High-power thin film thermopile laser power meter and preparation method thereof

Abstract

The invention discloses a high-power thin film thermopile laser power meter and a preparation method thereof, and relates to the technical field of laser detection equipment. The high-power thin-film thermopile laser power meter comprises a thermopile chip and a heat sink packaging shell, the thermopile chip comprises a substrate, a thermopile layer is arranged on the substrate, the thermopile layer comprises a plurality of thermocouple lines, the adjacent thermocouple lines are connected in series, the thermocouple lines are distributed in a square shape, the thermocouple lines are distributed in a step shape, and the thermopile chip is connected with the heat sink packaging shell. And a cold end thermal resistance layer and a hot end thermal resistance layer are respectively arranged above the cold end and below the hot end of the thermopile layer. The structure of the thermopile is optimized, the heat transfer path in the thermopile chip is regulated and controlled, the stability of the thermopile chip in a low laser power test is improved, the preparation process is improved, and the cost is reduced. The problems that an existing thin film thermopile laser power meter is low in sensitivity and poor in stability during low-power measurement, and a thermopile chip is prone to aging and poor in stability during high-power density measurement are effectively solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser detection equipment, and particularly relates to a high-power thin-film thermocouple laser power meter and a preparation method thereof. BACKGROUND

[0002] The thermocouple laser power meter is a device for measuring laser power based on the thermoelectric effect. Its core principle is to convert the incident laser energy into heat energy through an absorbing layer, which causes a temperature difference between the cold and hot ends of the thermocouple chip. Based on the Seebeck effect, this temperature difference is converted into a proportional electrical signal (voltage) by a thermocouple composed of multiple series-connected thermocouples. Finally, after amplification and calibration by a measurement circuit, the corresponding laser power value can be obtained.

[0003] A typical thermocouple laser power meter structure includes an absorbing layer, a thermocouple chip, a heat transfer substrate, and a packaging shell. Its measurement of laser power mainly includes the following steps: energy absorption and heat conversion: first, the laser beam is irradiated onto the absorbing layer of the thermocouple power meter, which absorbs the laser energy and converts it into heat energy; temperature difference generation: the heat energy raises the temperature of the hot end of the thermocouple chip, forming a temperature gradient between the cold and hot ends of the thermocouple; thermoelectric conversion: the thermocouple converts this temperature difference into an electrical signal based on the Seebeck effect; signal processing and output: the measurement circuit amplifies and calibrates the weak voltage signal, and finally outputs a value reflecting the incident laser power.

[0004] The thermocouple laser power meter has the advantages of wide response band (covering ultraviolet, visible to infrared), high measurement accuracy, low power consumption, and good portability. However, the response time of traditional thermocouple laser power meters is usually on the order of seconds, making it difficult to meet the needs of fast dynamic laser power measurement. With the development of micro-electro-mechanical systems (MEMS) technology, thin-film thermocouple laser power meters based on MEMS technology significantly reduce the size of the device and improve the response speed to the order of hundreds of milliseconds, thereby possessing the ability to be applied to dynamic laser power measurement.

[0005] However, the existing thin-film thermocouple laser power meter still has the following main deficiencies:

[0006] Structural limitations result in low sensitivity: current mainstream thin-film thermocouple chips mostly adopt a planar structure, i.e., the hot end and cold end of the thermocouple are deposited on the surface of the substrate and are in the same plane. This structure mainly relies on radial heat transfer of the substrate and deposition of a thermal resistance layer above the cold end to establish a cold-hot end temperature difference. After absorbing laser energy, the heat generated at the hot end is quickly dissipated through the substrate and heat sink path, significantly reducing the effective temperature difference (ΔT) actually formed between the cold and hot ends, ultimately restricting the thermoelectric conversion sensitivity of the device.

[0007] Low power measurement stability is poor: due to the small effective temperature difference mentioned above, the output signal of the thermoelectric laser power meter of such a planar structure has a low signal-to-noise ratio when measuring low laser power, and the measurement value is prone to obvious fluctuations or drift, which affects the stability and reliability of the measurement result.

[0008] Reliability and life under high power are limited: when used to measure high power density laser, the laser energy is concentrated on the absorption area of the thermoelectric chip, which is prone to cause local overheating. This local overheating can accelerate the aging and degradation of the thermoelectric material, and even cause irreversible local damage (such as ablation and structural failure). This not only significantly shortens the service life of the device, but also seriously affects the stability and accuracy of long-term measurement. SUMMARY

[0009] The purpose of the present application is to provide a high-power thin-film thermoelectric laser power meter and its preparation method, which optimizes the thermoelectric structure, controls the heat transfer path in the thermoelectric chip, improves its stability in low laser power test, and improves the preparation process, effectively solves the problems of low sensitivity, poor stability of the existing thin-film thermoelectric laser power meter in low power measurement, and the thermoelectric chip is prone to aging and poor stability in high power density measurement.

[0010] The technical solution of the present application to solve the above technical problems is as follows: a high-power thin-film thermoelectric laser power meter is provided, which comprises a thermoelectric chip and a heat sink packaging shell, the thermoelectric chip comprises a substrate, a thermoelectric layer is arranged on the substrate, the thermoelectric layer comprises a plurality of thermocouple lines, adjacent thermocouple lines are connected in series, the thermocouple lines are distributed in a square shape, the thermocouple lines are distributed in a stepped shape, and a cold end thermal resistance layer and a hot end thermal resistance layer are arranged above the cold end and below the hot end of the thermoelectric layer respectively.

[0011] The beneficial effects of the technical solution of the present application are: a plurality of thermocouple lines are uniformly arranged and connected in series by microprocessing to form a thermoelectric layer, and the overall compact square distribution reduces the nonlinear disturbance of local thermal non-uniformity on the overall output, effectively balancing the signal fluctuation in low laser power measurement. At the same time, a cold end thermal resistance layer and a hot end thermal resistance layer are arranged above the cold end and below the hot end of the thermoelectric layer respectively, and the thermocouple lines are distributed in a stepped shape. When the thermoelectric chip absorbs heat above, it significantly amplifies the temperature difference between the cold and hot ends, thereby improving the signal output sensitivity and signal-to-noise ratio of the device under low power. This structure overcomes the limitations of conventional planar thermoelectric in high thermal gradient area and is suitable for high-precision laser power monitoring.

[0012] Further, the substrate material is aluminum oxide, the cold end thermal resistance layer and the hot end thermal resistance layer are made of silicon dioxide, and the thermoelectric layer is made of Ni90Cr10 / Ni97.5Si2.5.

[0013] Further, the substrate thickness is 0.2-0.3mm, and the surface roughness is 4-6nm.

[0014] Further, the substrate thickness is 0.25mm, and the surface roughness is 5nm.

[0015] Further, the cold end thermal resistance layer and the hot end thermal resistance layer have a thickness of 0.5-1μm and a width of 0.3-0.5mm; and the thermocouple wire has 140-180 pairs.

[0016] Further, the cold end thermal resistance layer and the hot end thermal resistance layer have a thickness of 1μm and a width of 0.4mm; and the thermocouple wire has 150 pairs.

[0017] The application further provides a preparation method of the high-power thin-film thermoelectric pile laser power meter.

[0018] S1, the substrate is cleaned with deionized water, acetone and anhydrous ethanol for 10-20min, and dried by nitrogen blowing;

[0019] S2, a hot end thermal resistance layer is deposited on the cleaned substrate by radio frequency magnetron sputtering;

[0020] S3, a Ni90Cr10 thin film pattern is obtained by photoresist and photolithography mask plate one photoetching, and a Ni90Cr10 thin film is deposited by direct current magnetron sputtering;

[0021] S4, a Ni97.5Si2.5 thin film pattern is obtained by photoresist and photolithography mask plate two photoetching, and a Ni97.5Si2.5 thin film is deposited by direct current magnetron sputtering;

[0022] S5, a cold end thermal resistance layer is deposited on the cleaned substrate by radio frequency magnetron sputtering;

[0023] S6, a silicon dioxide protective layer is deposited on the thermoelectric pile chip except the electrode by radio frequency magnetron sputtering, and the high-power thin-film thermoelectric pile laser power meter is obtained by packaging.

[0024] Further, in steps S2, S5 and S6, when the radio frequency magnetron sputtering is deposited, the target material is a SiO2 target with a purity of 99.999%, the sputtering chamber base vacuum degree is less than 4.0×10 -4 Pa, the working vacuum degree is 0.4-0.6Pa, the sputtering atmosphere is a mixed gas of argon and oxygen, the mixing ratio of argon and oxygen is 80sccm:20sccm, and the sputtering power is 180-220W.

[0025] Further, in step S3, the photoresist is a positive photoresist AZ4620.

[0026] In the direct current magnetron sputtering deposition, the target material is a Ni90Cr10 target with a purity of 99.999%, the base vacuum degree of the sputtering chamber is less than 4.0*10 -4 Pa, the working vacuum degree is 0.4-0.6Pa, the working gas is argon, the gas flow is 70-90sccm, and the sputtering power is 90-110W.

[0027] Further, in the step S4, the photoresist is a positive photoresist AZ4620.

[0028] In the direct current magnetron sputtering deposition, the target material is a Ni90Cr10 target with a purity of 99.999%, the base vacuum degree of the sputtering chamber is less than 4.0*10 -4 Pa, the working vacuum degree is 0.4-0.6Pa, the working gas is argon, the gas flow is 70-90sccm, and the sputtering power is 90-110W.

[0029] Further, in the step S6, the compensation line and the electrode are bonded through conductive silver paste, baking is performed at 110-130 DEG C for 10 minutes, the thermoelectric pile chip and the heat sink top groove are connected through heat-conducting silicone grease, and the shielding signal line and the shell are welded.

[0030] Further, the compensation line is a 0.2mm-diameter high-purity oxygen-free silver enameled wire, and the conductive silver paste contains 85% of silver.

[0031] Further, the thickness of the silicon dioxide protective layer is 100nm.

[0032] The present application has the following beneficial effects:

[0033] 1. The thin-film thermoelectric pile laser power meter provided by the method has excellent sensitivity and linearity in low-power density laser testing by designing the structure of the thermoelectric pile chip; meanwhile, the thermoelectric pile can withstand high-power density by water-cooled shell packaging and material system selection. Specifically, in the multiple-power density laser testing of the thin-film thermoelectric pile laser power meter provided by the method, a laser heat source with a radius of 0.5cm is applied to the surface of the power meter, the laser wavelength is 1080nm, and a collection device is used to collect the laser-induced thermoelectric voltage (LITV) of the thermoelectric pile under different laser powers. It can be seen that the output voltage of the power meter steadily rises with the increase of the laser power, and there is a stable output voltage under the same power. Linear fitting of the output voltage shows that the thin-film thermoelectric pile laser power meter has good linear output (linearity 99.733%) and high sensitivity (52.21muV / Wcm -2 ), and high stability at low power density. The multiple testing results of the power meter show that the measurement error of the device increases with the increase of the power density, and the measurement error of the device increases with the increase of the power density.2 The maximum error in the power density is 2.12%, which indicates that the device has excellent high-power stability. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 It is a structural schematic diagram of the thermoelectric chip of the application;

[0035] Figure 2 It is a schematic diagram of a hard mask plate for radio frequency magnetron sputtering deposition; a diagram is a hard mask plate for depositing a hot end thermal resistance layer, and b diagram is a hard mask plate for depositing a cold end thermal resistance layer;

[0036] Figure 3 It is a photolithography mask plate for a thermoelectric stack; a diagram is a photolithography mask plate for depositing a Ni90Cr10 thin film pattern, and b diagram is a photolithography mask plate for depositing a Ni97.5Si2.5 thin film pattern;

[0037] Figure 4 It is a multi-power density laser test result of a laser power meter;

[0038] Figure 5 It is a linear fitting result of the output voltage of the laser power meter;

[0039] Figure 6 It is an error analysis result of the laser power meter;

[0040] In the figure: 1, base; 2, cold end thermal resistance layer; 3, thermoelectric stack; 4, hot end thermal resistance layer. DETAILED DESCRIPTION

[0041] The principles and characteristics of the application are described below in conjunction with the accompanying drawings, and the examples are only used to explain the application and are not used to limit the scope of the application.

[0042] A high-power thin film thermoelectric stack laser power meter, comprising a thermoelectric chip, as shown in Figure 1 The thermoelectric chip comprises a base 1, a thermoelectric stack 3 arranged on the base 1, the thermoelectric stack 3 comprising a plurality of thermocouple lines, the adjacent thermocouple lines being connected in series, the thermocouple lines being distributed in a square shape, the thermocouple lines being distributed in a stepped ladder shape, and a cold end thermal resistance layer 2 and a hot end thermal resistance layer 4 being arranged above the cold end and below the hot end of the thermoelectric stack 3, respectively.

[0043] The base 1 is made of aluminum oxide, and the cold end thermal resistance layer 2 and the hot end thermal resistance layer 4 are made of silicon dioxide; the thickness of the base 1 is 0.25 mm, and the surface roughness is 5 nm; the thickness of the cold end thermal resistance layer 2 and the hot end thermal resistance layer 4 is 1 μm, and the width is 0.4 mm; the thermocouple lines are 150 pairs.

[0044] The application uniformly arranges and connects several thermocouple wires through microprocessing to form a thermoelectric pile layer 3, and the whole adopts a compact square distribution to reduce the nonlinear disturbance of local thermal inhomogeneity on the overall output, effectively balancing the signal fluctuation when measuring low laser power. At the same time, a cold end thermal resistance layer 2 and a hot end thermal resistance layer 4 are arranged above and below the cold end and the hot end of the thermoelectric pile layer 3 respectively, and the thermocouple wires are arranged in a stepped distribution, which significantly amplifies the temperature difference between the cold end and the hot end when the thermoelectric pile chip absorbs heat above, thereby improving the signal output sensitivity and signal-to-noise ratio of the device at low power. The structure overcomes the limitations of conventional planar thermoelectric piles in high thermal gradient regions and is suitable for high-precision laser power monitoring.

[0045] The preparation method of the high-power thin-film thermoelectric pile laser power meter comprises the following steps:

[0046] S1, the substrate 1 is placed in a cleaning basket, and is ultrasonically cleaned with deionized water, acetone and anhydrous ethanol for 15 min, and is dried with nitrogen;

[0047] S2, the hot end thermal resistance layer 4 is deposited on the cleaned substrate 1 by radio frequency magnetron sputtering, and the hot end thermal resistance layer 4 uses a hard mask plate as shown in Figure 2 a; during radio frequency magnetron sputtering, the target material is a SiO2 target with a purity of 99.999%, the base vacuum degree of the sputtering chamber is less than 4.0*10 -4 Pa, the working vacuum degree is 0.5 Pa, the sputtering atmosphere is a mixed gas of argon and oxygen, the mixing ratio of argon and oxygen is 80 sccm:20 sccm, and the sputtering power is 200 W;

[0048] S3, a positive photoresist AZ4620 and a photoetching mask plate one Figure 3 a) are used to obtain a Ni90Cr10 thin film pattern by photoetching, and a Ni90Cr10 thin film is deposited by direct current magnetron sputtering; during direct current magnetron sputtering, the target material is a Ni90Cr10 target with a purity of 99.999%, the base vacuum degree of the sputtering chamber is less than 4.0*10 -4 Pa, the working vacuum degree is 0.5 Pa, the working gas is argon, the gas flow is 80 sccm, the sputtering power is 100 W, and the photoresist is removed by using acetone after deposition is completed;

[0049] S4, a positive photoresist AZ4620 and a photoetching mask plate two Figure 3 b) are used to obtain a Ni97.5Si2.5 thin film pattern by photoetching, and a Ni97.5Si2.5 thin film is deposited by direct current magnetron sputtering; during direct current magnetron sputtering, the target material is a Ni97.5Si2.5 target with a purity of 99.999%, the base vacuum degree of the sputtering chamber is less than 4.0*10 -4Pa, working vacuum degree is 0.5 Pa, working gas is argon, gas flow rate is 80 sccm, sputtering power is 100 W, and acetone is used to remove photoresist after deposition;

[0050] S5. A cold-end thermal resistance layer 2 is deposited on the cleaned substrate 1 by radio frequency magnetron sputtering. The hard mask used for the cold-end thermal resistance layer 2 is as follows: Figure 2 As shown in b; during RF magnetron sputtering deposition, the target material is a SiO2 target with a purity of 99.999%, and the background vacuum level of the sputtering chamber is less than 4.0 × 10⁻⁶. -4 Pa, working vacuum degree is 0.5 Pa, sputtering atmosphere is a mixture of argon and oxygen, the mixing ratio of argon and oxygen is 80 sccm: 20 sccm, sputtering power is 200 W;

[0051] S6. A 100 nm thick silicon dioxide protective layer is deposited on the thermopile chip (excluding the electrodes) by radio frequency magnetron sputtering to isolate moisture and oxygen. During radio frequency magnetron sputtering deposition, the target material is a SiO2 target with a purity of 99.999%, and the background vacuum level of the sputtering chamber is less than 4.0 × 10⁻⁶. -4 The working vacuum degree is 0.5 Pa, the sputtering atmosphere is a mixture of argon and oxygen with a mixing ratio of 80 sccm:20 sccm, and the sputtering power is 200 W. High-purity oxygen-free silver enameled wire with a diameter of 0.2 mm is used as the compensation wire, bonded to the electrode with conductive silver paste containing 85% silver. Baking at 120℃ for 10 min establishes good ohmic contact between the compensation wire and the electrode, creating a transmission channel for the electrical signal, allowing the output signal to be detected by a voltmeter or data acquisition module. Thermally conductive silicone grease is used to connect the thermopile chip and the heat sink, improving heat transfer. The shielded signal line is welded to the outer shell to form a complete electromagnetic shielding layer, reducing noise, resulting in a high-power thin-film thermopile laser power meter.

[0052] The high-power thin-film thermopile laser power meter obtained above was subjected to multi-power-density laser testing. A laser heat source with a radius of 0.5 cm and a laser wavelength of 1080 nm was applied to the surface of the power meter. The laser-induced thermoelectric voltage (LITV) of the thermopile under different laser powers was collected using an acquisition device. The results are as follows: Figure 4 As shown; then, a linear fit was performed on the output voltage, and the fitting result is shown in the appendix. Figure 5 As shown; meanwhile, the error analysis results of multiple tests of the power meter are as follows: Figure 6 As shown.

[0053] Depend on Figure 4 It can be seen that the output voltage of the power meter increases steadily with the increase of laser power, and has a stable output voltage at the same power.

[0054] Depend on Figure 5 It can be seen that the thin-film thermopile laser power meter has good linear output (linearity 99.733%) and high sensitivity (52.21 μV / Wcm). -2 Furthermore, the device exhibits high stability at low power densities.

[0055] Depend on Figure 6 It can be seen that the measurement error of the device increases with increasing power density, reaching 135 W / cm². 2 The maximum error within the power density is 2.12%, indicating that the device has excellent high power stability.

[0056] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-power thin-film thermopile laser power meter, characterized in that, The device includes a thermopile chip and a heat sink packaging shell. The thermopile chip includes a substrate on which a thermopile layer is disposed. The thermopile layer includes a plurality of thermocouple lines connected in series with adjacent thermocouple lines. The thermocouple lines are distributed in a square or stepped manner. A cold-end thermal resistance layer and a hot-end thermal resistance layer are respectively disposed above the cold end and below the hot end of the thermopile layer.

2. The high-power thin-film thermopile laser power meter according to claim 1, characterized in that, The substrate material is aluminum oxide, the cold end thermal resistance layer and the hot end thermal resistance layer are made of silicon dioxide, and the thermopile layer is made of Ni90Cr10 / Ni97.5Si2.

5.

3. The high-power thin-film thermopile laser power meter according to claim 1, characterized in that, The substrate has a thickness of 0.2-0.3 mm and a surface roughness of 4-6 nm.

4. The high-power thin-film thermopile laser power meter according to claim 1, characterized in that, The thickness of the cold-end thermal resistance layer and the hot-end thermal resistance layer is 0.5-1μm, and the width is 0.3-0.5mm; the thermocouple lines are 140-180 pairs.

5. The method for fabricating a high-power thin-film thermopile laser power meter according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Clean the substrate with deionized water, acetone and anhydrous ethanol for 10-20 minutes respectively, and then dry it with nitrogen. S2. A hot-end thermal resistance layer is deposited on the cleaned substrate by radio frequency magnetron sputtering; S3. Obtain the Ni90Cr10 thin film pattern using photoresist and photolithography through a photomask, and deposit the Ni90Cr10 thin film by DC magnetron sputtering. S4. Obtain the Ni97.5Si2.5 thin film pattern using photoresist and photolithography through a photomask, and deposit the Ni97.5Si2.5 thin film by DC magnetron sputtering. S5. Deposit a cold-end thermal resistance layer on the cleaned substrate by radio frequency magnetron sputtering; S6. A silicon dioxide protective layer is deposited on the thermopile chip (excluding the electrodes) by radio frequency magnetron sputtering, and then packaged to obtain a high-power thin-film thermopile laser power meter.

6. The method for fabricating a high-power thin-film thermopile laser power meter according to claim 5, characterized in that, In steps S2, S5, and S6, during RF magnetron sputtering deposition, the target material is a SiO2 target with a purity of 99.999%, and the background vacuum level of the sputtering chamber is less than 4.0 × 10⁻⁶. -4 Pa, working vacuum degree is 0.4-0.6 Pa, sputtering atmosphere is a mixture of argon and oxygen, the mixing ratio of argon and oxygen is 80 sccm: 20 sccm, sputtering power is 180-220 W.

7. The method for fabricating a high-power thin-film thermopile laser power meter according to claim 5, characterized in that, In step S3, the photoresist is a positive photoresist AZ4620; During DC magnetron sputtering deposition, the target material is a Ni90Cr10 target with a purity of 99.999%, and the background vacuum level in the sputtering chamber is less than 4.0 × 10⁻⁶. -4 Pa, working vacuum degree is 0.4-0.6 Pa, working gas is argon, gas flow rate is 70-90 sccm, sputtering power is 90-110 W.

8. The method for fabricating a high-power thin-film thermopile laser power meter according to claim 5, characterized in that, In step S4, the photoresist is a positive photoresist AZ4620; During DC magnetron sputtering deposition, the target material is a Ni97.5Si2.5 target with a purity of 99.999%, and the background vacuum level in the sputtering chamber is less than 4.0 × 10⁻⁶. -4 Pa, working vacuum degree is 0.4-0.6 Pa, working gas is argon, gas flow rate is 70-90 sccm, sputtering power is 90-110 W.

9. The method for fabricating a high-power thin-film thermopile laser power meter according to claim 5, characterized in that, In step S6, during encapsulation, the compensation line and electrodes are bonded together with conductive silver paste, baked at 110-130℃ for 10 minutes, the thermopile chip and the heat sink are connected with thermal grease, and the shielded signal line and the outer shell are soldered.

10. The method for fabricating a high-power thin-film thermopile laser power meter according to claim 9, characterized in that, The compensation wire is a 0.2mm diameter high-purity oxygen-free silver enameled wire, and the conductive silver paste contains 85% silver.

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