Preparation method of protective layer of thin film temperature sensor and thin film temperature sensor

Abstract

The invention discloses a preparation method of a protective layer of a thin film temperature sensor and the thin film temperature sensor, the preparation method of the protective layer adopts a spin coating film forming method, the surface of the sensor is uniformly coated with spin coating liquid, and then the protective layer is formed after sintering. According to the invention, a uniform and flat compact protection layer capable of completely covering the platinum thin-film resistor can be formed by adopting a spin-coating method, a compact film layer can be formed after the protection layer is sintered, the uniformity is good, diffusion of a sealing material to the platinum thin-film resistor in a high-temperature environment can be effectively isolated, the high-temperature environment of 1050 DEG C can be resisted, and the conditions of cracking, perforation and the like are avoided.

Description

Technical Field

[0001] The invention relates to the technical field of temperature sensors, and in particular to a method for preparing a protective layer of a thin film temperature sensor and a thin film temperature sensor. Background Art

[0002] Platinum thin film, as a material with high resistance stability and high temperature coefficient of resistance, is an ideal raw material for preparing high-temperature thin film temperature sensors with high temperature resistance tracking, high precision, high linearity, and a wide temperature measurement range (-50 to 850°C). Platinum thin film high-temperature temperature sensors are widely used in various industries due to their small size, low heat capacity, impact resistance, good consistency, and fast thermal response speed.

[0003] Since the mechanical strength of platinum film is low, it is easy to be mechanically damaged if it is not protected during use, which will affect its normal operation. At the same time, temperature sensors mostly work in high-temperature environments. If the platinum film is directly exposed to it, it is easy to volatilize or agglomerate, causing sensor failure. Therefore, it is necessary to package and protect the platinum film high-temperature temperature sensor. At present, glass sealing materials are widely used in the industry, and such materials generally contain Si. The Si element is easy to migrate to the platinum film in a high-temperature environment, causing silicon poisoning of the platinum film. Therefore, a protective layer needs to be applied between the platinum film and the sealing layer to avoid direct contact between the sealing material and the platinum film.

[0004] At present, the industry mostly uses physical vapor deposition or thick film screen printing to prepare protective layers. However, the protective layers made by these two methods have shortcomings: physical vapor deposition will introduce structural defects during the deposition process. As the grains of the protective layer grow in a high temperature environment, these defects will cause cracks and perforations on the film surface, destroying the continuity and protective ability of the film; the thick film screen printing method requires the film-forming material to be prepared into a printing paste and then printed on the resistor surface, and then the film is formed after debinding and sintering. This process is time-consuming and there will still be pores and defects after the film is formed.

[0005] Therefore, how to solve the defects of the current thin film temperature sensor such as surface cracking and perforation is an important problem that people in this field need to solve. In view of this, this patent application is proposed. Summary of the invention

[0006] In order to solve the above-mentioned technical problems of surface cracking, perforation and other defects of current thin film temperature sensors, the present invention provides a method for preparing a protective layer of a thin film temperature sensor, and also provides a thin film temperature sensor including the protective layer.

[0007] The present invention adopts the following technical solutions:

[0008] The first object of the present invention is to provide a method for preparing a protective layer of a thin film temperature sensor, wherein a spin coating method is used to uniformly coat the surface of the sensor with a spin coating liquid, and then the protective layer is formed after sintering.

[0009] The present invention adopts a spin coating method, and the spin coating liquid can be evenly dispersed on the surface of the substrate through the centrifugal force generated by the substrate material during the rotation process, forming a uniform and flat dense protective layer that can completely cover the platinum thin film resistor. The protective layer has a strong bonding force with the substrate, which can inhibit the volatilization and agglomeration of the platinum thin film in a high temperature environment, and can withstand a high temperature environment of 1050°C, avoiding cracking, perforation, etc., thereby improving the stability and measurement accuracy of the platinum thin film temperature sensor in a high temperature environment.

[0010] As a preferred design, the spin coating liquid is an aluminum oxide spin coating liquid, and the protective layer is an aluminum oxide protective layer.

[0011] In the present invention, alumina is used as an excellent thermal conductive material with fast thermal conductivity, good thermal stability and high melting point. It can be evenly distributed on the surface of the substrate by spin coating. After sintering, it can form a dense film layer with good uniformity, which can effectively isolate the diffusion of sealing materials to the platinum thin film resistor in a high-temperature environment. The alumina protection is the same component as the alumina ceramic substrate, and the bonding force between the two is strong, which can inhibit the volatilization and agglomeration of the platinum thin film in a high-temperature environment, and can withstand a high-temperature environment of 1050°C, avoiding cracking, perforation, etc., thereby improving the stability and measurement accuracy of the platinum thin film temperature sensor in a high-temperature environment.

[0012] As a preferred design, the aluminum oxide spin coating liquid includes the following components in parts by weight: 10-30 parts of aluminum oxide, 0-10 parts of deionized water, 50-100 parts of anhydrous ethanol, and 0-8 parts of glycerol.

[0013] For conventional spin coating processes, the spin coating solution is mostly pure liquid or colloid, which usually does not contain solid particles. At the same time, in order to ensure the film-forming effect, organic glue or other organic solvents are often added to the spin coating liquid to improve the film-forming properties. If a high-temperature environment is involved in the subsequent process or use, the structure of the organic colloid will be destroyed and the quality of the film layer will be affected. At the same time, the volatilization of organic solvents during the preparation process will also cause toxicity and environmental pollution problems. Since high-temperature thin-film temperature sensors work in high-temperature environments for a long time, in order to ensure that the protective layer can fully isolate the external environment from the contact with the thin-film resistor, the protective film layer generally needs to be subjected to high-temperature treatment to densify it and form a stable structure so as to have better high-temperature stability.

[0014] Since platinum thin film temperature sensors are used in high temperature environments (800-1000°C) for a long time, the conventional spin coating solution with organic glue or organic solvent is obviously not applicable in this case. A newly designed spin coating solution is needed to meet the long-term high temperature environment and ensure film forming properties. Based on this consideration, the inventor abandoned the use of organic glue and organic solvent, considered the use of mild solvents, and needed to ensure the dispersion effect of solid particles in the solvent, and selected ethanol as a carrier. Considering the bonding performance of the protective layer and the substrate, the spin coating solution designed in the present invention contains aluminum oxide solid particles, anhydrous ethanol is used as a carrier to carry aluminum oxide, and the dispersion state of aluminum oxide is adjusted by adding water and glycerol to form an aluminum oxide suspension, and then the aluminum oxide is evenly dispersed on the substrate surface by spin coating, and finally a dense and uniform aluminum oxide protective layer is obtained after sintering. Alumina and the aluminum oxide ceramic substrate are of the same component, and the bonding force between the two is strong, which can inhibit the volatilization and agglomeration of the platinum film in a high temperature environment.

[0015] As a preferred design, the process of spin coating is:

[0016] Fix the thin film temperature sensor on a spin coating machine, drip the aluminum oxide spin coating liquid to fully wet the sensor substrate surface, bake after one spin coating, and spin coat the film layer for a second time after the spin coating layer is fully dried;

[0017] The number of spin coating is at least 1 time, and baking and drying are performed after each spin coating. After all the spin coatings are completed, a second spin coating is performed at last.

[0018] Spin coating can be performed using a spin coater. Fix the spin coating substrate and fix the substrate covered with the platinum thin film resistor on the stage of the spin coater by vacuum adsorption. Add the spin coating liquid and use a pipette to vertically add 1-3 ml of the alumina spin coating liquid to the substrate to fully infiltrate the surface of the substrate.

[0019] As a preferred design, the spin coating speed during one spin coating is 8000-10000 rpm / min, the spin coating time is 5-20s, and the baking condition after one spin coating is baking at 100-200°C for 0.5-2h.

[0020] As a preferred design, the rotation speed of the secondary spin coating is 6000-9000 rpm / min, and the spin coating time is 15-25 s.

[0021] The present invention adopts at least two spin coating processes. In the first spin coating process, a relatively low rotation speed is used to complete the full infiltration of the ceramic substrate by the aluminum oxide spin coating liquid and fill the gaps between the platinum thin film resistor patterns, thereby improving the flatness of the substrate surface and providing convenience for subsequent spin coating. The second spin coating process uses a relatively high rotation speed to complete the uniform distribution of the aluminum oxide spin coating liquid on the ceramic substrate, so that the aluminum oxide completely covers the platinum thin film resistor, forming a uniform, flat and dense aluminum oxide coating.

[0022] As a preferred design, during sintering, the temperature is raised to 950-1200°C at a heating rate of 5-10°C / s, and after being kept at this temperature for 0.5-3h, the sintering is completed by cooling the furnace to room temperature.

[0023] Since the high-temperature thin-film temperature sensor works in a high-temperature environment for a long time, in order to ensure that the protective layer can fully isolate the contact between the external environment and the thin-film resistor, the protective film layer generally needs to be subjected to high-temperature treatment to densify it and form a stable structure with good high-temperature stability. Therefore, the present invention reasonably designs the spin coating liquid, the spin coating process, and the subsequent sintering temperature during the spin coating film formation process, and finally obtains a continuous and uniform film layer, good densification after sintering treatment, and a high-temperature (1050°C) resistant platinum thin-film resistor.

[0024] As a preferred design, the thickness of the aluminum oxide protective layer is 1-5 μm.

[0025] When the sensor with an aluminum oxide protective layer is subjected to a high temperature stability test, the test process is as follows: a lead is connected to a pin of a platinum thin film resistor pattern, and a multimeter is used to measure the resistance value of the high temperature thin film temperature sensor at different temperatures. The lead is coated with platinum slurry, and sintered in a sintering furnace at 900-1100° C. for 0.5-2 hours to complete the fixation of the lead. A platinum wire with a length of 2-5 mm and a diameter of 0.1-0.3 mm is used as the lead.

[0026] A second object of the present invention is to provide a thin film temperature sensor, comprising a thin film temperature sensor protective layer as described above.

[0027] As a preferred design, it also includes a substrate and a platinum film, and the platinum film is coated on the substrate by electron beam evaporation, ion beam evaporation, ion beam sputtering or magnetron sputtering technology, preferably magnetron sputtering technology; the thickness of the platinum film is 1-2μm, and the substrate is an oxide ceramic, a nitride ceramic, a boride ceramic or a silicide ceramic, preferably an alumina ceramic substrate.

[0028] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0029] The present invention provides a method for preparing a protective layer for a high-temperature thin-film temperature sensor. Aluminum oxide is coated on a ceramic substrate by spin coating, and a platinum thin-film resistor is completely covered to form a uniform and dense aluminum oxide protective layer. After sintering, a dense film layer with good uniformity can be formed, which can effectively isolate the diffusion of sealing materials to the platinum thin-film resistor in a high-temperature environment, thereby improving the stability and measurement accuracy of the platinum thin-film temperature sensor in a high-temperature environment (up to 1050°C). BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0031] Figure 1 The present invention is a process flow chart for preparing a protective layer of a platinum thin film resistor temperature sensor.

[0032] Figure 2 It is a schematic structural diagram of the protective layer of the platinum thin film resistor temperature sensor of the present invention.

[0033] Figure 3 a is a SEM morphology image of the surface of the bare platinum thin film resistor of Example 1; Figure 3 b is a SEM image of the surface of the platinum thin film resistor of the spin-coated protective layer of Example 1.

[0034] Figure 4 a is a cross-sectional SEM image of the bare platinum thin film resistor of Example 1, Figure 4 b is a cross-sectional SEM image of the platinum thin film resistor of the spin-coated protective layer of Example 1.

[0035] Figure 5 a is a thermal cycle test diagram of the bare platinum thin film resistor of Example 1 at 1050° C.; Figure 5 b is a thermal cycle test diagram of the platinum thin film resistor with a protective layer at 1050° C. in Example 1.

[0036] Figure 6 a is a surface SEM morphology image of the platinum thin film resistor with a spin-coated protective layer in Example 2; Figure 6 b is a cross-sectional SEM morphology image of the platinum thin film resistor of the spin-coated protective layer of Example 2; Figure 6 c is a thermal cycle test diagram of the bare platinum film of Example 2 at 1050°C; Figure 6 d is a thermal cycle test diagram of the platinum thin film resistor with a protective layer in Example 2 at 1050°C.

[0037] Figure 7a is a surface SEM morphology image of the platinum thin film resistor with a spin-coated protective layer in Example 3; Figure 7 b is a cross-sectional SEM morphology image of the platinum thin film resistor of the spin-coated protective layer of Example 3; Figure 7 c is a thermal cycle test diagram of the bare platinum film of Example 3 at 1050°C; Figure 7 d is a thermal cycle test diagram of the platinum thin film resistor with a protective layer in Example 3 at 1050°C.

[0038] Figure 8 This is the surface SEM morphology of the platinum thin film resistor with a spin-coated protective layer in Comparative Example 1.

[0039] Fig. 9 This is a surface SEM morphology image of the platinum thin film resistor with a spin-coated protective layer in Comparative Example 2 of the present invention.

[0040] Fig.10 This is a surface SEM morphology image of the platinum thin film resistor with a spin-coated protective layer in Comparative Example 3 of the present invention.

[0041] Fig.11 This is a surface SEM morphology image of the platinum thin film resistor with a spin-coated protective layer in Comparative Example 4 of the present invention.

[0042] Fig.12 This is a surface SEM morphology image of the platinum thin film resistor with a spin-coated protective layer in Comparative Example 5 of the present invention.

[0043] Fig.13 a is a surface SEM morphology image of the platinum thin film resistor with a spin-coated protective layer in Comparative Example 6 of the present invention; Fig.13 b is a cross-sectional SEM morphology image of the platinum thin film resistor with a spin-coated protective layer in Comparative Example 6 of the present invention.

[0044] The markings in the figure are: 1-alumina ceramic substrate, 2-thin film resistor, 3-alumina protective layer. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. The illustrative embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0046] Embodiment 1:

[0047] like Figure 1 As shown in , the preparation process of the protective layer of the thin film temperature sensor is:

[0048] Step 1: prepare a spin coating solution. Put 0.34 g of aluminum oxide into 1.36 g of anhydrous ethanol, and obtain an aluminum oxide ethanol dispersion by ultrasonic dispersion and high-speed oscillation; add 0.15 g of deionized water and 0.15 g of glycerol to the aluminum oxide ethanol dispersion in sequence, and mix the above materials thoroughly by high-speed oscillation to obtain a milky white aluminum oxide spin coating solution.

[0049] Step 2: Fix the spin-coated substrate. The alumina ceramic substrate covered with the platinum thin film resistor is fixed on the center of the stage of the spin-coating machine by vacuum adsorption.

[0050] Step 3: Add the spin coating liquid. Use a pipette to vertically add 2 ml of the alumina spin coating liquid onto the substrate, so that the spin coating liquid fully infiltrates the surface of the substrate and ensures that the spin coating liquid fills the gaps between the platinum thin film resistor patterns.

[0051] Step 4: Spin coating once. Set the parameters of the spin coating machine to low speed 500rpm / min, time 20s, to assist the spin coating liquid to fully infiltrate the substrate surface; high speed 9000rpm / min, time 10s, to complete the uniform dispersion of aluminum oxide on the substrate surface, so that it can fully infiltrate the substrate surface, fill the gaps between the platinum thin film resistor patterns, improve the flatness of the substrate surface, and provide a basis for preparing a flat and uniform aluminum oxide protective layer.

[0052] Step 5: Drying: Place the substrate that has been spin-coated once into an oven and bake at 150°C for 1 hour until the aluminum oxide film is fully dried. Then take it out and observe that the surface of the substrate is evenly covered with a flat, dense, white, translucent film.

[0053] Step 6: Second spin coating: Repeat the operation of step 3, and then set the spin coating speed to 7500 rpm / min and the spin coating time to 15 s, so that the aluminum oxide completely covers the platinum thin film resistor to form a uniform and smooth aluminum oxide film layer.

[0054] Step 7: Sintering. Place the substrate after the secondary spin coating into a sintering furnace, heat it to 150°C at a heating rate of 5°C / s, keep it warm for 1 hour to fully dry the film layer, and then continue to heat it to 1000°C and keep it warm for 2 hours for sintering. After sintering, cool it to room temperature with the furnace to obtain a high-temperature thin film temperature sensor with a dense and uniform aluminum oxide protective layer.

[0055] like Figure 2 , a schematic diagram of the structure of a thin film temperature sensor is shown in FIG. 1 , wherein the bottom layer is an aluminum oxide ceramic substrate 1 , the middle layer is a platinum thin film resistor 2 , and an aluminum oxide protective layer 3 is coated on the surface of the platinum thin film resistor.

[0056] The surface of the platinum thin film resistor containing the protective layer of this embodiment was tested by SEM, and the results are shown in Figure 3b, and the surface morphology of the bare platinum thin film resistor (i.e., there is no protective layer on the surface) is also compared. Figure 3 a. By Figure 3 b It can be observed that the surface of the aluminum oxide protective layer prepared by the present invention is flat and uniform without cracks, and can fully cover the platinum thin film resistor so that it is not in direct contact with the external environment.

[0057] The cross-section morphology of the platinum thin film resistor containing the protective layer of this embodiment and the cross-section morphology of the bare platinum thin film resistor were characterized by SEM. Figure 4 b. 4a. By Figure 4 b The cross-sectional morphology of the aluminum oxide protective layer can be observed. It can be seen that the protective layer prepared by the spin coating method has uniform thickness and dense structure, and is well bonded to the substrate. It can fully cover the platinum thin film resistor, inhibiting its volatilization or agglomeration in a high-temperature working environment, thereby improving its stability. At the same time, it also provides protection for the platinum thin film resistor, effectively improving the mechanical strength of the high-temperature thin film temperature sensor.

[0058] Furthermore, in this embodiment, the thin film temperature sensor with an aluminum oxide protective layer is wired, and the preparation method is as follows: two platinum wires with a length of 3 mm and a diameter of 0.25 mm are placed at the pattern pins, platinum slurry is applied, and sintered in a sintering furnace at 1100°C for 1 hour to complete the fixing of the leads. The resistance-temperature relationship is also measured.

[0059] Using the same preparation method, as a comparison, the platinum thin film temperature sensor without an aluminum oxide protective layer was wired and the resistance-temperature relationship was measured.

[0060] Figure 5 a and Figure 5 b are the resistance-temperature measurement curves of the platinum thin film resistor without an aluminum oxide protective layer and the platinum thin film resistor with an aluminum oxide protective layer from room temperature (25°C) to 1050°C, respectively.

[0061] Depend on Figure 5 As shown in Figure 1, the resistance-temperature curve of the unprotected platinum thin film resistor from room temperature to 1050°C is linear, but the test curves no longer overlap as the temperature rises. This shows that the directly exposed platinum thin film resistor is easily disturbed in a high temperature environment, and the high-temperature repeatability of its measurement results is poor. The resistance-temperature curve of the platinum thin film resistor with an aluminum oxide protective layer from room temperature to 1050°C is as follows Figure 5 As shown in b, it still shows a linear change, and the test curves are highly overlapped, showing excellent high temperature repeatability.

[0062] The aluminum oxide protective layer of this embodiment effectively isolates the platinum thin film resistor from the external environment by virtue of its dense and uniform structural characteristics and good chemical stability and high temperature stability, avoiding the contamination of the platinum electrode by impurities, and significantly reducing the influence of the external environment on the working stability of the platinum electrode. At the same time, the aluminum oxide protective layer not only provides protection for the platinum thin film resistor, but also forms a mechanical anchor for the platinum thin film, improves the bonding strength between the platinum thin film resistor and the aluminum oxide ceramic substrate, limits the agglomeration and volatilization of the platinum thin film, and further improves the high temperature stability of the platinum thin film resistor and the mechanical strength of the high temperature thin film temperature sensor.

[0063] Embodiment 2:

[0064] Step 1: prepare a spin coating solution. Put 0.2 g of aluminum oxide into 1.5 g of anhydrous ethanol, and obtain an aluminum oxide ethanol dispersion by ultrasonic dispersion and high-speed oscillation; add 0.15 g of deionized water and 0.15 g of glycerol to the aluminum oxide ethanol dispersion in sequence, and mix the above materials thoroughly by high-speed oscillation to obtain a milky white aluminum oxide spin coating solution.

[0065] Step 2: Fix the spin-coated substrate.

[0066] Step 3: Add the spin coating liquid. Use a pipette to vertically add 2 ml of the alumina spin coating liquid onto the substrate to allow the spin coating liquid to fully soak the substrate surface.

[0067] Step 4: Spin coating once: low speed 500 rpm / min, time 20 s, to allow the auxiliary spin coating liquid to fully infiltrate the substrate surface; high speed 10000 rpm / min, time 20 s.

[0068] Step 5: Drying: Bake at 150°C for 1 hour until the aluminum oxide film is fully dry and then take it out.

[0069] Step 6: Second spin coating: Spin coating speed is 9000 rpm / min, and spin coating time is 15 s.

[0070] Step 7: Sintering: The temperature is raised to 150°C at a heating rate of 5°C / s, and kept at this temperature for 1 hour to fully dry the film layer, and then the temperature is further raised to 1000°C and kept at this temperature for 2 hours for sintering. After sintering, the film is cooled to room temperature in the furnace.

[0071] The surface morphology and cross-sectional morphology of the platinum thin film resistor obtained in this embodiment were characterized respectively. Figure 6 a and 6b. Figure 6As shown, a continuous and dense aluminum oxide protective layer was successfully prepared by the method of this embodiment. Compared with Example 1, the thickness of the aluminum oxide protective layer covering the surface of the platinum thin film resistor is lower, but it can still achieve complete coverage of the thin film resistor and play a role in protecting the platinum thin film resistor. The platinum thin film temperature sensor equipped with the aluminum oxide protective layer of this embodiment shows good high temperature stability (see Figure 6 d, Figure 6 c as a comparison), the test results have good repeatability in high temperature environment.

[0072] Embodiment 3:

[0073] Step 1: prepare a spin coating solution. Put 0.6 g of aluminum oxide into 1.1 g of anhydrous ethanol, and obtain an aluminum oxide ethanol dispersion by ultrasonic dispersion and high-speed oscillation; add 0.15 g of deionized water and 0.15 g of glycerol to the aluminum oxide ethanol dispersion in sequence, and mix the above materials thoroughly by high-speed oscillation to obtain a milky white aluminum oxide spin coating solution.

[0074] Step 2: Fix the spin-coated substrate.

[0075] Step 3: Add the spin coating liquid. Use a pipette to vertically add 2 ml of the alumina spin coating liquid onto the substrate to allow the spin coating liquid to fully soak the substrate surface.

[0076] Step 4: Spin coating once: low speed 500 rpm / min, time 20 s, to allow the auxiliary spin coating liquid to fully infiltrate the substrate surface; high speed 8000 rpm / min, time 5 s.

[0077] Step 5: Drying: Bake at 150°C for 1 hour until the aluminum oxide film is fully dry and then take it out.

[0078] Step 6: Second spin coating: Spin coating speed is 6000 rpm / min, and spin coating time is 15 s.

[0079] Step 7: Sintering: The temperature is raised to 150°C at a heating rate of 5°C / s, and kept at this temperature for 1 hour to fully dry the film layer, and then the temperature is further raised to 1000°C and kept at this temperature for 2 hours for sintering. After sintering, the film is cooled to room temperature in the furnace.

[0080] like Figure 7 a and Figure 7 The surface morphology and cross-sectional morphology of the platinum thin film resistor measured in b. It can be seen that the method of this embodiment also successfully prepared a continuous and dense aluminum oxide protective layer. Compared with the method of Example 1, the aluminum oxide protective layer covering the surface of the platinum thin film resistor in this embodiment is thicker, but the density does not decrease due to the increase in thickness. It can still fully isolate the platinum thin film resistor from the external environment and effectively protect the thin film resistor. The platinum thin film temperature sensor equipped with the aluminum oxide protective layer of this embodiment shows good high temperature stability (see Figure 7 d, Figure 7 c as a comparison), the test results have good repeatability in high temperature environment.

[0081] Comparative Example 1:

[0082] The difference between this comparative example and Example 1 is that the spin coating solution does not contain deionized water and glycerol.

[0083] Step 1 of this comparative example is: preparing a spin coating solution: putting 0.34 g of aluminum oxide into 1.36 g of anhydrous ethanol, and obtaining an aluminum oxide ethanol dispersion by ultrasonic dispersion and high-speed oscillation. The rest is the same as in Example 1.

[0084] The surface morphology of the resistor obtained in this comparative example was characterized, and the results are shown in Figure 8 As shown in . Figure 8 It can be seen that the aluminum oxide film prepared by this method has a large number of cracks after sintering, and the aluminum oxide appears to be agglomerated and attached to the platinum thin film resistor, and the protective layer has lost its function. This is because the lack of deionized water and glycerol will cause the surface tension of the spin coating liquid to change, destroy the wettability between the spin coating liquid and the substrate, and affect the film quality.

[0085] Comparative Example 2:

[0086] The difference between this comparative example and Example 1 is that the content of aluminum oxide in the spin coating solution is reduced.

[0087] The process of step 1 in this comparative example is: prepare a spin coating liquid. Put 0.1g of aluminum oxide into 1.6g of anhydrous ethanol, and obtain an aluminum oxide ethanol dispersion liquid by ultrasonic dispersion and high-speed oscillation; add 0.15g of deionized water and 0.15g of glycerol to the aluminum oxide ethanol dispersion liquid in turn, and mix the above materials thoroughly and evenly by high-speed oscillation to obtain a milky white aluminum oxide spin coating liquid. The rest is the same as Example 1.

[0088] The surface morphology of the resistor obtained in this comparative example was characterized, and the results are shown in Fig. 9 As shown in . Fig. 9 It can be seen that the aluminum oxide film prepared by this method has only a small amount of aluminum oxide particles attached to the substrate surface, and after sintering, it forms independent aluminum oxide particles, and does not form a continuous film. This is because the reduction of aluminum oxide content will reduce the viscosity of the spin coating liquid. During the spin coating process, a large amount of aluminum oxide is thrown off the substrate surface under the action of centrifugal force, resulting in the aluminum oxide being unable to remain on the substrate surface to form a continuous film layer.

[0089] Comparative Example 3:

[0090] The difference between this comparative example and Example 1 is that the spin coating speed is reduced during the first spin coating in step 4. Specifically:

[0091] The process of step 4 in this comparative example is: one spin coating. Low speed 500 rpm / min, time 20s, to fully wet the surface of the substrate with the auxiliary spin coating liquid; high speed 5000 rpm / min, time 10s. The rest is the same as Example 1.

[0092] The surface morphology of the resistor obtained in this comparative example was characterized, and the results are shown in Fig.10 As shown in . Fig.10 It can be seen that the surface of the aluminum oxide protective layer prepared by this method is not smooth, and there is aluminum oxide accumulation at the edge of the etching pattern of the platinum thin film resistor, which cracks after sintering and cannot complete the isolation and protection of the platinum thin film resistor. It can be seen that reducing the spin coating speed during the first spin coating will cause the spin coating liquid to fail to fully and evenly spread on the substrate surface, and aluminum oxide particles are easy to agglomerate and accumulate in the grooves of the platinum thin film resistor, resulting in an uneven coating surface and uneven film formation during the second spin coating.

[0093] Comparative Example 4:

[0094] The main difference between this comparative example and Example 1 is that the spin coating speed is changed, and the spin coating speed is reduced in the secondary spin coating, specifically:

[0095] The process of step 6 of this comparative example is: secondary spin coating, spin coating speed of 5000 rpm / min, spin coating time of 15 s, and the rest is the same as that of Example 1.

[0096] The surface morphology of the resistor obtained in this comparative example was characterized, and the results are shown in Fig.11 As shown in . Fig.11 It can be seen that the surface of the aluminum oxide protective layer prepared by this method is not smooth, and there is aluminum oxide accumulation in some areas. It cracks after sintering and cannot complete the isolation and protection of the platinum thin film resistor. It can be seen that reducing the spin coating speed in the secondary spin coating will cause the spin coating liquid to fail to fully and evenly spread on the substrate surface, resulting in uneven film formation.

[0097] Comparative Example 5:

[0098] The difference between this comparative example and Example 1 lies in the sintering temperature in step 7, which is specifically:

[0099] Step 7: Sintering: The temperature is raised to 150°C at a heating rate of 5°C / s, and kept at this temperature for 1 hour to allow the film layer to be fully dried, and then the temperature is further raised to 800°C and kept at this temperature for 2 hours for sintering. After sintering, the film is cooled to room temperature in the furnace.

[0100] The surface morphology of the resistor obtained in this comparative example was characterized, and the results are shown in Fig.12 As shown in . Fig.12It can be seen that the aluminum oxide protective layer prepared by this method cannot be sintered densely, and the aluminum oxide is still attached to the substrate surface in a granular state, and has not formed a dense and continuous film layer, which cannot play the role of isolating the platinum thin film resistor from the external environment. Therefore, when the aluminum oxide protective layer is sintered, the low sintering temperature will cause the aluminum oxide film layer to fail to densify.

[0101] Comparative Example 6:

[0102] The difference between this comparative example and Example 1 is the sintering temperature, specifically:

[0103] Step 7: Sintering: The temperature is raised to 150°C at a heating rate of 5°C / s, and kept at this temperature for 1 hour to fully dry the film layer, and then the temperature is further raised to 1300°C and kept at this temperature for 2 hours for sintering. After sintering, the film is cooled to room temperature in the furnace.

[0104] The surface morphology and cross-sectional morphology of the resistor obtained in this comparative example were characterized respectively. Fig.13 a、13b. From Fig.13 It can be seen that the aluminum oxide protective layer prepared by the method of this comparative example becomes very dense after high-temperature sintering, but the platinum thin film resistor expands and deforms severely, causing the aluminum oxide film layer to crack and fail to effectively isolate the outside world. This is because the density of the aluminum oxide protective layer can be further improved with the increase of sintering temperature, but too high a temperature will cause the grain growth of the platinum thin film resistor, resulting in a significant change in its morphology and structure, causing the resistor to expand and deform severely.

[0105] Embodiment 4:

[0106] The present invention also discloses a thin film temperature sensor, wherein the surface of the platinum thin film resistor is coated with a protective layer as described in any one of embodiments 1 to 3.

[0107] The above specific implementation methods further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific implementation methods of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a protective layer of a thin film temperature sensor, characterized in that: The spin coating liquid is uniformly coated on the sensor surface by the spin coating film forming method, and then a protective layer is formed after sintering.

2. The method for preparing a protective layer of a thin film temperature sensor according to claim 1, characterized in that: The spin coating liquid is an aluminum oxide spin coating liquid, and the protective layer is an aluminum oxide protective layer.

3. The method for preparing a protective layer of a thin film temperature sensor according to claim 2, characterized in that: The aluminum oxide spin coating liquid comprises the following components in parts by weight: 10-30 parts of aluminum oxide, 0-10 parts of deionized water, 50-100 parts of anhydrous ethanol, and 0-8 parts of glycerol.

4. The method for preparing a protective layer of a thin film temperature sensor according to claim 2, characterized in that: The process of spin coating is: Fix the thin film temperature sensor on the spin coating machine, drip the aluminum oxide spin coating liquid to fully infiltrate the surface of the sensor substrate, bake after one spin coating, and spin coat the film layer for a second time after it is fully dried; the number of spin coatings is at least 1, and each spin coating is baked and dried, and the second spin coating is finally performed after all the spin coatings are completed.

5. The method for preparing a protective layer of a thin film temperature sensor according to claim 4, characterized in that: The spin coating speed is 8000-10000 rpm / min, the spin coating time is 5-20s, and the baking condition after the spin coating is 100-200° C. for 0.5-2h.

6. The method for preparing a protective layer of a thin film temperature sensor according to claim 4, characterized in that: The rotation speed of the secondary spin coating is 6000-9000 rpm / min, and the spin coating time is 15-25s.

7. The method for preparing a protective layer of a thin film temperature sensor according to claim 1, characterized in that: During sintering, the temperature is raised to 950-1200°C at a heating rate of 5-10°C / s, and after being kept at this temperature for 0.5-3h, the sintering is completed by cooling the furnace to room temperature.

8. The method for preparing a protective layer of a thin film temperature sensor according to claim 2, characterized in that: The thickness of the aluminum oxide protective layer is 1-5 μm.

9. A thin film temperature sensor, characterized in that: The invention comprises a thin film temperature sensor protective layer prepared by the method according to any one of claims 1 to 8.

10. A thin film temperature sensor according to claim 9, characterized in that: It also includes a substrate and a platinum film, wherein the platinum film is coated on the substrate by electron beam evaporation, ion beam evaporation, ion beam sputtering or magnetron sputtering technology, the thickness of the platinum film is 1-2 μm, and the substrate is oxide ceramic, nitride ceramic, boride ceramic or silicide ceramic.

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