Thin film heat flow sensor based on reticulated cavity thermal resistance layer structure and preparation method thereof

Abstract

This invention provides a thin-film heat flow sensor based on a mesh-cavity thermal resistance layer structure and its fabrication method, belonging to the technical field of thin-film heat flow sensors. It is known that the thermal conductivity of air is much lower than that of the thermal resistance layer material. Therefore, when a mesh-cavity structure is formed inside the thermal resistance layer, its overall thermal conductivity will decrease. When heat flows across the sensor surface, the mesh-cavity thermal resistance layer can create a larger temperature difference than a regular thermal resistance layer, thereby increasing the thermoelectric potential output of the heat flow sensor and achieving increased sensitivity. The response time of the heat flow sensor is partly determined by the isobaric specific heat capacity and density of the thermal resistance layer. The mesh-cavity thermal resistance layer has a smaller isobaric specific heat capacity and density than a regular thermal resistance layer, shortening the response time of the heat flow sensor. This invention provides a structurally reliable mesh-cavity thermal resistance layer for thin-film heat flow sensors that can increase sensor sensitivity and improve response speed.

Description

Technical Field

[0001] This invention belongs to the field of thin-film heat flow sensor technology, and specifically relates to a thin-film heat flow sensor based on a mesh cavity thermal resistance layer structure and its fabrication method. Background Technology

[0002] In aerospace equipment, hot-end components exhibit numerous heat transfer phenomena during operation. The magnitude and distribution of heat flux density are crucial reference indicators during the design and verification of these components. Therefore, accurate measurement and analysis of the distribution and changes in heat transfer are essential. Consequently, real-time and precise measurement of heat transfer on the surface of hot-end components is necessary in practical applications and research. This serves as a vital indicator for assessing the actual working environment or state of aerospace equipment, making it particularly important in the early design and validation stages.

[0003] With the continuous development of aerospace technology, the operating temperature of hot-end components is getting higher and higher, and the working environment is becoming increasingly harsh, making it more urgent to have higher performance thin-film heat flow sensors.

[0004] Current thin-film heat flow sensors involve sputtering a thin-film thermopile onto a substrate, followed by sputtering thermal resistance layers of varying thicknesses onto the thermopile. When heat flows across the sensor surface, according to Fourier's law, a temperature difference will occur on the substrate surface beneath the different thermal resistance layers. This temperature difference is converted into a thermoelectric potential signal by the thermopile, thus enabling the measurement of heat flow on the surface of the object being measured. However, because the thickness of the thermal resistance layer in current thin-film heat flow sensors is on the micro-nano scale, the temperature difference across the layer is small, resulting in a small thermoelectric potential signal output. This leads to low sensitivity of such sensors, making them insensitive to minute changes in heat flow and resulting in large measurement errors. Consequently, they no longer meet the current requirements for accurate heat flow measurement. Summary of the Invention

[0005] The technical problem this invention aims to solve is to overcome the shortcomings of existing technologies and increase the sensitivity of thin-film heat flow sensors. The thermal conductivity of air is much lower than that of the thermal resistance layer material. Therefore, when a mesh-like cavity structure is formed inside the thermal resistance layer, its overall thermal conductivity will decrease, thereby increasing the sensitivity of the heat flow sensor. This invention provides a reliable thin-film heat flow sensor based on a mesh-like cavity thermal resistance layer structure, which can increase the sensitivity and improve the response speed of the heat flow sensor.

[0006] The technical solution of the present invention is as follows:

[0007] A thin-film heat flow sensor based on a mesh cavity thermal resistance layer structure and its fabrication method are disclosed. The thin-film heat flow sensor includes a substrate 1, a thermopile thin film, and a mesh cavity thermal resistance layer 2. The thermopile thin film is deposited on the substrate, and the thermopile thin film includes a first electrode 3 and a second electrode 4. The first electrode 3 and the second electrode 4 are spaced apart horizontally and vertically and connected end to end in sequence to form an electrode array. The electrode array is an S-shaped loop. There are also two electrode disks above the substrate, which are connected to the two external terminals located at the first row of the electrode array via external leads. A mesh cavity thermal resistance layer is covered above the thermopile thin film at every other row of the terminals of the first electrode 3 and the second electrode 4, so that a temperature difference is formed at the two ends of a single electrode. The mesh cavity thermal resistance layer is formed on the thermal resistance layer thin film by micromachining technology to create crisscrossing mesh cavity lines.

[0008] The principle behind the increased sensitivity and response speed of a heat flow sensor using a mesh-like cavity thermal resistance layer is as follows: Since the thermal conductivity of air is much lower than that of the thermal resistance layer material, the overall thermal conductivity decreases after a mesh-like cavity is formed within the thermal resistance layer. When heat flows across the sensor surface, the mesh-like cavity thermal resistance layer creates a larger temperature difference than a regular thermal resistance layer, thereby increasing the thermoelectric potential output of the heat flow sensor and thus enhancing sensitivity. The response time of a heat flow sensor is partly determined by the isobaric specific heat capacity and density of the thermal resistance layer. The mesh-like cavity thermal resistance layer has a smaller isobaric specific heat capacity and density compared to a regular thermal resistance layer, thus shortening the response time of the heat flow sensor.

[0009] A method for fabricating a thin-film heat flow sensor based on a mesh cavity thermal resistance layer structure includes the following steps:

[0010] Step 1, Substrate surface treatment: Select a material with high thermal conductivity as the substrate, clean the surface of the substrate, and dry it under a nitrogen atmosphere after cleaning.

[0011] Step 2: Sputtering the first electrode material of the thermopile on the substrate surface: The substrate surface after Step 1 is processed by photolithography, and the first electrode pattern of the thermopile is formed on the substrate surface by coating, exposure and development. The substrate is placed in a vacuum environment, Pt metal is used as the target material, nitrogen gas is introduced as the sputtering medium, and the first electrode material Pt of the thermopile is deposited on the substrate surface by DC magnetron sputtering technology. Then, the photoresist on the substrate surface is removed by acetone to obtain the first electrode array of the thermopile in n rows and m columns and the electrode disks located on the left and right sides of the electrode array.

[0012] Step 3: Sputtering the second electrode material of the thermopile on the substrate surface: After cleaning the substrate processed in Step 2, the second electrode pattern of the thermopile is formed on the substrate surface by photolithography, coating, exposure, and development. The substrate is placed in a vacuum environment, and PtRh10 alloy is used as the target material to deposit the second electrode material of the thermopile, PtRh10, on the substrate surface using DC magnetron sputtering technology. Then, the photoresist on the substrate surface is removed by acetone to obtain an n-row m-column second electrode array; finally, a thermopile thin film is obtained by the first electrode and the second electrode being spaced apart and connected in an S-shape.

[0013] Step 4: Annealing of the thermopile film: The substrate treated in step 3 is annealed in a vacuum environment to eliminate various defects generated during the film deposition process, improve the density of the thermopile film, and reduce the resistance.

[0014] Step 5: Forming a mesh-like NaCl film on the substrate surface where the thermopile film has been deposited: After cleaning the substrate processed in Step 4, a mesh pattern is formed on the surface of the thermopile film using photolithography, through coating, exposure, and development. The substrate is placed in a vacuum environment, and electron beam evaporation technology is used to bombard sodium chloride placed in a crucible with accelerated electrons, causing the sodium chloride to evaporate, rise, and be transported to the sample stage. Finally, a NaCl film is deposited on the substrate surface, and the photoresist on the substrate surface is peeled off using anhydrous acetone. After the photoresist is completely peeled off, a mesh-like NaCl film is obtained.

[0015] Step 6: Deposit a thermal resistance layer film on top of the mesh NaCl film: Align the substrate processed in step 5 with a hard mask and deposit a Si3N4 film using radio frequency magnetron sputtering; wherein, the transparent area of ​​the hard mask is the mesh cavity thermal resistance layer area, that is, the area above each row of electrode contacts.

[0016] Step 7: Formation of the mesh cavity thermal resistance layer: Immerse the substrate treated in step 6 in deionized water to dissolve the NaCl inside the thermal resistance layer film, thereby forming a mesh cavity structure between the bottom of the thermal resistance layer film and the top of the thermopile junction.

[0017] Step 8: Connecting the wires: Use high-temperature platinum paste to connect a 100μm Pt wire to the thermopile electrode disk on the substrate treated in Step 7. This yields the thin-film heat flow sensor described in this invention.

[0018] Compared with the prior art, the advantages of the present invention are as follows:

[0019] 1. This invention uses photolithography-deposition process to prepare a mesh cavity thermal resistance layer film on top of a thermopile film. Since the mesh cavity thermal resistance layer film has a very small thickness, a small density and a small specific heat capacity at constant pressure, it has a faster response speed, with a response time of about 12 μs.

[0020] 2. The mesh cavity thermal resistance layer film in this invention has a lower thermal conductivity after the thermal resistance layer material is mixed with air, which improves the sensitivity of the heat flow sensor using the mesh cavity thermal resistance layer by 60% compared with the heat flow sensor using the ordinary thermal resistance layer.

[0021] 3. The mesh cavity structure design in this invention makes the thin-film heat flow sensor more reliable and stable when used in harsh environments such as high temperature and strong erosion. Attached Figure Description

[0022] Figure 1 The output curve of the thin-film heat flux sensor under pulsed laser irradiation is shown.

[0023] Figure 2 For wind tunnel environmental testing and evaluation of thin-film heat flux sensors;

[0024] Figure 3 A schematic diagram of the structure of the thin-film heat flow sensor provided by the present invention: wherein 1 is an alumina ceramic substrate, 2 is a mesh cavity thermal resistance layer, 3 is a first electrode, and 4 is a second electrode;

[0025] Figure 4 A top view of the thin-film heat flow sensor provided by the present invention: wherein 1 is an alumina ceramic substrate, 2 is a mesh cavity thermal resistance layer, 3 is a first electrode, and 4 is a second electrode;

[0026] Figure 5 Photolithographic patterns of the first electrode 3 and the second electrode 4 of the thermopile film of the thin-film heat flow sensor provided by the present invention.

[0027] Figure 6 A cross-sectional view of the thin-film heat flow sensor provided by the present invention: wherein 1 is an alumina ceramic substrate, 2 is a mesh cavity thermal resistance layer, 3 is a first electrode, and 4 is a second electrode;

[0028] Figure 7 A top view of the rigid mask plate of the thin-film heat flow sensor provided by the present invention;

[0029] Figure 8 This is a schematic diagram of the mesh cavity thermal resistance layer structure provided by the present invention;

[0030] Figure 9 This is a top view of the mesh cavity thermal resistance layer provided by the present invention; wherein the isosceles right-angled triangle portion is the support structure, and the 100μm wide line surrounding the isosceles right-angled triangle is the cavity structure. Detailed Implementation

[0031] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0032] Example

[0033] like Figures 3-8 The above is an embodiment of the thin-film heat flow sensor provided by the present invention, comprising an alumina ceramic substrate 1, a sensitive layer thermopile film sputtered and deposited on one side of the substrate 1, the thermopile film being formed by a first electrode 3 and a second electrode 4 being arranged at intervals and connected in series in an S-shape; a mesh cavity thermal resistance layer 2 is covered above the thermopile film at every interval of a row of electrode contacts.

[0034] The fabrication method of the thin-film heat flow sensor described in this embodiment specifically includes the following steps:

[0035] Step 1, Surface treatment of substrate: Select 96 alumina ceramic material with high thermal conductivity as substrate, with a size of 12×12×0.65mm. Clean the surface of the substrate with acetone, ethanol and deionized water in sequence, and dry it under nitrogen atmosphere after cleaning.

[0036] Step 2: Sputtering the first electrode material Pt of the thermopile onto the substrate surface: Using photolithography, the first electrode pattern of the thermopile is formed on one side of the substrate after the treatment in Step 1 through photolithography, coating, exposure, and development. The substrate is then placed under a vacuum of 2×10⁻⁶. - 4 In a vacuum environment of Pa, using Pt metal as the target material, nitrogen gas with a purity of 99.999% (volume percentage) was introduced as the sputtering medium. The sputtering pressure was 0.4 Pa and the sputtering power was 120 W. Pt, the first electrode material of the thermopile, was deposited on the substrate surface using DC magnetron sputtering technology. The deposition thickness was 300 nm. The photoresist on the substrate surface was then stripped with acetone to obtain the first electrode of the thermopile.

[0037] The first electrode pattern consists of a plurality of electrodes, each 1100 μm long and 100 μm wide, arranged in 48 columns with 4 rows each from left to right. The first row of electrodes in even-numbered columns is shaped like an inverted "L", the last row of electrodes in odd-numbered columns is shaped like an "L", and the remaining electrodes are shaped like "I". The rows are arranged alternately. Above the first row of electrodes in the 1st and 48th columns, there are two electrode disks. The contacts of the electrode disks extend to the first row, parallel to the first row of electrodes and with the same spacing.

[0038] Step 3: Sputtering the second electrode material PtRh10 of the thermopile onto the substrate surface: After cleaning the substrate processed in Step 2, the second electrode pattern of the thermopile is formed on the substrate surface using photolithography, through coating, exposure, and development. The substrate is then placed under a vacuum of 2×10⁻⁶. -4 In a vacuum environment of Pa, using PtRh10 alloy as the target material and sputtering power of 100W, DC magnetron sputtering technology is used to deposit the second electrode material of the thermopile PtRh10 on the substrate surface. Then, acetone is used to remove the photoresist on the substrate surface to obtain the second electrode PtRh10 thin film connected to the first electrode, wherein the thickness of the PtRh10 thin film is 300nm.

[0039] The second electrode pattern consists of a plurality of electrodes, each 1000 μm long and 100 μm wide, arranged in 4 rows and 48 columns. Each electrode is shaped like an "I". The rows are spaced apart, and the first row of the second electrode is in the same row as the first electrode. The individual electrodes are spaced apart with equal left and right spacing. After sputtering, the two ends of each electrode of the second electrode are connected to the electrode contacts of the adjacent first electrode. The whole electrode is connected in an S-shape to obtain a thermopile thin film.

[0040] Step 4: Annealing of the thermopile film: The substrate treated in step 3 is annealed at 800°C for 60 minutes in a vacuum environment to eliminate various defects generated during the film deposition process, improve the density of the thermopile film, and reduce the resistance. The resistance of the thermopile film after annealing is about 2.7kΩ.

[0041] Step 5: Forming a mesh-like NaCl film line on the substrate surface where the thermopile film has been deposited: After cleaning the substrate treated in Step 4, a mesh-like pattern is formed on the surface of the thermopile film using photolithography through coating, exposure, and development. The substrate is then placed under a vacuum of 5 × 10⁻⁶. -4 In a vacuum environment of Pa, the beam current was adjusted to 20 mA, and electron beam evaporation technology was used. Accelerated electrons bombarded sodium chloride placed in a crucible, causing the sodium chloride to evaporate, rise, and be transported to the sample stage. Finally, it condensed on the substrate surface to form a sodium chloride film. The deposition rate of the sodium chloride film was [missing information]. After 5 minutes of deposition, a NaCl film with a thickness of 300 nm was deposited on the substrate surface. Then, the photoresist on the substrate surface was peeled off with anhydrous acetone. After the photoresist was completely peeled off, the sodium chloride mesh lines were retained. The sample was carefully dried with a rubber bulb for later use. After peeling, the sodium chloride film lines on the sample surface were clear and had not been dissolved, resulting in a mesh NaCl film.

[0042] Step 6: Deposit a thermal resistance layer film on top of the mesh NaCl film: Align the substrate treated in Step 5 with a hard mask and place it under a vacuum of 2×10⁻⁶. -4 In a vacuum environment of Pa, using Si as the target material, nitrogen and argon gas with a purity of 99.999% in a ratio of 5:25 were introduced. The sputtering pressure was 0.4 Pa and the sputtering power was 200 W. A Si3N4 thin film with a length of 10 mm, a width of 1 mm and a thickness of 500 nm was deposited by radio frequency magnetron sputtering.

[0043] In this case, the permeable area of ​​the rigid mask is the mesh cavity thermal resistance layer region, such as... Figure 7 As shown, there are four rectangular areas above each row of electrode contacts.

[0044] Step 7: Formation of the mesh cavity thermal resistance layer: Immerse the substrate treated in step 6 in deionized water to dissolve the NaCl inside the thermal resistance layer film, thereby forming a mesh cavity structure between the thermal resistance layer and the thermopile junction.

[0045] Step 8: Connecting the wires: Use high-temperature platinum paste to connect a 100μm Pt wire to the thermopile electrode disk on the substrate treated in Step 7. This yields the thin-film heat flow sensor described in this invention.

[0046] This invention introduces a novel thermal resistance layer structure, which effectively improves the sensitivity of the heat flow sensor while reducing the response time. The selection of high-temperature resistant materials and the design of the thermal resistance layer structure enable the sensor to operate stably and reliably in harsh environments such as high temperature, strong erosion, and high heat flow. Experimental results are shown in Table 1. The mesh cavity thermal resistance layer can improve the sensitivity of the thin-film heat flow sensor by 60%, and the average response time is as follows: Figure 1 As shown, it can reach 12.7 microseconds. This was verified through wind tunnel environmental testing. Figure 2 As shown, the thin-film heat flux sensor can work stably for a long time in a wind tunnel environment and responds quickly to changes in heat flux density.

[0047] Table 1. Output potential and sensitivity of thin-film heat flux sensors with different thermal resistance layer structures under wind tunnel conditions of 500℃ and Mach 0.1.

[0048]

[0049]

[0050] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims without affecting the essence of the present invention.

Claims

1. A thin-film heat flow sensor based on a mesh cavity thermal resistance layer structure, characterized in that, The thin-film heat flow sensor includes a substrate (1), a thermopile film, and a mesh cavity thermal resistance layer (2). The substrate is coated with a thermopile film, which includes a first electrode (3) and a second electrode (4). The first electrode (3) and the second electrode (4) are spaced apart in both the horizontal and vertical directions and connected end to end in sequence to form an electrode array. The electrode array is an S-shaped loop. There are also two electrode disks above the substrate, which are connected to the two external terminals on the left and right sides of the first row of the electrode array through external leads. A mesh cavity thermal resistance layer covers the terminals of the first electrode (3) and the second electrode (4) every other row above the thermopile film. The terminals covered with the mesh cavity thermal resistance layer form hot junctions, and the terminals not covered with the mesh cavity thermal resistance layer form cold junctions, so that a temperature difference is formed between the two ends of a single electrode. The mesh cavity thermal resistance layer is formed by first forming a NaCl sacrificial layer before depositing the thermal resistance layer material and then dissolving and removing the NaCl sacrificial layer after depositing the thermal resistance layer material, thus forming crisscrossing mesh cavity lines inside the thermal resistance layer. The substrate is made of 96 alumina ceramic material, the first electrode and electrode disk are made of Pt, and the second electrode is made of PtRh10. The formed thermopile film has a thickness of 300 nm, the mesh cavity thermal resistance layer material is Si3N4 with a thickness of 500 nm, and the external lead is a 100 μm Pt wire.

2. A method for fabricating a thin-film heat flow sensor based on a mesh cavity thermal resistance layer structure, characterized in that, Includes the following steps: Step 1, Substrate surface treatment: Select a material with high thermal conductivity as the substrate, clean the surface of the substrate, and dry it under a nitrogen atmosphere after cleaning. Step 2: Sputtering the first electrode material of the thermopile on the substrate surface: The substrate surface after Step 1 is processed by photolithography, and the first electrode pattern of the thermopile is formed on the substrate surface by coating, exposure and development. The substrate is placed in a vacuum environment, Pt metal is used as the target material, nitrogen gas is introduced as the sputtering medium, and DC magnetron sputtering technology is used to deposit the first electrode material Pt of the thermopile on the substrate surface. Then, acetone is used to remove the photoresist on the substrate surface to obtain the first electrode array and electrode disk of the thermopile. Step 3: Sputtering the second electrode material of the thermopile on the substrate surface: After cleaning the substrate processed in Step 2, the second electrode pattern of the thermopile is formed on the substrate surface by photolithography, coating, exposure and development. The substrate is placed in a vacuum environment, and PtRh10 alloy is used as the target material. DC magnetron sputtering technology is used to deposit the second electrode material of the thermopile PtRh10 on the substrate surface. Then, the photoresist on the substrate surface is removed by acetone to obtain the second electrode array. Finally, a thermopile thin film with the first electrode and the second electrode spaced apart and connected in an S-shape is obtained. Step 4: Annealing of the thermopile film: The substrate treated in step 3 is annealed in a vacuum environment to eliminate various defects generated during the film deposition process, improve the density of the thermopile film, and reduce the resistance. Step 5: Forming a mesh-like NaCl film on the substrate surface where the thermopile film has been deposited: After cleaning the substrate processed in Step 4, a mesh pattern is formed on the surface of the thermopile film using photolithography, through coating, exposure, and development. The substrate is placed in a vacuum environment, and electron beam evaporation technology is used to bombard sodium chloride placed in a crucible with accelerated electrons, causing the sodium chloride to evaporate, rise, and be transported to the sample stage. Finally, a NaCl film is deposited on the substrate surface, and the photoresist on the substrate surface is peeled off using anhydrous acetone. After the photoresist is completely peeled off, a mesh-like NaCl film is obtained. Step 6: Deposit a thermal resistance layer film on top of the mesh NaCl film: Align the substrate processed in step 5 with a hard mask and deposit a Si3N4 film using radio frequency magnetron sputtering; wherein, the transparent area of ​​the hard mask is the mesh cavity thermal resistance layer area, that is, the area above each row of electrode contacts. Step 7: Formation of the mesh cavity thermal resistance layer: Immerse the substrate treated in step 6 in deionized water to dissolve the NaCl inside the thermal resistance layer film, thereby forming a mesh cavity structure between the bottom of the thermal resistance layer film and the top of the thermopile junction. Step 8: Connecting wires: Connect the 100μm Pt wire to the thermopile electrode disk on the substrate after step 7 using platinum paste to obtain the thin film heat flow sensor. When cleaning the substrate surface, acetone, ethanol and deionized water are used in sequence to clean the substrate surface; The vacuum level of the vacuum environment in steps 2 and 3 is 2 × 10⁻⁶. -4 Pa, the vacuum level of the vacuum environment in step 5 is 5 × 10 Pa. -4 Pa; When performing DC magnetron sputtering, nitrogen gas with a volume percentage of 99.999% is introduced as the sputtering medium, the sputtering pressure is 0.4 Pa, the power is 120 W when sputtering Pt, the power is 100 W when sputtering PtRh10, and the thermopile film deposition thickness is 300 nm. The annealing temperature was 800 ℃ and the time was 60 min. When using electron beam evaporation technology, the beam current was adjusted to 20 mA, the deposition rate of sodium chloride film was 10 Å, the deposition time was 5 min, and the NaCl film thickness was 300 nm. During radio frequency magnetron sputtering, nitrogen and argon with a purity of 99.999% were introduced in a ratio of 5:25, the sputtering pressure was 0.4 Pa, the sputtering power was 200 W, and the resulting Si3N4 thin film had a deposition thickness of 500 nm.

3. The method for fabricating a thin-film heat flow sensor based on a mesh cavity thermal resistance layer structure according to claim 2, characterized in that, The first electrode pattern described in step 2 is specifically composed of a plurality of electrodes arranged in m columns and n rows from left to right. The first row of electrodes in even-numbered columns is shaped like an inverted "L", the last row of electrodes in odd-numbered columns is shaped like an "L", and the remaining electrodes are shaped like "I". The rows are arranged alternately. There are also two electrode disks at the top of the first row of electrodes in the 1st column and the first row of the mth column. The contacts of the electrode disks extend to the first row, are parallel to the first row of electrodes, and are spaced at the same distance. The second electrode pattern described in step 3 is specifically composed of a plurality of electrodes arranged in n rows and m columns. Each electrode is in the shape of an "I". The rows are arranged alternately, and the first row of the second electrode is in the same row as the first electrode. The individual electrodes are arranged alternately with equal left and right spacing. After sputtering, the two ends of each individual electrode of the second electrode are connected to the electrode contacts of the adjacent first electrode, forming an S-shaped series connection to obtain a thermopile thin film.

Images