A low-dimensional material in-situ transmission thermal testing device and testing method

Abstract

The present invention discloses an in-situ transmission thermal testing device and testing method for low-dimensional materials. The device comprises a silicon substrate with a hollow structure in the middle and two suspended platform structures as electrical and thermal insulation substrates for a metal layer. The two suspended platforms are provided with thermocouple structure temperature sensors, metal resistors, and metal electrodes, wherein each suspended platform is provided with a thermocouple structure temperature sensor, a metal resistor, and a metal electrode. Thermal isolation islands made of square silicon nitride are embedded in a uniform sequence in the electrical signal path connecting the thermocouples, metal resistors, and metal electrodes on the cantilever to the external electrodes. The metal electrodes on each suspended platform are close to the thermocouple structure temperature sensor, so that the temperature at the sample end is closer to the temperature sensed by the temperature sensor, ensuring high-precision measurement. At the same time, a corresponding standard micro-nano processing process suitable for mass processing is designed.

Description

Technical Field

[0001] The invention relates to an in-situ transmission thermal testing device and a testing method for low-dimensional materials. Background Art

[0002] Low-dimensional nanomaterials possess excellent optical, electrical, magnetic, mechanical, and thermal properties, making them suitable for a wide range of applications. However, current research on the properties of low-dimensional materials focuses primarily on their electrical, optical, and mechanical properties, with limited research on their thermal properties. Regarding thermal properties, the limited dimensionality of these materials limits phonon transport, leading to novel thermal conductivity properties. Factors such as material size, number of layers, and isotopic composition alter phonon-boundary and phonon-defect scattering, thus affecting the material's thermal conductivity. Furthermore, due to the size constraints of low-dimensional nanomaterials, interfacial interactions also have a significant impact on thermal conductivity. Molecular-level design can create continuously tunable two-dimensional interfaces, potentially enabling the construction of optimized micro- and nanoscale heat conduction pathways for diverse applications, such as directional heat dissipation in micro- and nanodevices and thermal protection in extreme environments. Therefore, research on the thermal conductivity properties of low-dimensional materials is of great significance.

[0003] Currently, research on measuring the thermal parameters of low-dimensional materials is limited, with three main approaches. The first is the suspended thermal bridge method, based on the principle of MEMS thermal resistors. In 2001, Li et al. at the University of California, Berkeley, first used this method to measure the thermal conductivity of multi-walled carbon nanotubes. The second is the Raman method, which was first used by Balandin et al. in 2008 to measure the thermal conductivity of single-layer graphene. The third is time-domain thermoreflectometry (TDTR). In 1983, Eeslty et al. first applied picosecond pulsed lasers to probe the heat transport of copper in metal layers. After more than 30 years of development, TDTR has been widely used to measure the thermal properties of materials. Currently, measuring the thermal conductivity of low-dimensional materials presents significant challenges. For example, when using the Raman method, the Raman laser can cause the core of the material to overheat, resulting in low measurement accuracy. Furthermore, the time-domain thermoreflectometry method requires high surface smoothness and requires a metal coating, which can affect the phonon transmission properties of the surface. There are very few methods suitable for in-situ thermal parameter measurement. Among them, the suspended thermal bridge method based on the MEMS thermal resistor principle is the only method that can be applied to the in-situ testing of low-dimensional materials. However, the structure of the suspended thermal bridge method based on the MEMS thermal resistor principle determines that the thermal resistor measures the average temperature of the serpentine resistor structure, rather than the actual temperature at both ends of the sample to be measured. The error is large during the measurement process. Since the accuracy of the resistance value measurement directly determines the accuracy of the thermal parameter test, the accuracy of the thermal parameter test is not high. The advantage of in-situ transmission electron microscopy parameter testing is that it can observe the fine structural relationship of atoms. It is particularly suitable for studying and measuring the effects of defects, doping, etc. on the thermal properties of materials. Therefore, the test chip needs to have higher measurement accuracy to meet the detection of defects, doping, etc. on thermal parameters. How to improve the measurement accuracy of the in-situ thermal parameters of low-dimensional materials is one of the hot spots and difficulties in the current frontier research field. Summary of the Invention

[0004] Purpose of the invention: In view of the above-mentioned existing technologies, an in-situ transmission thermal testing device and testing method for low-dimensional materials are proposed to improve the measurement accuracy of in-situ parameter testing of transmission electron microscopy.

[0005] Technical solution: A low-dimensional material in-situ transmission thermal testing device, which is a MEMS device, including a silicon substrate and a metal layer on the silicon substrate, and a suspended platform is formed on the silicon substrate; the metal layer includes two parts arranged on the suspended platform and symmetrical on the left and right; each part includes a thermocouple temperature sensor, a piezoelectric film, a heating resistor, and a metal electrode, the thermocouple junction of the thermocouple temperature sensor is located on the piezoelectric film, the thermocouple temperature sensor, the heating resistor and the metal electrode are arranged in sequence at intervals, and the metal electrodes are located on the relative inner sides of the plane, and the metal electrodes of the left and right parts are used to jointly load the sample to be tested; the thermocouple temperature sensor, the heating resistor and the metal electrode are respectively connected to the external electrodes through electrical signal paths, and square silicon nitride is evenly embedded in the metal strips constituting the electrical signal path, so that the electrical signal path forms a square wave shape; the silicon substrate of the suspended platform part serves as the electrical and thermal insulation substrate of the metal layer.

[0006] Furthermore, the thermocouple temperature sensor is composed of two metal strips of different materials that meet the difference in Seebeck coefficients. The two metal strips arranged in parallel in the main body are respectively located on silicon substrates of the same shape and spaced apart. Square silicon nitride is evenly embedded in the two metal strips in sequence, so that the metal strips form a square wave shape. The two metal strips are combined together at the hot end to form the thermocouple junction.

[0007] The testing method of the low-dimensional material in-situ transmission thermal testing device includes the following steps:

[0008] Step 1: Place the sample to be tested on the test device, with both ends of the sample in contact with the metal electrodes on the left and right parts respectively, and then place the entire device in a vacuum system;

[0009] Step 2: Apply a DC current to one of the heating resistors to heat it up, and measure the voltage V across the thermocouple temperature sensor on that side. h , and simultaneously measure the voltage V across another thermocouple temperature sensor s , and measure the potential difference V between two metal electrodes seebeck ;

[0010] Step 3: Calculate the thermal conductivity of the sample to be tested as Gs;

[0011] Gs=Gb×(Ts–T0) / (Th–Ts)

[0012]

[0013] Where Gb is the thermal conductivity of the thermocouple temperature sensor cantilever, Th is the voltage V h The calculated temperature, Ts, is based on the voltage V sThe calculated temperature, T0 is the ambient temperature, and Q is the Joule heat generated by the heating resistor;

[0014] Step 4: Calculate the thermal conductivity k of the material of the sample to be tested and calculate the thermal conductivity k according to the potential difference V seebeck Calculate the Seebeck coefficient S of the sample to be tested;

[0015]

[0016]

[0017] Where L is the length of the sample, w is the width of the sample, and t is the thickness of the sample.

[0018] Beneficial effects: In terms of device structure and performance: First, the test device structure designed by the present invention adopts a dual-mechanism enhanced structure, which integrates the common temperature sensing of the thermocouple structure and the piezoelectric film layer. The output voltage includes the thermovoltage of the thermocouple and the piezoelectric voltage of the piezoelectric film layer, which effectively enhances the output voltage of the device, thereby improving the measurement accuracy. Second, the thermocouple structure in the test device structure designed by the present invention is used as a temperature sensor to sense temperature. The sensed temperature is the hot end of the thermocouple structure. The hot end and the end of the sample to be measured can be very close, which can effectively improve the measurement accuracy. The existing classic suspended thermal bridge method is based on the working principle of thermistor temperature measurement. The temperature sensed by the thermistor structure as a temperature sensor is the average temperature of the entire thermistor, rather than the actual temperature at both ends of the sample to be measured, resulting in a large measurement error. Third, the electrical signal path connecting the external electrode is uniformly sequenced with square silicon nitride embedded in the metal strip. Since the thermal conductivity of silicon nitride is low and the thermal conductivity of metal is high, the heat transfer process needs to bypass the silicon nitride pattern boundary and pass through the metal, increasing the heat transfer length and reducing the cross-sectional area of heat transfer, thereby effectively increasing the thermal resistance of the electrical signal path. That is, silicon nitride is used as a thermal isolation island to enhance the thermal isolation effect of the suspended platform, thereby improving test accuracy.

[0019] Device function: The device can be used for high-precision in-situ testing of thermal parameters using a transmission electron microscope, while also realizing the microscopic structure-activity relationship between thermal parameters and atomic structure, as well as its defects and doping.

[0020] In terms of test equipment requirements, since the working principle of thermistor is not required, the resistance of the heating resistor can be reduced, and the requirements for the accuracy of the DC current source can be lowered. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the structure of the test device of the present invention;

[0022] Figure 2 Schematic diagram of the metal layer structure of the test device of the present invention;

[0023] Figure 3 It is a structural cross-sectional view of the first step of preparing a test device according to the present invention;

[0024] Figure 4 This is a structural cross-sectional view of the second step of preparing the test device according to the present invention;

[0025] Figure 5 is a structural cross-sectional view of the third step of preparing a test device according to the present invention;

[0026] Figure 6 is a structural cross-sectional view of the fourth step of preparing a test device according to the present invention;

[0027] Figure 7 is a structural cross-sectional view of the fifth step of preparing a test device according to the present invention;

[0028] Figure 8 is a structural cross-sectional view of the sixth step of preparing a test device according to the present invention;

[0029] Figure 9 is a structural cross-sectional view of the seventh step of preparing a test device according to the present invention;

[0030] Figure 10 is a structural cross-sectional view of the eighth step of preparing a test device according to the present invention;

[0031] Figure 11 This is a temperature simulation diagram of a classic MEMS thermal bridge structure;

[0032] Figure 12 This is a temperature simulation diagram of the test device of the present invention;

[0033] Figure 13 Schematic diagram of potential distribution of thermal conductivity test device of the present invention;

[0034] Figure 14 This is a schematic diagram of the structure of the test device for testing thermal conductivity of the present invention. DETAILED DESCRIPTION

[0035] The present invention will be further explained below with reference to the accompanying drawings.

[0036] like Figure 1 、 Figure 2As shown, a MEMS device for in-situ transmission thermal testing of low-dimensional materials includes a silicon substrate 101 and a metal layer on the silicon substrate. The central portion of the silicon substrate 101 is a hollow structure 102, with a first suspended platform 103 and a second suspended platform 104 formed above it, both symmetrically. The metal layer includes two symmetrical parts, one on each suspended platform. The left part includes a first thermocouple temperature sensor 105, a first heating resistor 107, a first metal electrode 109, and a first piezoelectric film 111. The right part includes a second thermocouple temperature sensor 106, a second heating resistor 108, a second metal electrode 110, and a second piezoelectric film 112. In the left and right structures, the thermocouple temperature sensors, heating resistors, and metal electrodes are spaced apart in sequence, and the metal electrodes are located on opposite inner sides of the plane. The first metal electrode 109 and the second metal electrode 110 are used to jointly load the sample to be tested.

[0037] In both the left and right sections, the thermocouple temperature sensors consist of two metal strips made of different materials with different Seebeck coefficients. The two parallel metal strips are located on a silicon substrate of the same shape and spaced apart. In this embodiment, they are composed of a platinum metal layer and a nickel metal layer, which are bonded together at the hot end to form a thermocouple junction. The thermocouple junctions of the thermocouple temperature sensors are located on their respective piezoelectric films: the first thermocouple temperature sensor 105's thermocouple junction is located on the first piezoelectric film 111, and the second thermocouple temperature sensor 106's thermocouple junction is located on the second piezoelectric film 112.

[0038] In the left and right sections, the thermocouple temperature sensor, heating resistor, and metal electrodes are connected to external electrodes via electrical signal paths 114. Thermal isolation islands 113, formed by square silicon nitride, are evenly embedded in the metal strips that make up this signal path, creating a square wave pattern. Furthermore, square silicon nitride is also evenly embedded in the two metal strips of the thermocouple temperature sensor, creating a square wave pattern.

[0039] In the above structure, the suspended platform portion only retains a silicon substrate directly below the corresponding metal layer structure, and the retained silicon substrate serves as an electrical and thermal insulation substrate for the metal layer. The first thermocouple temperature sensor 105 and the second thermocouple temperature sensor 106 can be regarded as cantilever structures.

[0040] The preparation method of the above device comprises the following steps:

[0041] Step 1: Prepare a silicon nitride layer on both sides of the silicon substrate 101 by chemical vapor deposition. The upper silicon nitride 2 serves as the electrical and thermal insulation substrate of the metal layer, and the lower silicon nitride 3 serves as a mask for etching the silicon substrate. Figure 3 shown.

[0042] Step 2: Deposit a piezoelectric film layer 4 on the upper silicon nitride layer 2, and then pattern it by photolithography to obtain the first piezoelectric film 111 and the second piezoelectric film 112 corresponding to the left and right parts of the device, as shown in FIG. Figure 4 In this embodiment, the piezoelectric film layer is made of zinc oxide or aluminum nitride.

[0043] Step 3: Prepare the first metal layer 5 by using a lift-off process to form a first metal layer portion 114 constituting the first thermocouple temperature sensor and a first metal layer portion 115 constituting the second thermocouple temperature sensor, as shown in FIG. Figure 5 shown.

[0044] Step 4: Prepare the second metal layer 6 by using a lift-off process to form the first metal electrode 109, the second metal electrode 110, the first heating resistor 107, the second heating resistor 108, and the second metal layer portion 116 of the first thermocouple temperature sensor and the second metal layer portion 117 of the second thermocouple temperature sensor, respectively. Figure 6 The two parts constituting the first thermocouple temperature sensor and the second thermocouple temperature sensor are respectively combined together at the hot end to form a complete first thermocouple temperature sensor 105 and a complete second thermocouple temperature sensor 106 .

[0045] Step 5: Use a lift-off process to prepare square silicon nitride corresponding to the isolation island 113 to achieve thermal isolation between electrical signal paths.

[0046] Step 6: Etch the upper silicon nitride 2 according to the shape of the suspended platform, such as Figure 7 shown.

[0047] Step 7: Etch the lower silicon nitride 3 to form an etching window, such as Figure 8 shown.

[0048] Step 8: Etch the silicon substrate from the bottom to form a hollow structure and release the suspended platform.

[0049] like Figure 14 As shown, after the sample to be tested is placed on the low-dimensional material in-situ transmission thermal test device of the present invention, a DC current is passed through the first heating resistor 107 to heat the first suspended platform 103, and the Joule heat generated is Q h The DC current also heats the first thermocouple temperature sensor 105, generating a total Joule heat of 2Q l Half of it remains on the first suspended platform 103, and the other half flows into the substrate environment, so the total Joule heat remaining on the heater can be approximated as Q h +Q lAssuming that the amount of heat transferred from the first suspended platform 103 to the environment is Q1, and the amount of heat transferred from the second suspended platform 104 to the environment is Q2, the total heat Q = Q1 + Q2 = Q h +Q l .

[0050] The heat transferred from the first suspended platform 103 to the second suspended platform 104 through the sample is the same as the heat transferred from the second suspended platform 104 to the environment through the cantilever. Let the thermal conductivity of the sample be G s , let the thermal conductivity of the thermocouple temperature sensor cantilever be G b , the temperature of the first suspended platform 103 is T h , the temperature of the second suspended platform 104 is T s , the ambient temperature is T0, then:

[0051] Q1=Gb×(Th–T0)

[0052] Q2=Gs×(Th–Ts)=Gb×(Ts–T0)

[0053] So we can get:

[0054] Gs=Gb×(Ts–T0) / (Th–Ts)

[0055] and:

[0056] Q=Qh+Qs=Q1+Q2=Gb×(Th–T0)+Gb×(Ts–T0)

[0057] According to the above formula, the thermal conductivity G of the sample can be calculated s , and then according to the formula of thermal conductivity:

[0058]

[0059] The thermal conductivity k can be further calculated. Where L is the length of the sample, w is the width of the sample, and t is the thickness of the sample.

[0060] The temperature T of the first suspended heat island 103 h The temperature T of the second suspended platform 104 can be measured by the first thermocouple temperature sensor 105. s The temperature can be measured by the second thermocouple temperature sensor 106. The proximity of the first metal electrode 109 and the second metal electrode 110 to the thermocouple temperature sensor 105 and the second thermocouple temperature sensor 106, respectively, makes the sample end temperature more closely aligned with the test temperature, ensuring measurement accuracy. Placed in a vacuum system, heat conduction in the vacuum can be ignored; only the cantilever conducts heat to the environment, maintaining the hot and cold junctions while effectively improving the sensor's sensitivity.

[0061] According to the above principles, the method for testing thermal conductivity and Seebeck coefficient of a low-dimensional material in-situ transmission thermal testing device according to the present invention comprises the following steps:

[0062] Step 1: Place the sample to be tested on the test device, with both ends of the sample in contact with the metal electrodes on the left and right parts respectively, and then place the entire device in a vacuum system.

[0063] Step 2: Apply a DC current to one of the heating resistors to heat it up, and measure the voltage V across the thermocouple temperature sensor on that side. h , and simultaneously measure the voltage V across another thermocouple temperature sensor s , and measure the potential difference V between two metal electrodes seebeck .

[0064] Step 3: Calculate the thermal conductivity of the sample to be tested as Gs;

[0065] Gs=Gb×(Ts–T0) / (Th–Ts)

[0066]

[0067] Where Gb is the thermal conductivity of the cantilever, Th is the voltage V h The calculated temperature, Ts, is based on the voltage V s The calculated temperature, T0 is the ambient temperature, and Q is the Joule heat generated by the heating resistor.

[0068] Step 4: Calculate the thermal conductivity k of the material of the sample to be tested and calculate the thermal conductivity k according to the potential difference V seebeck Calculate the Seebeck coefficient S of the sample to be tested;

[0069]

[0070]

[0071] Where L is the length of the sample, w is the width of the sample, and t is the thickness of the sample.

[0072] like Figure 11 、 Figure 12 As shown, the simulation results show that although there is also a temperature gradient inside the suspended platform when measuring using the dual-mechanism enhanced test device of the present invention, due to the smaller size of the suspended platform of the present invention, the temperature detection point is closer to both ends of the sample than the traditional MEMS thermal resistor thermal bridge structure. When the temperature of the sample at the heating end is 300.15K, the average temperature of the heating resistor on the heating platform is 300.29K, and the temperature difference is 0.14K. When the temperature of the sample at the sensing end is 294.54K, the average temperature of the heating resistor on the sensing platform is 294.46K, and the temperature difference is 0.09K. Figure 12 As shown in the simulation diagram, when the temperature of the sample at the heating end is also 300.15K, the temperature at the thermocouple junction on the heating platform is 300.20K, with a temperature difference of 0.05K from the actual temperature. When the temperature of the sample at the sensing end is 294.50K, the temperature at the thermocouple junction on the sensing platform is 294.43K, with a temperature difference of 0.07K. The simulation results show that the temperature measured by the test device of the present invention is closer to the actual temperature than that of the traditional thermal resistor-type suspended thermal bridge device, thus helping to improve the accuracy of thermal conductivity measurement.

[0073] like Figure 13 As shown, when the temperature of the suspended platform increases, taking the left structure as an example, due to the Seebeck effect, the first metal layer portion 114 and the second metal layer portion 116 of the first thermocouple temperature sensor 105 both generate thermoelectric potentials V1 and V2. The direction of the potential is designed by designing the metal layer material so that the potential is superimposed as shown in the figure. The first piezoelectric film 111 has internal stress due to the different thermal expansion coefficients from silicon nitride. According to the piezoelectric effect, the potential V3 generated at both ends of the piezoelectric film further increases V total Improved the sensitivity of the device.

[0074] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A low-dimensional material in-situ transmission thermal testing device, characterized in that: The device is a MEMS device, comprising a silicon substrate and a metal layer on the silicon substrate, with a suspended platform formed on the silicon substrate; the metal layer comprises two parts arranged on the suspended platform and symmetrical on the left and right; each part comprises a thermocouple temperature sensor, a piezoelectric film, a heating resistor, and a metal electrode, the thermocouple junction of the thermocouple temperature sensor being located on the piezoelectric film, the thermocouple temperature sensor, the heating resistor, and the metal electrode being arranged in sequence and spaced apart, and the metal electrodes being located on the relatively inner sides of the plane, and the metal electrodes on the left and right parts being used to jointly load a sample to be tested; the thermocouple temperature sensor, the heating resistor, and the metal electrode are respectively connected to external electrodes through electrical signal paths, and square silicon nitride is uniformly embedded in a sequence in the metal strips constituting the electrical signal paths, so that the electrical signal paths form a square wave shape; the silicon substrate of the suspended platform portion serves as an electrical and thermal insulating substrate for the metal layer; The thermocouple temperature sensor is composed of two metal strips made of different materials that meet the difference in Seebeck coefficient. The two metal strips are arranged in parallel on the main body and are respectively located on a silicon substrate of the same shape and spaced apart. Square silicon nitride is evenly embedded in the two metal strips in a uniform sequence, so that the metal strips form a square wave shape. The two metal strips are combined at the hot end to form the thermocouple junction.

2. The method for testing a low-dimensional material in-situ transmission thermal testing device according to claim 1, characterized in that: The steps include: Step 1: Place the sample to be tested on the test device, with both ends of the sample in contact with the metal electrodes on the left and right parts respectively, and then place the entire device in a vacuum system; Step 2: Apply a DC current to one of the heating resistors to heat it up, and measure the voltage V across the thermocouple temperature sensor on that side. h , and simultaneously measure the voltage V across another thermocouple temperature sensor s , and measure the potential difference V between two metal electrodes seebeck ; Step 3: Calculate the thermal conductivity of the sample to be tested as Gs ; in, Gb is the thermal conductivity of the thermocouple temperature sensor cantilever, Th According to the voltage V h The calculated temperature, Ts According to the voltage V s The calculated temperature, T 0 is the ambient temperature, Q The Joule heat generated by the heating resistor; Step 4: Calculate the thermal conductivity of the material of the sample to be tested k , and according to the potential difference V seebeck Calculate the Seebeck coefficient of the sample to be tested S ; in, L is the length of the sample, w is the width of the sample, t is the thickness of the sample.

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