Thin film resistive temperature sensor integrated with micro thermoelectric device in situ and method of making

Abstract

The application relates to a thin-film resistance temperature sensor integrated with a micro thermoelectric device in situ and a preparation method thereof, which comprises the following steps: depositing an insulating layer on the micro thermoelectric device, depositing a heat-sensitive thin film on the insulating layer, and finally obtaining the thin-film resistance temperature sensor integrated with the micro thermoelectric device in situ after the heat-sensitive thin film is patterned; through the design of the thin-film resistance temperature sensor with high sensitivity, high response, high reliability and a wide response range, a compatible micro-processing method is developed, the in-situ integration with the micro thermoelectric device is realized, the temperature difference measurement of the thermoelectric device in a performance test scene is carried out, and the performance evaluation of the micro thermoelectric device is optimized.

Description

[0001] The application belongs to the technical field of thin-film thermoelectric devices, and particularly relates to a thin-film resistance temperature sensor integrated with a micro thermoelectric device in situ and a preparation method thereof. BACKGROUND

[0002] With the wide application of the Internet of Things and wearable electronic devices, chip micro-area refrigeration and self-powered sensing have put forward more stringent requirements, so that the micro thermoelectric device which can be attached to a high-dissipation chip to achieve rapid cooling or waste heat collection has attracted widespread attention and research. The thermoelectric device can realize the mutual conversion of heat energy and electric energy, and is composed of n / p thermoelectric arms, a substrate and a metal electrode. The size of the micro thermoelectric device reported at present can reach 1-10 mm, and the total thickness is less than 1 mm, in which the density of the thermoelectric arms can even reach 1000 / cm 2 , and the characteristic size is 100-200 μm. At the same time, the performance of the micro thermoelectric device is closely related to the temperature distribution of the thermoelectric arms, and therefore it is crucial to accurately measure the temperature difference between the two ends of the thermoelectric arms in order to evaluate the output performance of the thermoelectric device. At present, the temperature characterization of the thermoelectric device is mainly realized by using a thermocouple, however, the temperature sensing area of the thermocouple is mainly the thermocouple junction, and the diameter of several hundred microns is much larger than the area of the thermoelectric arms, and is comparable to the thickness of the micro thermoelectric device. At the same time, the introduction of the thermocouple produces an additional thermal resistance, which may cause additional heat loss and disturb the establishment of the temperature field in the original thermoelectric device. In addition, the deviation of the measurement position of the thermocouple attached to the substrate of the thermoelectric device will also cause errors between the actual temperature of the thermoelectric arms.

[0003] The resistance temperature sensor (RTD) is composed of a simple metal, has a simple structure, high linearity and wide temperature sensing range, and has been applied to the fields of human body temperature measurement, sweat analysis, lithium ion battery temperature monitoring and the like. Chinese documents report that a gold-based temperature sensor is deposited inside a fuel cell to record the temperature distribution in the plane of the fuel cell, but will produce an unnegligible interference to the gas transfer and electron transfer in the interior of the cell. Although it is tried in the literature to deposit a metal coil in the blank area of the device substrate to test the temperature in the central region of the out-of-plane thermoelectric refrigerator, the accurate temperature measurement of the out-of-plane thermoelectric device with a complex three-dimensional structure and small unit size still faces the problem of integration. In addition, in order to obtain the in-situ temperature of the micro thermoelectric device, the temperature sensor needs to comprehensively consider the performance parameters such as sensitivity, temperature resolution, response time and compatibility with the thermoelectric device. SUMMARY

[0004] In order to solve the above problems existing in the prior art, the application provides a thin film resistance temperature sensor in-situ measurement method of a micro thermoelectric device. The application discloses a thin film resistance temperature sensor in-situ measurement method of a micro thermoelectric device.

[0005] The technical scheme adopted by the application is as follows:

[0006] A preparation method of a thin film resistance temperature sensor in-situ integrated with a micro thermoelectric device comprises the following steps:

[0007] (1) encapsulating an active region of the micro thermoelectric device by using an insulating layer;

[0008] (2) depositing a temperature-sensitive film on the active region and the substrate of the micro thermoelectric device after the step (1) treatment, the temperature-sensitive film crossing the height gradient of the micro thermoelectric device structure, and forming a stable electrical connection covering the thermoelectric device;

[0009] (3) patterning the temperature-sensitive film of the measurement region in the integrated device obtained in the step (2), and obtaining the thin film resistance temperature sensor in-situ integrated with the micro thermoelectric device.

[0010] In the step (1), the micro thermoelectric device is first subjected to nitrogen cleaning pretreatment, and then the insulating layer is deposited.

[0011] The structure of the micro thermoelectric device comprises a substrate, an electrode and a thermoelectric arm.

[0012] In the step (2), the temperature-sensitive film is a metal film with a positive temperature coefficient of resistance.

[0013] The insulating layer and the temperature-sensitive film are prepared by physical vapor deposition.

[0014] The measurement region is a single pair or multiple pairs of thermoelectric arms.

[0015] The number of temperature sensors for temperature measurement of the measurement region is single or multiple.

[0016] In step (3), the patterning of the thermosensitive thin film is performed by a photolithography-etching process.

[0017] The thin film resistance temperature sensor is a ring pattern, and the pattern area of the ring pattern needs to match the size of the required measurement area in the integrated device. In addition, the key parameters of the thin film resistance temperature sensor, the initial resistance value (R0) and the temperature response characteristic (AR), need to be controlled by adjusting the width and total length (l) of the ring pattern, so as to match the temperature measurement requirements of the integrated device. The theoretical calculation formula is R0 = pl / A and AR = TCR x R0 x AT, wherein p is the resistivity of the thermosensitive thin film, A is the cross-sectional area of the sensor pattern, TCR is the resistance temperature coefficient of the thermosensitive thin film, and AT is the temperature change amount.

[0018] The thin film resistance temperature sensor of the in-situ integrated micro thermoelectric device prepared by the method.

[0019] The beneficial effects of the present application are:

[0020] (1) The preparation method of the thin film resistance temperature sensor of the in-situ integrated micro thermoelectric device, by first depositing an insulating layer on the micro thermoelectric device, then depositing a thermosensitive thin film on the insulating layer, and finally patterning the obtained thermosensitive thin film to obtain the thin film resistance temperature sensor of the in-situ integrated micro thermoelectric device. The present application designs a thin film resistance temperature sensor with high sensitivity, high response, high reliability and wide response range, develops a compatible microfabrication method, realizes in-situ integration with the micro thermoelectric device, and thus performs temperature difference measurement of the thermoelectric device in the performance test scene, and optimizes the performance evaluation of the micro thermoelectric device.

[0021] (2) The thin film resistance temperature sensor of the in-situ integrated micro thermoelectric device, by designing the ring pattern of the resistance temperature sensor, which is beneficial to the temperature resolution and reliability of the micro sensor, and can be adapted to the size of the thermoelectric arm, greatly improving the integration compatibility and yield of the micro thermoelectric device.

[0022] (3) The thin film resistance temperature sensor of the in-situ integrated micro thermoelectric device, by adjusting the number, measurement area and pattern area of the sensor, the temperature information of different temperature measurement areas can be obtained, so as to analyze the temperature distribution and output performance of the micro thermoelectric device.

[0023] (4) The thin film resistance temperature sensor of the in-situ integrated micro thermoelectric device, which uses an oxide ceramic material as an insulating layer, can reduce the damage to the micro thermoelectric device during the integration process, and prevent the thermosensitive thin film layer from causing short circuit of the thermoelectric device.

[0024] (5) The thin-film resistance temperature sensor of the in-situ integrated micro thermoelectric device described in this invention uses photolithography-etching to pattern the thermosensitive thin film layer in situ. Compared with traditional attached measurement, the temperature sensor integrated with the thermoelectric arm has low thermal resistance and high positional accuracy, which effectively reduces the error of the measuring element and the interference to the micro thermoelectric device. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a process flow diagram of the fabrication of the micro thermoelectric device described in this invention;

[0027] Figure 2a A traditional temperature measurement diagram for a miniature thermoelectric device;

[0028] Figure 2b This is an in-situ temperature measurement diagram of the miniature thermoelectric device based on a thin-film resistive temperature sensor according to the present invention.

[0029] Figure 3a The image shows a physical picture of a nickel-based resistive temperature sensor, with the inset showing a Ni thin film composed of fine grains and a sensor pattern.

[0030] Figure 3b This is a graph showing the linear relationship between resistance and temperature for a nickel-based resistive temperature sensor.

[0031] Figure 3c This refers to the response of a nickel-based resistive temperature sensor to temperature changes.

[0032] Figure 3d The resistance value of a nickel-based resistive temperature sensor changes over time when the temperature gradient is 0.1℃.

[0033] Figure 4a SEM top view of a miniature thermoelectric device for an in-situ integrated resistive temperature sensor.

[0034] Figure 4b SEM cross-sectional view of a miniature thermoelectric device for an in-situ integrated resistive temperature sensor;

[0035] Figure 4c Information on the location and material thickness of the miniature thermoelectric device for in-situ integrated resistive temperature sensors;

[0036] Figure 4dSEM top view of the hot end temperature sensor (H-RTD) and the cold end temperature sensor (C-RTD);

[0037] Figure 5a Thermal sensitivity of the integrated back temperature sensor;

[0038] Figure 5b Temperature results of the commercial thermocouple and the integrated resistive temperature sensor in the micro thermoelectric device performance test scenario;

[0039] Figure 5c Temperature difference measured by the commercial thermocouple and the thin film resistive temperature sensor in the present application. DETAILED DESCRIPTION

[0040] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the scope of protection of the present application.

[0041] Embodiment 1

[0042] The present embodiment provides a design and preparation method of a resistive temperature sensor device for in-situ temperature measurement of a micro thermoelectric device, as shown in Figure 1 The method comprises the following steps:

[0043] (1) Pretreatment of the micro thermoelectric device

[0044] The micro thermoelectric device is cleaned by nitrogen (flow rate 5-10 sccm) to obtain a pretreated thermoelectric device, and the surface impurities are removed to improve the adhesion with the subsequent thin film; the thermoelectric device comprises a substrate (aluminum nitride), an electrode layer (copper), and a thermoelectric arm (bismuth telluride, antimony telluride), wherein the electrode layer and the thermoelectric arm have been patterned;

[0045] (2) Depositing an insulating layer on the active area of the pretreated micro thermoelectric device

[0046] After shielding the lead-out electrode and the blank substrate part of the thermoelectric device with a polyimide tape, the device is placed into an evaporation cavity, and an aluminum oxide ceramic thin film (100℃) is deposited on the pretreated thermoelectric device by electron beam evaporation, preferably with a thickness of 1 μm;

[0047] (3) Depositing a thermal sensitive thin film on the surface of the thermoelectric device encapsulated by the aluminum oxide ceramic

[0048] The lead-out electrode of the micro thermoelectric device is covered by a polyimide adhesive tape and the sample is fixed, and then is placed in a magnetron sputtering cavity to deposit a thermosensitive film on the sample, wherein the thermosensitive film is specifically a Ni film, and the thickness of the Ni film is preferably 120 nm; the thermosensitive material Ni is sputtered by using a direct current (50 W, 30 minutes) at a pressure of 0.012 Torr; and after the sputtering is completed, the sample is taken out from the magnetron cavity.

[0049] (4) Pattern design of the thin-film resistance temperature sensor

[0050] To measure the cold and hot end temperatures of a single pair of thermoelectric arms in the micro thermoelectric device, the pattern size of the temperature sensor is designed to be one quarter of the size of the single pair of thermoelectric arms, and the area is 10 4 μm 2 (see Figure 3a ), in addition, the width and total length of the thermosensitive line in the annular pattern are 5 μm and 1600 μm, respectively, so as to control the initial resistance value and the temperature response characteristics of the micro thin-film resistance temperature sensor.

[0051] (5) Patternization of the thermosensitive film by using a photolithography-etching process

[0052] S1813 photoresist is spin-coated on the surface of the sample, and a pre-designed sensor pattern is exposed by using ultraviolet exposure at the position of the thermoelectric arms of the micro thermoelectric device by using a photolithography method, and the exposure energy is 150 mJ / cm 2 . After development and fixing, the sample is subjected to wet etching by using a 2.5 wt% FeCl3 solution, so as to realize the preparation of the resistance temperature sensor, and finally, the residual photoresist on the surface is removed by using acetone, so as to obtain the thin-film resistance temperature sensor integrated with the micro thermoelectric device in situ.

[0053] Embodiment 2

[0054] The embodiment provides a design and preparation method of a resistance temperature sensor for in-situ temperature measurement of a micro thermoelectric device, and the difference from the embodiment 1 is that in the step (1), the insulating layer material is boron nitride, and the deposition thickness is 1 μm, and the other operation conditions are the same as those in the embodiment 1.

[0055] Embodiment 3

[0056] The embodiment provides a design and preparation method of a resistance temperature sensor for in-situ temperature measurement of a micro thermoelectric device, and the difference from the embodiment 1 is that in the step (2), the thermosensitive material is platinum, and the deposition conditions and the other operation conditions are the same as those in the embodiment 1.

[0057] Embodiment 4

[0058] The embodiment provides a design and preparation method of a resistive temperature sensor for in-situ temperature measurement of a micro thermoelectric device, which is different from the embodiment 1 only in that in step (3), the length of the nickel wire in the temperature sensor is increased to 3200 mu m, and the integrated position is two pairs of thermoelectric arms in the micro thermoelectric device, and other operation conditions are the same as those in the embodiment 1.

[0059] Embodiment 5

[0060] The embodiment provides a design and preparation method of a resistive temperature sensor for in-situ temperature measurement of a micro thermoelectric device, which is different from the embodiment 1 only in that in step (3), two pairs of thermoelectric arms in the integrated micro thermoelectric device are respectively integrated with a single thin film resistive temperature sensor in-situ, and the operation is repeated twice for the two pairs of different thermoelectric arms during photoetching and etching patterning, and other operation conditions are the same as those in the embodiment 1.

[0061] Embodiment 6

[0062] The embodiment provides a design and preparation method of a resistive temperature sensor for in-situ temperature measurement of a micro thermoelectric device, which is different from the embodiment 1 only in that in step (3), the area of the resistive temperature sensor pattern is 2.5*10 3 mu m 2 , and other operation conditions are the same as those in the embodiment 1.

[0063] Experimental example

[0064] The related performance of the temperature sensor obtained in the embodiment 1 and the micro thermoelectric device integrated with the temperature sensor is detected.

[0065] For the temperature characterization problem in the performance evaluation of the micro thermoelectric device, the in-situ deposited functional material layer (including an insulating material and a temperature-sensitive material) significantly reduces the thickness of the heat conduction layer (heat-conducting silicone grease) and the measurement layer relative to the temperature measurement of the traditional commercial thermocouple. Figure 2a As shown in a traditional temperature measurement diagram (top view) of the micro thermoelectric device, the thickness of the heat conduction layer of the traditional commercial thermocouple is about 200 mu m, and the thickness of the measurement layer is 200 mu m. Figure 2b As shown in an in-situ temperature measurement diagram of the resistive temperature sensor, the thickness of the heat conduction layer is 20 mu m, and the thickness of the measurement layer is about 120 nm, so that the micro thermoelectric device has better thermal contact with the external cold and hot source, the thermal resistance of the temperature measurement element in the measurement layer is reduced, the ratio of the thermal resistance of the thermoelectric arm to the overall thermal resistance is improved, and the effective temperature difference between the two ends of the thermoelectric arm is improved. In addition, the in-situ integration with the thermoelectric arm makes the temperature sensor closer to the real temperature at the two ends of the thermoelectric arm, and has better compatibility with the micro thermoelectric device.

[0066] As shown in Figure 3aThe image shows the surface and cross-sectional morphology of a nickel-based resistive temperature sensor and nickel as the thermistor material. The film thickness is 118.3 nm, and the annular pattern size is 100 μm × 100 μm, with a nickel line width of 5 μm and a total length of 1600 μm. During room temperature fabrication, the low particle mobility and diffusion rate on the substrate surface result in fine grains and agglomeration on the film surface. Figure 3b The linear change in the resistance of the temperature sensor with temperature was demonstrated, and the temperature coefficient of resistance (TCR) of the thermistor film can be determined to be 3.36 × 10⁻⁶. -3 / ℃, and the resistance value and temperature show a highly linear correlation, with a correlation coefficient reaching 0.9988. Compared with bulk nickel, the TCR of the thin film is much lower. The internal defects of the thin film increase the proportion of residual resistivity in the resistivity, resulting in a decrease in the temperature dependence of resistivity. The sensor's instantaneous temperature response characteristics are as follows: Figure 3c As shown, when the sensor is placed in a constant temperature oil bath at 50°C from room temperature air to simulate the sudden temperature change in actual application, the sensor's resistance value can reach 63.2% of the maximum value in just 47ms.

[0067] To analyze the sensor's ability to resolve minute temperature changes, the sensor was placed on a heating stage and heated from 50°C to 50.5°C in increments of 0.1°C. Each temperature was allowed to stabilize for one hour. The corresponding rate of change of resistance was recorded as follows: Figure 3d As shown. The sensor's temperature resolution sensitivity is 0.03% / ℃, enabling it to detect temperature changes of up to 0.1℃.

[0068] To characterize the in-situ temperature and heat transfer process at both ends of the thermoelectric arms in a micro thermoelectric device, a temperature sensor needs to be integrated onto the surface of a single pair of thermoelectric arms in the micro thermoelectric device. Figure 4a n-type Bi₂Te₃, p-type Sb₂Te₃, Cu, Al₂O₃, and Ni thin films were deposited on an AlN substrate by magnetron sputtering (details of the operation are given in Example 1). The cross-sectional view of the micro thermoelectric device integrating the temperature sensor is shown below. Figure 4b As shown, the total thickness is 11.5 μm. Figure 4c This is a schematic diagram of the integrated device. The temperature sensor for the hot end of the micro thermoelectric device is located on the surface of a single pair of thermoelectric arms (H-RTD). Simultaneously, a temperature sensor is deposited on the substrate surface for measuring the cold end temperature of the thermoelectric device (C-RTD). Due to the high thermal conductivity of the AlN and Cu thin films, the error is negligible. A top view of the micro thermoelectric arm with integrated temperature sensing is shown below. Figure 4d As shown, the light-colored area is the Ni thin film, and the dark-colored area is the substrate. The boundary between the pattern and the substrate can be clearly observed, and the whole is connected to form a circuit. Due to the variation in surface roughness caused by the multilayer deposition process, the sensor pattern exhibits small undulations, but it does not damage the thermoelectric arms and electrode layers.

[0069] Figure 5a The thermal sensitivity of the integrated temperature sensor is demonstrated, and the resistance of the temperature sensor increases with temperature, with a linearity of ~0.98. The value of the temperature coefficient of resistance of the integrated sensor decreases due to the change in the state of the substrate surface. In order to simulate the testing conditions of the actual device, when the cold source is fixed at 10℃, the hot source is set to 30℃, 35℃, 40℃, 45℃, 50℃ and 55℃, respectively. Figure 5b The temperature measured by the commercial thermocouple and the integrated temperature sensor shows that the temperature of the hot end thermocouple (TH-T) increases linearly with the increase of the temperature of the hot source, and the temperature of the cold end thermocouple (TH-C) also shows an upward trend. The temperature measured by the thin film temperature sensor shows a similar upward trend, but the TH-RTD obtained is lower than TH-T, and the TC-RTD is higher than TH-C, so as shown in Figure 5c The temperature difference of the micro thermoelectric device in the two measurement methods shows a linear increase trend. At the same time, the relationship between the temperature difference of the thermoelectric arm measured by the integrated temperature sensor and the commercial thermocouple can be calculated as ΔT RTDs = 0.497ΔT Thermocouples , with a linearity of 0.9966. The low thermal resistance temperature measuring element effectively reduces the interference on the output performance of the thermoelectric device, and the in-situ integration improves the accuracy of the thermoelectric arm temperature measurement, which can realize the accurate measurement of the micro area temperature in the microelectronic device.

[0070] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any skilled person in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for fabricating a thin-film resistive temperature sensor with in-situ integrated micro thermoelectric devices, characterized in that, Includes the following steps: (1) The micro thermoelectric device has an out-of-plane structure and includes a substrate, electrodes and thermoelectric arms; the active area of ​​the micro thermoelectric device is encapsulated by an insulating layer; (2) A thermistor film is deposited on the active region and the substrate of the micro thermoelectric device after the treatment in step (1). The thermistor film crosses the height gradient of the micro thermoelectric device structure to form a stable electrical connection covering the thermoelectric device. (3) Pattern the thermal thin film of the required measurement area in the integrated device obtained in step (2). The measurement area is a single pair or multiple pairs of thermoelectric arms, that is, a thin film resistance temperature sensor of in-situ integrated micro thermoelectric device is made on the thermoelectric arms after packaging and on the substrate.

2. The method for fabricating a thin-film resistive temperature sensor with in-situ integrated micro thermoelectric devices according to claim 1, characterized in that, In step (1), the insulating layer is an oxide ceramic thin film.

3. The method for fabricating a thin-film resistive temperature sensor with in-situ integrated micro thermoelectric devices according to claim 1, characterized in that, In step (2), the thermistor film is a metal film with a positive temperature coefficient of resistance.

4. The method for fabricating a thin-film resistive temperature sensor with in-situ integrated micro thermoelectric devices according to claim 1, characterized in that, The insulating layer and the thermal thin film were prepared by physical vapor deposition.

5. The method for fabricating a thin-film resistive temperature sensor with in-situ integrated micro thermoelectric devices according to claim 1, characterized in that, The number of temperature sensors used to measure the temperature in the measurement area may be one or more.

6. The method for fabricating a thin-film resistive temperature sensor with in-situ integrated micro thermoelectric devices according to claim 1, characterized in that, In step (3), the thermal thin film is patterned by photolithography-etching process.

7. The method for fabricating a thin-film resistive temperature sensor with in-situ integrated micro thermoelectric devices according to claim 1, characterized in that, The thin-film resistive temperature sensor has a ring pattern, and the area of ​​the ring pattern needs to match the size of the measurement area required in the integrated device.

8. A thin-film resistive temperature sensor for an in-situ integrated micro thermoelectric device prepared by the method according to any one of claims 1-7.

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