:

[0027] Step 2 Thermal evaporation coating: Place the palladium diselenide film prepared in step 1 in a thermal evaporation chamber, control the background vacuum to be lower than 1×10 -4 Pa, first evaporate indium / bismuth / chromium with a thickness control of 5-20 nanometers, and then evaporate gold / silver with a thickness control of 30-500 nanometers. Control the width of the metal inter-channel to be 1-500 microns through a metal mask or photolithography to obtain a metal electrode.

[0028] The specific process of step 3 is as follows:

[0029] Step 3 Spin coating and encapsulation: Place the device prepared in step 2 on a spin coater, drop PMMA on the palladium diselenide film, turn on the rotation, and the rotation speed is 600-3500 revolutions per minute;

[0030] Spin coating PI: The above steps can be referred to;

[0031] Parylene-c deposition: Place it in a parylene vacuum chemical vapor deposition system and deposit a 5-50 micron film;

[0032] After completion, it is encapsulated to prepare a stable flexible thermal sensor device.

[0033] The present invention has the following advantages:

[0034] 1) The present invention selects palladium diselenide, a two-dimensional material with excellent mechanical properties, optoelectronic properties, and good stability, as the thermal sensing element; it has a high negative TCR, so it has high sensitivity, good stability, and good flexibility as a flexible thermal sensor.

[0035] 2) To prepare the palladium diselenide thin film in the present invention, a palladium thin film is first prepared by magnetron sputtering or thermal evaporation vacuum coating, and then the palladium thin film is selenized; this method is simple, the film thickness is controllable, and a uniform thin film can be prepared on a large scale without introducing other impurity ions and organic solvents. It is then obtained by PECVD selenization. This process has the advantages of low synthesis temperature, can be directly grown on a flexible substrate (PI) in addition to a hard substrate, the prepared thin film is uniform, the surface is clean, and the synthesis speed is fast.

[0036] 3) The present invention can transfer the palladium diselenide thin film to a flexible substrate by a transfer method, thus expanding the selection types of the growth substrate of the palladium diselenide thin film and the flexible substrate of the thermistor device.

[0037] 4) The flexible thermal sensor structure prepared in the present invention is simple, the process is concise, there is no need to transfer materials, it is easy to integrate, and the device has low power consumption, a wide working range, high sensitivity, stable performance, is convenient for large-scale industrial production, and has great application prospects. Description of the Drawings

[0038] Figure 1 It is a schematic diagram of the device structure provided by the present invention.

[0039] Figure 2 It is the Raman spectrum image of the prepared palladium diselenide thin film provided by the present invention.

[0040] Figure 3 It is the curve of the normalized resistance of the flexible thermal sensor provided by the present invention varying with temperature from -100°C to 30°C.

[0041] Figure 4 It is the curve of the normalized resistance of the flexible thermal sensor provided by the present invention varying with temperature from 30°C to 80°C.

[0042] Figure 5 It is the curve of the normalized resistance of the flexible thermal sensor provided by the present invention varying with temperature after bending cycles.

[0043] Figure 6 It is the curve of the normalized resistance of the flexible thermal sensor prepared by transferring the palladium diselenide thin film to a flexible substrate provided by the present invention varying with temperature from 30°C to 80°C. Detailed implementation mode

[0044] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention.

[0045] Embodiment 1

[0046] A flexible thermal sensor includes a PI substrate, a palladium diselenide thin film layer located on the PI substrate, and an indium-gold electrode plated on the palladium diselenide thin film layer; the thickness of the palladium diselenide thin film layer is 4.5 nanometers; the electrode is an indium-gold electrode, the electrode spacing is 20 micrometers, and the electrode thickness is 60 nanometers.

[0047] The preparation method of the above flexible thermal sensor is as follows:

[0048] (1) Ultrasonically clean the PI substrate (with a thickness of 200 micrometers) in acetone, absolute ethanol and deionized water for 5 minutes respectively, and blow dry with nitrogen;

[0049] (2) Place the PI substrate processed in step (1) in the magnetron sputtering vacuum chamber with the PI surface facing the target; place the metal palladium target with a purity of 99.99% on the corresponding target position, and pump the air pressure in the vacuum chamber to 2×10 -3 Pa through a mechanical pump and a molecular pump; introduce 80 sccm of argon gas, adjust the radio frequency power of the radio frequency source to 15 watts, adjust the air pressure in the vacuum chamber to 3.5 Pa through a control valve, and turn off the radio frequency source after continuous sputtering for 1 minute to obtain a palladium thin film sputtered on the PI substrate;

[0050] (3) Place the PI substrate sputtered with the metal palladium thin film in step (2) in the central area of the PECVD tube furnace, place 1 gram of selenium powder with a purity of 99.9% in a quartz boat, and place the quartz boat upstream in the quartz tube (in the tube furnace); pump out the remaining air in the quartz tube through a mechanical pump, then introduce 200 sccm of argon gas to clean the quartz tube for 20 minutes, and adjust the argon gas flow rate to 10 sccm after 20 minutes; turn on the tube furnace for heating, heat the furnace body center to 250 °C within 20 minutes, then turn on the radio frequency power supply, adjust the power to 400 watts, generate plasma and keep warm for 30 minutes; then cool the product to room temperature by natural cooling to obtain a palladium diselenide thin film covering the PI substrate; as Figure 2 , Figure 2 is the Raman spectrum image of the palladium diselenide thin film prepared in the embodiment of the present invention;

[0051] (4) Place the palladium diselenide thin film prepared in step (3) on a thermal evaporation tray, fix the metal mask on the palladium diselenide thin film, and then place it in the thermal evaporation chamber. Pump the vacuum pressure to 5×10 -5Pa, and then indium and gold are evaporated, with thicknesses of 8 nanometers and 50 nanometers respectively, that is, a palladium diselenide device with a channel of 20 micrometers is fabricated.

[0052] (5) Place the device prepared in step (4) on a spin coater, and spin coat PMMA on the device channel for encapsulation at a rotation speed of 1500 revolutions per minute, that is, a flexible thermal sensor is fabricated.

[0053] Place the flexible thermal sensor prepared in this document in environments at different temperatures for testing, such as Figure 3 、 Figure 4 and Figure 5 as shown. Figure 3 is the curve of the normalized resistance of the flexible thermal sensor prepared by the present invention varying with temperature from -100 °C to 30 °C; Figure 4 is the curve of the normalized resistance of the flexible thermal sensor prepared by the present invention varying with temperature from 30 °C to 80 °C; Figure 6 is the curve of the normalized resistance varying with temperature after 500 bending cycles of the flexible thermal sensor prepared by the present invention. It can be seen from the above figure that the flexible thermal sensor prepared by the present invention has a wide working range, high sensitivity and good stability.

[0054] Example 2

[0055] A flexible thermal device includes a PI substrate, a palladium diselenide thin film layer on the PI substrate, and a gold electrode plated on the palladium diselenide thin film layer; the thickness of the palladium diselenide thin film layer is 13 nanometers; the electrode is an indium-gold electrode, the electrode spacing is 5 micrometers, and the electrode thickness is 60 nanometers.

[0056] The preparation method of the above flexible thermal sensor is as follows:

[0057] (1) Ultrasonically clean the PI and SiO 2 / Si substrate (with a thickness of 200 micrometers) in acetone, absolute ethanol and deionized water for 5 minutes respectively, and dry with nitrogen;

[0058] (2) Place the SiO 2 / Si substrate processed in step (1) in a thermal evaporation vacuum chamber, and pump the air pressure in the vacuum chamber to 5×10 -5 Pa through a mechanical pump and a molecular pump; adjust the thermal evaporation rate of palladium to 0.5 angstroms per second, and evaporate for 2 minutes to obtain a palladium thin film sputtered on the SiO 2 / Si substrate with a thickness of 6 nanometers;

[0059] (3) The SiO 2The SiO₂ / Si substrate is placed in the central area of the PECVD tube furnace. 1 gram of selenium powder with a purity of 99.9% is placed in a quartz boat, and the quartz boat is placed upstream in the quartz tube (inside the tube furnace). The residual air in the quartz tube is pumped out by a mechanical pump, and then 200 sccm of argon gas is introduced to clean the quartz tube for 20 minutes. After 20 minutes, the argon gas flow rate is adjusted to 10 sccm. The tube furnace is turned on for heating, and the temperature in the center of the furnace body is raised to 250 °C within 20 minutes. Then the radio frequency power supply is turned on, and the power is adjusted to 400 watts to generate plasma and keep it warm for 60 minutes. After that, the product is cooled to room temperature by natural cooling to obtain palladium diselenide thin film covering on the SiO₂ 2 / Si substrate.

[0060] (4) Take the palladium diselenide thin film grown on the SiO₂ 2 / Si substrate in step (3), and spin-coat a 5% mass fraction of PMMA anisole solution on the surface of the palladium diselenide thin film; bake it at 60 °C for 15 minutes; the baked product is placed in a 25% mass fraction of hydrofluoric acid solution and reacted for 5 minutes until the PMMA and the palladium diselenide thin film are peeled off from the substrate and float in the solution; the floating PMMA and palladium diselenide thin film are fished out and repeatedly washed 2 times in deionized water; the PMMA and palladium diselenide thin film in deionized water are fished out with a flexible PI substrate and baked at 80 °C for 5 minutes; then the obtained product is put into acetone to wash off the PMMA on the surface, and the palladium diselenide thin film transferred to the flexible PI substrate is prepared.

[0061] (5) Pattern the palladium diselenide thin film prepared in step (4) by lithography. After development, the material size left after Ar plasma treatment is 200×500 microns. Pattern the electrode again by lithography, and then develop.

[0062] (6) Place the product prepared in step (5) in a thermal evaporation chamber. The vacuum pressure is pumped to 3×10 -5 Pa by a mechanical pump and a molecular pump, and then bismuth and gold are evaporated with thicknesses of 6 nanometers and 60 nanometers respectively, that is, a palladium diselenide device with a 5-micron channel is prepared.

[0063] (6) Place the device prepared in step (5) on a spin coater, and spin-coat PMMA at the channel of the device for encapsulation at a rotation speed of 3500 revolutions per minute, that is, a flexible thermal sensor is prepared.

[0064] The flexible thermal sensor prepared by transferring the palladium diselenide thin film to a flexible substrate in the present invention is placed at different temperatures for testing. For example, Figure 6 is the change curve of the normalized resistance of the device with temperature from 30 °C to 80 °C. It can be seen from the figure that a highly sensitive flexible thermal sensor can also be prepared by the method of transferring the palladium diselenide thin film.

Claims

1. A flexible thermal sensor, characterized by comprising, from bottom to top: (1) a flexible substrate, (2) a palladium diselenide thermal film, (3) a metal electrode, and (4) a polymer film encapsulation layer.

2. The flexible thermal sensor according to claim 1, wherein, the palladium diselenide film layer is prepared by magnetron sputtering or thermal evaporation of a layer of palladium metal film on the substrate and then plasma-enhanced chemical vapor deposition of selenium; the thickness of the palladium diselenide film layer is 2 - 50 nanometers.

3. The flexible thermal sensor according to claim 1, wherein, the flexible substrate is PI, PDMS, PU, or PET.

4. The flexible thermal sensor according to claim 1, wherein, the electrode is a metal electrode, the channel width between the electrodes is 1 - 500 micrometers, and the electrode thickness is 30 - 500 nanometers.

5. The flexible thermal sensor according to claim 1, wherein, the encapsulation material is polymethyl methacrylate, PI, or parylene film.

6. A preparation method of the flexible thermal sensor according to any one of claims 1 - 5, wherein, it comprises the following steps: Step 1: Use vacuum coating technologies such as magnetron sputtering or thermal evaporation to form a layer of palladium film on the substrate, and after the palladium film is subjected to plasma-enhanced chemical vapor deposition of selenium, a palladium diselenide film layer is obtained; Step 2: Use photolithography and a metal mask to form a two-terminal electrode structure, and use vacuum coating technology to deposit a metal electrode on the palladium diselenide film layer; Step 3: Spin-coat a layer of polymethyl methacrylate, PI, or parylene film on the palladium diselenide film layer to encapsulate it into a flexible thermal sensor.

7. The preparation method of the flexible thermal sensor according to claim 6, wherein, the specific process of Step 1 is: Step 1-1 Magnetron sputtering method: Place the substrate in the magnetron sputtering chamber. Use palladium metal as the target. Control the background vacuum degree of the chamber to be lower than 1×10 -3 Pa. Introduce argon gas with a flow rate of 40 - 100 sccm. Under a radio frequency power of 10 - 100 watts and a sputtering pressure of 1 - 10 Pa, sputter for 1 - 6 minutes to obtain a palladium thin film sputtered on the substrate with a thickness of 2 - 10 nanometers; Thermal evaporation method: Place the substrate in a thermal evaporation chamber, use palladium metal particles as the evaporation material, control the background vacuum degree of the chamber to be lower than 1×10 -4 Pa, control the thermal evaporation rate to be 0.3 - 2 Å / s, sputter for 1 - 10 minutes to obtain a palladium thin film sputtered on the substrate with a thickness of 2 - 10 nm; Step 1 - 2 Plasma-enhanced chemical vapor deposition method: Place the palladium film prepared in Step 1 - 1 in the quartz tube of the tube furnace of the inductively coupled plasma generation device, pump the air pressure in the quartz tube to a vacuum degree of 1 - 5 Pa, and inject argon at the front end of the tube furnace, with its flow rate controlled at 5 - 20 sccm; place selenium powder upstream of the palladium film, heat the central area of the tube furnace from room temperature to 250 °C within 20 minutes, turn on the plasma, with the radio frequency source power being 200 - 400 watts, keep the temperature for 30 - 60 minutes, and then naturally cool down to obtain the palladium diselenide film.

8. The preparation method of the flexible thermal sensor according to claim 7, wherein, Step 1-1 or 1-2 uses a hard substrate such as SiO 2 / Si, and further includes step 1-3 of transferring the palladium diselenide film onto a flexible substrate. The specific process of step 1-3 is as follows: Step 1-3(1): Take a palladium diselenide thin film grown on a SiO 2 / Si substrate, and spin-coat a polymethyl methacrylate-anisole solution with a mass fraction of 5% on the surface of the palladium diselenide thin film; 1 - 3(2): Bake the product processed in Step 1 - 3(1) at 60 - 100 °C for 5 - 15 minutes; 1 - 3(3): Place the product baked in Step 1 - 3(2) in a hydrofluoric acid solution with a mass fraction of 5 - 25% and react for 3 - 10 minutes; until the polymethyl methacrylate and the palladium diselenide film are peeled off from the substrate and float in the solution; 1-3(4): Lift the floating polymethyl methacrylate and palladium diselenide film obtained in step 1-3(3) and place it in deionized water for repeated washing 2-4 times; 1-3(5): Lift the polymethyl methacrylate and palladium diselenide film in step 1-3(4) with a flexible substrate and bake it at 60-80 °C for 5 minutes; 1-3(6): Place the product obtained in step 1-3(5) in acetone to wash off the polymethyl methacrylate on the surface, and obtain a palladium diselenide film transferred onto the flexible substrate.

9. The method for preparing a flexible thermal sensor according to claim 6, characterized in that, the specific process of step 2 is as follows: Step 2: Thermal evaporation coating: Place the palladium diselenide film prepared in Step 1 into the thermal evaporation chamber, and control the background vacuum to be lower than 1×10 -4 Pa. First, evaporate indium / bismuth / chromium with a thickness controlled at 5 - 20 nm, and then evaporate gold / silver with a thickness controlled at 30 - 500 nm. Control the width of the inter-metal channel to be 1 - 500 μm through a metal mask or photolithography to obtain a metal electrode.

10. The method for preparing a flexible thermal sensor according to claim 8, characterized in that, the specific process of step 3 is as follows: Spin coating and encapsulation in step 3: Place the sensor prepared in step 2 on a spin coater, drop polymethyl methacrylate on the palladium diselenide film, turn on the rotation, and the rotation speed is 600-3500 revolutions per minute; Spin coating PI: The above steps can be referred to; Parylene film deposition: Place it in a parylene vacuum chemical vapor deposition system and deposit a 5-50 micron film; After completion, a stable flexible thermal sensor is prepared by encapsulation.

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