Platinum film for automobile exhaust temperature sensor, preparation method and temperature sensor

Abstract

The invention discloses a platinum film for an automobile exhaust temperature sensor, a preparation method and a temperature sensor, and the preparation method comprises the steps: sputtering a transition layer on a ceramic substrate, sputtering a platinum film through a mask in a selective region, and carrying out the third heat treatment to obtain the platinum film. The transition layer is selected from one or more of tungsten, molybdenum and rhenium. The obtained platinum film is compact and uniform, impurities and defects are controllable, the resistance temperature coefficient can reach 3850 ppm DEG C, the grain size of the platinum film can reach 20 microns, and the platinum film subjected to selective sputtering is high in circuit precision and can be used for a platinum film resistance temperature sensor.

Description

Technical Field

[0001] The present invention relates to the technical field of temperature sensors, and particularly to a platinum thin film for an automotive exhaust temperature sensor, a preparation method thereof, and a temperature sensor. Background Art

[0002] Existing temperature sensor sensitive elements are diverse and are components used to measure temperature, mainly including thermoelectric type, resistive type, and bimetallic type. Among them, thin film resistor temperature sensor sensitive elements are widely used in fields such as household appliances, aerospace, medical, and military. The automotive exhaust temperature sensor requires a relatively large operating temperature range. Among various metal thin films, platinum has a good resistance-temperature linear relationship at -200°C - 850°C. According to the change in the platinum resistance value, the change in temperature is reflected, so it is often used in thin film resistor temperature sensors. Compared with traditional wire-wound platinum resistance temperature sensors, platinum thin film resistance temperature sensors have the characteristics of small volume, short response time, accurate temperature measurement, and low cost.

[0003] Currently, due to the difficulty of the platinum thin film preparation process, including: small temperature coefficient of resistance (TCR), poor adhesion, and poor resistance thermal stability, only a few companies at home and abroad have the ability to manufacture platinum thin films. Among them, TCR is the most critical parameter, which is mainly affected by the following several parameters: (1) Lattice vibration scattering (phonon scattering): Electron scattering caused by the thermal vibration of atoms in the platinum crystal, whose intensity increases with the increase in temperature and is the main contribution source of TCR, having a clear temperature dependence; (2) Interface scattering: including thin film surface scattering and thin film-substrate interface scattering, whose intensity is determined by the thin film thickness, surface roughness, and interface quality and is independent of temperature; (3) Defect scattering: Electron scattering caused by grain boundaries, dislocations, and impurity atoms inside the thin film, whose intensity depends on the thin film preparation process and material purity and is also independent of temperature. Therefore, only lattice vibration is related to temperature, while the other two influencing factors will lead to too small or unstable temperature coefficient of resistance, restricting the application of platinum thin film resistance temperature sensors. The poor adhesion of the platinum thin film is mainly due to the lattice mismatch between platinum and the substrate and the residual stress during the preparation process. In addition, during the manufacturing and use processes, the migration of impurity atoms into the platinum thin film will also affect the service life of the platinum thin film temperature sensor.

[0004] For the platinum thin film of a high-temperature sensor, having a large and stable resistance temperature coefficient is an important indicator. At high temperatures, the adhesion between the thin film and the substrate is poor, the platinum grain size is small, and impurity atoms migrate. To solve the above problems, some researchers have solved them by adding a transition layer and performing long-term annealing at high temperatures. For example, in the published patent document CN114807859 A, PtO is used as the transition layer. Although the adhesion of the platinum thin film can be ensured, there is a problem of reduced kinetic energy of sputtered atoms, which reduces the density of the platinum thin film. In addition, due to the presence of platinum oxide, decomposition occurs during the annealing process, forming holes on the platinum thin film. In addition, the non-dense sputtering of the platinum thin film by the traditional sputtering method leads to the formation of holes during annealing, which will also affect the resistance value of the platinum thin film and the resistance temperature coefficient of the platinum thin film.

[0005] Therefore, there is an urgent need to develop a platinum thin film with a high resistance temperature coefficient and high-temperature stability. In view of this, this patent application is proposed. Summary of the Invention

[0006] To solve the above problems, the present invention provides a preparation method for a platinum thin film for an automotive exhaust gas temperature sensor, and also provides a platinum thin film prepared by this method, as well as a thin film temperature sensor.

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

[0008] The first object of the present invention is to provide a preparation method for a platinum thin film for an automotive exhaust gas temperature sensor. A transition layer is sputtered on a ceramic substrate, and then a platinum thin film is sputter-deposited by mask plate selective area, and then three heat treatments are carried out to obtain the platinum thin film.

[0009] The transition layer is selected from one or more of tungsten, molybdenum, and rhenium, and preferably molybdenum is used.

[0010] In the present invention, the transition layer adopted is one or more of tungsten, molybdenum, and rhenium. The self-diffusion coefficients of these metals are relatively small (at 1100 °C, tungsten is 10 -19 m 2 / s, molybdenum is 10 -18 m 2 / s, rhenium is 10 -17 m 2 / s), and the crystal structures and thermal expansion coefficients of these metals are relatively matched with alumina and platinum. There is no need to introduce traditional metals (such as titanium, chromium, etc.) as the transition layer, avoiding the migration of impurity atoms. Then, when sputter-depositing the platinum thin film by mask plate selective area, high-precision patterning of the platinum thin film is achieved through the mask plate, and the subsequent etching step can also be avoided. Finally, through three heat treatments, the internal stress of the platinum thin film can be reduced, the adhesion and density of the platinum thin film to the substrate can be improved, and the internal defects of the platinum thin film can be reduced, so that the platinum thin film has a large resistance temperature coefficient.

[0011] As a preferred design, the ceramic substrate is a single-crystal or polycrystalline alumina or zirconia ceramic substrate; preferably alumina;

[0012] The ceramic substrate is cleaned with a mixed solution of potassium dichromate and sulfuric acid solution. After cleaning, the surface roughness of the ceramic substrate is less than 100 nm. Preferably, it is immersed in the mixed solution of potassium dichromate and sulfuric acid solution to clean and polish the surface of the substrate. The temperature of the mixed solution is preferably designed to be 40-70 °C, and the time is 40-70 min. Preferably, the surface roughness of the cleaned ceramic substrate is less than 20 nm. Such a design is to avoid the formation of holes on the surface of the sputtered thin film due to excessive roughness of the substrate.

[0013] As a preferred design, when sputtering the transition layer, it is carried out in an oxygen-free or reducing atmosphere, using a radio frequency power supply and setting a bias voltage, and selectively sputtering through a mask plate;

[0014] The material of the mask plate is quartz glass or silicon nitride. The thickness of the transition layer is 50-150 nm. The purpose of such a design is to avoid that an overly thick transition layer will increase the cost and the risk of migration. In the present invention, when sputtering the transition layer, a radio frequency power supply is used and a bias voltage is set, which can make the sputtered atoms have higher energy, increase the density and reduce the damage, and avoid atomic migration. And when sputtering the transition layer, selective area sputtering with a mask plate can achieve higher precision and avoid subsequent etching steps.

[0015] As a preferred design, when sputtering the transition layer, the sputtering power is 800-1000 W, the sputtering gas pressure is 0.1-0.4 Pa, the sputtering time is 10-30 s, and the bias voltage set by the radio frequency voltage is 50-100 V. In the present invention, setting the bias voltage is to increase the adhesion of the thin film, but an overly large bias voltage will increase the internal stress of the thin film and cause the risk of peeling off during subsequent annealing.

[0016] As a preferred design, when selectively depositing a platinum thin film with a mask plate, it is carried out in an oxygen-free atmosphere or a reducing atmosphere, using a radio frequency power supply and setting a bias voltage, and selectively depositing a platinum thin film through a mask plate with a thickness of 1.5-1.9 μm. Since there will be electron scattering between the platinum thin film and the transition layer and on the surface of the platinum thin film, in order to avoid scattering, the thickness of the platinum thin film needs to be at least 1 μm. In addition, considering the resistance adjustment, the thickness of the deposited platinum thin film is selected to be 1.5-1.9 μm in the present invention.

[0017] The material of the mask plate is quartz glass or silicon nitride.

[0018] As a preferred design, when sputtering a platinum thin film in a selected area of the mask plate, the bias voltage of the radio frequency voltage is set to 50 - 100 V, the sputtering power is 1000 - 1200 W, the sputtering gas pressure is 0.1 - 0.4 Pa, and the sputtering time is 5 - 10 min. Similarly, setting a bias voltage when sputtering the platinum thin film can increase the adhesion of the thin film. The bias voltage is set to 100 V because an excessive bias voltage will increase the internal stress of the thin film, leading to a risk of peeling off during subsequent annealing.

[0019] As a preferred design, when sputtering the transition layer and the platinum thin film in a selected area, the preparation method of the mask plate used is as follows:

[0020] Sputter a layer of alumina on the quartz glass, and then prepare the mask plate and the support by means of photolithography or etching. In the present invention, a support is designed on the mask plate, which mainly plays a supporting role, so that there is a certain gap between the mask plate and the substrate, thereby avoiding the mask plate sticking tightly to the substrate, resulting in damage to the pattern due to stress when the mask plate is disassembled.

[0021] As a preferred design, the heat treatment process is as follows:

[0022] The temperature of the first heat treatment is 400 - 500 °C, and the treatment time is 1 - 2 hours;

[0023] The temperature of the second heat treatment is 800 - 900 °C, and the treatment time is 0.5 - 3 hours;

[0024] The temperature of the third heat treatment is 1000 - 1300 °C, and the heat treatment time is 2 - 6 hours.

[0025] As a preferred design, the heating rate of the first heat treatment is 1 - 5 °C / min, the heating rate of the second heat treatment is 5 - 10 °C / min, and the heating rate of the third heat treatment is 5 - 10 °C / min;

[0026] The treatment atmosphere used in each heat treatment stage is any one of nitrogen, argon, and a reducing atmosphere.

[0027] In the present invention, during the first heat treatment process, a protective or reducing atmosphere can inhibit the oxidation of the platinum thin film circuit and ensure the densification of the platinum thin film during subsequent heat treatment. A slower heating rate and a lower heat treatment temperature can release the internal stress during the sputtering process of the platinum thin film and reduce the thermal stress between the thin film and the substrate during subsequent high-temperature heat treatment. For the second heat treatment, the selected temperature is 800 - 900 °C. Since platinum starts to form platinum oxide at around 500 °C and platinum oxide decomposes at around 800 °C, heat treatment at 800 - 900 °C can further reduce the extremely small amount of platinum oxide generated during the sputtering process to platinum. Moreover, at this temperature, the thermal stress caused by too rapid heating can also be alleviated, and the platinum thin film will aggregate and grow. For the third heat treatment, the selected temperature is 1000 - 1300 °C, which can ensure that platinum grains aggregate and grow sufficiently through grain boundary migration, reducing defects inside the platinum thin film, such as pores, grain boundaries, dislocations, etc.

[0028] The platinum thin film obtained by the present invention is dense and uniform, with controllable impurities and defects. The resistance temperature coefficient can reach 3850 ppm / °C, the grain size of the platinum thin film can reach about 20 μm, and the precision of the platinum thin film circuit prepared by selective area sputtering is relatively high. It can be used in platinum thin film resistance temperature sensors and can withstand high temperatures up to 850 °C. The low self-diffusion coefficient of the transition layer can reduce the migration of impurities, ensuring that the platinum thin film has good thermal stability. By using a radio frequency power supply and applying a bias voltage, the ion energy can be increased, enabling the deposition atoms to have an increased mobility on the substrate surface, thereby reducing the porosity of the thin film, improving the density, and ultimately enhancing the adhesion of the thin film. The three-step heat treatment can also release the residual stress during the sputtering process, stabilize the structure, and finally, reduction, aggregation, dewetting, etc. will occur during the heat treatment, promoting the growth of platinum grains.

[0029] The second object of the present invention is to provide a platinum thin film for an automotive exhaust gas temperature sensor, which is prepared by using the method described in any one of the above.

[0030] The third object of the present invention is to provide a thin film temperature sensor, which includes the platinum thin film for an automotive exhaust gas temperature sensor described above.

[0031] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0032] The platinum thin film obtained by the present invention is dense and uniform, with controllable impurities and defects. The resistance temperature coefficient can reach 3850 ppm °C, the grain size of the platinum thin film can reach 20 μm or more, and the precision of the platinum thin film circuit prepared by selective area sputtering is relatively high. It can be used in platinum thin film resistance temperature sensors. Specifically:

[0033] 1. In the method of the present invention, a metal with a low self-diffusion coefficient is used for the transition layer, which can reduce the migration of impurities and ensure that the platinum thin film has good thermal stability. The three-step heat treatment can release the residual stress during the sputtering process, stabilize the structure, and finally, reduction, aggregation, dewetting, etc. will occur during the heat treatment to promote the growth of platinum grains.

[0034] 2. Further, in the present invention, by using a radio frequency power supply and applying a bias voltage, the ion energy can be increased, so that the mobility of the deposited atoms on the substrate surface is increased, thereby reducing the porosity of the thin film, improving the density, and ultimately enhancing the adhesion of the thin film. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and thus should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can also be obtained based on these drawings without creative efforts. In the drawings:

[0036] Figure 1 It is a schematic diagram for manufacturing a sputtering mask template;

[0037] Figure 2 It is a schematic diagram of the process of obtaining a platinum thin film circuit by sputtering a platinum thin film in the present invention;

[0038] Figure 3 It is an SEM image of a platinum thin film circuit prepared by an etching method in Comparative Example 10;

[0039] Figure 4 It is an SEM of a platinum thin film circuit prepared by a selective area sputtering method in Example 1;

[0040] Figure 5 It is a cross-sectional SEM image of the platinum thin film obtained in Comparative Example 1;

[0041] Figure 6 It is a cross-sectional SEM image of the platinum thin film obtained in Comparative Example 4;

[0042] Figure 7 It is a cross-sectional SEM image of the platinum thin film obtained in Example 1;

[0043] Figure 8 It is a cross-sectional SEM image of the platinum thin film obtained in Comparative Example 7;

[0044] Figure 9 It is a cross-sectional SEM image of the platinum thin film obtained in Comparative Example 9;

[0045] Figure 10 It is a comparison diagram of the migration of impurity atom aluminum formed between the platinum thin films obtained in each example and Comparative Examples 1-9 at the interface between the thin film and the substrate.

[0046] Figure 11 It is a comparison diagram of the migration of impurity atom molybdenum formed between the platinum thin films obtained in each example and Comparative Examples 1-6 at the interface between the thin film and the substrate.

[0047] Figure 12 It is a diagram of the migration of chromium atoms between the platinum thin film obtained in Comparative Example 7 at the interface between the thin film and the substrate and the migration of titanium atoms at the interface between the thin film and the substrate in Comparative Example 8;

[0048] Figure 13 It is a diagram of the test results of the thermal stability of the platinum thin films of each example and comparative examples;

[0049] Figure 14 It is an SEM diagram of the circuit pad of the platinum thin film obtained in Example 1.

[0050] The markings in the figure are: 1 - quartz glass, 2 - alumina, 3 - alumina mask support, 4 - mask, 5 - alumina substrate, 6 - film circuit, 7 - platinum atoms, 8 - platinum target, 9 - molybdenum transition layer, 10 - chromium oxide formed by migration. Specific implementation manners

[0051] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments. The illustrative embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0052] Example 1:

[0053] The preparation method of the mask is: (1) sputter a layer of alumina (with a thickness of 5-10 um) on quartz glass (with a thickness of 10-50 um); (2) prepare the mask and the support by photolithography or etching methods.

[0054] The preparation method of the platinum thin film is:

[0055] (1) Immerse the alumina ceramic substrate in a mixed solution of potassium dichromate and sulfuric acid solution. The temperature of the mixed solution is 40-70 °C and the time is 40-70 min. After the substrate is cleaned and polished, the roughness is in the range of 10-100 nm.

[0056] (2) Use a magnetron sputtering system, set the sputtering mask, and then press the mask tightly against the ceramic substrate through a specific mold (fix the mask on the sample holder, slowly push the ceramic substrate from below, and finally press it tightly against the ceramic substrate).

[0057] Using a radio frequency power supply, the bias voltage set by the radio frequency voltage is 50 - 100 V, the sputtering atmosphere is argon, a molybdenum-containing thin film is sputtered on the polished surface of the ceramic substrate, the sputtering power is 800 - 1000 W, the target-substrate distance is 10 cm, the substrate rotation rate is 1 revolution / min, the sputtering gas pressure is 0.1 - 0.4 Pa, and the sputtering time is 10 - 30 s. The thickness of the deposited molybdenum layer obtained is 50 - 150 nm.

[0058] (3) A magnetron sputtering system is adopted. Using a radio frequency power supply and setting a bias voltage of 50 - 100 V, the sputtering atmosphere is argon. To ensure a low oxygen content in the atmosphere, a reducing atmosphere can be introduced. The sputtering power is 1000 - 1200 W, the sputtering gas pressure is 0.1 - 0.4 Pa, the target-substrate distance is 10 cm, the substrate rotation rate is 1 revolution / min, and the sputtering time is 5 - 10 min. A deposited platinum thin film with a thickness of 1.5 - 1.9 μm is obtained.

[0059] (4) Heat treatment is carried out in three steps:

[0060] For the first step of heat treatment, the atmosphere is any one of nitrogen, argon, or a reducing atmosphere, the heating rate is 1 - 5 °C / min, the heat treatment temperature is 400 - 500 °C, and the heat treatment time is 1 - 2 hours.

[0061] For the second step of heat treatment, the atmosphere is any one of nitrogen, argon, or a reducing atmosphere, the heating rate is 5 - 10 °C / min, the heat treatment temperature is 800 - 900 °C, and the heat treatment time is 1 - 2 hours.

[0062] For the third step of heat treatment, the atmosphere is any one of nitrogen, argon, or a reducing atmosphere, the heating rate is 5 - 10 °C / min, the heat treatment temperature is 1000 - 1300 °C, and the heat treatment time is 3 - 6 hours.

[0063] Finally, a platinum thin film for an automotive exhaust gas temperature sensor is obtained.

[0064] Among them, as Figure 1 shows the schematic diagram of the production of the mask plate. An alumina layer 2 is sputtered on quartz glass, and then the quartz glass layer 1 is etched to obtain a mask pattern on the quartz glass layer 1, thereby obtaining the mask plate 4, and the alumina layer 2 is etched to obtain the alumina mask plate support 3, thus completing the production.

[0065] Figure 2 shows the schematic diagram of the sputtered platinum thin film. A molybdenum layer is sputtered on the alumina substrate 5, and then using the mask plate and support prepared as in Figure 1 , through selective area sputtering and using a platinum target 8 to deposit a platinum thin film, a platinum thin film circuit 6 is obtained.

[0066] The inventors also measured the SEM image at the pad of the platinum thin film circuit obtained in Example 1. It can be seen from the figure that the grain size of the platinum thin film can reach 20 μm or more.

[0067] Example 2:

[0068] The difference between this example and Example 1 is that the ceramic substrate used is zirconia, and the rest are the same as those in Example 1.

[0069] Comparative Example 1:

[0070] The difference from Example 1 is that the heat treatment process has one stage: the heating rate is 1 - 5 °C / min, the heat treatment temperature is 400 - 500 °C, and the heat treatment time is 1 - 2 hours.

[0071] Comparative Example 2:

[0072] The difference from Example 1 is that the heat treatment process has one stage: the heating rate is 5 - 10 °C / min, the heat treatment temperature is 800 - 900 °C, and the heat treatment time is 1 - 2 hours.

[0073] Comparative Example 3:

[0074] The difference from Example 1 is that the heat treatment process has one stage: the heating rate is 5 - 10 °C / min, the heat treatment temperature is 1000 - 1300 °C, and the heat treatment time is 3 - 6 hours.

[0075] Comparative Example 4:

[0076] The difference from Example 1 is that the heat treatment process has two stages: the first stage: the heating rate is 1 - 5 °C / min, the heat treatment temperature is 400 - 500 °C, and the heat treatment time is 1 - 2 hours; then the second stage is: the heating rate is 5 - 10 °C / min, the heat treatment temperature is 800 - 900 °C, and the heat treatment time is 1 - 2 hours.

[0077] Comparative Example 5:

[0078] The difference from Example 1 is that the heat treatment process has two stages: the first stage: the heating rate is 1 - 5 °C / min, the heat treatment temperature is 400 - 500 °C, and the heat treatment time is 1 - 2 hours; then the second stage is: the heating rate is 5 - 10 °C / min, the heat treatment temperature is 1000 - 1300 °C, and the heat treatment time is 3 - 6 hours.

[0079] Comparative Example 6:

[0080] The difference from Example 1 lies in that the heat treatment process has two stages: the first stage: the heating rate is 5-10 °C / min, the heat treatment temperature is 800-900 °C, and the heat treatment time is 1-2 hours. Then the second stage is: the heating rate is 5-10 °C / min, the heat treatment temperature is 1000-1300 °C, and the heat treatment time is 3-6 hours.

[0081] Comparative Example 7:

[0082] The difference from Example 1 lies in that the transition layer is a chromium layer, and the rest is the same as in Example 1.

[0083] Comparative Example 8:

[0084] The difference from Example 1 lies in that the transition layer is a titanium layer, and the rest is the same as in Example 1.

[0085] Comparative Example 9:

[0086] The difference from Example 1 lies in that the transition layer is platinum oxide, and the rest is the same as in Example 1.

[0087] The inventor characterized the cross-sections of the platinum thin films obtained from the above examples and comparative examples. Figure 5 Corresponding to Comparative Example 1, Figure 6 Corresponding to Comparative Example 4, Figure 7 Corresponding to Example 1, Figure 8 Corresponding to Comparative Example 7, Figure 9 Corresponding to Comparative Example 9.

[0088] It can be seen from Figure 7 that in Example 1, three heat treatment processes were carried out, and molybdenum was used as the transition layer. In the cross-sectional view of the thin film, it is shown that the molybdenum transition layer 9 did not migrate, and the cross-section of the thin film was relatively dense, with a very low porosity ratio. In Comparative Example 1, one heat treatment was carried out, and the heat treatment temperature was relatively low. The cross-section of the obtained platinum thin film showed Figure 5 more pores. In Comparative Example 4, two heat treatments were carried out, and the cross-section of the platinum thin film showed Figure 6 more pores than Figure 7 in.

[0089] When chromium was used as the transition layer in Comparative Example 7, migration occurred on the thin film, and chromium oxide 10 was formed due to the migration. When titanium was used as the transition layer in Comparative Example 8, migration also occurred, forming titanium oxide. When platinum oxide was used as the transition layer in Comparative Example 9, Figure 9 showed more holes, which was caused by the decomposition of platinum oxide during the annealing stage.

[0090] The inventor further measured the platinum thin films obtained from each example and Comparative Examples 1-9, and evaluated the film adhesion, surface porosity, and temperature coefficient of resistance. The results are shown in Table 1 below.

[0091] Table 1

[0092]

[0093]

[0094] Explanation of Table 1:

[0095] Heat treatment method:

[0096] A The heating rate is 1 - 5 °C / min, the heat treatment temperature is 400 - 500 °C, and the heat treatment time is 1 - 2 hours.

[0097] B The heating rate is 5 - 10 °C / min, the heat treatment temperature is 800 - 900 °C, and the heat treatment time is 1 - 2 hours.

[0098] C The heating rate is 5 - 10 °C / min, the heat treatment temperature is 1000 - 1300 °C, and the heat treatment time is 3 - 6 hours.

[0099] D is ① The heating rate is 1 - 5 °C / min, the heat treatment temperature is 400 - 500 °C, and the heat treatment time is 1 - 2 hours; then ② The heating rate is 5 - 10 °C / min, the heat treatment temperature is 800 - 900 °C, and the heat treatment time is 1 - 2 hours.

[0100] E The heating rate is 1 - 5 °C / min, the heat treatment temperature is 400 - 500 °C, and the heat treatment time is 1 - 2 hours; then the heating rate is 5 - 10 °C / min, the heat treatment temperature is 1000 - 1300 °C, and the heat treatment time is 3 - 6 hours.

[0101] F is ① The heating rate is 5 - 10 °C / min, the heat treatment temperature is 800 - 900 °C, and the heat treatment time is 1 - 2 hours, then ② The heating rate is 5 - 10 °C / min, the heat treatment temperature is 1000 - 1300 °C, and the heat treatment time is 3 - 6 hours.

[0102] G is ① The heating rate is 1 - 5 °C / min, the heat treatment temperature is 400 - 500 °C, and the heat treatment time is 1 - 2 hours; then ② The heating rate is 5 - 10 °C / min, the heat treatment temperature is 800 - 900 °C, and the heat treatment time is 1 - 2 hours, and finally ③ The heating rate is 5 - 10 °C / min, the heat treatment temperature is 1000 - 1300 °C, and the heat treatment time is 3 - 6 hours.

[0103] The surface energy porosity in Table 1 is obtained by calculating the three-dimensional morphology of the platinum thin film through atomic force microscopy, using the formula:

[0104] Surface porosity = (1 - volume of surface platinum thin film / total volume of surface squares) × 100%

[0105] In Table 1, the evaluation method for adhesion uses the nano-scratch method, with the vertical load ranging from 0 - 450 mN. If the adhesion force > 450 mN, it is ★; if the adhesion force is 350 - 450 mN, it is ▲; if the adhesion force is less than 350 mN, it is ○.

[0106] It can be seen from the results in Table 1 that the adhesion of the platinum thin films obtained by the method of this embodiment is all higher than 450 mN, the surface porosities are 5.1% and 6.3% respectively, which are significantly lower than the surface porosities of each comparative example, and the TCR is as high as 3850 ppm / °C. In Examples 1 and 2, the types of ceramic substrates were changed, and it had little effect on the performance of the obtained platinum thin films.

[0107] In Comparative Example 1, due to one heat treatment with a relatively low temperature, the adhesion was significantly lower than that of the examples, especially the difference in surface porosity and TCR was more obvious; in Comparative Example 2, one heat treatment was carried out with a heat treatment temperature of 800 - 900 °C, and the adhesion force, porosity, and TCR were all inferior to those of each example. In Comparative Example 3, although the TCR reached 3580 ppm / °C, the surface porosity and adhesion were both inferior to those of the examples. Similarly, for Comparative Examples 4, 5, and 6, two-stage heat treatments were carried out. Although the adhesion force was acceptable, the porosity and TCR were both inferior to those of the examples. In Comparative Examples 7, 8, and 9, the transition layer was changed. Although the adhesion was acceptable, the surface porosity and TCR were both inferior to those of each example. It can be seen that the methods of each comparative example cannot take into account strong adhesion, low surface porosity, and high-temperature resistance temperature coefficient at the same time. Using the heat treatment method of the present invention can significantly improve the adhesion force of the platinum thin film, reduce the surface porosity, and achieve a relatively high resistance temperature coefficient.

[0108] Comparative Example 10:

[0109] The difference from Example 1 is that after sputtering the transition layer on the ceramic substrate, the platinum thin film circuit is obtained by the etching method. The rest is the same as Example 1.

[0110] Scanning electron microscope characterization was carried out on the platinum thin film circuits obtained from Comparative Example 10 and Example 1, and the results are respectively as Figure 3 and Figure 4 shown. It can be seen from the figure that there are burrs at the edges of the platinum thin film circuits prepared by the methods of Comparative Example 10 and Example 1. Among them, there are some platinum particles between the platinum thin film circuits obtained by selective area sputtering in Example 1, but it will not cause short circuit of the platinum thin film, and the precision is relatively high.

[0111] The inventors also compared the migration of impurity atoms during the heat treatment process between the examples and the comparative examples.

[0112] As Figure 10As shown, it is the migration situation of impurity atom aluminum between the platinum thin film and the substrate interface obtained in each embodiment and Comparative Examples 1-9. It can be seen that the migration of aluminum atoms at the interface in Comparative Examples 7, 8, and 9 is obvious, while the migration amounts in each embodiment and Comparative Examples 1-6 are small. This is related to the fact that the transition layers used in Comparative Examples 7, 8, and 9 are not molybdenum.

[0113] As Figure 11 shown, it is the migration situation of molybdenum atoms between the platinum thin film and the substrate interface obtained in each embodiment and Comparative Examples 1-6. It can be seen that the migrations are not obvious.

[0114] As Figure 12 shown, it is the migration situation of chromium atoms between the platinum thin film and the substrate interface obtained in Comparative Example 7, and the migration situation of titanium atoms between the platinum thin film and the substrate interface obtained in Comparative Example 8. It can be seen that there is also a certain amount of migration. It can be seen that when Mo is used as the transition layer, the migration of impurity atoms can be inhibited to a great extent.

[0115] The inventors further studied the thermal stability test of the platinum thin film resistor temperature sensor prepared from the platinum thin film obtained in the embodiments of the present invention. During the test, the platinum thin films of each embodiment and comparative example were rapidly heated from room temperature to 850 °C and then rapidly cooled to room temperature, and the resistance change rate of the thin film was detected to detect its thermal cycle stability performance. As Figure 13 shown, except for Comparative Examples 7, 8, and 9, the resistance change rates of other embodiments and comparative examples are less than 0.2% after 500 cycles, and the resistance change rates of Embodiment 1 and Embodiment 2 are the smallest. It can be seen that the platinum thin film prepared by the present invention has good thermal stability, which depends on its good adhesion, the ability of Mo to inhibit the migration of impurity elements, and the crystallization state.

[0116] The platinum thin film obtained by the present invention is dense and uniform, the impurities and defects are controllable, the resistance temperature coefficient can reach 3850 ppm / °C, the grain size of the platinum thin film can reach about 20 μm, the circuit precision of the platinum thin film prepared by selective area sputtering is relatively high, and it can be used for platinum thin film resistor temperature sensors. The low self-diffusion coefficient of molybdenum can reduce the migration of impurities and ensure that the platinum thin film has good thermal stability. By using a radio frequency power supply and applying a bias voltage, the ion energy can be increased, so that the migration rate of deposited atoms on the substrate surface increases, thereby reducing the porosity of the thin film and improving the density, and finally enhancing the adhesion of the thin film. The three-step heat treatment can also release the residual stress during the sputtering process, stabilize the structure, and finally reduction, aggregation, dewetting, etc. will occur during the heat treatment to promote the growth of platinum grains.

[0117] In the above specific embodiments, the object, technical solution and beneficial effects of the present invention have been further described in detail. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a platinum thin film for an automotive exhaust gas temperature sensor, characterized in that, Sputter a transition layer on a ceramic substrate, then sputter a platinum thin film by selective area sputtering through a mask plate, and then perform three heat treatments to obtain the platinum thin film; The transition layer is selected from one or more of tungsten, molybdenum, and rhenium.

2. The preparation method of a platinum thin film for an automotive exhaust gas temperature sensor according to claim 1, wherein The ceramic substrate is a single-crystal or polycrystalline alumina or zirconia ceramic substrate; The ceramic substrate is cleaned with a mixed solution of potassium dichromate and sulfuric acid solution, and the surface roughness of the ceramic substrate after cleaning is 10-100 nm.

3. The preparation method of a platinum thin film for an automotive exhaust gas temperature sensor according to claim 1, characterized in that, When sputtering the transition layer, in an oxygen-free or reducing atmosphere, use a radio frequency power supply and set a bias voltage, and perform selective area sputtering through a mask plate; The material of the mask plate is quartz glass or silicon nitride, and the thickness of the transition layer is 50-150 nm.

4. The preparation method of a platinum thin film for an automotive exhaust gas temperature sensor according to claim 3, characterized in that When sputtering the transition layer, the sputtering power is 800-1000 W, the sputtering gas pressure is 0.1-0.4 Pa, the sputtering time is 10-30 s, and the bias voltage set by the radio frequency voltage is 50-100 V.

5. The preparation method of a platinum thin film for an automotive exhaust gas temperature sensor according to claim 1, characterized in that, When performing selective area sputtering of the platinum thin film through the mask plate, in an oxygen-free atmosphere or a reducing atmosphere, use a radio frequency power supply and set a bias voltage, and deposit the platinum thin film by selective area sputtering through the mask plate, with a thickness of 1.5-1.9 um; The material of the mask plate is quartz glass or silicon nitride.

6. The preparation method of a platinum thin film for an automotive exhaust gas temperature sensor according to claim 5, characterized in that, When performing selective area sputtering of the platinum thin film through the mask plate, the bias voltage of the radio frequency voltage is set to 50-100 V, the sputtering power is 1000-1200 W, the sputtering gas pressure is 0.1-0.4 Pa, and the sputtering time is 5-10 min.

7. A method for preparing a platinum thin film for an automotive exhaust gas temperature sensor according to claim 1 or 6, characterized in that, When performing selective area sputtering of the transition layer and the platinum thin film, the preparation method of the mask plate adopted is: Sputter a layer of alumina on quartz glass, and then prepare a mask template and a support by photolithography or etching methods.

8. The preparation method of a platinum thin film for an automotive exhaust gas temperature sensor according to claim 1, characterized in that, The heat treatment process is: The temperature of the first heat treatment is 400-500 °C, and the treatment time is 1-2 hours; The temperature of the second heat treatment is 800-900 °C, and the treatment time is 0.5-3 hours; The temperature of the third heat treatment is 1000-1300 °C, and the heat treatment time is 2-6 hours; Preferably, the heating rate of the first heat treatment is 1-5 °C / min, the heating rate of the second heat treatment is 5-10 °C / min, and the heating rate of the third heat treatment is 5-10 °C / min; The treatment atmosphere adopted in each heat treatment stage is any one of nitrogen, argon, and reducing atmosphere.

9. A platinum thin film for an automotive exhaust gas temperature sensor, characterized in that, Obtained by using the preparation method according to any one of claims 1 to 8.

10. A temperature sensor, characterized in that, Including the platinum thin film according to claim 9.

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