A high-sensitivity micro-distance measurement system and method based on micro-nano mechanical coupling effect

Abstract

The application discloses a high-sensitivity micro-distance measurement system and method based on micro-nano electromechanical coupling effect. The system comprises a micro-nano sensing front end, a closed-loop driving module and a signal processing module. The MEMS resonant unit is physically coupled with a silicon nanowire field effect transistor, the high-gain characteristic of the sub-threshold region of the transistor is utilized to amplify and read the distance micro-disturbance sensed by the MEMS in situ. The closed-loop driving locks the resonant frequency, and the signal processing module removes the common-mode noise through differential operation. The application supports automatic switching of amplitude modulation / frequency modulation detection modes according to the signal-to-noise ratio, and effectively solves the problems of large parasitic interference and low sensitivity of traditional capacitive sensors by combining nonlinear correction and self-checking algorithms, thereby realizing high-signal-to-noise-ratio and high-precision micron-level distance measurement.

Description

Technical Field

[0001] This invention belongs to the field of precision measurement and micro / nanoelectronic systems technology, specifically relating to a high-sensitivity micro-distance measurement system and method based on micro / nano electromechanical coupling effect. Background Technology

[0002] With the rapid development of semiconductor manufacturing, precision micro-assembly, biomedical detection, and atomic force microscopy, the demand for precise measurement of displacement and distance at the micrometer and even nanometer scales is becoming increasingly urgent. In ranging applications at the microscale, the system not only needs to have extremely high spatial resolution, but also requires the sensor to have characteristics such as miniaturization, low power consumption, and ease of integration.

[0003] Existing micro-measurement technologies are mainly divided into two categories: optical detection methods and electrical detection methods. While optical interferometry (such as laser interferometers) offers high measurement accuracy, its systems are bulky, optical path calibration is complex, and costs are high, making it difficult to deploy in confined spaces or achieve large-scale array applications. Traditional electrical detection methods mainly include capacitive MEMS sensors and piezoresistive MEMS sensors. While capacitive sensors have a simple structure, during miniaturization, the sensing capacitance decreases drastically, and the signal is often overwhelmed by parasitic capacitance, leading to a significant drop in the signal-to-noise ratio and susceptibility to electromagnetic interference. Traditional bulk silicon piezoresistive sensors suffer from inherent defects such as low sensitivity and large temperature drift, making them unsuitable for detecting weak signals at the sub-micron level.

[0004] Furthermore, a single detection mode often limits the dynamic range of a sensor, making it difficult to simultaneously achieve both large range and high resolution. Developing a micro-measurement system that can overcome the bottleneck of traditional electrical readout noise while achieving monolithic integration and high-stability measurement has become a pressing technical challenge in the field of micro-nano sensing. Summary of the Invention

[0005] This invention provides a high-sensitivity micro-distance measurement system based on micro-nano electromechanical coupling effect to solve the problems existing in the prior art. The system is characterized by comprising: a micro-nano sensing front end, a closed-loop driving module, and a signal processing module.

[0006] The micro / nano sensing front end includes a physically coupled MEMS resonant unit and a silicon nanowire field-effect transistor readout unit; the MEMS resonant unit is used to sense the distance change of the target under test and generate a disturbance of the vibration state; the silicon nanowire field-effect transistor readout unit serves as a signal conversion interface, using its nanoscale field-effect characteristics to convert the disturbance into an electrical signal.

[0007] The closed-loop drive module is connected to the MEMS resonant unit and is used to provide an excitation signal to maintain the MEMS resonant unit in a preset resonant mode.

[0008] The signal processing module is connected to the silicon nanowire field-effect transistor reading unit to acquire its drain current signal and demodulate the frequency offset, phase difference or amplitude change, and then calculate the measured distance.

[0009] The system amplifies the weak mechanical disturbances of the MEMS resonant unit in situ by utilizing the high transconductance characteristics of silicon nanowire field-effect transistors.

[0010] Furthermore, the closed-loop drive module includes a phase-locked loop circuit and an automatic gain control circuit; the phase-locked loop circuit is used to track the inherent frequency drift of the MEMS resonant unit in real time to ensure that the system is always locked at the resonant point with a high quality factor; the automatic gain control circuit is used to maintain the constant vibration amplitude and prevent nonlinear vibration from introducing measurement errors.

[0011] Furthermore, the micro / nano sensing front end adopts a monolithic integrated architecture. The MEMS resonant unit and the silicon nanowire field-effect transistor readout unit are fabricated on the same CMOS compatible wafer. The two are electrically isolated by a deep trench isolation structure and signal coupling is achieved by a floating gate structure or stress transfer beam to minimize parasitic capacitance interference.

[0012] Furthermore, the silicon nanowire field-effect transistor readout unit includes a silicon nanowire array structure; the silicon nanowire array structure is composed of multiple parallel silicon nanowires, which reduces the shot noise of the device and increases the output drive current through the parallel structure, thereby improving the signal-to-noise ratio of the measurement system.

[0013] Furthermore, the surface of the nanowires in the silicon nanowire field-effect transistor readout unit is covered with a high dielectric constant insulating layer or a specific charge-sensitive modification layer; the charge-sensitive modification layer is used to enhance the modulation effect of the external electric field on the nanowire channel, or to shield the background noise drift caused by changes in ambient humidity.

[0014] Furthermore, the signal processing module integrates a differential cancellation unit; the micro-nano sensing front end is configured as a differential pair structure, including a sensing probe and a fully shielded reference probe; the differential cancellation unit removes common-mode noise and temperature drift signals through subtraction operations, and outputs a clean distance-related signal.

[0015] Furthermore, the system is also equipped with a multi-mode switching module, which is used to switch the working mode according to the range of the distance being measured: when measuring at long distances, the amplitude modulation detection mode is used to measure distance using amplitude attenuation; when measuring at close distances, the system switches to the frequency modulation detection mode to measure distance using frequency offset.

[0016] A high-sensitivity macro measurement method, characterized by comprising the following steps:

[0017] S1 Operating Point Initialization: Start the closed-loop drive module, lock the inherent resonant frequency of the MEMS resonant unit, and adjust the back gate voltage of the silicon nanowire field-effect transistor readout unit to make it operate in the subthreshold swing region.

[0018] S2 Coupling of the Test Field: The target under test is moved into the sensing field of the micro-nano sensing front end. The change in the distance between the target under test and the MEMS resonant unit changes the equivalent parasitic parameters of the system.

[0019] S3 Electromechanical Modulation: The vibration frequency or phase of the MEMS resonant unit shifts with the change of parasitic parameters. This shift directly modulates the conductive channel of the silicon nanowire field-effect transistor readout unit through electric field or stress.

[0020] S4 Signal Readout and Decomposition: The signal processing module monitors the source and drain current changes of the silicon nanowire field-effect transistor readout unit in real time, extracts the AC component frequency information, and calculates the micrometer-level distance value based on the preset frequency distance calibration model.

[0021] Furthermore, in step S4, the method also includes a nonlinear correction step: using the pre-stored transfer characteristic curve of the silicon nanowire field-effect transistor, the acquired nonlinear current signal is linearized and compensated by a digital algorithm to eliminate the sensitivity difference of the nanowire field-effect transistor under different bias voltages.

[0022] Furthermore, the method also includes a self-test and calibration step: before measurement, a standard pulse signal is applied to the side gate of the silicon nanowire field-effect transistor readout unit to simulate the electric field disturbance caused by the change in unit distance, and the coefficients of the calibration model are automatically calibrated according to the system output response to compensate for long-term drift caused by device aging or environmental changes.

[0023] The present invention has the following beneficial effects:

[0024] This invention constructs a measurement system comprising a micro / nano sensing front-end, a closed-loop driving module, and a signal processing module. Utilizing a MEMS resonant unit as a frequency reference and employing a silicon nanowire field-effect transistor (SiNW-FET) as a high-sensitivity readout interface, it significantly improves the signal-to-noise ratio and accuracy of micro-distance measurements. Specifically, this invention leverages the high transconductance characteristics and nanoscale surface effects of SiNW-FETs to amplify in-situ the weak mechanical disturbances (frequency or phase shifts) generated by distance changes in the MEMS resonant unit. This effectively solves the problems of large parasitic capacitance interference and difficulty in extracting weak signals in traditional capacitive detection, achieving detection sensitivity exceeding that of traditional bulk silicon devices.

[0025] This invention integrates a phase-locked loop (PLL) and an automatic gain control (AGC) circuit into a closed-loop drive module, enabling real-time tracking and locking of the resonator's natural frequency, ensuring the system always operates at a high quality factor. This closed-loop control mechanism, combined with the differential cancellation unit in the signal processing module, not only suppresses measurement errors caused by nonlinear vibrations but also effectively removes the effects of common-mode noise and ambient temperature drift through differential operations, thus overcoming the shortcomings of traditional piezoresistive sensors, such as large temperature drift and poor long-term stability.

[0026] This invention employs a monolithic integrated architecture based on CMOS-compatible technology, achieving homogeneous integration and electrical isolation between the MEMS structure and SiNW-FET devices. This significantly reduces system size while ensuring device consistency and scalability. Combined with the system's multi-mode switching capability, this invention can flexibly switch between amplitude modulation and frequency modulation modes based on the measured distance, resolving the contradiction between range and resolution that is difficult to balance in a single detection mode. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the system architecture of the present invention;

[0028] Figure 2 Flowchart for integrated optical ranging method. Detailed Implementation

[0029] The invention will now be further described with reference to the accompanying drawings.

[0030] Example 1:

[0031] This embodiment provides a high-sensitivity micro-distance measurement system based on the micro-nano electromechanical coupling effect. For example... Figure 1 As shown, the system is mainly composed of three core parts in its overall architecture: a micro-nano sensing front-end, a closed-loop driving module, and a signal processing module.

[0032] The micro / nano sensing front-end is an integrated chip fabricated on a silicon-on-insulator (SOI) wafer. However, in its physical implementation, this front-end internally contains a physically coupled MEMS resonant unit and a silicon nanowire field-effect transistor (SFET) readout unit. The MEMS resonant unit is designed as a double-ended fixed-beam structure, with a beam length of 20μm to 50μm, a width of 2μm to 5μm, and a thickness of 200nm. This resonant unit is released via deep reactive ion etching (DRIE) and suspended above the substrate, with an inherent resonant frequency designed between 10MHz and 50MHz. To achieve high-sensitivity readout, the SFET readout unit is integrated into the stress concentration region at the root of the resonant beam. This readout unit is not a single nanowire but rather an array structure composed of 20 parallel silicon nanowires, each with a linewidth of 30nm to 50nm. This array design increases the effective cross-sectional area of ​​the conductive channels, boosting the device's output drive current to the microampere level, while simultaneously reducing shot noise by approximately 4.5 times using statistical averaging principles.

[0033] For the micro-interface processing of the device, a 5nm thick hafnium oxide (HfO2) high-dielectric-constant insulating layer is deposited on the surface of the silicon nanowire using atomic layer deposition. Above this insulating layer, a self-assembled monolayer with amino or carboxyl group terminations is further modified. This modified layer enhances the control of the external electric field over the charge carriers inside the nanowire and acts as a passivation layer to isolate environmental moisture and prevent fluctuations in surface state density with humidity. To avoid interference from the high-voltage drive signal on the weak readout signal, a 1μm wide deep trench isolation structure is set on the chip layout between the MEMS resonant unit and the readout unit. The trench is filled with silicon dioxide insulating dielectric, achieving complete electrical isolation between the two.

[0034] like Figure 1 As shown, the closed-loop drive module is connected to the MEMS resonant unit at the micro / nano sensing front end, forming a self-excited oscillation circuit. This module integrates a phase-locked loop (PLL) circuit, whose phase detector input is connected to the output of the readout unit, and its output is connected to a voltage-controlled oscillator (VCO). The loop bandwidth of the PLL circuit is set to 1 kHz to quickly track the drift of the resonant frequency. In addition, the module also integrates an automatic gain control (AGC) circuit, which sets a reference voltage threshold. When the voltage signal corresponding to the detected vibration amplitude exceeds this threshold, the AGC circuit automatically reduces the excitation voltage; conversely, it increases it, thereby stabilizing the amplitude of the MEMS resonant unit within the range allowed by linear Hooke's law.

[0035] The signal processing module is connected to the readout unit of the micro / nano sensing front end. To further improve measurement accuracy, the micro / nano sensing front end is configured with a differential pair structure in its chip layout: it includes an externally exposed sensing probe and a reference probe encapsulated in a metal shielding layer. The differential cancellation unit (such as an instrumentation amplifier) ​​integrated within the signal processing module performs a subtraction operation on the signals from the two probes. Let the output signal of the sensing probe be... The reference probe output signal is The output after difference operation This eliminates common-mode temperature drift and power supply noise.

[0036] Example 2:

[0037] This embodiment provides an operation method for performing high-sensitivity macro measurements using the above-described system. For example... Figure 2 As shown, this method includes initialization, coupling modulation, multimode switching, and signal decoding processes.

[0038] Step S1 is executed to initialize the operating point. After the system is powered on, the closed-loop drive module performs a frequency sweep excitation on the MEMS resonant unit to lock its natural resonant frequency. Simultaneously, the back gate voltage of the silicon nanowire field-effect transistor is adjusted. This positions its operating point at the center of the subthreshold swing region. In this region, the transistor's source-drain current... With gate voltage Satisfies the exponential relationship:

[0039]

[0040] in The amount of electron charge. Boltzmann's constant, Absolute temperature This is the subthreshold swing factor. This exponential characteristic ensures that even small potential disturbances can cause significant current changes.

[0041] Perform step S2, coupling the target field, and step S3, electromechanical modulation. When the target is moved into the sensing field, the distance between the target surface and the MEMS resonant unit... Changes will cause equivalent parasitic capacitance The change in frequency leads to a shift in the resonant frequency. The relationship between frequency shift and distance approximately satisfies:

[0042]

[0043] in For initial stiffness, This represents the change in equivalent stiffness caused by the electrostatic force gradient.

[0044] During the measurement process, the system executes a multi-mode switching strategy. When the system detects that the signal-to-noise ratio (SNR) is lower than a preset threshold (e.g., 10 dB), it determines the distance to be far (>50 μm) and activates the amplitude modulation detection mode, using the amplitude attenuation caused by edge capacitance effect to invert the distance. When the SNR is higher than the threshold, it determines the distance to be short (<10 μm) and the system automatically switches to the frequency modulation detection mode.

[0045] Step S4 involves signal readout and processing. The signal processing module acquires the drain current of the silicon nanowire transistor in real time, extracts the fundamental frequency component using Fast Fourier Transform (FFT), and calculates the frequency offset. To eliminate the nonlinearity error inherent in the device, a nonlinear correction stage is introduced in the signal processing. The transfer characteristic curve of the silicon nanowire is pre-measured. The data is stored in the processor's lookup table. The processor uses a polynomial fitting algorithm to process the acquired nonlinear current signal. The physical quantity is mapped back to linear, compensating for the sensitivity differences under different bias voltages.

[0046] Furthermore, to address the drift issue after long-term use, the method also includes self-test and calibration steps. Before each measurement, an amplitude of [value missing] is applied through the side gate. A standard pulse signal is used to simulate the electric field generated by a change in distance per unit distance. The system measures the output response at this time. and compared with the factory standard value Compare and calculate calibration coefficients In subsequent distance calculations, all measurements are multiplied by this coefficient. This automatically compensates for systematic errors caused by device aging or slight environmental changes.

[0047] The present invention has been described in detail above. However, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, any modifications or improvements that do not depart from the spirit of the present invention are within the scope of protection of the present invention.

Claims

1. A high-sensitivity micro-distance measurement system based on micro-nano electromechanical coupling effect, characterized in that, include: Micro-nano sensing front-end, closed-loop drive module and signal processing module; The micro / nano sensing front end includes a physically coupled MEMS resonant unit and a silicon nanowire field-effect transistor readout unit; the MEMS resonant unit is used to sense the distance change of the target under test and generate a disturbance of the vibration state; the silicon nanowire field-effect transistor readout unit serves as a signal conversion interface, using its nanoscale field-effect characteristics to convert the disturbance into an electrical signal. The closed-loop drive module is connected to the MEMS resonant unit and is used to provide an excitation signal to maintain the MEMS resonant unit in a preset resonant mode. The signal processing module is connected to the silicon nanowire field-effect transistor reading unit to acquire its drain current signal and demodulate the frequency offset, phase difference or amplitude change, and then calculate the measured distance. The system amplifies the weak mechanical disturbances of the MEMS resonant unit in situ by utilizing the high transconductance characteristics of silicon nanowire field-effect transistors. The micro / nano sensing front end adopts a monolithic integrated architecture. The MEMS resonant unit and the silicon nanowire field-effect transistor readout unit are fabricated on the same CMOS compatible wafer. The two are electrically isolated by a deep trench isolation structure and signal coupling is achieved by a floating gate structure or stress transfer beam to minimize parasitic capacitance interference.

2. The system according to claim 1, characterized in that, The closed-loop drive module includes a phase-locked loop circuit and an automatic gain control circuit. The phase-locked loop circuit is used to track the inherent frequency drift of the MEMS resonant unit in real time to ensure that the system is always locked at the resonant point with a high quality factor. The automatic gain control circuit is used to maintain the constant vibration amplitude and prevent nonlinear vibration from introducing measurement errors.

3. The system according to claim 1, characterized in that, The silicon nanowire field-effect transistor readout unit includes a silicon nanowire array structure; the silicon nanowire array structure is composed of multiple parallel silicon nanowires, and the parallel structure reduces the shot noise of the device and increases the output drive current, thereby improving the signal-to-noise ratio of the measurement system.

4. The system according to claim 1, characterized in that, The surface of the silicon nanowire field-effect transistor readout unit is covered with a high dielectric constant insulating layer or a specific charge-sensitive modification layer. The charge-sensitive modification layer is used to enhance the modulation effect of the external electric field on the nanowire channel, or to shield the background noise drift caused by changes in ambient humidity.

5. The system according to claim 1, characterized in that, The signal processing module integrates a differential cancellation unit; the micro-nano sensing front end is configured as a differential pair structure, including a sensing probe and a fully shielded reference probe; the differential cancellation unit removes common-mode noise and temperature drift signals through subtraction operations, and outputs a clean distance-related signal.

6. The system according to claim 1, characterized in that, The system is also equipped with a multi-mode switching module, which is used to switch the working mode according to the range of the distance being measured: when measuring at long distances, the amplitude modulation detection mode is used to measure distance using amplitude attenuation; when measuring at close distances, the system switches to the frequency modulation detection mode to measure distance using frequency offset.

7. A high-sensitivity macro measurement method using the system described in any one of claims 1 to 6, characterized in that, Includes the following steps: S1 Operating Point Initialization: Start the closed-loop drive module, lock the inherent resonant frequency of the MEMS resonant unit, and adjust the back gate voltage of the silicon nanowire field-effect transistor readout unit to make it operate in the subthreshold swing region. S2 Coupling of the Test Field: The target under test is moved into the sensing field of the micro-nano sensing front end. The change in the distance between the target under test and the MEMS resonant unit changes the equivalent parasitic parameters of the system. S3 Electromechanical Modulation: The vibration frequency or phase of the MEMS resonant unit shifts with the change of parasitic parameters. This shift directly modulates the conductive channel of the silicon nanowire field-effect transistor readout unit through electric field or stress. S4 Signal Readout and Decomposition: The signal processing module monitors the source and drain current changes of the silicon nanowire field-effect transistor readout unit in real time, extracts the AC component frequency information, and calculates the micrometer-level distance value based on the preset frequency distance calibration model.

8. The method according to claim 7, characterized in that, In step S4, the method further includes a nonlinear correction step: using the pre-stored transfer characteristic curve of silicon nanowire field-effect transistor, the acquired nonlinear current signal is linearized and compensated by a digital algorithm to eliminate the sensitivity difference of nanowire field-effect transistor under different bias voltages.

9. The method according to claim 7, characterized in that, The method also includes a self-test and calibration step: before measurement, a standard pulse signal is applied to the side gate of the silicon nanowire field-effect transistor readout unit to simulate the electric field disturbance caused by the change in unit distance, and the coefficients of the calibration model are automatically calibrated according to the system output response to compensate for long-term drift caused by device aging or environmental changes.

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