A thermopile structure for calibrating a MEMS-based extreme ultraviolet detector

Abstract

The application discloses a thermoelectric pile structure for calibrating a far ultraviolet ultraviolet detector based on MEMS, which comprises a silicon substrate, a support layer, an absorption layer, a thermocouple pair, aluminum wires, aluminum electrodes and a single crystal silicon material structure on the silicon substrate. The double-layer thermocouple stacking structure is adopted to improve the device duty ratio, more thermocouple pairs can be laid in the case of keeping the size of the one-layer structure unchanged, and the response rate of the detector is improved. The circular structure conforms to the distribution trend that the temperature is radially diffused from the center of the absorption layer to the periphery in a decreasing manner, the hot end of the thermocouple pair can be closer to the area with higher temperature, the temperature of the hot end of the thermocouple pair is more uniform, and the response rate of the detector is improved. The radiant energy of the far ultraviolet ultraviolet radiation source is converted into an output thermoelectric electromotive force, a mathematical model of Fourier's law and the Seebeck effect is established for calculation, and the heat flux density of the far ultraviolet ultraviolet radiation source is measured.

Description

Technical Field

[0001] This invention belongs to the field of far-ultraviolet (EUL) detection, specifically relating to a MEMS-based thermopile structure for calibrating EULV detectors, and a method for measuring the heat flux density of EULV radiation sources using this MEMS-based EULV detector calibration thermopile structure. Background Technology

[0002] Ultraviolet (UV) detection technology is a new type of dual-use (military and civilian) detection technology developed after laser and infrared detection technologies. In the military, it is mainly used for missile early warning, UV-IR composite guidance, UV communication, and biochemical analysis. In civilian applications, it is mainly used to detect solar UV radiation intensity, fire detection, ozone detection, and analyze and detect details of cellular pathological changes. The UV detector is the key component of a UV light detection system; therefore, conducting research and design on UV detectors is of great significance and value.

[0003] Detectors that convert ultraviolet radiation energy into electrical energy can be categorized into thermoelectric detectors and photoelectric detectors based on the thermoelectric and photoelectric effects. Among these, thermopile detectors, as thermoelectric conversion devices, are widely used in various fields, such as non-contact infrared temperature sensors and gas sensors. A thermopile is a thermoelectric conversion device that operates based on the Seebeck effect. It consists of multiple pairs of thermocouples connected in series, with the thermocouple being the basic building block. Thermocouples are typically composed of two different metal or semiconductor materials connected in series. If the temperatures of the two junctions are different, a thermoelectric electromotive force (EMF) will appear in the circuit, generating a current. For a given thermocouple, the EMF depends only on the temperatures of the hot and cold junctions. When the cold junction temperature is fixed, the EMF is a single-valued function of the hot junction temperature. Therefore, for a thermopile composed of N pairs of thermocouples, the total EMF generated is equal to the sum of the EMFs generated by each individual thermocouple pair.

[0004] In recent years, the development of MEMS (Micro Electro-Mechanical Systems) has made it possible to mass-produce and miniaturize devices at low cost. MEMS thermopile detectors are non-contact temperature measurement devices that sense temperature by receiving thermal radiation emitted by the object being measured. Ideally, the absorption layer used can completely absorb the radiation energy, allowing it to operate at room temperature. They have advantages such as simple structure, high sensitivity, no need for chopping, no need for external bias voltage, miniaturization, and low cost. Summary of the Invention

[0005] The purpose of this invention is to provide a MEMS-based thermopile structure for calibrating a far-ultraviolet detector and a method for measuring the heat flux density of a far-ultraviolet radiation source using this MEMS-based thermopile structure.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] A thermopile structure for calibration of a MEMS-based far-ultraviolet detector includes a silicon substrate, characterized in that a support layer, an absorption layer, a thermocouple pair, an aluminum wire, an aluminum electrode, and a single-crystal silicon material structure are present on the silicon substrate.

[0008] The silicon substrate is a ring-shaped column with an inner radius of 300 μm, an outer radius of 500 μm, and a thickness of 300 μm;

[0009] The support layer is located on a silicon substrate and consists of three layers from bottom to top: a silicon dioxide film, a silicon nitride film, and a silicon dioxide film. The silicon dioxide film has a bottom radius of 500 μm and a thickness of 0.6 μm, the silicon nitride film has a bottom radius of 500 μm and a thickness of 0.4 μm, and the silicon dioxide film has a bottom radius of 500 μm and a thickness of 0.3 μm.

[0010] The absorption layer is located on top of the support layer and coincides with the center point of the support layer. The absorption layer is a silicon nitride film with a bottom radius of 150 μm and a thickness of 1.5 μm, which is used to convert radiant energy into temperature rise.

[0011] The thermocouples are arranged in a double-layer structure. The lower thermocouple material layer is in contact with the support layer, while the upper thermocouple material layer is located 1 μm above the support layer. Both thermocouple material layers are 0.3 μm thick. The cross-section of each structure in both thermocouple material layers is a fan-shaped ring with an inner radius of 150 μm, an outer radius of 450 μm, and a central angle of 2°. The central angle between adjacent thermocouple material structures in the same layer is 1°. Therefore, 120 thermocouple material structures can be laid in one layer. The positions of the upper and lower thermocouple material structures correspond to each other, and the upper and lower material structures at the same position are considered as a pair of thermocouples, resulting in a total of 120 pairs of thermocouples. The thermocouples are made of N-type semiconductor materials and P-type semiconductor materials.

[0012] The thermocouples are connected in series by aluminum wires. The 120 aluminum wires at the hot end of the thermocouple have a fan-shaped cross-section with an inner radius of 148 μm, an outer radius of 150 μm, a thickness of 1.3 μm, and a central angle of 2°. The aluminum wires at the cold end of the thermocouple have a fan-shaped cross-section with an inner radius of 450 μm, an outer radius of 452 μm, a thickness of 0.3 μm, and a central angle of 5°.

[0013] The aluminum electrodes are used to measure the output potential, and the two aluminum electrodes are respectively connected to two adjacent upper thermocouple material structures.

[0014] The monocrystalline silicon material structure is located on the support layer, with a circular cross-section, an inner radius of 450 μm, an outer radius of 500 μm, and a thickness of 1.5 μm.

[0015] The method for measuring the heat flux density of a far-ultraviolet radiation source using the aforementioned MEMS-based thermopile structure for calibrating a far-ultraviolet detector is characterized by the following steps:

[0016] Step 1: Adjust the position of the ultraviolet radiation source so that the absorption layer of the thermopile structure absorbs ultraviolet radiation energy, thereby increasing the temperature of the absorption layer of the thermopile structure.

[0017] Step 2: As the temperature of the absorption layer in the thermopile structure increases, the heat conduction differential equation is derived based on the law of conservation of energy and Fourier's law. The boundary conditions can be determined through the thermopile structure, thus solving for the relationship between the temperature at the hot junction of the thermocouple and the heat flux density radiated to the absorption layer. Equation I is then used to calculate the temperature at the hot junction of the thermocouple:

[0018]

[0019] In the formula, ΔT is the temperature difference between the hot and cold junctions of the thermocouple, k is the proportionality constant, q is the heat flux density radiated to the absorption layer, r1 is the radius of the absorption layer, d is the thickness of the absorption layer, λ2 is the thermal conductivity of the thermocouple material, and r2 is the outer radius of the thermocouple.

[0020] Step 3: Based on the Seebeck effect, determine the temperature difference between the hot and cold ends of the thermocouple and the thermopile structure. Then, use Equation II to calculate the output thermoelectric electromotive force at the electrodes.

[0021] V = NV out =Nα AB ·ΔT Formula II

[0022] In the formula, V is the thermoelectric electromotive force output at the electrodes of the thermopile structure, N is the number of thermocouple pairs in the thermopile, and V out α is the thermoelectric potential generated by a pair of thermocouples. AB The Seebeck coefficient difference between the P-type and N-type semiconductor materials used in thermocouples;

[0023] Step 4: Measure the output thermoelectric potential of the thermopile structure using an external voltmeter, and then calculate the heat flux density of the ultraviolet radiation source using Equations I and II.

[0024] The technological innovation of the MEMS-based thermopile structure for calibrating far-ultraviolet detectors in this invention compared with existing technologies lies in:

[0025] (1) A double-layer thermocouple stacking structure is adopted to improve the device duty cycle, so that more thermocouple pairs can be laid while keeping the size of one layer unchanged, thereby improving the detector response rate.

[0026] (2) A circular thermopile structure is adopted, which conforms to the distribution trend of temperature spreading radially from the center of the absorption layer to the surrounding area and decreasing. This is to make the hot end of the thermocouple pair closer to the higher temperature area and make the temperature of the hot end of the thermocouple pair more uniform. This improves the output voltage of the thermopile structure and thus improves the response rate of the detector.

[0027] (3) A mathematical model corresponding to the MEMS thermopile structure was established based on the mathematical formula of heat transfer characteristics and Seebeck effect, so that the heat flux density of the far-ultraviolet radiation source can be calculated based on the measured output thermoelectric potential. Attached Figure Description

[0028] Figure 1 This is a front view of the thermopile structure for calibration of MEMS-based far-ultraviolet detectors;

[0029] Figure 2 This is a top view of the thermopile structure for calibration of a MEMS-based far-ultraviolet detector.

[0030] The markings in the figure represent: 1. Silicon substrate, 2. Support layer, 3. Absorbing layer, 4. Thermocouple pair, 5. Aluminum wire, 6. Aluminum electrode, 7. Single crystal silicon material structure.

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0032] See Figure 1 and Figure 2 This embodiment provides a MEMS-based thermopile structure for calibrating a far-ultraviolet detector, comprising a silicon substrate 1, a support layer 2, an absorption layer 3, thermocouple pairs 4, aluminum wires 5, aluminum electrodes 6, and a single-crystal silicon material structure 7 on the silicon substrate 1, wherein:

[0033] The silicon substrate 1 is a ring-shaped column with an inner radius of 300 μm, an outer radius of 500 μm, and a thickness of 300 μm;

[0034] The support layer 2 is located on the silicon substrate 1 and consists of three layers from bottom to top: a silicon dioxide film, a silicon nitride film, and a silicon dioxide film. The silicon dioxide film has a bottom radius of 500 μm and a thickness of 0.6 μm, the silicon nitride film has a bottom radius of 500 μm and a thickness of 0.4 μm, and the silicon dioxide film has a bottom radius of 500 μm and a thickness of 0.3 μm.

[0035] The absorption layer 3 is above the support layer 2 and coincides with the center point of the support layer 2. The absorption layer 3 is a silicon nitride film with a bottom radius of 150μm and a thickness of 1.5μm, which is used to convert radiation energy into temperature rise.

[0036] The thermocouple pairs 4 are arranged in a double-layer structure. The lower thermocouple material layer is connected to the support layer 2, while the upper thermocouple material layer is located 1 μm above the support layer 2. The thickness of both thermocouple material layers is 0.3 μm. The cross-section of each structure in the two thermocouple material layers is a fan-shaped ring with an inner radius of 150 μm, an outer radius of 450 μm, and a central angle of 2°. At the same time, the central angle between adjacent thermocouple material structures in the same layer is 1°. Therefore, 120 thermocouple material structures are laid in one layer. The positions of the upper and lower thermocouple material structures are the same. The upper and lower thermocouple material structures located in the same position are regarded as a pair of thermocouples, and a total of 120 pairs of thermocouples are arranged.

[0037] The thermocouple is a closed circuit made of N-type and P-type semiconductor materials. When a temperature gradient exists between the two ends, current flows through the circuit, creating an electromotive force (EMF) between them, known as the thermoelectric EMF. This is the so-called Seebeck effect. The two homogeneous conductors of different compositions are the thermoelectrodes. The end with the higher temperature is the working end, and the end with the lower temperature is the free end, which is usually kept at a constant temperature.

[0038] The thermocouple pairs 4 are connected in series by aluminum wires 5. The 120 aluminum wires located at the hot end of the thermocouple have a fan-shaped cross-section with an inner radius of 148μm, an outer radius of 150μm, a thickness of 1.3μm, and a central angle of 2°. The aluminum wires located at the cold end of the thermocouple have a fan-shaped cross-section with an inner radius of 450μm, an outer radius of 452μm, a thickness of 0.3μm, and a central angle of 5°.

[0039] The aluminum electrode 6 is used to measure the output potential, and the two aluminum electrodes 6 are respectively connected to two adjacent upper thermocouple material structures.

[0040] The single-crystal silicon material structure 7 is located on the support layer 2, with a circular cross-section, an inner radius of 450 μm, an outer radius of 500 μm, and a thickness of 1.5 μm.

[0041] In this embodiment, a simulation model of a thermopile structure for calibration of a far-ultraviolet detector based on MEMS is established using the multiphysics coupling simulation software COMSOL Multiphysics, and simulation calculations are performed for verification. The specific steps are as follows:

[0042] Step 1: Based on the dimensional parameters and material properties of the thermopile structure used for calibration of the MEMS far-ultraviolet detector, establish a simulation model of the MEMS far-ultraviolet thermopile detector.

[0043] Step 2: Set the physical field of the thermoelectric effect used, that is, set the parameters of the physical field of solid heat transfer and the physical field of current. Set the initial temperature of the model and the temperature of the single crystal silicon structural domain connected to the cold junction of the thermocouple to 293.15K, and set the initial potential value of the model and the potential of one of the electrodes to 0V.

[0044] Step 3: Apply loads to the established model, that is, add a fixed generalized inward heat flux density to the upper surface of the absorption layer structure, construct the mesh and perform simulation analysis to obtain temperature cloud maps and potential cloud maps under different heat flux densities, as well as specific thermocouple hot junction temperature values ​​and output potential values.

[0045] By comparing and analyzing the simulated hot-end temperature and output potential values ​​with the theoretical calculations, it was confirmed that the MEMS-based thermopile structure for calibrating far-ultraviolet detectors in this embodiment can measure the heat flux density of far-ultraviolet radiation sources.

[0046] The method for measuring the heat flux density of a far-ultraviolet radiation source using the MEMS-based far-ultraviolet detector calibration thermopile structure of this embodiment is performed according to the following steps:

[0047] Step 1: Adjust the position of the ultraviolet radiation source so that the absorption layer of the thermopile structure absorbs ultraviolet radiation energy, thereby increasing the temperature of the absorption layer of the thermopile structure.

[0048] Step 2: As the temperature of the absorption layer in the thermopile structure increases, the heat conduction differential equation is derived based on the law of conservation of energy and Fourier's law. The boundary conditions can be determined through the thermopile structure, thus solving for the relationship between the temperature at the hot junction of the thermocouple and the heat flux density radiated to the absorption layer. Equation I is then used to calculate the temperature at the hot junction of the thermocouple:

[0049]

[0050] In the formula, ΔT is the temperature difference between the hot and cold junctions of the thermocouple, k is the proportionality constant, q is the heat flux density radiated to the absorption layer, r1 is the radius of the absorption layer, d is the thickness of the absorption layer, λ2 is the thermal conductivity of the thermocouple material, and r2 is the outer radius of the thermocouple.

[0051] Step 3: Based on the Seebeck effect, determine the temperature difference between the hot and cold ends of the thermocouple and the thermopile structure, i.e., calculate the output thermoelectric electromotive force at the electrodes using Equation II:

[0052] V = NV out =NαAB ·ΔT Formula II

[0053] In the formula, V is the thermoelectric electromotive force output at the electrodes of the thermopile structure, N is the number of thermocouple pairs in the thermopile, and V out α is the thermoelectric potential generated by a pair of thermocouples. AB The Seebeck coefficient difference between the P-type and N-type semiconductor materials used in thermocouples;

[0054] Step 4: Measure the output thermoelectric potential of the thermopile structure using an external voltmeter, and then calculate the heat flux density of the ultraviolet radiation source using Equations I and II.

Claims

1. A thermopile structure for calibration of a MEMS-based far-ultraviolet detector, comprising a silicon substrate (1), characterized in that, A support layer (2), an absorption layer (3), a thermocouple pair (4), an aluminum wire (5), an aluminum electrode (6), and a single-crystal silicon material structure (7) are disposed on a silicon substrate (1), wherein: The silicon substrate (1) is a ring-shaped column with an inner radius of 300 μm, an outer radius of 500 μm, and a thickness of 300 μm; The support layer (2) is located on the silicon substrate (1) and consists of three layers from bottom to top: a silicon dioxide film, a silicon nitride film, and a silicon dioxide film. The silicon dioxide film has a bottom radius of 500 μm and a thickness of 0.6 μm, the silicon nitride film has a bottom radius of 500 μm and a thickness of 0.4 μm, and the silicon dioxide film has a bottom radius of 500 μm and a thickness of 0.3 μm. The absorption layer (3) is above the support layer (2) and coincides with the center point of the support layer (2). The absorption layer (3) is a silicon nitride film with a bottom radius of 150 μm and a thickness of 1.5 μm, which is used to convert radiation energy into temperature rise. The thermocouple pairs (4) are arranged in a double-layer structure. The lower thermocouple material layer is connected to the support layer (2), while the upper thermocouple material layer is located 1 μm above the support layer (2). The thickness of both thermocouple material layers is 0.3 μm. The cross-section of each structure in the two thermocouple material layers is a fan-shaped ring with an inner radius of 150 μm, an outer radius of 450 μm, and a central angle of 2°. At the same time, the central angle between adjacent thermocouple material structures in the same layer is 1°. Therefore, 120 thermocouple material structures are laid in one layer. The positions of the upper and lower thermocouple material structures are the same. The upper and lower thermocouple material structures located in the same position are regarded as a pair of thermocouples, and a total of 120 pairs of thermocouples are arranged. The thermocouples are made of N-type semiconductor material and P-type semiconductor material. The thermocouple pairs (4) are connected in series by aluminum wires (5). The 120 aluminum wires located at the hot end of the thermocouple have a fan-shaped cross-section with an inner radius of 148 μm, an outer radius of 150 μm, a thickness of 1.3 μm, and a central angle of 2°. The aluminum wires located at the cold end of the thermocouple have a fan-shaped cross-section with an inner radius of 450 μm, an outer radius of 452 μm, a thickness of 0.3 μm, and a central angle of 5°. The aluminum electrode (6) is used to measure the output potential, and the two aluminum electrodes (6) are respectively connected to two adjacent upper thermocouple material structures; The single-crystal silicon material structure (7) is on the support layer (2), with a circular cross-section, an inner radius of 450μm, an outer radius of 500μm, and a thickness of 1.5μm.

2. The method for measuring the heat flux density of a far-ultraviolet radiation source using the MEMS-based thermopile structure for calibration of a far-ultraviolet detector as described in claim 1, characterized in that... Follow these steps: Step 1: Adjust the position of the ultraviolet radiation source so that the absorption layer of the thermopile structure absorbs ultraviolet radiation energy, thereby increasing the temperature of the absorption layer of the thermopile structure. Step 2: As the temperature of the absorption layer in the thermopile structure increases, the heat conduction differential equation is derived based on the law of conservation of energy and Fourier's law. The boundary conditions can be determined through the thermopile structure, thus solving for the relationship between the temperature at the hot junction of the thermocouple and the heat flux density radiated to the absorption layer. Equation I is then used to calculate the temperature at the hot junction of the thermocouple: In the formula, ΔT is the temperature difference between the hot and cold junctions of the thermocouple, k is the proportionality constant, q is the heat flux density radiated to the absorption layer, r1 is the radius of the absorption layer, d is the thickness of the absorption layer, λ2 is the thermal conductivity of the thermocouple material, and r2 is the outer radius of the thermocouple. Step 3: Based on the Seebeck effect, determine the temperature difference between the hot and cold ends of the thermocouple and the thermopile structure, i.e., calculate the output thermoelectric electromotive force at the electrodes using Equation II: V = NV out = Nα AB ·ΔT Equation II In the formula, V is the thermoelectric electromotive force output at the electrodes of the thermopile structure, N is the number of thermocouple pairs in the thermopile, and V out α is the thermoelectric potential generated by a pair of thermocouples. AB The Seebeck coefficient difference between the P-type and N-type semiconductor materials used in thermocouples; Step 4: Measure the output thermoelectric potential of the thermopile structure using an external voltmeter, and then calculate the heat flux density of the ultraviolet radiation source using Equations I and II.

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