A high-sensitivity array tactile sensor with needle-like structure

Abstract

The application discloses a high-sensitivity array tactile sensor with a needle-shaped structure. The application comprises a metal electrode, a sensitive unit, a silicon beam, a piezoresistance and a chip frame; the application adopts a mass block with a supporting structure to connect the top of a contactor and a micro beam structure to achieve the effect of detecting and separating vertical force and horizontal force. The micro beam structure changes the original torsional deformation, and through a straight pulling and straight pressing mode, most of the stress and strain are concentrated on the beam, which contributes to the detection of the piezoresistance. Compared with the traditional piezoresistance sensor, the sensitivity of the sensor is greatly improved. The piezoresistance principle is adopted to measure the friction, pressure and other tactile forces, and the beam structure is adopted for the measurement of the normal force and the shear force. Under the same load, compared with the capacitive sensor, the chip miniaturization is realized without sacrificing the sensitivity.

Description

Technical Field

[0001] This invention relates to the field of tactile sensor technology, and more particularly to a tactile sensing structure with high sensitivity in the "direct pull and direct pressure" mode. Background Technology

[0002] With the development of robotics technology, tactile sensors, which can be widely used in intelligent sensing technology and human-computer interaction systems, are gradually gaining importance. To achieve a natural interactive experience, the external environmental information acquired by tactile sensors is crucial. Robots can make corresponding behavioral decisions based on the complex and diverse tactile information they obtain, including but not limited to pressure, temperature, humidity, and slippage.

[0003] In robotics, tactile perception is defined as the continuous sensing of variable contact forces. This information helps robots determine whether they are in contact with an object, whether their grasp is stable, identify object information, and provide feedback on control forces. Analyzing object manipulation tasks using tactile information obtained from tactile sensors can further improve the robot's versatility; therefore, tactile sensors are essential for robots to achieve dexterity. Sliding friction is mainly detected by sensors through changes in pressure mapping to determine the displacement of an object, and is closely related to sliding detection, material identification, and sliding roughness identification. In recent years, various novel piezoresistive, capacitive, piezoelectric, and magnetic permeability sensor structures have been developed. Compared to capacitive sensors, piezoresistive sensors have simpler design rules and are smaller, but they have lower sensitivity. Furthermore, the mechanical sensing direction of this sensing technology is mainly concentrated on the normal force, making it impossible to measure three-dimensional forces, thus limiting its application in tactile interaction.

[0004] In existing technologies, MEMS-based tactile sensors can detect tactile information, such as sliding friction. In 2021, the University of Tokyo proposed a MEMS-based local sliding sensor for fall prevention. This sensor chip consists of sidewall-doped silicon beams for shear stress sensing and surface-doped silicon beams for normal stress sensing. The response of the silicon beams is not only proportional to the applied stress but also unaffected by other stresses, exhibiting a decoupling-free characteristic. The chip is completely covered by an elastic material (such as PDMS), the two ends of the silicon beams are fixed, and there is no air cavity beneath the beams. This design significantly reduces the sensor's sensitivity.

[0005] Compared to human fingertip touch, the aforementioned sensors can help robots perceive tactile information about objects, but there is still much room for improvement in the sensitivity of these sensors. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method that, under the premise of being able to measure multiple tactile information, is based on a high-sensitivity detection principle, and whose sensor does not use elastomers (or polymers), thus reducing the force loss caused by elastomers, and is achieved solely through silicon micromechanical structures.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0008] This invention includes a metal electrode, a sensitive unit, a silicon beam, a varistor, and a chip frame;

[0009] The sensitive unit uses a needle-shaped contactor, and multiple contactors within the chip frame are arranged at intervals to simulate the cross-section of a human fingerprint.

[0010] The chip frame provides support for the sensitive unit and silicon beam, and also serves as a support platform for the varistor detection circuit.

[0011] The metal electrode is located on the surface of the silicon chip frame and is used to connect with the varistor to form a Wheatstone bridge.

[0012] The varistor is located on the silicon beam, and the longitudinal and lateral movements of each sensitive unit are detected by a Wheatstone bridge circuit formed by connecting individual varistors.

[0013] The silicon beams are divided into two groups. One group consists of two transverse side beams, which are arranged horizontally on both sides of the top of the sensitive unit. The other group consists of four microbeams, which are arranged in pairs on the upper and lower ends of the same side of the mass block. One end of each microbeam is connected to the chip frame, and the other end is connected to the mass block, which is located on the top of the sensitive unit.

[0014] The microbeam deforms into axial tension or compression during the stress process, and is used for normal stress sensing;

[0015] The side beam deforms into a torsion pattern during the stress process, which is used for shear stress sensing.

[0016] Preferably, the spacing between the contactors is 500 μm, which is close to the average fingerprint spacing of human skin.

[0017] Preferably, the contactor tip is designed as a needle tip to reduce the contact area between the sensitive unit and the object, expand the range of detectable objects, and increase the resolution of the sensor.

[0018] Preferably, the varistor is obtained by doping the upper surface of a silicon beam.

[0019] Preferably, the microbeams are 3μm wide and 60μm long, and each microbeam has a varistor with a length of 40μm and a thickness of 100nm.

[0020] Preferably, the side beams are 10 μm wide and 180 μm long, and each side beam also has a varistor with a length of 150 μm and a thickness of 100 nm.

[0021] Preferably, the two sets of microbeams on the mass block are spaced 30 μm apart.

[0022] The beneficial effects of this invention are as follows: A mass block with a supporting structure connects the top of the contactor to the microbeam structure, achieving the effect of detecting and separating vertical and lateral forces. The microbeam structure alters the original torsional deformation, concentrating most of the stress and strain on the beam through a direct tension and compression mode, contributing to the detection of the piezoresistive sensor. Compared to traditional piezoresistive sensors, this significantly improves the sensor's sensitivity. The piezoresistive principle is used to measure tactile forces such as friction and pressure. The beam structure is used for both normal and shear force measurements. Under the same load, compared to capacitive sensors, chip miniaturization is achieved without sacrificing sensitivity. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of the present invention.

[0024] Figure 2 This is a schematic diagram of a single array unit of the sensor.

[0025] Figure 3 This is an enlarged schematic diagram showing the microbeam structure details of the sensor.

[0026] Figure 4 This is an enlarged schematic diagram showing the details of the side beam structure of the sensor.

[0027] Figure 5 This is a schematic diagram of a tactile sensor array unit with a needle-like structure operating under normal force.

[0028] Figure 6 This is a magnified schematic diagram showing the stress details of a microbeam structure.

[0029] Figure 7 This is a schematic diagram of the operation of a tactile sensor array unit when subjected to tangential force.

[0030] Figure 8 This is a flowchart of the fabrication process for the microbeam in the tactile sensor. Detailed Implementation

[0031] The sensor described in this invention mainly comprises six needle-like sharp contactors of the same length, arranged neatly, a silicon beam structure, and a chip frame. The contact ends are made into needle tips and arranged at equal intervals to form a sensing array to obtain tactile signals with higher resolution. The beam structure includes two types: microbeams and side beams. Using a small-sized beam structure can change torsional deformation to direct tension and compression deformation, concentrating stress and improving the sensor's sensitivity.

[0032] This invention employs a piezoresistive sensing principle. The chip consists of six needle-shaped contactors of equal length, 12 pairs of microbeams (24 in total), six pairs of horizontally arranged side beams (12 in total), and a chip frame. The microbeam structure deforms under stress through axial tension / compression, with most of the stress evenly distributed within the beam structure. Therefore, the majority of the strain can be considered to contribute to the detection of the piezoresistor. The side beams, located at the top of the contactors, are used for shear stress sensing, while the microbeams are connected to the contactors via mass blocks for normal stress sensing. The beam structure is etched using deep ion reaction technology. The piezoresistors are formed as surface-doped piezoresistive strips on the upper silicon layer of SOI using ion implantation. The movement of the contactors is detected by a Wheatstone bridge circuit integrated on the chip frame.

[0033] In this invention, the contactors, which are microstructures that directly contact objects, are arranged neatly at 500μm intervals, approximating the average fingerprint gap on human skin. Their tips are designed as needle-like points to capture more subtle tactile information. The contactor tips are designed as a set of transverse side beams. During sweeping, the contactor tips twist, causing deformation of the transverse side beams. The deformation is obtained by measuring the change in the surface-doped varistor. Two pairs of microbeams are connected above the contactors. The microbeams are designed to be smaller than the transverse side beams, and their ends undergo axial deformation under stress, concentrating stress and strain in the microbeam portion. Unlike the torsional deformation produced by the side beams, the microbeams produce a "direct tension and compression" effect. Under the vertical movement of the contactor, the microbeams are axially stretched / compressed, creating a stress difference. The change in the varistor is also obtained by measuring the change in the output voltage of the Wheatstone bridge.

[0034] This invention significantly reduces the size of the microbeam structure, thereby changing its deformation mode. Under the action of force, the bending deformation is transformed into the axial deformation of the microbeam under tension and compression. This deformation concentrates the dispersed stress on the microbeam, with one microbeam being axially stretched and another being axially compressed, forming a stress difference. At this point, the change in resistance of the varistor reaches its maximum.

[0035] This invention employs a Wheatstone bridge as the measurement circuit. The Wheatstone bridge is a detection method used in MEMS piezoresistive pressure sensors to detect changes in piezoresistive resistance. Connecting the piezoresistive resistors into a Wheatstone bridge achieves the purpose of detecting changes in their resistance. A full-bridge circuit offers advantages such as providing full-scale output and reducing zero-point temperature drift. Under the action of force, when one microbeam is directly pulled, the other microbeam is directly compressed, resulting in the same resistance change ΔR in the piezoresistive resistors. This ΔR is then converted into a voltage signal for output via the bridge circuit.

[0036] The embodiments of the present invention will be described below with reference to the accompanying drawings:

[0037] This embodiment comprises five parts: a metal electrode, a sensing unit, a silicon beam, a varistor, and a chip frame. The silicon beam is divided into two groups: one group consists of two 10μm wide transverse side beams arranged horizontally on both sides of the contactor top; the other group consists of four 60μm long microbeams, arranged in pairs at 30μm intervals on the same side of the mass block, one end connected to the chip frame, and the other end connected to the top of the needle-like structure via the mass block. The sensing unit contains six needle-like contactors of equal length, arranged at 500μm intervals, approximating the average fingerprint gap of human skin. This is intended to simulate the cross-section of a human fingerprint. The needle-like tips reduce the contact area between the sensing unit and the object, expanding the detectable object range and increasing the sensor's resolution. The chip frame provides support for the contactors and silicon beams, and also serves as a support platform for the varistor detection circuit. The metal electrode is located on the surface of the silicon chip frame and is used to connect with the varistor to form a Wheatstone bridge. The varistor is located on the silicon beam, and the surface doping can be obtained through ion diffusion process. The longitudinal and lateral movements of each contactor are detected by a Wheatstone bridge circuit formed by connecting individual varistors.

[0038] like Figure 1 This is a schematic diagram of an array-type tactile sensor with a needle-like structure. Area A is a magnified view of the microbeam structure details, and area B is a magnified view of the side beam structure details. Figure 2 This is a schematic diagram of a single array unit of the sensor. 1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h, 1i, 1j, 1k, 1l, 1m, 1n, 1o, and 1p are fixed metal electrodes, connected to a varistor to form a Wheatstone bridge circuit. 2a, 2b, 2c, 2d, 2e, and 2f are the sensor's sensing units (contactors). These six contactors are arranged with a 500μm spacing to simulate the gaps in human fingerprints. The contactors are also needle-tip shaped to increase the sensor's contact range with objects. 3a, 3b, 3c, 3d, 3e, 3f, 3g, 3h, 3i, 3j, 3k, and 3l are microbeam structures. A detailed enlarged schematic diagram of the microbeam structure is shown below. Figure 3As shown, the microbeam is 3μm wide and 60μm long, connecting the mass block and the chip frame. The right side shows an enlarged view of the microbeam. C represents the varistor on the microbeam; each microbeam corresponds to one varistor, which is 40μm long and 100nm thick, located at the center of the beam structure. 4a, 4b, 4c, 4d, 4e, and 4f are side beams; a detailed enlarged schematic diagram of the side beam structure is shown below. Figure 4 As shown, the side beams are 10μm wide and 180μm long. C is a varistor on the side beam, with one varistor per side beam. Each varistor is 150μm long and 100nm thick, and is also located at the center of the beam structure. 5a, 5b, 5c, 5d, 5e, and 5f are mass blocks. 6 is the chip frame. The side beams undergo torsional deformation with the lateral movement of the contactor, and the change in the varistor detects the frictional force on the sensitive part of the sensor. The microbeams undergo "direct pull and direct pressure" deformation with the vertical movement of the contactor, and the change in the varistor detects the normal force on the sensitive part of the sensor. One array unit includes 2 pairs of microbeams, 1 pair of side beams, and 3 pairs of varistors (2 pairs are located on the surface of the microbeams, and 1 pair is located on the surface of the side beams). The sensor includes 6 array units, with a total of 18 pairs of varistors. 12 pairs of varistors (located on the surface of the microbeams) are paired to form a Wheatstone bridge for detecting normal force, and 6 pairs of varistors (located on the surface of the side beams) are paired to detect lateral forces.

[0039] Figure 5 This is a schematic diagram of a tactile sensor array unit with a needle-like structure operating under normal force.

[0040] Figure 6 This is a magnified schematic diagram showing the stress details of the microbeam structure on the tactile sensor.

[0041] The working principle of the normal force in this example is as follows: Figure 5 As shown: When the contactor is subjected to a normal force, it causes the top mass block to move, resulting in a certain displacement, and ultimately axial deformation at the microbeam. An enlarged schematic diagram of area D is shown below. Figure 6 The diagram illustrates the working principle of the microbeam structure. The left end of the microbeam is fixed, and the right end is movable. The length of the microbeam is designed to be much greater than its width and thickness. Under this characteristic, when subjected to force, the microbeam undergoes axial deformation under the influence of the mass block, concentrating most of the strain on the microbeam. One beam is subjected to axial tension, and the other to axial compression, both with a length change of Δl. This creates a stress difference between the two beams, ultimately causing a change in the resistance of the doped varistor.

[0042] Figure 7 This is a schematic diagram of a tactile sensor array unit with a needle-like structure operating under tangential force.

[0043] The working principle of the tangential force in this example is as follows: the contactor's needle-like structure contacts the object's surface, the object contacts the contact point and generates a reaction force, and the force signal is amplified by the beam structure on the contactor. When subjected to a tangential force, the contactor deflects at a certain angle, causing the upper side beam to deform and form a stress difference. The varistor is located at the center of the side beam, and the resulting deformation and stress difference are output through a bridge circuit to obtain a linear relationship between voltage and resistance.

[0044] Figure 8 The fabrication process flow diagram for the micro-silicon beam in an array-type tactile sensor with a needle-like structure is shown below.

[0045] (a) Prepare an SOI wafer with a top silicon layer thickness of 20 μm, a bottom silicon layer thickness of 20 μm, an intermediate oxide layer thickness of 10 μm, and a back oxide layer thickness of 10 μm, and clean it thoroughly. Use KOH etching solution to thin the top silicon layer to a suitable thickness;

[0046] (b) High-temperature oxidation and photolithography to form the beam structure region. A dilute boron ion diffusion process is used to fabricate the varistor, followed by thermal annealing.

[0047] (c) Silica formed during the diffusion and redistribution of dilute boron ions is used as a mask to cover the piezoresistive strip, while the remaining areas are subjected to the diffusion process of concentrated boron ions.

[0048] (d) A thin film is sputtered on the front side of the wafer to form a mask pattern, and a movable structure is fabricated using RIE etching technology;

[0049] (e) Polyimide is used to protect the front structure, photoresist is thickly coated on the back of the wafer to form a pattern, the movable sensor structure is etched using DRIE etching technology, and the silicon dioxide layer is etched with hydrofluoric acid solution to release the movable structure.

[0050] In this example, the silicon-on-insulator (SOI) used in the sensor can achieve a uniform structure and high-precision material parameters that are difficult to obtain with other processes, such as film thickness, elastic modulus, doping characteristics, etc. For example, the intermediate silicon oxide layer of the SOI silicon wafer can be used to achieve self-stopping DRIE etching and accurately determine the dimensions of each part of the structure.

[0051] In summary, this sensor features high sensitivity, miniaturization, low crosstalk, and the ability to separate perpendicular and tangential forces. Adjusting the position and size of the sensor's microbeams can more effectively reduce crosstalk and stress concentration issues between forces. The microbeam structure concentrates most of the stress and strain into the piezoresistive detection, resulting in higher sensitivity. Finally, the needle-shaped contactor amplifies the force signal while reducing the contact area, increasing the sensor's resolution and expanding the detectable object range.

Claims

1. A high-sensitivity array-type tactile sensor with a needle-like structure, characterized in that: It includes metal electrodes, sensing units, silicon beams, varistors, and chip frames; The sensitive unit uses a needle-shaped contactor, and multiple contactors within the chip frame are arranged at intervals to simulate the cross-section of a human fingerprint. The chip frame provides support for the sensitive unit and silicon beam, and also serves as a support platform for the varistor detection circuit. The metal electrode is located on the surface of the silicon chip frame and is used to connect with the varistor to form a Wheatstone bridge. The varistor is located on the silicon beam, and the longitudinal and lateral movements of each sensitive unit are detected by a Wheatstone bridge circuit formed by connecting individual varistors. The silicon beams are divided into two groups. One group consists of two transverse side beams, which are arranged horizontally on both sides of the top of the sensitive unit. The other group consists of four microbeams, which are arranged in pairs on the upper and lower ends of the same side of the mass block. One end of each microbeam is connected to the chip frame, and the other end is connected to the mass block, which is located on the top of the sensitive unit. The microbeam deforms into axial tension or compression during the stress process, and is used for normal stress sensing; The side beam deforms into a torsion pattern during the stress process, which is used for shear stress sensing.

2. A high-sensitivity array-type tactile sensor with a needle-like structure according to claim 1, characterized in that: The spacing between the contactors is 500µm, which is close to the average fingerprint spacing of human skin.

3. A high-sensitivity array-type tactile sensor with a needle-like structure according to claim 1, characterized in that: The contactor tip is designed in the shape of a needle tip to reduce the contact area between the sensitive unit and the object, expand the range of detectable objects, and increase the resolution of the sensor.

4. A high-sensitivity array-type tactile sensor with a needle-like structure according to claim 1, characterized in that: The varistor is obtained by doping the upper surface of a silicon beam.

5. A high-sensitivity array-type tactile sensor with a needle-like structure according to any one of claims 1-4, characterized in that: The microbeams are 3µm wide and 60µm long, and each microbeam has a varistor that is 40µm long and 100nm thick.

6. A high-sensitivity array-type tactile sensor with a needle-like structure according to claim 5, characterized in that: The side beams are 10µm wide and 180µm long. Each side beam also has a varistor, which is 150µm long and 100nm thick.

7. A high-sensitivity array-type tactile sensor with a needle-like structure according to claim 6, characterized in that: The two sets of microbeams on the mass block are spaced 30µm apart.

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