Based on VO 2 Thin film temperature sensor and preparation method thereof

Abstract

The present invention provides a VO-based 2 A thin film temperature sensor and a preparation method thereof, belonging to the technical field of temperature sensors, wherein the VO based 2 The thin film temperature sensor includes a metal electrode, a single crystal silicon substrate, a protective layer, a buffer layer, a VO 2 Thin film, metal electrode. In the temperature sensor based on VO2 thin film of the present invention, the phase transition temperature of VO2 thin film reaches 73.6°C, and the phase transition amplitude R reaches 1097.31, so that it can adapt to the working environment higher than the intrinsic phase transition temperature of VO2, and has excellent electrical properties.

Description

Technical Field

[0001] The present invention belongs to the technical field of temperature sensors and particularly relates to a method based on VO 2 A thin film temperature sensor and a method for preparing the same. Background Art

[0002] A temperature sensor is a device that converts temperature variables into a transmittable standardized output signal. It has important applications in many fields. It can sense the temperature information of the measured object and convert the sensed temperature information into electrical signals or other required forms of information output according to certain rules to meet the requirements of information transmission, processing, storage, display, recording and control.

[0003] Vanadium dioxide (VO 2 ) is a typical phase change material. Pure vanadium dioxide undergoes a reversible and ultrafast (sub-picosecond) transition from a low-temperature semiconductor phase to a high-temperature metal phase at 68°C, accompanied by a transition from a monoclinic structure to a tetragonal rutile structure. This process is also accompanied by a mutation in a variety of basic physical properties such as electrical properties, optical properties, mechanical properties, electrochemical properties, magnetic properties, and thermal properties, which has attracted widespread attention. Based on these mutations in physical properties, VO 2 Can be made into various devices.

[0004] In recent years, smart sensors based on phase change materials have attracted people's attention. 2 The excellent phase change characteristics of VO have great development potential. Since the phase change width (i.e. the temperature interval between the phase change) is only a dozen degrees Celsius, but the phase change amplitude (the amplitude of the resistance change before and after the phase change) reaches 3-4 orders of magnitude, the RT (resistance-temperature) characteristic curve is extremely steep, showing extremely sensitive characteristics to temperature. 2 The prepared temperature sensor will show extremely sensitive response when working near the phase transition temperature. 2 The phase transition temperature is low, only 68°C, and cannot adapt to temperatures higher than VO 2 The intrinsic phase transition temperature of the working environment, and VO 2 The poor growth quality and reduced phase change characteristics on single crystal silicon substrates also seriously affect the VO-based 2 Electrical properties of thin film devices. Summary of the invention

[0005] In view of this, the present invention provides a VO-based 2 Thin film temperature sensor and preparation method thereof, the VO based 2 Thin film temperature sensors can adapt to higher than VO 2 The working environment of intrinsic phase transition temperature has excellent electrical properties.

[0006] The technical solution adopted by the present invention to solve the technical problem is as follows:

[0007] A VO-based 2 The thin film temperature sensor includes a metal electrode, a single crystal silicon substrate, a protective layer, a buffer layer, a VO 2 Thin film, metal electrodes.

[0008] Preferably, the buffer layer is GeO 2 film.

[0009] Preferably, the protective layer is an Au thin film.

[0010] Preferably, the metal electrode is a gold electrode.

[0011] Preferably, the VO 2 The thickness of the film is 100-300nm.

[0012] The present invention also provides a VO-based 2 A method for preparing a thin film temperature sensor comprises the following steps:

[0013] Step 1: Cleaning the single crystal silicon substrate, ultrasonically cleaning the single crystal silicon substrate with anhydrous ethanol and deionized water in sequence, and then drying it with nitrogen for later use;

[0014] Step 2: Prepare a gold electrode on the non-polished surface of a single crystal silicon substrate by magnetron sputtering to obtain sample 1;

[0015] Step 3: Using magnetron sputtering method to prepare Au thin film as protective layer on the polished surface of single crystal silicon substrate to obtain sample 2;

[0016] Step 4: Deposit GeO on the surface of sample 2 prepared in step 3 by magnetron sputtering 2 The film was used as a buffer layer and annealed to obtain sample 3;

[0017] Step 5: Deposit VO on the surface of sample 3 prepared in step 4 by magnetron sputtering 2 The film was annealed to obtain sample 4;

[0018] Step 6: Prepare another gold electrode on the surface of sample 4 prepared in step 5 by magnetron sputtering, and obtain VO based 2 Thin film temperature sensor.

[0019] Preferably, the magnetron sputtering conditions used in steps 2, 3 and 6 are: sputtering time is 180-200 s, vacuum degree is 0.6-0.8 Pa, and current is 10 mA.

[0020] Preferably, the magnetron sputtering process in step 4 and step 5 is as follows: the chamber is evacuated to 3.4×10 -4 Pa, use argon to purge the cavity three times, then continue to introduce argon at a flow rate of 60sccm, adjust the mechanical pump valve to adjust the cavity vacuum to 0.6Pa, then turn on the RF power, sputter at a power of 80w for 9-10min, and anneal the sputtered film at 540-550℃ for four hours.

[0021] It can be seen from the above technical solution that the present invention provides a VO-based 2 Compared with the prior art, the thin film temperature sensor has the following advantages: 2 The thin film temperature sensor includes a metal electrode, a single crystal silicon substrate, a protective layer, a buffer layer, a VO 2 Thin film, metal electrode, the current direction of the sensor is perpendicular to VO when working 2 The direction of the film interface, that is, the current passes through the single crystal silicon substrate, protective layer, buffer layer, VO 2 Thin film, by setting a protective layer on the surface of the single crystal silicon substrate to prevent the silicon dioxide layer produced by oxidation of the single crystal silicon substrate surface from blocking the current loop, improving the verticality of the sensor to VO 2 The electrical properties in the film interface direction are determined by setting the buffer layer to VO 2 Provide a suitable environment for the growth of thin films to improve VO 2 The crystallinity and quality of the film, at the same time, the synergistic growth of the protective layer and the buffer layer promotes the VO 2 The crystallinity of the film is improved, thereby improving VO 2 The phase change characteristics of the film. 2 Thin film temperature sensor VO 2 The phase transition temperature of the film reaches 73.6°C and the phase transition amplitude R reaches 1097.31, which enables it to adapt to higher than VO 2 The working environment of intrinsic phase transition temperature (68℃) has excellent electrical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The present invention is based on VO 2 Schematic diagram of the structure of a thin film temperature sensor.

[0023] Figure 2 The VO-based 2 Schematic diagram of the structure of a thin film temperature sensor.

[0024] Figure 3 The VO based2 RT characteristic curve of thin film temperature sensor.

[0025] In the figure: T represents VO 2 The phase transition temperature of the film, Tc represents the phase transition temperature of the cooling curve, Th represents the phase transition temperature of the heating curve, and H represents VO 2 The thermal hysteresis width, R, of the film represents the amplitude of the phase transition. DETAILED DESCRIPTION

[0026] The technical solutions and technical effects of the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings of the present invention.

[0027] The present invention provides a VO-based 2 The thin film temperature sensor includes a metal electrode, a single crystal silicon substrate, a protective layer, a buffer layer, a VO 2 Thin film, metal electrodes.

[0028] Furthermore, the buffer layer is GeO 2 Thin film. 2 The growth of thin films is highly dependent on the crystal structure of the substrate material. VO is directly prepared on single crystal silicon. 2 It is not easy to obtain high-quality thin films. GeO 2 The crystal has a rutile-like structure and is similar to VO 2 High temperature is similar, making VO 2 Easier to grow than GeO 2 VO prepared on 2 The film has high crystallinity and quality, and the resistance change before and after the phase change can reach 3-4 orders of magnitude.

[0029] Furthermore, the protective layer is an Au film. The surface of single crystal silicon is easily oxidized to produce a layer of silicon dioxide, which has a large resistance. When the silicon dioxide layer is thicker, the current loop in the direction perpendicular to the film interface is equivalent to being disconnected, which will reduce the electrical performance of the device. The present invention uses an Au film to cover the surface of single crystal silicon as a protective layer, which can prevent the single crystal silicon from being oxidized to produce a silicon dioxide layer.

[0030] Furthermore, the metal electrode is a gold electrode.

[0031] Furthermore, the VO 2 The thickness of the film is 100-300nm.

[0032] The present invention is based on VO 2 A method for preparing a thin film temperature sensor comprises the following steps:

[0033] Step 1: Cleaning the single crystal silicon substrate, ultrasonically cleaning the single crystal silicon substrate with anhydrous ethanol and deionized water in sequence, and then drying it with nitrogen for later use;

[0034] Step 2: Prepare a gold electrode on the non-polished surface of a single crystal silicon substrate by magnetron sputtering to obtain sample 1;

[0035] Step 3: Using magnetron sputtering method to prepare Au thin film as protective layer on the polished surface of single crystal silicon substrate to obtain sample 2;

[0036] Step 4: Deposit GeO on the surface of sample 2 prepared in step 3 by magnetron sputtering 2 The film was used as a buffer layer and annealed to obtain sample 3;

[0037] Step 5: Deposit VO on the surface of sample 3 prepared in step 4 by magnetron sputtering 2 The film was annealed to obtain sample 4;

[0038] Step 6: Prepare another gold electrode on the surface of sample 4 prepared in step 5 by magnetron sputtering, and obtain VO based 2 Thin film temperature sensor.

[0039] Furthermore, the magnetron sputtering conditions used in steps 2, 3 and 6 are: sputtering time is 180-200 s, vacuum degree is 0.6-0.8 Pa, and current is 10 mA.

[0040] Furthermore, the magnetron sputtering process in step 4 and step 5 is as follows: the chamber is evacuated to 3.4×10 -4 Pa, use argon to purge the cavity three times, then continue to introduce argon at a flow rate of 60sccm, adjust the mechanical pump valve to adjust the cavity vacuum to 0.6Pa, then turn on the RF power, sputter at a power of 80w for 9-10min, and anneal the sputtered film at 540-550℃ for four hours.

[0041] Example 1

[0042] The present invention is based on VO 2 A method for preparing a thin film temperature sensor comprises the following steps:

[0043] Step 1: Cleaning the single crystal silicon substrate, ultrasonically cleaning the single crystal silicon substrate with anhydrous ethanol and deionized water in sequence, and then drying it with nitrogen for later use;

[0044] Step 2: A gold electrode is prepared on the non-polished surface of a single crystal silicon substrate by magnetron sputtering to obtain sample 1; specifically, an ion sputtering apparatus is used to sputter a small area of ​​Au film on the polished surface of the device single crystal silicon substrate as the gold electrode 1; the sputtering time is 200 s, the vacuum degree is 0.6-0.8 Pa, and the current is 10 mA;

[0045] Step 3: Using magnetron sputtering method to prepare Au thin film as protective layer on the polished surface of single crystal silicon substrate to obtain sample 2;

[0046] Step 4: Deposit GeO on the surface of sample 2 prepared in step 3 by magnetron sputtering 2 The film was used as a buffer layer and annealed to obtain sample 3. Before sputtering, the chamber was evacuated to 3.4×10 -4 Pa, argon gas was used to purge the chamber three times, and then argon gas was continuously introduced at a flow rate of 60 sccm, and the mechanical pump valve was adjusted to adjust the vacuum degree of the chamber to 0.6 Pa. At this time, the RF power was turned on, and sputtering was performed at a power of 80w for 10min. The sputtered film was annealed at 550℃ for four hours;

[0047] Step 5: Deposit VO on the surface of sample 3 prepared in step 4 by magnetron sputtering 2 The film is annealed under the same annealing conditions as step 4 to obtain sample 4;

[0048] Step 6: Use magnetron sputtering to prepare a gold electrode 2 on the surface of the sample 4 prepared in step 5, so as to obtain a VO-based 2 The sputtering conditions are the same as those in step 3. The structure is as follows: Figure 1 shown.

[0049] To embody the present invention based on VO 2 The advantages of thin film temperature sensors, the following three temperature sensors were prepared as comparisons, please refer to Figure 2 , Figure 2 The VO-based 2 Schematic diagram of the structure of the thin film temperature sensor, where: a is the comparative example 1 without GeO 2 a is a schematic diagram of the structure of the buffer layer, b is a schematic diagram of the structure of comparative example 2 without the Au protective layer, and c is a schematic diagram of the structure of comparative example 3 only with the device current parallel to the film interface direction.

[0050] Comparative Examples 1-3 based on VO 2 The thin film temperature sensor is prepared as follows:

[0051] Comparative Example 1: Based on VO according to Example 1 2The device preparation method of the thin film temperature sensor omits step 3 and prepares the temperature sensor without the Au protective film.

[0052] Comparative Example 2: Based on VO according to Example 1 2 The device preparation method of the temperature sensor of the thin film is omitted, and the device preparation method of the temperature sensor without GeO is prepared. 2 Buffer film temperature sensor.

[0053] Comparative Example 3: According to the device preparation method of Example 1, step 6 is repeated, and another gold electrode is prepared on the upper surface of the sample in step 6. The gold electrode cannot contact with another gold electrode on the upper surface of the sample.

[0054] The electrical properties of the sensors based on the critical temperature of vanadium dioxide thin films prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were tested and analyzed. Figure 3 (a)-(d) are RT curves (temperature-resistivity change curves) of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3, respectively. The test range is from room temperature to 120°C, and the films under the conditions of temperature increase and temperature decrease are measured respectively. By performing differential processing on the RT curve, the dlogR / dT curve is obtained, as shown in FIG. Figure 3 (e)-(h), it is easy to observe the phase transition temperature and thermal hysteresis width of each device. Figure 3 (a), (b), (c), (d) and (e), (f), (g), (h) correspond to each other. T represents the phase transition temperature of VO2 film, Tc represents the phase transition temperature of the cooling curve, Th represents the phase transition temperature of the heating curve, H represents the thermal hysteresis width of VO2 film, and R represents the phase transition amplitude.

[0055] Table 1: VO in different devices 2 RT data of thin films

[0056] T(℃) Th(℃) Tc(℃) H(℃) R Example 1 73.6 77.1 70.1 7 1097.31 Comparative Example 1 70.65 76.3 65 11.3 14.95 Comparative Example 2 75.15 81.3 69 12.3 34.21 Comparative Example 3 74.6 78.1 71.1 7 215.59

[0057] T stands for VO 2 The phase transition temperature of the film, Tc represents the phase transition temperature of the cooling curve, Th represents the phase transition temperature of the heating curve, and H represents VO 2 The thermal hysteresis width of the film, R represents the phase transition amplitude; T is the average value of Th and Tc, and H is the difference between Th and Tc.

[0058] from Figure 3It can be seen from Table 1 that in the process of heating and cooling, the phase transition temperature of Example 1 starts from 77.1°C and 70.1°C respectively, produces 7°C H, the phase transition temperature takes an average value of 73.6°C, and the phase transition amplitude R reaches 1097.31. Since the thermal hysteresis H is caused by the latent heat of the first-order phase transition, which is determined by the microstructure of the film such as the crystallinity and grain orientation, the phase transition amplitude R is due to the presence of grains, defects and strains in the film. The phase transition amplitude of Example 1 is the highest, reaching 3 orders of magnitude, and the thermal hysteresis width is also small. This shows that the VO in Example 1 2 The film is excellent in crystallinity and grain orientation, which is mainly due to the VO 2 The film is GeO 2 Growth on buffer layer, GeO 2 It is a tetragonal structure, with VO 2 High temperature is similar, it is VO 2 The good substrate for growth leads to a higher crystallinity. 2 buffer layer, so the comparative example 1 has poor performance in the three indicators of phase transition temperature, phase transition amplitude and thermal hysteresis width, especially the phase transition temperature is only about 70°C, while the embodiment 1 and comparative examples 2 and 3 have GeO 2 The phase transition temperature of Comparative Example 2 is about 75°C. Although the phase transition temperature of Example 1 is not much different from that of Comparative Example 2, the phase transition amplitude and thermal hysteresis width are obviously worse. The only difference between the two examples is whether there is an Au protective layer. It can be seen that the Au protective layer also has an important influence on the device performance. This is because GeO 2 Direct contact between the buffer layer and the single crystal silicon substrate is not conducive to the GeO 2 The crystal growth of GeO 2 The crystallinity of the buffer layer decreases and defects increase, which indirectly reduces the upper VO 2 The growth quality of the nanostructured carbon nanotubes results in a decrease in performance such as the phase transition amplitude.

[0059] From the preparation process, Example 1 and Comparative Example 3 have the same three-layer film structure, and the only difference between the two is the electrode position, while Comparative Examples 1 and Comparative Examples 2 have only two-layer film structures, which shows that a single Au protective layer or a single GeO 2 Buffer layers are not conducive to high-quality VO 2 The reason is that compared with the growth of GeO on a single crystal silicon substrate 2 , GeO grown on Au protective layer 2 The crystallinity is better, which is mainly due to the stable chemical properties of Au. GeO is grown on the Au protective layer. 2 As a buffer layer, Au atoms will not interact with Ge 4+ or 2- A significant chemical reaction occurs to destroy GeO 2The crystal structure or the introduction of additional defects. This indirectly improves the VO 2 The present invention adopts the growth conditions of VO 2 Au / GeO is introduced between the film and the single crystal silicon substrate 2 The layered structure can prevent the single crystal silicon substrate from being oxidized to form silicon dioxide, thereby reducing the electrical performance of the device; on the other hand, the synergistic growth of the Au protective layer and the GeO2 buffer layer promotes the VO 2 The crystallinity of the film is improved, thereby improving VO 2 Phase change properties of thin films.

[0060] In addition, in Comparative Example 3, the device current is parallel to the film interface direction. In Comparative Example 3, although the phase transition temperature and thermal hysteresis width are not much different from those in Example 1, the phase transition amplitude is significantly reduced. This difference is mainly due to its VO 2 The microstructure of the film causes VO 2 The film can only grow one layer of grains in the vertical direction, and the grains are columnar. In the horizontal direction, the grains are bounded by grain boundaries. The grain resistance and grain boundary resistance of the crystal are generally quite different. The current loop in the horizontal direction is equivalent to a series connection of devices with resistivity equal to the grain resistance and grain boundary resistance, and the vertical direction is equivalent to a parallel connection. Therefore, the electron transmission efficiency in the vertical direction is higher. Moreover, as the structural transformation accompanied by the phase change occurs, the volume change effect will also cause new strain in the film. This strain starts from the interface and extends inward, causing microcracks in the film. The extension direction of this crack is consistent with the strain direction. The columnar grains will be divided into smaller columnar grains, resulting in an increase in the grain boundary resistance in the horizontal direction, while having little effect on the vertical direction. VO 2 The lattice mismatch at the film interface causes the lattice at the film interface to shrink to a certain extent, that is, strain occurs, and the strain gradually decays away from the interface. Since the transition from the low-temperature phase to the high-temperature phase is a process of unit cell expansion, the lattice shrinkage means that the transition from the low-temperature phase to the high-temperature phase is more difficult, and higher energy is required to trigger the phase change. Therefore, the phase change temperature increases, and the greater the degree of shrinkage, the higher the phase change temperature. In the vertical direction, the degree of strain is large near the interface, and the phase change temperature is high, and it gradually decays away from the interface. Since the size of the interface mismatch is determined by the lattice difference between the film and the substrate material, the degree of mismatch at the entire interface is basically the same, and the degree of lattice shrinkage in the horizontal plane at the same vertical height away from the interface is also basically the same. This means that VO 2 The phase transition temperature of grains at different depths of the film is different, but the phase transition temperature at the same depth is the same. This means that the vertical crystal structure changes at different positions on the same horizontal plane are basically the same, and the carrier transmission is more stable, thereby improving its electrical performance.

[0061] What is disclosed above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. A person skilled in the art can understand that all or part of the processes of the above embodiments and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A temperature sensor based on VO2 thin film, characterized in that: It includes a metal electrode, a single crystal silicon substrate, a protective layer, a buffer layer, a VO2 film, and a metal electrode stacked in sequence from bottom to top; the buffer layer is a GeO2 film; the protective layer is an Au film; the synergistic growth of the Au protective layer and the GeO2 buffer layer promotes the improvement of the crystallinity and phase change characteristics of the VO2 film.

2. The temperature sensor based on VO2 thin film according to claim 1, characterized in that: The metal electrode is a gold electrode.

3. The temperature sensor based on VO2 thin film according to claim 1, characterized in that: The thickness of the VO2 film is 100-300nm.

4. A method for preparing a temperature sensor based on VO2 thin film according to any one of claims 1 to 3, characterized in that: The following steps are involved: Step 1: Cleaning the single crystal silicon substrate, ultrasonically cleaning the single crystal silicon substrate with anhydrous ethanol and deionized water in sequence, and then drying it with nitrogen for later use; Step 2: Prepare a gold electrode on the non-polished surface of a single crystal silicon substrate by magnetron sputtering to obtain sample 1; Step 3: Using magnetron sputtering method to prepare Au thin film as protective layer on the polished surface of single crystal silicon substrate to obtain sample 2; Step 4: Deposit a GeO2 thin film as a buffer layer on the surface of the sample 2 prepared in step 3 by magnetron sputtering, and perform annealing to obtain sample 3; Step 5: Deposit a VO2 thin film on the surface of the sample 3 prepared in step 4 by magnetron sputtering, and perform annealing to obtain sample 4; Step 6: Prepare another gold electrode on the surface of sample 4 prepared in step 5 by magnetron sputtering, thus obtaining a temperature sensor based on VO2 thin film.

5. The method for preparing a temperature sensor based on VO2 thin film according to claim 4, characterized in that: The magnetron sputtering conditions used in steps 2, 3 and 6 are: sputtering time is 180-200 s, vacuum degree is 0.6-0.8 Pa, and current is 10 mA.

6. The method for preparing a temperature sensor based on VO2 thin film according to claim 4, characterized in that: The process of magnetron sputtering in step 4 and step 5 is as follows: the chamber is evacuated to 3.4×10 -4 Pa, use argon to purge the cavity three times, then continue to introduce argon at a flow rate of 60sccm, adjust the mechanical pump valve to adjust the cavity vacuum to 0.6Pa, then turn on the RF power, sputter at a power of 80w for 9-10min, and anneal the sputtered film at 540-550℃ for four hours.

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