Platinum thin film for automobile exhaust temperature sensor, method for manufacturing the same, and temperature sensor

Abstract

The application discloses a platinum thin film for a vehicle exhaust temperature sensor, a preparation method and a temperature sensor. The preparation method comprises the following steps: sputtering a transition layer on a ceramic substrate, then sputtering a platinum thin film through a mask, and then performing three times of heat treatment, so that the platinum thin film is obtained; and the transition layer is selected from one or more of tungsten, molybdenum and rhenium. The platinum thin film obtained by the method is dense and uniform, impurities and defects are controllable, the resistance temperature coefficient can reach 3850ppm℃, the grain size of the platinum thin film can reach 20um, the circuit precision of the platinum thin film sputtered by selection is high, and the platinum thin film can be used for a platinum thin film resistance temperature sensor.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of temperature sensors, and particularly relates to a platinum thin film for an automobile exhaust temperature sensor, a preparation method of the platinum thin film, and a temperature sensor. BACKGROUND

[0002] The existing temperature sensor sensitive elements are various, are elements for measuring temperature, mainly include thermoelectric type, resistance type and bimetallic strip type. Among them, the thin film resistance temperature sensor sensitive element is widely used in household appliances, aerospace, medical treatment, military and other fields. The automobile exhaust temperature sensor needs a large temperature range, among various metal thin films, platinum has a good resistance-temperature linear relationship at-200 DEG C-850 DEG C, and the change of platinum resistance value reflects the change of temperature, so it is often used in thin film resistance temperature sensors. Compared with the traditional wire-wound platinum resistance temperature sensor, the platinum thin film resistance temperature sensor has the characteristics of small size, short response time, accurate temperature measurement and low cost.

[0003] At present, the preparation process of platinum thin film is very difficult, including: small resistance temperature coefficient (TCR), poor adhesion, poor resistance thermal stability, only a few companies at home and abroad have the ability to manufacture platinum thin film. Among them, TCR is the most critical parameter, which is mainly affected by the following parameters: (1) lattice vibration scattering (phonon scattering): the scattering of electrons caused by the thermal vibration of atoms in the platinum crystal, which increases with the increase of temperature, is the main source of TCR, and has a clear temperature dependence; (2) interface scattering: including thin film surface scattering and thin film-substrate interface scattering, its intensity is determined by the thickness of the thin film, the surface roughness and the interface quality, and is independent of temperature; (3) defect scattering: the scattering of electrons caused by the grain boundaries, dislocations and impurity atoms in the thin film, its intensity depends on the preparation process and material purity of the thin film, and is also independent of temperature. Therefore, only the lattice vibration is related to temperature, and the other two influencing factors will cause the resistance temperature coefficient to be too small or unstable, which limits the application of platinum thin film resistance temperature sensor. The poor adhesion of platinum thin film is mainly due to the lattice mismatch between platinum and substrate and the residual stress in the preparation process. In addition, during the manufacturing and using process, 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 high-temperature sensor platinum thin film, having a large and stable resistance temperature coefficient is an important indicator. The adhesion of the thin film to the substrate is poor at high temperature, the platinum grain size is small, and impurity atoms migrate. In order to solve the above problems, some researchers have solved it by increasing the transition layer and annealing at high temperature for a long time. For example, the published patent document CN114807859 A uses PtO as a transition layer, which can ensure the adhesion of the platinum thin film, but there is a problem of reducing the sputtering atomic kinetic energy, which reduces the density of the platinum thin film; In addition, due to the presence of platinum oxide, decomposition occurs during annealing, which forms holes on the platinum thin film. In addition, the platinum thin film sputtered by the traditional sputtering method is not dense, which will affect the resistance of the platinum thin film formed by annealing, and also affect the resistance temperature coefficient of the platinum thin film.

[0005] Therefore, it is urgent to develop a platinum thin film with high resistance temperature coefficient and high temperature stability. In view of this, the present patent application is proposed. SUMMARY

[0006] In order to solve the above problems, the present application provides a preparation method of a platinum thin film for an automobile exhaust temperature sensor, and also provides a platinum thin film prepared by the method and a thin film temperature sensor.

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

[0008] The first object of the present application is to provide a preparation method of a platinum thin film for an automobile exhaust temperature sensor, which sputters a transition layer on a ceramic substrate, then sputters a platinum thin film through a mask, and then performs three heat treatments to obtain a platinum thin film.

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

[0010] In the present application, the transition layer is one or more of tungsten, molybdenum and rhenium, which has a small self-diffusion coefficient (at 1100℃, tungsten is 10 -19 m 2 / s, molybdenum is 10 -18 m 2 / s, and rhenium is 10 -17 m 2 / s), and the crystal structure and thermal expansion coefficient of these metals are matched with alumina and platinum, so there is no need to introduce traditional metals (such as titanium, chromium, etc.) as a transition layer, which avoids the migration of impurity atoms; When sputtering the platinum thin film through the mask, a high-precision platinum thin film patterning is achieved through the mask, 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, the internal defects of the platinum thin film can be reduced, and the platinum thin film has a larger resistance temperature coefficient.

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

[0012] The ceramic substrate is cleaned by a mixed solution of potassium dichromate and sulfuric acid solution, and the surface roughness of the cleaned ceramic substrate is less than 100 nm. Preferably, the substrate surface is cleaned and polished by immersion in a mixed solution of potassium dichromate and sulfuric acid solution, and the temperature of the mixed solution is preferably designed to be 40-70℃, and the time is 40-70min. Preferably, the surface roughness of the cleaned ceramic substrate is less than 20nm, which is designed to avoid the formation of holes on the surface of the sputtered film due to the excessive roughness of the substrate.

[0013] As a preferred design, the transition layer is sputtered in an oxygen-free or reducing atmosphere, using a radio frequency power source and setting a bias voltage, and using a mask for selective sputtering.

[0014] The material of the mask is quartz glass or silicon nitride, and the thickness of the transition layer is 50-150nm, which is designed to avoid the increase of cost and the risk of migration caused by the excessive thickness of the transition layer. In the present application, the use of a radio frequency power source and the setting of a bias voltage during the sputtering of the transition layer can make the sputtered atoms have a higher energy, increase the density and reduce the damage, and avoid atomic migration. Moreover, the use of a mask for selective sputtering during the sputtering of the transition layer can achieve higher precision and avoid subsequent etching steps.

[0015] As a preferred design, the sputtering power is 800-1000W, the sputtering pressure is 0.1-0.4Pa, the sputtering time is 10-30s, and the radio frequency voltage bias is set to 50-100V. In the present application, the bias voltage is set to increase the adhesion of the film, but excessive bias voltage will increase the internal stress of the film, which will lead to the risk of falling off during subsequent annealing.

[0016] As a preferred design, the platinum film is selectively sputtered by a mask in an oxygen-free or reducing atmosphere, using a radio frequency power source and setting a bias voltage, and the platinum film is deposited by a mask to a thickness of 1.5-1.9um. Since there will be electron scattering between the platinum film and the transition layer and on the surface of the platinum film, the thickness of the platinum film needs to be at least 1um to avoid scattering. In addition, considering the resistance adjustment, the thickness of the deposited platinum film is selected to be 1.5-1.9um in the present application.

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

[0018] As a preferred design, when the mask is used for selective sputtering of the platinum film, the bias voltage of the radio frequency is set to 50-100 V, the sputtering power is 1000-1200 W, the sputtering pressure is 0.1-0.4 Pa, and the sputtering time is 5-10 min. Similarly, setting the bias voltage when sputtering the platinum film can increase the adhesion of the film, and the bias voltage is set to 100 V because too large bias voltage will increase the internal stress of the film, which will lead to the risk of falling off in subsequent annealing.

[0019] As a preferred design, when the mask is used for selective sputtering of the transition layer and the platinum film, the mask is prepared by the following method:

[0020] An aluminum oxide layer is sputtered on the quartz glass, and then a mask and a support are prepared by photolithography or etching. In the present application, the support is designed on the mask, which mainly serves as a support to provide a certain gap between the mask and the substrate, thereby avoiding the mask being tightly attached to the substrate, which will cause the pattern to be damaged due to stress when the mask is removed.

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

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

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

[0024] The third heat treatment temperature is 1000-1300℃, 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℃ / min, the heating rate of the second heat treatment is 5-10℃ / min, and the heating rate of the third heat treatment is 5-10℃ / 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 application, the protective or reducing atmosphere used in the first heat treatment process can inhibit oxidation of the platinum thin film circuit, ensuring the density of the platinum thin film in subsequent heat treatment; the slow heating rate and low heat treatment temperature can release the internal stress in the platinum thin film during sputtering, reducing the thermal stress between the thin film and the substrate during subsequent high-temperature heat treatment, etc. The second heat treatment is selected at a temperature of 800-900℃. Since platinum begins to form platinum oxide at about 500℃, and the platinum oxide decomposes at about 800℃, the heat treatment at 800-900℃ can further reduce the small amount of platinum oxide generated during sputtering to platinum, and at this temperature, the thermal stress caused by rapid heating can be relieved, and the platinum thin film will grow and gather. The third heat treatment is selected at 1000-1300℃, which can ensure that the platinum grains migrate through the grain boundaries to grow and gather sufficiently, reducing defects in the platinum thin film, such as pores, grain boundaries, dislocations, etc.

[0028] The platinum thin film obtained by the present application is dense and uniform, with controllable impurities and defects, and the resistance temperature coefficient can reach 3850ppm / ℃. The grain size of the platinum thin film can reach about 20um, and the precision of the platinum thin film circuit obtained by selective sputtering is high, which can be used for platinum thin film resistance temperature sensors and can withstand high temperatures of 850℃. 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, the mobility of deposited atoms on the substrate surface can be increased, the porosity of the thin film can be reduced, the density can be increased, and finally the adhesion of the thin film can be enhanced. The three-step heat treatment can also release the residual stress during sputtering, stabilize the structure, and finally reduce, gather, and dehydrate during heat treatment, promoting the growth of platinum grains.

[0029] The second object of the present application is to provide a platinum thin film for an automobile exhaust temperature sensor prepared by the method of any one of the above.

[0030] The third object of the present application is to provide a thin film temperature sensor comprising the platinum thin film for an automobile exhaust temperature sensor as described above.

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

[0032] The platinum thin film obtained by the present application is dense and uniform, with controllable impurities and defects, and the resistance temperature coefficient can reach 3850ppm / ℃. The grain size of the platinum thin film can reach about 20um, and the precision of the platinum thin film circuit obtained by selective sputtering is high, which can be used for platinum thin film resistance temperature sensors. Specifically:

[0033] 1. The method of the present application, the transition layer uses a metal with low self-diffusion coefficient, which can reduce the migration of impurities and ensure that the platinum thin film has good thermal stability; and the three-step heat treatment can release the residual stress in the sputtering process, stabilize the structure, and finally cause reduction, aggregation, and moisture removal during heat treatment, thereby promoting the growth of platinum grains.

[0034] 2. The present application further uses a radio frequency power source and an applied bias to increase the ion energy, thereby increasing the mobility of deposited atoms on the substrate surface, reducing the porosity of the thin film, improving the density, and ultimately enhancing the adhesion of the thin film. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present application, the following will briefly introduce the drawings needed in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be considered as limiting the scope. For those skilled in the art, other related drawings can also be obtained without creative labor. In the drawings:

[0036] Figure 1 Schematic diagram for making a mask plate for sputtering;

[0037] Figure 2 Process schematic diagram for sputtering platinum thin film circuit in the present application;

[0038] Figure 3 SEM diagram for platinum thin film circuit prepared by etching method in Comparative Example 10;

[0039] Figure 4 SEM for platinum thin film circuit prepared by selective sputtering method in Example 1;

[0040] Figure 5 Cross-sectional SEM diagram for platinum thin film obtained in Comparative Example 1;

[0041] Figure 6 Cross-sectional SEM diagram for platinum thin film obtained in Comparative Example 4;

[0042] Figure 7 Cross-sectional SEM diagram for platinum thin film obtained in Example 1;

[0043] Figure 8 Cross-sectional SEM diagram for platinum thin film obtained in Comparative Example 7;

[0044] Figure 9 Cross-sectional SEM diagram for platinum thin film obtained in Comparative Example 9;

[0045] Figure 10 Impurity atom aluminum migration comparison diagram between the thin film and the substrate interface for the platinum thin films obtained in each example and Comparative Examples 1-9.

[0046] Figure 11 Figure 1 is a diagram showing the migration of impurity atoms of molybdenum between the interface of the platinum thin film and the substrate obtained in each example and Comparative Examples 1-6.

[0047] Figure 12 Figure 2 is a diagram showing the migration of chromium atoms between the interface of the platinum thin film and the substrate obtained in Comparative Example 7 and the migration of titanium atoms between the interface of the thin film and the substrate in Comparative Example 8;

[0048] Figure 13 Figure 3 is a diagram showing the results of the thermal stability test of the platinum thin film in each example and the comparative examples;

[0049] Figure 14 Figure 4 is a SEM image of the circuit pad of the platinum thin film obtained in Example 1.

[0050] The labels 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-migration formed chromium oxide. DETAILED DESCRIPTION

[0051] In order to make the objects, technical solutions and advantages of the present application clearer, below, the present application is further described in detail in combination with examples, the illustrative embodiments of the present application and the description thereof are only used to explain the present application, and do not limit the present application.

[0052] Example 1:

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

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

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

[0056] (2) using a magnetron sputtering system, setting the sputtering mask, and then tightly pressing the mask against the ceramic substrate by a special tool (fixing the mask on the sample support, slowly pushing the ceramic substrate from below, and finally tightly pressing the ceramic substrate).

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

[0058] (3) The platinum film is deposited using a magnetron sputtering system, a radio frequency power source, a bias of 50-100V, an argon sputtering atmosphere, a sputtering power of 1000-1200W, a sputtering gas pressure of 0.1-0.4Pa, a target-substrate distance of 10cm, a substrate rotation rate of 1 turn / min, and a sputtering time of 5-10min. The deposited platinum film has a thickness of 1.5-1.9um.

[0059] (4) The heat treatment is divided into three steps:

[0060] The first step of heat treatment is performed in an atmosphere of nitrogen, argon or a reducing atmosphere, at a heating rate of 1-5℃ / min, a heat treatment temperature of 400-500℃, and a heat treatment time of 1-2 hours.

[0061] The second step of heat treatment is performed in an atmosphere of nitrogen, argon or a reducing atmosphere, at a heating rate of 5-10℃ / min, a heat treatment temperature of 800-900℃, and a heat treatment time of 1-2 hours.

[0062] The third step of heat treatment is performed in an atmosphere of nitrogen, argon or a reducing atmosphere, at a heating rate of 5-10℃ / min, a heat treatment temperature of 1000-1300℃, and a heat treatment time of 3-6 hours.

[0063] The platinum film for an automobile exhaust temperature sensor is obtained.

[0064] In the present application, the mask plate is prepared as shown in Fig. 1. An aluminum oxide layer 2 is sputtered on a quartz glass layer 1, and the quartz glass layer 1 is etched to obtain a mask pattern on the quartz glass layer 1, thereby obtaining a mask plate 4. The aluminum oxide layer 2 is etched to obtain an aluminum oxide mask plate support 3, thereby completing the preparation. Figure 1

[0065] Fig. 2 shows a schematic diagram of the sputtered platinum film. A molybdenum layer is sputtered on an aluminum oxide substrate 5, and the platinum film is deposited using a platinum target 8 by selective sputtering using the mask plate and the support prepared as shown in Fig. 1, thereby obtaining a platinum film circuit 6. Figure 2 Figure 1

[0066] ​​The inventors also determined the SEM image of the platinum thin film circuit pad obtained in Example 1, and the grain size of the platinum thin film can reach 20 um 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 is the same as Example 1.

[0069] Comparative Example 1

[0070] The difference from Example 1 is that the heat treatment process is 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 is 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 is 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 is 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; and then the second 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.

[0077] Comparative Example 5

[0078] The difference from Example 1 is that the heat treatment process is 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; and then the second 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.

[0079] Comparative Example 6

[0080] The difference from Example 1 is that the heat treatment process consists of two stages: the first stage is a heating rate of 5-10℃ / min, a heat treatment temperature of 800-900℃, and a heat treatment time of 1-2 hours; the second stage is a heating rate of 5-10℃ / min, a heat treatment temperature of 1000-1300℃, and a heat treatment time of 3-6 hours.

[0081] Comparative Example 7:

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

[0083] Comparative Example 8:

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

[0085] Comparative Example 9:

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

[0087] The inventors characterized the cross-sections of the platinum films obtained in the above embodiments 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] Depend on Figure 7 It can be seen that in Example 1, three heat treatment processes were performed, and molybdenum was used as the transition layer. The cross-sectional image of the thin film shows that the molybdenum transition layer 9 did not migrate, and the film cross-section was relatively dense with a very low porosity. In contrast, in Comparative Example 1, only one heat treatment was performed at a lower temperature, resulting in a platinum thin film cross-section with... Figure 5 The sample exhibits numerous pores. Comparative Example 4 underwent two heat treatments, and the cross-section of the platinum thin film showed... Figure 6 The middle presents a comparison Figure 7 It has a relatively large number of pores.

[0089] In Comparative Example 7, when chromium was used as the transition layer, migration occurred on the film, resulting in the formation of chromium oxide 10. In Comparative Example 8, when titanium was used as the transition layer, migration also occurred, forming titanium oxide. In Comparative Example 9, when platinum oxide was used as the transition layer… Figure 9 The presence of numerous pores is due to the decomposition of platinum oxide during the annealing stage.

[0090] The inventors further measured the platinum films obtained in each embodiment and comparative examples 1 to 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 is a heating rate of 1-5°C / min, a heat treatment temperature of 400-500°C, and a heat treatment time of 1-2 hours.

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

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

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

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

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

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

[0103] The surface energy porosity of the surface in Table 1 is calculated by atomic force microscope testing of the three-dimensional morphology of a platinum thin film, by the formula:

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

[0105] The evaluation method for adhesion in Table 1 uses a nano-scratch method, and the vertical load loading range is 0-450 mN. If the adhesion is > 450 mN, it is marked as ★, if the adhesion is 350-450 mN, it is marked as ▲, and if the adhesion is < 350 mN, it is marked as ○.

[0106] As can be seen from the results in Table 1, the adhesion of the platinum thin film obtained by the method of the present embodiment is all higher than 450 mN, and the surface porosity is 5.1% and 6.3%, respectively, which is significantly lower than the surface porosity of each comparative example, and the TCR is as high as 3850 ppm / ℃. The ceramic substrate type is changed in Examples 1 and 2, and the performance of the obtained platinum thin film is not significantly affected.

[0107] In Comparative Example 1, the adhesion is significantly lower than that of the examples due to one heat treatment at a low temperature, and the difference in surface porosity and TCR is more obvious. In Comparative Example 2, one heat treatment is performed at a temperature of 800-900℃, and the adhesion, porosity, and TCR are all not as good as those of each example. In Comparative Example 3, although the TCR reaches 3580 ppm / ℃, the surface porosity and adhesion are not as good as those of the examples. Similarly, Comparative Examples 4, 5, and 6 all perform two-stage heat treatment, and although the adhesion is acceptable, the porosity and TCR are not as good as those of the examples. In Comparative Examples 7, 8, and 9, the transition layer is changed, and although the adhesion is acceptable, the surface porosity and TCR are not as good as those of each example. It can be seen that the methods of each comparative example cannot simultaneously achieve strong adhesion, low surface porosity, and high temperature resistance temperature coefficient. The heat treatment method of the present application can significantly improve the adhesion of the platinum thin film, reduce the surface porosity, and achieve a 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 etching. The rest is the same as Example 1.

[0110] The platinum thin film circuits obtained in Comparative Example 10 and Example 1 were characterized by scanning electron microscopy, and the results are shown in Figure 3 and Figure 4 As can be seen from the figures, the platinum thin film circuits prepared by the methods of Comparative Example 10 and Example 1 both have burrs at the edges. In Example 1, there are some platinum particles between the platinum thin film circuits obtained by selective sputtering, but they do not cause short circuit of the platinum thin film, and the precision is high.

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

[0112] As can be seen from the figures, the platinum thin film circuits prepared by the methods of Comparative Example 10 and Example 1 both have burrs at the edges. In Example 1, there are some platinum particles between the platinum thin film circuits obtained by selective sputtering, but they do not cause short circuit of the platinum thin film, and the precision is high. Figure 10The migration of impurity atoms of aluminum between the interface of the platinum thin film and the substrate obtained by each example and Comparative Examples 1-9 is shown in Table 1, and it can be seen that the migration of aluminum atoms at the interface is obvious in Comparative Examples 7, 8 and 9, and the migration amount is small in each example and Comparative Examples 1-6. This is not related to the transition layer of molybdenum used in Comparative Examples 7, 8 and 9.

[0113] As shown in Table 2, the migration of molybdenum atoms between the interface of the platinum thin film and the substrate obtained by each example and Comparative Examples 1-6 is shown in Table 2, and it can be seen that the migration is not obvious. Figure 11 As shown in Table 3, the migration of chromium atoms between the interface of the platinum thin film and the substrate obtained by Comparative Example 7 and the migration of titanium atoms between the interface of the platinum thin film and the substrate obtained by Comparative Example 8 are shown in Table 3, and it can be seen that there is also a certain migration. It can be seen that when Mo is used as the transition layer, the migration of impurity atoms can be greatly inhibited.

[0114] Figure 12 As shown in Table 4, the thermal stability test of the platinum thin film resistance temperature sensor prepared by the platinum thin film obtained by each example of the present application is shown in Table 4. During the test, the platinum thin film of each example and Comparative Example was 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 the thermal cycle stability performance thereof. As shown in Table 4, the resistance change rate of each example and Comparative Example is less than 0.2% after 500 cycles, and the resistance change rate of Example 1 and Example 2 is the smallest. It can be seen that the platinum thin film prepared by the present application has good thermal stability, which depends on its good adhesion, the inhibition of the migration of impurity elements by Mo and the crystallization state.

[0115] As shown in Table 4, the thermal stability test of the platinum thin film resistance temperature sensor prepared by the platinum thin film obtained by each example of the present application is shown in Table 4. During the test, the platinum thin film of each example and Comparative Example was 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 the thermal cycle stability performance thereof. As shown in Table 4, the resistance change rate of each example and Comparative Example is less than 0.2% after 500 cycles, and the resistance change rate of Example 1 and Example 2 is the smallest. It can be seen that the platinum thin film prepared by the present application has good thermal stability, which depends on its good adhesion, the inhibition of the migration of impurity elements by Mo and the crystallization state. Figure 13 The platinum thin film obtained by the present application is dense and uniform, the impurities and defects are controllable, the resistance temperature coefficient can reach 3850ppm℃, the grain size of the platinum thin film can reach about 20um, the selected sputtered platinum thin film circuit has high precision, and can be used for platinum thin film resistance temperature sensors. The low self-diffusion coefficient of molybdenum can reduce the migration of impurities to 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 improved, the mobility of the deposited atoms on the substrate surface can be increased, the porosity of the thin film can be reduced, the density can be improved, and finally the adhesion of the thin film can be enhanced. The three-step heat treatment can also release the residual stress in the sputtering process, stabilize the structure, and finally reduction, aggregation and moisture removal will occur during the heat treatment, which promotes the growth of platinum grains.

[0116]

[0117] ​​The above detailed description of the specific implementation is further detailed for the purpose, technical solution and beneficial effect of the present application, and it should be understood that the above is only the specific implementation of the present application and is not used to limit the protection scope of the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for producing a platinum thin film for an automobile exhaust temperature sensor, characterized by, Sputtering a transition layer on a ceramic substrate, then sputtering a platinum film through a mask, and then performing three heat treatments to obtain a platinum film; The transition layer is selected from one or more of tungsten, molybdenum and rhenium; The first heat treatment is performed at a temperature of 400-500 ℃, the second heat treatment is performed at a temperature of 800-900 ℃, and the third heat treatment is performed at a temperature of 1000-1300 ℃; The first heat treatment is performed at a temperature increasing rate of 1-5 ℃ / min.

2. The method for preparing a platinum thin film for an automotive exhaust temperature sensor according to claim 1, characterized in that, 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, and the surface roughness of the cleaned ceramic substrate is 10-100 nm.

3. The method for preparing a platinum thin film for an automotive exhaust temperature sensor according to claim 1, characterized in that, The transition layer is sputtered in an oxygen-free or reducing atmosphere, using a radio frequency power source and setting a bias voltage, and sputtering through a mask; The mask is made of quartz glass or silicon nitride, and the thickness of the transition layer is 50-150 nm.

4. The method of claim 3, wherein the platinum thin film is formed by a method comprising: forming a platinum thin film on a substrate; and annealing the platinum thin film at a temperature of 500°C to 700°C for 1 to 10 hours in an atmosphere containing 5 to 20% of hydrogen gas. When sputtering the transition layer, the sputtering power is 800-1000 W, the sputtering pressure is 0.1-0.4 Pa, the sputtering time is 10-30 s, and the bias voltage of the radio frequency power source is set to 50-100 V.

5. A method for preparing a platinum thin film for an automotive exhaust temperature sensor according to claim 1, characterized in that, When sputtering the platinum film through the mask, the sputtering is performed in an oxygen-free or reducing atmosphere, using a radio frequency power source and setting a bias voltage, and the platinum film is deposited through the mask, with a thickness of 1.5-1.9 um. The mask is made of quartz glass or silicon nitride.

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

7. The method of claim 3 or 6, wherein the platinum thin film is formed by sputtering a platinum target in an atmosphere of argon gas and hydrogen gas. The mask used in the sputtering of the transition layer and the platinum film is prepared by: Sputtering a layer of alumina on quartz glass, and then preparing a mask and support by photolithography or etching.

8. The method for preparing a platinum thin film for an automotive exhaust temperature sensor according to claim 1, characterized in that, The heat treatment process is as follows: The first heat treatment is performed for 1-2 hours; The second heat treatment is performed for 0.5-3 hours; The third heat treatment is performed for 2-6 hours.

9. The method for preparing a platinum thin film for an automotive exhaust temperature sensor according to claim 1, characterized in that, The temperature increasing rate of the second heat treatment is 5-10 ℃ / min, and the temperature increasing rate of the third heat treatment is 5-10 ℃ / min. The treatment atmosphere used in each heat treatment stage is any one of nitrogen, argon or a reducing atmosphere.

10. A platinum thin film for an automotive exhaust temperature sensor, characterized in that, Obtained by the preparation method of any one of claims 1-9.

11. A temperature sensor, characterized by The platinum film of claim 10.

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