A MEMS force sensor based on comb-tooth capacitor structure

Abstract

The present application provides a MEMS force sensor based on a comb-tooth capacitor structure, which belongs to the field of micro-electromechanical system processing technology, wherein a first comb-tooth capacitor structure is connected to a second fixed anchor point, and a second comb-tooth capacitor structure is symmetrically arranged on the upper, lower, left, and right sides of the middle main beam; the comb teeth of the first comb-tooth capacitor structure and the second comb-tooth capacitor structure are nested to form a differential comb-tooth capacitor array; the first fixed anchor point is used to apply a bias voltage to linearize the electrostatic force between the first comb-tooth capacitor structure and the second comb-tooth capacitor structure; the second fixed anchor point is used to apply a driving AC voltage and a high-frequency carrier; the driving AC voltage is used to make the needle tip vibrate at its own resonant frequency; the high-frequency carrier is used to monitor the distance between the first comb-tooth capacitor structure and the second comb-tooth capacitor structure when a force is applied between the needle tip and the sample, so as to obtain the interaction force between the needle tip and the sample. The MEMS force sensor provided by the present application can detect tiny force changes with high precision and high sensitivity.

Description

Technical Field

[0001] The present application belongs to the field of micro-electromechanical system processing technology, and more specifically, relates to a MEMS force sensor based on a comb-tooth capacitor structure. Background Art

[0002] In the field of microscale scientific research, high-precision detection of material morphology and physical properties is an extremely challenging task. A common approach is to convert the information to be measured into the interaction of forces between the probe and the material. The main challenges faced can be divided into two aspects: one is the interference of background noise, and the other is the weakness of the response signal. At present, atomic force microscopy (AFM) is an important information for material surface testing. It usually relies on photodetectors to detect the reflected light signal of the cantilever beam to obtain material surface information. This process requires multiple components, and the integrated assembly technology is complex, the operation process is cumbersome, and it is not convenient to integrate with other micro-manipulation tools, which limits its applicability in complex experimental environments. MEMS force sensors (Micro Electro-Mechanical System) based on silicon-based processing technology have the characteristics of high efficiency, low cost and high integration, which facilitates the large-scale integrated production of detection structures and maintains their high performance. However, in the field of micro-nanoscale force detection, force sensors based on capacitive displacement detection are often difficult to achieve high-sensitivity and high-precision integrated force sensing structures due to structural limitations. Summary of the Invention

[0003] In response to the defects of the existing technology, the purpose of this application is to provide a MEMS force sensor based on a comb-tooth capacitor structure, aiming to solve the problem in the existing force detection field that force sensors based on capacitive displacement detection are often difficult to achieve high-sensitivity and high-precision integrated force sensing structure due to structural limitations.

[0004] To achieve the above objectives, in a first aspect, the present application provides a MEMS force sensor based on a comb-tooth capacitor structure, comprising: an elastic support beam, a first fixed anchor point, a second fixed anchor point, a first comb-tooth capacitor structure, a second comb-tooth capacitor structure, an intermediate main beam, and a needle tip;

[0005] The elastic support beam, the first comb-tooth capacitor structure, the second comb-tooth capacitor structure, and the middle main beam are all suspended; the first comb-tooth capacitor structure is connected to the second fixed anchor point, and the first comb-tooth capacitor structure is located between the second fixed anchor point and the middle main beam; the second comb-tooth capacitor structure is symmetrically arranged above, below, left, and right on the middle main beam; the comb teeth of the first comb-tooth capacitor structure and the second comb-tooth capacitor structure are nested to form a differential comb-tooth capacitor array; the elastic support beam is located on the upper and lower sides of the differential comb-tooth capacitor array and is symmetrical about the middle main beam, and the elastic support beam is connected to the first fixed anchor point; the needle tip is located at the bottom end of the middle main beam;

[0006] The first fixed anchor point is used to apply a bias voltage to linearize the electrostatic force between the first comb-tooth capacitor structure and the second comb-tooth capacitor structure; the second fixed anchor point is used to apply a driving AC voltage and a high-frequency carrier; wherein the driving AC voltage is used to make the needle tip vibrate at its own resonant frequency; the high-frequency carrier is used to monitor the distance between the first comb-tooth capacitor structure and the second comb-tooth capacitor structure based on the linearization of the electrostatic force between the first comb-tooth capacitor structure and the second comb-tooth capacitor structure and the vibration of the needle tip at its own resonant frequency when a force is applied between the needle tip and the sample, so as to obtain the interaction force between the needle tip and the sample.

[0007] Further preferably, the middle main beam adopts a hole-digging structure to reduce mass and enhance dynamic response;

[0008] Further preferably, the elastic support beam is a serpentine support beam;

[0009] Further preferably, the MEMS force sensor is prepared using a top device layer of an insulating substrate type silicon wafer, and the first fixed anchor point and the second fixed anchor point are connected to the base layer silicon through an intermediate insulating silicon oxide layer.

[0010] Further preferably, an etching technique is used to prepare a protruding needle tip at the lower end of the middle main beam, or the needle tip structure is placed on the protruding portion of the middle main beam by bonding.

[0011] Further preferably, the needle tip is a gold-plated ball.

[0012] In a second aspect, based on the above-mentioned MEMS force sensor based on the comb-tooth capacitor structure, the present application provides a corresponding force sensing detection method, comprising the following steps:

[0013] Step 1: Apply a bias voltage to the first fixed anchor point to linearize the electrostatic force between the first comb-tooth capacitor structure and the second comb-tooth capacitor structure; simultaneously apply a high-frequency carrier and a driving AC voltage to the second fixed anchor point, use the driving AC voltage to vibrate the MEMS force sensor at its own resonant frequency, and use the high-frequency carrier to monitor the distance between the first comb-tooth capacitor structure and the second comb-tooth capacitor structure;

[0014] Step 2: Obtain the interaction force between the needle tip and the sample based on the distance between the first comb-teeth capacitance structure and the second comb-teeth capacitance structure measured when the needle tip and the sample interact.

[0015] In general, the above technical solutions conceived by this application have the following beneficial effects compared with the existing technologies:

[0016] The present application provides a MEMS force sensor based on a comb-tooth capacitor structure, in which when the needle tip is subjected to the force to be measured between the samples, the spacing between the capacitor plates in the first comb-tooth capacitor array and the second comb-tooth capacitor array will change. The variable-spacing comb-tooth capacitor structure, by arranging different plate spacings, plate facing areas, and comb tooth pairs, can achieve high-sensitivity measurement of tiny forces according to the change in the spacing between the plates of the comb-tooth capacitor array. Compared with the traditional variable-area structure, this design improves sensitivity and reduces the number of plate pairs required under the same measurement requirements. By arranging the four-part first comb-tooth capacitor structure and the second comb-tooth capacitor structure symmetrically, the present application not only improves the detection sensitivity, but also reduces the number of anchor points required to apply voltage, simplifies the force sensor structure, and the hollowing out of the middle main beam further reduces the inspection mass and improves the response speed of the sensor.

[0017] The present application provides a voltage multiplexing method, which enables the driving AC voltage and high-frequency carrier of the force sensor to be multiplexed on the same comb-tooth capacitor structure. This not only reduces the required number of comb teeth, but also utilizes the resonance amplification effect while maintaining a simple structure. The present application can achieve high-precision detection of tiny force changes and expand the application range of MEMS force sensors.

[0018] The present application provides a MEMS force sensor based on a comb-tooth capacitor structure. The force sensor is manufactured using a standard SOI process and achieves a high-sensitivity response in the sensitive axis direction along the middle main beam through a carefully designed elastic support beam and comb-tooth capacitor structure. Specifically, the present application adopts structures such as serpentine support beams, which have high sensitivity to forces in the sensitive axis direction, thereby improving the overall performance of the sensor.

[0019] The force sensor tip design of the present application is not limited to traditional ion etching technology, but can also be achieved by sticking a spherical tip on the protruding part of the middle main beam. This method allows the shape and size of the tip to be precisely controlled according to specific application requirements, further improving the performance and applicability of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 1 is a schematic diagram of a three-dimensional configuration of a MEMS force sensor based on a comb-tooth capacitor structure provided in an embodiment of the present application;

[0021] Figure 2 Schematic diagram of a planar configuration of a MEMS force sensor based on a comb-tooth capacitor structure provided in an embodiment of the present application;

[0022] Figure 3 is a schematic diagram of an elastic support beam provided in an embodiment of the present application;

[0023] Figure 4This is a schematic diagram of the middle main beam and movable comb teeth provided in an embodiment of the present application;

[0024] Figure 5 Schematic diagram of the overall structure of the comb capacitor structure provided in an embodiment of the present application;

[0025] Figure 6 is a partial schematic diagram of a comb-tooth capacitor structure provided in an embodiment of the present application;

[0026] In all the drawings, the same figure marks are used to represent the same elements or structures, where: 1 is a serpentine support beam; 2 is a first fixed anchor point; 3 is a second fixed anchor point; 32 is a first comb-tooth capacitor structure (fixed comb-tooth capacitor); 41 is a hole structure; 42 is a second comb-tooth capacitor structure (movable comb-tooth capacitor); 4 is an intermediate main beam; 5 is a gold-plated ball; 6 is an intermediate insulating silicon oxide layer; and 7 is a base layer of silicon. DETAILED DESCRIPTION

[0027] The embodiments of the present application are described below in conjunction with the drawings in the embodiments of the present application.

[0028] like Figure 1 and Figure 2 As shown, the present application provides a high-precision MEMS force sensor based on a comb-tooth capacitor structure, comprising: a serpentine support beam 1, 2n first fixed anchor points 2, 4n second fixed anchor points 3, a first comb-tooth capacitor structure 32, a second comb-tooth capacitor structure 42, an intermediate main beam 4, and a protruding needle tip; in this embodiment, the needle tip is a gold-plated ball 5; except for the first fixed anchor point 2 and the second fixed anchor point 3, the other structures are suspended; there is a protruding needle tip at the front end of the intermediate main beam, and when the force sensor is subjected to the force to be measured between the needle tip and the sample, the intermediate movable part can be moved. (i.e., the middle main beam 4, the serpentine support beam 1 and the second comb-tooth capacitor structure 42) generate movement, thereby causing the capacitance between the electrodes of the second comb-tooth capacitor structure 42 and the first comb-tooth capacitor structure 32 to change, thereby achieving high-sensitivity response and accurate capacitance change detection under the action of a small force; wherein, n is a positive integer; the serpentine support beam 1, 2n first fixed anchor points 2, 4n second fixed anchor points 3, the first comb-tooth capacitor structure 32, the second comb-tooth capacitor structure 42, the middle main beam 4 and the protruding needle tip are all conductive by surface aluminum plating.

[0029] Figure 3 The serpentine support beam 1 and its first fixed anchor point 2, Figure 4 The middle main beam 4 and the second comb-teeth capacitor structure 42 (movable comb teeth) are Figure 5 and Figure 6It is the comb-tooth capacitor structure of the force sensor; four or more second comb-tooth capacitor structures 42 are arranged on the middle main beam, forming a symmetrical layout in both vertical and horizontal directions, and cooperate with the first comb-tooth capacitor structure 32 (fixed comb teeth) connected to the anchor point to form a differential comb-tooth capacitor array to improve the sensitivity and accuracy of force detection. Among them, in the initial state, d1 = d2, d3 = d4. 1、 d2 is the distance between the first comb-teeth capacitor structure 32 and the second comb-teeth capacitor structure 42 which is closer to the first comb-teeth capacitor structure 32; 3、 d4 is the distance between the first comb-teeth capacitor structure 32 and the second comb-teeth capacitor structure 42 which is farther away; when the force sensor vibrates, d 1、 d4 has the same spacing variation, d 2、 d3 has the same spacing changes, but with d 1、 The spacing of d4 changes in the opposite direction. 1、 If d4 decreases, then d 2、 d3 increases; if d 1、 If d4 increases, then d 2、 d3 decreases.

[0030] Figure 4 The force sensor comprises a central main beam 41 and a second comb-tooth capacitor structure 42. The central main beam 4 utilizes a hollow structure 41 to reduce the mass of the force sensor and optimize its dynamic response. The front end of the force sensor is equipped with a structure such as a serpentine support beam 1, which provides low stiffness along the sensitive axis and high stiffness in other directions. In this force sensor, the sensitive axis strictly follows the geometric centerline of the central main beam, ensuring that force detection propagates longitudinally along the beam, achieving highly sensitive detection of forces in specific directions.

[0031] Further preferably, the driving voltage and detection voltage of the force sensor are multiplexed on the same comb-tooth capacitor structure; specifically, by applying a high-frequency carrier and a driving AC voltage to the second fixed anchor point 3, and applying a bias voltage to the first fixed anchor point 2, wherein the high-frequency carrier is used to detect the distance between the first comb-tooth capacitor structure and the second comb-tooth capacitor structure; the bias voltage is used to linearize the electrostatic force between the first comb-tooth capacitor structure and the second comb-tooth capacitor structure; and the driving AC voltage is used to make the force sensor vibrate at its own resonant frequency.

[0032] It should be pointed out here that since the frequency of the high-frequency carrier is much higher than the frequency of the driving AC voltage, in order to achieve frequency separation during detection, the high-frequency carrier and the driving AC voltage can be applied to the second fixed anchor point 3 at the same time, thereby achieving multiplexing. Compared with the commonly used technology, the high-frequency carrier and the driving AC voltage require different anchor points to be applied, and the number of anchor points set is reduced, thereby reducing the required number of comb teeth. Through this voltage multiplexing method, the force sensor achieves high-sensitivity detection of force changes while maintaining a simple structure.

[0033] The driving AC voltage causes the force sensor to vibrate at its own resonant frequency. That is, the resonant state of the force sensor amplifies the amplitude change of the force sensor, thereby significantly enhancing the detection sensitivity to tiny force changes.

[0034] The MEMS force sensor is made of a silicon on insulator (SOI) wafer. The entire force sensor is made of the top device layer. Except for the first fixed anchor point 2 and the second fixed anchor point 3 connected to the base silicon layer 7 through the intermediate insulating silicon oxide layer 6, the rest of the force sensor is suspended to improve the sensitivity and response speed of the sensor.

[0035] Further preferably, the protruding needle tip of the middle main beam 41 of the force sensor can be formed into an integrated structure by dry or wet etching technology, or other structures can be transferred to the protruding part of the main beam by bonding or other methods to be used as the needle tip.

[0036] The working principle of this application is as follows: Figure 5 As shown, when the needle tip is subjected to the force to be measured between it and the sample, the spacings d1, d2, d3, and d4 between the capacitor plates in the first and second comb-tooth capacitor arrays change, thereby changing the total capacitance of the comb-tooth capacitor structure. The spacings of the two comb-tooth arrays at the top of the force sensor change at the same rate, while the spacing of the comb-tooth array at the bottom also changes at the same rate, but in the opposite direction to the spacing at the top. By arranging different plate spacings, plate facing areas, and the number of comb teeth, the force sensor achieves highly sensitive measurement of small forces based on the changes in the spacing between the plates in the comb-tooth arrays.

[0037] On the other hand, based on the high-precision MEMS force sensor with the comb-tooth capacitor structure provided above, the present application provides a corresponding force sensing detection method, which specifically includes the following steps:

[0038] Step 1: First, a DC bias voltage is applied to the first fixed anchor point 2 through an electrical connection. This voltage is transmitted through the serpentine support beam 1 connected to the first fixed anchor point 2 to the intermediate main beam 4, the second comb-tooth capacitor structure 42, and the protruding needle tip 5, linearizing the electrostatic force between the differential comb-tooth capacitor structures. Simultaneously, a high-frequency carrier voltage and a driving AC voltage are applied to the second fixed anchor point 3. This voltage is transmitted to the first comb-tooth capacitor structure 32, causing the force sensor to vibrate at its resonant frequency. In addition, the applied high-frequency carrier voltage is used to monitor the amplitude change of the force sensor.

[0039] Step 2: Connect the applied high-frequency carrier voltage to the modem and conventional capacitance detection circuit. When an interaction force exists between the force sensor tip and the sample, the vibration amplitude of the force sensor changes. This change causes the spacing between the first and second comb-tooth capacitor structures to change, thereby changing the total capacitance between the two structures. Based on this capacitance change, the change in the spacing between the comb-tooth capacitor structures is calculated, thereby accurately determining the interaction force between the force sensor and the sample.

[0040] In summary, compared with the prior art, this application has the following advantages:

[0041] This application utilizes a variable-pitch comb-tooth capacitor structure. Compared to traditional variable-area structures, this design improves sensitivity and reduces the number of electrode pairs required for the same measurement requirements. By arranging the four-part capacitor structure symmetrically, this application not only improves detection sensitivity but also reduces the number of anchor points required for voltage application, simplifying the force sensor structure. The hollowing out of the central main beam further reduces the inspection mass and improves the sensor's response speed.

[0042] This application provides a voltage multiplexing method that multiplexes the drive and detection voltages of a force sensor on the same comb-tooth capacitor structure. This design not only reduces the number of comb teeth required but also maintains a simple structure. By leveraging the resonance amplification effect, this application enables high-precision detection of minute force changes, expanding the application range of MEMS force sensors.

[0043] This application provides a high-precision MEMS force sensor based on a comb-tooth capacitor structure. This force sensor is fabricated using a standard SOI process. Through the carefully designed elastic support beam and comb-tooth capacitor structure, it achieves a highly sensitive response along the sensitive axis of the central main beam. Specifically, this application utilizes structures such as serpentine support beams, which are highly sensitive to forces acting along the sensitive axis, thereby improving the overall performance of the sensor.

[0044] The force sensor tip design of the present application is not limited to traditional ion etching technology, but can also be achieved by sticking a spherical tip on the protruding part of the middle main beam. This method allows the shape and size of the tip to be precisely controlled according to specific application requirements, further improving the performance and applicability of the sensor.

[0045] In summary, this application significantly improves the detection sensitivity of MEMS force sensors through a simple structural design, based on existing process achievable results. The sensor's performance can be optimized by adjusting the size of the folded beam, the number of folds, and the number of capacitor plate pairs, giving it a wide range of application prospects.

[0046] It should be understood that expressions such as "include" and "may include" used in this application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In this application, terms such as "include" and / or "have" may be interpreted as indicating specific characteristics, numbers, operations, constituent elements, components, or combinations thereof, but may not be interpreted as excluding the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0047] In addition, in this application, the expression "and / or" includes any and all combinations of the associated listed words. For example, the expression "A and / or B" may include A, may include B, or may include both A and B.

[0048] In the description of the embodiments of the present application, it should be noted that, unless otherwise clearly specified and limited, the term "connection" should be understood in a broad sense. For example, "connection" can be a detachable connection or a non-detachable connection; it can be a direct connection or an indirect connection through an intermediate medium. Among them, "fixed connection" means that the two are connected to each other and the relative position relationship after the connection remains unchanged. "Rotational connection" means that the two are connected to each other and can rotate relative to each other after the connection. "Sliding connection" means that the two are connected to each other and can slide relative to each other after the connection. The directional terms mentioned in the embodiments of the present application, such as "top", "bottom", "inside", "outside", "left", "right", etc., are only reference to the directions of the accompanying drawings. Therefore, the directional terms used are for better and clearer explanation and understanding of the embodiments of the present application, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0049] In addition, in the embodiments of the present application, the mathematical concepts mentioned include symmetry, equality, parallelism, and perpendicularity. These limitations are all for the current state of the art, rather than being absolutely strict definitions in a mathematical sense. A small amount of deviation is allowed, and it is possible to be approximately symmetric, approximately equal, approximately parallel, or approximately perpendicular. For example, A and B are parallel, which means that A and B are parallel or approximately parallel, and the angle between A and B can be between 0 and 10 degrees. A and B are perpendicular, which means that A and B are perpendicular or approximately perpendicular, and the angle between A and B can be between 80 and 100 degrees.

[0050] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A MEMS force sensor based on a comb-tooth capacitor structure, characterized in that: include: An elastic support beam, a first fixed anchor point, a second fixed anchor point, a first comb-tooth capacitor structure, a second comb-tooth capacitor structure, an intermediate main beam, and a needle tip; The elastic support beam, the first comb-tooth capacitor structure, the second comb-tooth capacitor structure, and the middle main beam are all suspended; the first comb-tooth capacitor structure is connected to the second fixed anchor point, and the first comb-tooth capacitor structure is located between the second fixed anchor point and the middle main beam; the second comb-tooth capacitor structure is symmetrically arranged above, below, left, and right on the middle main beam; the comb teeth of the first comb-tooth capacitor structure and the second comb-tooth capacitor structure are nested to form a differential comb-tooth capacitor array; the elastic support beam is located on both sides of the differential comb-tooth capacitor array and is symmetrical about the middle main beam, and the elastic support beam is connected to the first fixed anchor point; the needle tip is located at the bottom end of the middle main beam; The first fixed anchor point is used to apply a bias voltage to linearize the electrostatic force between the first comb-tooth capacitor structure and the second comb-tooth capacitor structure; the second fixed anchor point is used to apply a driving AC voltage and a high-frequency carrier; wherein the driving AC voltage is used to make the needle tip vibrate at its own resonant frequency; the high-frequency carrier is used to monitor the distance between the first comb-tooth capacitor structure and the second comb-tooth capacitor structure based on the linearization of the electrostatic force between the first comb-tooth capacitor structure and the second comb-tooth capacitor structure and the vibration of the needle tip at its own resonant frequency when a force is applied between the needle tip and the sample, so as to obtain the interaction force between the needle tip and the sample.

2. The MEMS force sensor according to claim 1, wherein: The middle main beam adopts a hole-digging structure.

3. The MEMS force sensor according to claim 1 or 2, characterized in that: The elastic support beam is a serpentine support beam.

4. The MEMS force sensor according to claim 1, wherein: The MEMS force sensor is prepared by using the top device layer of an insulating substrate type silicon wafer, and the first fixed anchor point and the second fixed anchor point are connected to the base layer silicon through an intermediate insulating silicon oxide layer.

5. The MEMS force sensor according to claim 1 or claim 4, characterized in that: The needle tip is a protruding needle tip prepared at the lower end of the middle main beam by using an etching technology, or the needle tip is placed on the protruding part of the middle main beam by bonding.

6. The MEMS force sensor according to claim 5, wherein: The needle tip is a gold-plated ball.

7. A force sensing detection method based on the MEMS force sensor according to any one of claims 1 to 6, characterized in that: The following steps are involved: Step 1: applying a bias voltage to the first fixed anchor point to linearize the electrostatic force between the first comb-tooth capacitor structure and the second comb-tooth capacitor structure; A high-frequency carrier and a driving AC voltage are simultaneously applied to the second fixed anchor point, the driving AC voltage is used to vibrate the MEMS force sensor at its own resonant frequency, and the high-frequency carrier is used to monitor the distance between the first comb-tooth capacitor structure and the second comb-tooth capacitor structure; Step 2: Obtain the interaction force between the needle tip and the sample based on the distance between the first comb-tooth capacitance structure and the second comb-tooth capacitance structure measured when the needle tip is used for interaction between the sample.

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