A thermal triode based on a mems thermal bridge device

Abstract

This invention discloses a thermal transistor based on a MEMS thermal bridge device. Its structure includes a silicon substrate and a silicon nitride support film. The silicon substrate has a hollow center with a source, drain, gate, and thermocouple suspended platforms. Source, drain, and gate suspended platforms house source, drain, and gate resistance temperature sensors for heating and temperature measurement, respectively. Thermocouple suspended platforms house a pair of thermocouple temperature sensors for temperature measurement. The thermal interface material and parts of the source, drain, and gate materials are also in contact with the upper surface of the thermocouple suspended platforms. The transistor material consists of source, drain, gate, and thermal interface materials, arranged in a T-shape. The left end of the source material is in contact with the upper surface of the source substrate, the right end of the drain material is in contact with the upper surface of the drain substrate, and the lower end of the gate material is in contact with the upper surface of the gate substrate.

Description

Technical Field

[0001] This invention relates to a thermal logic device, particularly a thermal transistor based on a MEMS thermal bridge device. Background Technology

[0002] One of the fundamental controls of current in electronic circuits is the control of its direction, i.e., asymmetric unidirectional conductivity. Based on this, inventions such as the electric diode and other current control technologies have greatly propelled the advancement of electronic technology. Consequently, there is a desire to manipulate heat flow like electric current to achieve the goal of processing information using phonons. Analogous to electric diodes and transistors are thermal diodes and thermal transistors. However, thermal diodes are much more difficult to implement because phonons are not real particles but quantized quasi-particles, and external electric and magnetic fields do not affect phonon transport. In 1930, Starr et al. first discovered asymmetric heat conduction at the copper-copper oxide interface. This macroscopic asymmetric heat conduction is usually caused by changes in the interface contact. With the development of integrated circuits, device sizes are becoming smaller and smaller. Realizing thermal logic devices at the micro- and nano-scale has a beneficial effect on chip heat dissipation. In the early 21st century, Terraneeo et al., based on resonance theory and the characteristics of energy spectrum changes with temperature in nonlinear systems, realized thermal rectification on a lattice model. Subsequently, many scholars explored the necessary conditions and influencing factors for realizing thermal rectification and thermal triodes from a lattice perspective. Experimentally, only a handful of studies have achieved thermal rectification in low-dimensional materials. For example, Zhang et al. used nanotubes with asymmetric mass distribution to achieve microscale solid-state thermal rectification.

[0003] In 2006, Li Baowen's research group proposed a theoretical model of a thermal triode from the perspective of a crystal lattice model. This model allows for the switching and amplification of heat flow, similar to a linear field-effect transistor (FET). They also proposed that a crucial factor in constructing a thermal triode is the negative differential thermal resistance (NDTR). This has led to numerous theoretical studies on NDTR. In 2020, Yang et al. proposed the principle of constructing NDTR on a macroscopic scale and conducted simulations. This patent, based on previous research, proposes a method for realizing a thermal triode using MEMS thermal bridge devices, thus contributing to the practical application of thermal triodes. Summary of the Invention

[0004] Purpose of the Invention: The purpose of this invention is to propose a thermal transistor based on MEMS thermal bridge devices, based on theoretical research. This fills the gap in current domestic and international thermal transistors, which are only constructed on lattice models without practical applications. The test structure of this embodiment includes a silicon substrate and a silicon nitride support film. The silicon substrate has a hollow structure in the middle, with a source, drain, gate, and thermocouple suspended platform on it. Source, drain, and gate suspended platforms are equipped with source, drain, and gate RTD temperature sensors for heating and temperature measurement, respectively. Thermocouple suspended platforms are equipped with a pair of thermocouple temperature sensors for temperature measurement. The thermal interface material and part of the source, drain, and gate materials are also in contact with the upper surface of the thermocouple suspended platform. The transistor consists of a source material, a drain material, a gate material, and a thermal interface material, arranged in a T-shape. The left end of the source material contacts the upper surface of the source substrate, the right end of the drain material contacts the upper surface of the drain substrate, and the lower end of the gate material contacts the upper surface of the gate substrate. The thermal interface material connects the right end of the source material, the left end of the drain material, and the upper end of the gate material. The thermocouple temperature sensor's hot junction is close to the thermal interface material, used to measure the temperature in this area.

[0005] During testing, a certain DC current is applied to the source, drain, and gate resistance temperature sensors for heating and temperature measurement, respectively, so that the source temperature T... S Gate temperature T G Drain temperature T D Within this temperature range, the gate temperature is varied, while the temperature T of the thermal interface material is measured using a thermocouple temperature sensor. C =T D =T I This allows us to obtain the source, gate, and drain heat flow curves, thereby determining the switching temperature point of the thermal transistor.

[0006] Beneficial effects

[0007] This invention represents the first successful realization of a thermal transistor device model, enabling heat flow control similar to that of electrical transistors, including heat flow amplification and control of heat flow switching. The source, drain, gate, and thermal interface materials used are simple, readily available, and widely selectable. MEMS-based thermal bridge devices facilitate low-dimensional thermal measurements and allow for in-situ measurements within a vacuum chamber, with relatively simple manufacturing processes and low implementation difficulty. Compared to previous studies constructing NDTRs based on atomic chains, nanostructures, or small quantum systems, this invention utilizes interfacial thermal effects to realize negative differential thermal resistance, allowing for better application in classical systems. Temperature measurement employs resistance temperature detectors (RTDs) and thermocouples, resulting in easily measurable and highly accurate signals. This patent provides valuable reference for the practical application of thermal logic devices and holds promise for applications in phonon computers built with acoustic logic devices. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of a thermal triode model based on a MEMS thermal bridge device.

[0009] Figure 2 This is a schematic cross-sectional view of a thermal triode model based on a MEMS thermal bridge device.

[0010] Figure 3 This is a schematic diagram of a thermal transistor based on a MEMS thermal bridge device.

[0011] Figure 4 This is a heat flow variation diagram based on a thermal triode model of a MEMS thermal bridge device;

[0012] Figure 5 This is a temperature simulation diagram of an NDTR constructed based on the drain material in a thermal transistor using a MEMS thermal bridge device.

[0013] Figure 6 This is a stress simulation diagram of an NDTR constructed from the drain material in a thermal transistor based on a MEMS thermal bridge device.

[0014] Figure 7 This is a curve showing the temperature change at the interface between the homojunction and heterojunction of the drain material of a thermal transistor based on a MEMS thermal bridge device.

[0015] Figure 8 This is a curve showing the pressure variation at the interface between the homojunction and heterojunction of the drain material of a thermal transistor based on a MEMS thermal bridge device.

[0016] Figure 9 It is a curve showing the drain heat flow variation of a thermal transistor based on a MEMS thermal bridge device; Detailed Implementation

[0017] like Figure 1 As shown in the structural diagram. Figure 2 for Figure 1The cross-sectional view of the structure is shown in the dashed line. The test structure in this embodiment includes a silicon substrate 15 and a silicon nitride support film 8. The silicon substrate has a hollow structure in the middle, with a source suspension platform 16, a drain suspension platform 17, a gate suspension platform 18, and a thermocouple suspension platform 3 on top. Source, drain, and gate suspension platforms are equipped with source RTD temperature sensors 4, drain RTD temperature sensors 10, and gate RTD temperature sensors 14, used for heating and temperature measurement. Thermocouple suspension platforms are equipped with a pair of thermocouple temperature sensors (2, 3) for temperature measurement. The transistor material consists of source material 5, drain materials (11, 12, 13), gate material 6, and thermal interface material 9, arranged in a T-shape. The thermal interface material and parts of the source, drain, and gate materials are also in contact with the upper surface of the thermocouple suspension platform. The drain material consists of left drain material 13, right drain material 11, and the interface 12 formed in the middle. The left end of the source material is in contact with the upper surface of the source substrate, the right end of the drain material is in contact with the upper surface of the drain substrate, and the lower end of the gate material is in contact with the upper surface of the gate substrate. A thermal interface material connects the right end of the source material, the left end of the drain material, and the upper end of the gate material. The hot junction of the thermocouple temperature sensor is close to the thermal interface material and is used to measure the temperature in this region.

[0018] During testing, a certain DC current is applied to the source, drain, and gate resistance temperature sensors for heating and temperature measurement, respectively, so that the source temperature T... S Gate temperature T G Drain temperature T D Within this temperature range, the gate temperature is varied, while the temperature T of the thermal interface material is measured using a thermocouple temperature sensor. C =T D =T I This allows us to obtain the source, gate, and drain heat flow curves, thereby determining the switching temperature point of the thermal transistor.

[0019] In this embodiment, the thermal transistor based on the MEMS thermal bridge device is entirely in a vacuum environment, so heat conduction in the vacuum can be ignored. Only the cantilever conducts heat to the environment, thereby maintaining the hot and cold junction while effectively improving the sensor's sensitivity. The silicon nitride support used has a low thermal conductivity and can be considered a thermal insulating material.

[0020] The specific implementation method of this embodiment is as follows:

[0021] Figure 3 This is a schematic diagram of a thermal transistor based on a MEMS thermal bridge device. Section AB represents the contact area between the source material (section AC) and the heat source, with an average temperature of T. S The GH section represents the contact section between the drain electrode material (DH section) and the heat source, with an average temperature of T. D The JK segment represents the contact area between the gate material (IK segment) and the heat source, with an average temperature of T.G Segments CD and CI represent the thermal interface materials (TI-Ms) between the source, drain, and gate materials, respectively, characterized by high thermal conductivity and low volume thermal resistance. Therefore, it can be assumed that points C, D, and I have the same temperature (T). C =T D =T I The source and gate materials are both single homogeneous materials, while the drain material consists of two segments (DE segment and GH segment). The EF segment is only used to describe the homojunction / heterojunction interface formed by the two segments, and its actual length is negligible and temperature-dependent.

[0022] The temperature T of the fixed source electrode S =T - For low temperature, the drain temperature T D =T + For high temperature, T S <T C =T D =T I <T D The resulting temperature difference generates a heat flow J from the drain electrode to points C, D, and I, which is the source electrode heat flow. S and the heat flow from points C, D, and I to the drain electrode J D The changes in source thermal resistance and drain thermal resistance (equivalent thermal resistance) are as follows:

[0023]

[0024]

[0025] Under normal circumstances, the greater the temperature difference, the greater the heat flow, therefore R S >0,R D >0. When the temperature T of the control gate is controlled... G Gate heat flow can be controlled J G Then control T I T C T D When the temperatures at points C, D, and I change, J S and J D The changes are as follows:

[0026]

[0027]

[0028] From the law of conservation of energy:

[0029] DJ G =dJ S -dJ D

[0030] Based on the working principle of a transistor, when the gate current is very small, the current from the drain to the source can be controlled by controlling the gate voltage. To achieve a similar effect, the drain heat flow J must be controlled. D With source heat flow J S When they are equal, the gate heat flow J is at this time. G Approximately zero, similar to the amplification region of a transistor. The amplification factor of a hot transistor can be defined as:

[0031]

[0032] To ensure the thermal transistor exhibits an amplification effect, i.e., α > 1, therefore R S and R D One of the thermal resistances must be less than zero, meaning one must be a negative differential thermal resistance. The greater the temperature difference across the conductor, the smaller the heat flow through the system.

[0033] The heat flow between the source and drain electrodes can be obtained from Fourier's law:

[0034]

[0035]

[0036] L BC L DE L FG These represent the lengths of segments BC, DE, and FG, respectively. T C T S T E T D T G T F Let κ represent the temperatures at points C, S, E, D, G, and F, respectively. S (T), κ DL (T), κ DR (T) represents the thermal conductivity of the source material (BC segment), the left half of the drain material (DE segment), and the right half of the drain material (FG segment) as a function of temperature, respectively. i (T E ,T F The interfacial thermal resistance of segment EF is related to the temperatures at points E and F.

[0037] When T C As the temperature rises from a low temperature to a high temperature, the temperature difference between B and C increases, thereby causing J to... SThe DG segment utilizes the temperature dependence of interfacial thermal resistance to construct a negative differential thermal resistance. When the temperature difference between DG segments decreases, the average temperature of the two materials increases, leading to an increase in the average temperature of the interfaces at both ends of EF. Since both materials are thermally expanding, the pressure at the interfaces at both ends of EF increases due to expansion stress. Because the extrinsic interfacial thermal resistance (ITR) is caused by incomplete contact between the materials at the interface and decreases with increasing pressure, while the intrinsic thermal resistance (Kapitza ITR) is derived from the vibrational characteristics of the different materials constituting the carrier scattering interface and decreases with increasing temperature, the total interfacial thermal resistance R... i (T E ,T F The length L of the material at both ends of the drain electrode is reduced. DE L FG The temperature difference remains almost constant, thus increasing the heat flux. When the increasing heat flux caused by the change in interfacial pressure outweighs the decreasing heat flux caused by the decrease in temperature difference, a negative differential thermal resistance phenomenon occurs, thereby enabling the transistor to perform amplification and switching functions.

[0038] Figure 4 The figure shows the heat flow variation of a thermal transistor model based on a MEMS thermal bridge device. When T... G By T S The low temperature gradually increases to T D At high temperatures, heat flow J is generated. D and J S The change, when adjusted to T ON and T G At two temperatures, J S =J D J G =0, meaning no heat flow is drawn from the gate. At this time, the drain heat flow and source heat flow J S =J D The significant difference between these two points allows it to function as a good thermal switch, i.e., it can be controlled by the gate temperature T. G This enables the thermal transistor to turn on or off. Furthermore, the gate thermal flow J is adjusted. G Its tiny changes can achieve J S and J D The major change is that the heat transfer tube now has the function of amplifying heat flux.

[0039] Figure 5 and Figure 6The figures show the temperature and stress simulations of the NDTR constructed from the drain material in a MEMS thermal bridge device-based thermal transistor model. The temperature at the left end of the five material segments is fixed at 100K, while the temperatures on the right side of the five segments, from top to bottom, are 100K, 105K, 110K, 115K, and 120K respectively. Each material segment consists of a left drain material, a right drain material, and a middle interface, all using silicon materials from the material library. The middle end is used only to simulate interface thermal resistance, and its thermal conductivity decreases with increasing stress. The temperature and stress simulations show that as the temperature difference between the two ends increases, the temperature difference between the left and right drain materials also gradually increases, the interface contraction effect becomes more pronounced, and the interface stress increases. This indicates that the increased average interface temperature leads to increased contraction stress, thereby increasing the interface thermal resistance.

[0040] Figure 7 and Figure 8 The figures show the temperature and stress variation curves at the interface between the homojunction and heterojunction of the drain material in a MEMS thermal bridge-based thermal transistor. As the temperature at the right end of the drain material increases, the stress at both ends of the interface increases due to thermal expansion. The temperature at the right end of the interface rises, while the temperature at the left end initially rises and then falls. This indicates that the increased thermal resistance caused by the increased interface stress due to the increased average interface temperature has a greater hindering effect on heat flow than the promoting effect of the increased temperature difference. This results in a negative differential thermal resistance phenomenon.

[0041] Figure 9 This is a graph showing the drain heat flow variation of a thermal transistor based on a MEMS thermal bridge device. As can be seen from the graph, in the latter half of the curve, the heat flow decreases as the temperature difference increases, exhibiting a negative differential thermal resistance phenomenon. This can be used to construct... Figure 3 The drain heat flow shown is used to construct a thermal transistor with heat flow amplification and switching function.

Claims

1. A thermal transistor based on a MEMS thermal bridge device, characterized in that: Its structure includes a silicon substrate and a silicon nitride support film. The silicon substrate has a hollow structure in the middle, with a source floating platform, a drain floating platform, a gate floating platform and a thermocouple floating platform on it. The source, drain, and gate are suspended on the platform, where source, drain, and gate resistance temperature sensors are used for heating and temperature measurement. A pair of thermocouple temperature sensors are mounted on the thermocouple suspension platform for temperature measurement. The thermal interface material and some source, drain, and gate materials are also in contact with the upper surface of the thermocouple suspension platform. The transistor consists of a source material, a drain material, a gate material, and a thermal interface material, arranged in a T-shape. The left end of the source material is in contact with the upper surface of the source substrate, the right end of the drain material is in contact with the upper surface of the drain substrate, and the lower end of the gate material is in contact with the upper surface of the gate substrate. The thermal interface material connects the right end of the source material, the left end of the drain material, and the upper end of the gate material. The hot end of the thermocouple temperature sensor is close to the thermal interface material and is used to measure the temperature in this area.

2. A thermal transistor based on a MEMS thermal bridge device according to claim 1, characterized in that: The source-floating platform, drain-floating platform, gate-floating platform, and thermocouple-floating platform are all made of silicon nitride, which has the characteristics of low thermal conductivity and electrical insulation, and are used as a support substrate for the polycrystalline silicon layer. Resistance temperature sensors, made of platinum resistance thermometers, are connected to platinum metal pads for applying current and measuring electrical signals; thermocouple temperature sensors, made of p-type and n-type polysilicon, utilize the Seebeck effect to measure temperature, offering high accuracy and compatibility with CMOS processes.

3. A thermal transistor based on a MEMS thermal bridge device according to claim 1, characterized in that: The thermal interface material is composed of polymer-based materials with high thermal conductivity. It is lightweight, electrically insulating and has high mechanical strength, which can make the source, drain and gate terminals have the same temperature.

4. A thermal transistor based on a MEMS thermal bridge device according to claim 1, characterized in that: The drain material consists of a left drain material, a right drain material, and an interface homojunction / heterojunction. The two materials have high coefficients of thermal expansion. When the overall average temperature of the drain material changes, a contraction / expansion effect will occur, causing a change in the thermal resistance of the interface homojunction / heterojunction, thereby affecting the heat flux of the drain material.

5. A thermal transistor based on a MEMS thermal bridge device according to claim 1, characterized in that: The source material is silicon dioxide, which has a low coefficient of thermal expansion and a small change in thermal conductivity with temperature. Its heat flux increases linearly with the increase of the temperature difference between the two ends. In addition, silicon material has a low coefficient of thermal expansion, and its length and interfacial pressure hardly change with the average temperature.

6. A thermal transistor based on a MEMS thermal bridge device according to claim 1, characterized in that: The gate material is a ceramic-based material with low thermal conductivity and high thermal resistance, and the heat flow change caused by the temperature change at both ends is very small.

7. A thermal transistor based on a MEMS thermal bridge device according to claim 1, characterized in that: During testing, a certain DC current is applied to the source, drain, and gate resistance temperature sensors for heating and temperature measurement, respectively, so that the source temperature T... S Gate temperature T G Drain temperature T D Within this temperature range, the gate temperature is varied, while the temperature T of the thermal interface material is measured using a thermocouple temperature sensor. C =T D =T I This allows us to obtain the source, gate, and drain heat flow curves, thereby determining the switching temperature point of the thermal transistor.

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