Hot-pressing resistance PT symmetrical micromechanical temperature sensor

Abstract

The invention discloses a hot-pressing resistance PT symmetrical micro-mechanical temperature sensor, which comprises two micro-mechanical resonators with the same structure, namely a first resonator and a second resonator, the two resonators are connected by a group of coupling spring beams, and two ends of the resonators are fixed on a substrate through anchor areas. A layer of aluminum film is deposited below the substrate of the second resonator, and the two anchor areas of the first resonator are connected with a constant current source to form hot-pressing resistance feedback. A first resonator with hot resistance feedback and a second resonator without feedback form a PT symmetric system, and the system is arranged at an Exception Point (EP) point. When the temperature changes, the aluminum material below the second resonator substrate deforms due to the high thermal expansion coefficient, the second resonator substrate is bent, the positions of anchor areas at the two ends of the second resonator are changed, the rigidity of the second resonator is changed, asymmetric disturbance is introduced into the system, the original PT symmetry of the system is destroyed, and the temperature of the system is reduced. The system eigenfrequency is split into two parts from one original frequency, and the frequency splitting amount corresponds to the temperature change. As the EP point has large response to tiny disturbance, the micro-mechanical temperature sensor with symmetrical thermal resistance PT can detect tiny temperature change and has high sensitivity.

Description

Technical Field

[0001] The present invention is a thermopiezoresistive PT-symmetric micromechanical temperature sensor, belonging to the technical field of sensors. Background Art

[0002] With the development of microelectromechanical system (MEMS) technology, MEMS temperature sensors can be widely used in various fields such as industry, medical care, and consumer electronics due to their small size, fast response, low power consumption, and high integration. Compared with traditional temperature sensors (such as thermocouples, thermistors, and platinum resistors), MEMS temperature sensors have significant advantages in terms of size, flexibility, and cost, and are particularly suitable for miniaturized and integrated applications. Although MEMS temperature sensors have many advantages, existing MEMS temperature sensors still face technical challenges in terms of sensitivity and precise measurement of small temperature changes. Measuring small temperature changes and improving sensitivity have become one of the core research topics. Summary of the Invention

[0003] Technical Problem: In view of the above problems, the present invention provides a thermopiezoresistive parity-time (PT)-symmetric micromechanical temperature sensor. The temperature sensor causes a change in the stiffness of the corresponding resonator due to local thermal expansion of the substrate caused by temperature changes, generating an asymmetric perturbation in PT symmetry and breaking the PT symmetry of the system. The PT-symmetric system was originally biased at the EP point with a unique eigenfrequency. After being perturbed, the eigenfrequency splits, and the amount of frequency splitting is proportional to the square root of the perturbation. Therefore, for very small temperature changes, it can exhibit very high sensitivity. The proposed system can be fully compatible with MEMS processes and has advantages such as miniaturization and easy integration.

[0004] Technical solution: To achieve the above object, the present invention provides a technical solution for a thermally piezoresistive PT-symmetric micromechanical temperature sensor. The sensor includes two micromechanical resonators with the same structure, namely a first resonator and a second resonator. The two resonators are connected by a set of coupling spring beams, and both ends of the resonators are fixed to the substrate through anchor regions. A layer of aluminum film is deposited under the substrate of the second resonator, and a silicon dioxide film is deposited under the substrate of the first resonator. Two anchor regions of the first resonator are connected to a constant current source to form a thermally piezoresistive feedback. The specific form of the thermally piezoresistive feedback is as follows: When the constant current source is connected to the anchor regions, a current path is formed between the anchor regions and the resonators. When the resonator vibrates, the displacement of the resonator causes strain in the narrow beam. Due to the piezoresistive effect, the resistance of the narrow beam changes in relation to the displacement. Since the current is constant under the action of the constant current source, the change in the Joule heat power on the narrow beam is determined by the change in resistance. Due to the thermal expansion effect, the change in Joule heat breaks the balance of heat conduction and heat diffusion, causing a temperature change. The changing temperature causes a thermally expanded stress to change on the narrow beam, and according to Hooke's law, the thermal expansion force acts on the displacement of the resonator in turn, forming a feedback process. Since the action form of this process is consistent with that of damping but in the opposite direction, it can be equivalent to the gain part in the PT-symmetric system. The second resonator is not connected to a constant current source, and the potential of the entire resonator is the same, operating under lossy conditions. Therefore, the first resonator with thermally piezoresistive feedback and the second resonator without feedback form a PT-symmetric system. When the system is set at the EP point, initially, since the system is PT-symmetric and biased at the EP point, the system has and only has one eigenfrequency, manifested as a steady-state oscillation at a single frequency. When the temperature changes, the high coefficient of thermal expansion material under the substrate of the second resonator deforms, causing the substrate of the second resonator to bend, and the positions of the two anchor regions at both ends of the second resonator change, resulting in a change in the stiffness of the second resonator. An asymmetric perturbation is introduced into the PT-symmetric system, destroying the original PT symmetry of the system, and the eigenfrequency splits from the original one frequency into two, and the difference between the two frequencies after the frequency splitting corresponds to the temperature change. The frequency splitting amount can be expressed as:

[0005]

[0006] where k is the stiffness of the resonator when not perturbed, k c is the stiffness of the coupling spring beam, and m is the effective mass of the resonator, all of which are known parameters; δ = Δk / k is the stiffness perturbation of the second resonator caused by temperature, where Δk is the change in the stiffness of the second resonator caused by temperature. The frequency splitting amount is proportional to the square root of the stiffness change. Therefore, for very small temperature changes, δ << 1, and the frequency splitting amount has an order-of-magnitude improvement compared to the linear case.

[0007] According to the obtained frequency splitting amount, the normalized sensitivity of the system is:

[0008]

[0009] Since δ << 1, then 1 / δ >> 1. The sensitivity of the system is much higher than that of a traditional resonant temperature sensor with a linear frequency variation (the normalized sensitivity is 0.5). Moreover, the smaller the temperature change, the more obvious the improvement in sensitivity.

[0010] Beneficial effects: For a thermopiezoresistive PT-symmetric micromechanical temperature sensor of the present invention, the temperature sensor forms a PT-symmetric system by establishing a thermopiezoresistive feedback in a pair of coupled resonators. When the system is biased at the EP point, a temperature-sensitive material is added to the substrate of one of the resonators, and the stiffness affected by temperature causes an asymmetric perturbation in the PT-symmetric system, destroying the PT symmetry of the system and resulting in the splitting of the eigenfrequency. The amount of frequency splitting is proportional to the square root of the perturbation. Therefore, for extremely small temperature perturbations, a sensitivity improvement on the order of magnitude can be achieved. In addition, this temperature sensor can be fully compatible with the MEMS process and has advantages such as miniaturization and easy integration. Description of the Drawings

[0011] Figure 1 is a top view of the thermopiezoresistive PT-symmetric micromechanical temperature sensor.

[0012] Figure 2 is a cross-sectional view of the thermopiezoresistive PT-symmetric micromechanical temperature sensor.

[0013] Figure 3 is a schematic diagram of the thermopiezoresistive feedback process.

[0014] Figure 4 is a comparison of the normalized sensitivities between the temperature sensor with a square root frequency variation in the embodiment of the present invention and a traditional resonant temperature sensor with a linear frequency variation.

[0015] In the figure: a, the first resonator; b, the second resonator; 3a1, the first anchor region 1; 3a2, the first anchor region 2; 1a1, the first narrow beam 1; 1a2, the first narrow beam 2; 1a3, the first mass block; 3b1, the second anchor region 1; 3b2, the second anchor region 2; 1b1, the second narrow beam 1; 1b2, the second narrow beam 2; 1b3, the second mass block; 4a1, the first coupling spring beam; 4a2, the second coupling spring beam; 7, silicon oxide layer; 8, substrate; 6a, silicon dioxide thin film; 6b, aluminum thin film. Detailed Embodiments

[0016] To deepen the understanding of the present invention, the present invention will be further described below with reference to the drawings. Embodiment: The thermopiezoresistive PT-symmetric micromechanical temperature sensor involved in the present invention is shown in Figure 1 and Figure 2, including two micromachined resonators with the same structure, namely the first resonator (a) and the second resonator (b). The first resonator (a) includes two anchor regions, namely the first anchor region one (3a1) and the first anchor region two (3a2), two narrow beams with piezoresistive effect, namely the first narrow beam one (1a1) and the first narrow beam two (1a2), and the first mass block (1a3). The second resonator (b) includes two anchor regions, namely the second anchor region one (3b1) and the second anchor region two (3b2), two narrow beams with piezoresistive effect, namely the second narrow beam one (1b1) and the second narrow beam two (1b2), and the second mass block (1b3). The first narrow beam one (1a1) is connected to the first anchor region one (3a1), the first narrow beam two (1a2) is connected to the first anchor region two (3a2), and the first mass block (1a3) connects the first narrow beam one (1a1) and the first narrow beam two (1a2). The second narrow beam one (1b1) is connected to the second anchor region one (3b1), the second narrow beam two (1b2) is connected to the second anchor region two (3b2), and the second mass block (1b3) connects the second narrow beam one (1b1) and the second narrow beam two (1b2). The first coupling spring beam (4a1) is connected to the first narrow beam one (1a1) and the second narrow beam one (1b1), and the second coupling spring beam (4a2) is connected to the first narrow beam two (1a2) and the second narrow beam two (1b2), forming a coupling between the first resonator (a) and the second resonator (b). The two ends of the first resonator (a) and the second resonator (b) are fixed on the silicon oxide layer (7) through the anchor regions, namely the first anchor region one (3a1), the first anchor region two (3a2), the second anchor region one (3b1), and the second anchor region two (3b2). The silicon oxide layer (7) is located above the substrate (8).

[0017] The schematic diagram of the thermal piezoresistive feedback process of the thermal piezoresistive PT - symmetric micromachined temperature sensor involved in the present invention is shown in Figure 3 . When the constant - current source (5) is connected to the first anchor region one (3a1) and the first anchor region two (3a2), a current path is formed between the anchor regions, namely the first anchor region one (3a1), the first anchor region two (3a2), and the first resonator (a). When the first resonator (a) vibrates, the displacement of the first resonator (a) causes strain to be generated in the first narrow beam one (1a1) and the first narrow beam two (1a2). Due to the piezoresistive effect, the resistance of the first narrow beam one (1a1) and the first narrow beam two (1a2) changes in relation to the displacement. Since the current is constant under the action of the constant - current source (5), the change in the Joule heat power on the narrow beams (1a1) and (1a2) is determined by the change in resistance. Due to the thermal expansion effect, the change in Joule heat breaks the balance of heat conduction and heat diffusion, causing a temperature change. The changing temperature generates a changing thermal expansion stress on the first narrow beam one (1a1) and the first narrow beam two (1a2), and according to Hooke's law, the thermal expansion force acts on the displacement of the first resonator (a) in turn, forming a feedback process.

[0018] Since the effect of the thermal piezoresistive process is consistent with damping but in the opposite direction, it can be equivalent to the gain part in the PT symmetric system. The second resonator (b) is not connected to a constant current source and works in a lossy state. The first resonator (a) with thermal piezoresistive feedback and the second resonator (b) without feedback form a PT symmetric system. In the initial state, the size of the constant current source (5) is adjusted so that the system is set at the EP point. The system has one and only one eigenfrequency, which is manifested as a steady-state oscillation at a single frequency. When the temperature changes, the aluminum film (6b) under the substrate (8) corresponding to the second resonator (b) deforms due to its high thermal expansion coefficient, causing the substrate (8) and the second resonator (b) to bend at the corresponding position. The positions of the second anchor area 1 (3b1) and the second anchor area 2 (3b2) at both ends of the second resonator (b) change, resulting in a change in the stiffness of the second resonator (b). Asymmetric disturbances are introduced into the PT symmetric system, destroying the original PT symmetry of the system. The system eigenfrequency is split from one frequency to two. The frequency splitting amount caused by the stiffness change caused by temperature is

[0019]

[0020] The frequency splitting amount can be converted into a change in stiffness. The magnitude of the thermal expansion force can be obtained based on the change in stiffness caused by the calibrated thermal expansion force, and the temperature to be measured can be calculated based on the thermal expansion coefficient of the aluminum film (6b).

[0021] The frequency splitting amount is obtained by reading the alternating current signal caused by the vibration of the resonator. The alternating and direct current signals are superimposed on the anchor area (3a2). The direct current signal is filtered out by the filter capacitor (6) to obtain the alternating current signal, and the frequency splitting amount is obtained through Fourier transformation.

[0022] The criteria for distinguishing whether it is this structure are as follows:

[0023] (a) A micromechanical resonator with PT symmetry.

[0024] (b) The narrow beam with thermo-piezoresistive effect provides gain for the PT symmetric system;

[0025] (c) Temperature sensitivity is achieved by inducing asymmetric perturbations in the PT symmetric system through two thin film structures with different thermal expansion coefficients under the substrate.

[0026] A structure that meets the above three conditions should be regarded as a temperature sensor of the structure.

[0027] The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiment. Any equivalent modifications or changes made by ordinary technicians in this field based on the contents disclosed by the present invention should be included in the protection scope recorded in the claims.

Claims

1. A thermally piezoresistive PT-symmetric micromachined temperature sensor, characterized in that, The temperature sensor includes two micro - mechanical resonators with the same structure, namely the first resonator (a) and the second resonator (b). The first resonator (a) includes two anchor regions, namely the first anchor region one (3a1) and the first anchor region two (3a2), two narrow beams with piezoresistive effect, namely the first narrow beam one (1a1) and the first narrow beam two (1a2), and the first mass block (1a3). The second resonator (b) includes two anchor regions, namely the second anchor region one (3b1) and the second anchor region two (3b2), two narrow beams with piezoresistive effect, namely the second narrow beam one (1b1) and the second narrow beam two (1b2), and the second mass block (1b3); the first narrow beam one (1a1) is connected to the first anchor region one (3a1), the first narrow beam two (1a2) is connected to the first anchor region two (3a2), and the first mass block (1a3) connects the first narrow beam one (1a1) and the first narrow beam two (1a2); the second narrow beam one (1b1) is connected to the second anchor region one (3b1), the second narrow beam two (1b2) is connected to the second anchor region two (3b2), and the second mass block (1b3) connects the second narrow beam one (1b1) and the second narrow beam two (1b2). The first coupling spring beam (4a1) is connected to the first narrow beam one (1a1) and the second narrow beam one (1b1), and the second coupling spring beam (4a2) is connected to the first narrow beam two (1a2) and the second narrow beam two (1b2), forming a coupling between the first resonator (a) and the second resonator (b); both ends of the first resonator (a) and the second resonator (b) are fixed on the silicon oxide layer (7) through the anchor regions, namely the first anchor region one (3a1), the first anchor region two (3a2), the second anchor region one (3b1), and the second anchor region two (3b2). The silicon oxide layer (7) is located above the substrate (8).

2. The thermally piezoresistive PT symmetric micromachined temperature sensor according to claim 1, wherein An aluminum thin film (6b) is deposited under the substrate (8) where the second resonator (b) is located, and a silicon dioxide thin film (6a) is deposited under the substrate (8) of the first resonator (a). The constant - current source (5) is connected to the two anchor regions of the first resonator (a), namely the first anchor region one (3a1) and the first anchor region two (3a2), to form a thermal piezoresistive feedback. The filter capacitor (6) is connected to the first anchor region two (3a2) to read the vibration signal.

3. The thermopiezoresistive PT symmetric micro-machined temperature sensor according to claim 2, characterized in that: Under the action of the constant current source (5), Joule heat is generated at the narrow beams of the first resonator (a), namely the first narrow beam one (1a1) and the first narrow beam two (1a2), and thermal expansion is induced. The first narrow beam one (1a1) and the first narrow beam two (1a2) have piezoresistive effects. The thermal expansion generates deformation, causing changes in the resistance of the first narrow beam one (1a1) and the first narrow beam two (1a2), resulting in changes in the Joule heat generated under the action of the constant current source (5), forming a thermopiezoresistive feedback. The first resonator (a) with thermopiezoresistive feedback and the second resonator (b) without feedback together constitute a PT - symmetric system through the coupling effects generated by the first coupling spring beam (4a1) and the second coupling spring beam (4a2). The system is set at the EP point, and the two eigenfrequencies of the system are combined into one. When the temperature changes, the aluminum film (6b) under the substrate (7) of the second resonator (b) has a high coefficient of thermal expansion and deforms, causing the substrate (7) of the second resonator (b) to bend. The positions of the two end anchor regions of the second resonator (b), namely the second anchor region one (3b1) and the second anchor region two (3b2), change, resulting in a change in the stiffness of the second resonator (b). An asymmetric perturbation is introduced into the PT - symmetric system, destroying the original PT symmetry of the system. The eigenfrequency splits from the original single frequency into two, and the frequency splitting amount corresponds to the temperature change. The frequency splitting amount is obtained by filtering the alternating current change caused by the resistance change on the first resonator (a) through the filter capacitor (6) and then performing a Fourier transform.

4. The thermopiezoresistive PT - symmetric micro - mechanical temperature sensor according to claim 3, characterized in that: The system is initially at the PT - symmetric EP point. The temperature change introduces an asymmetric perturbation in the PT - symmetric system, destroying the PT symmetry of the system. The eigenfrequency of the system splits from the original single frequency into two, and the difference between the two frequencies after splitting corresponds to the temperature change. The frequency splitting amount is expressed as: where k is the stiffness of the resonator when undisturbed, and k c is the stiffness of the coupled spring beam, and m is the effective mass of the resonator, all of which are known parameters; δ = Δk / k is the stiffness perturbation of the second resonator caused by temperature, where Δk is the change in the stiffness of the second resonator caused by temperature. The frequency splitting is proportional to the square root of the stiffness change. Therefore, for very small temperature changes, δ << 1, and the frequency splitting has an order-of-magnitude improvement compared to the linear case.

5. The thermopiezoresistive PT - symmetric micro - mechanical temperature sensor according to claim 4, characterized in that: According to the obtained frequency splitting amount, the normalized sensitivity of the system is: Since δ << 1, then 1 / δ >> 1. The sensitivity of the system is much higher than that of a traditional resonant temperature sensor with a linear frequency change amount (the normalized sensitivity is 0.5), and the smaller the temperature change, the more obvious the improvement in sensitivity.

Images