Piezoresistive sensor for micro electro mechanical system and preparation method thereof

Abstract

The invention discloses a piezoresistive sensor for a micro electro mechanical system and a preparation method thereof, and the piezoresistive sensor comprises a substrate, a resistor strip formed on the substrate, a lead electrically connected with the resistor strip, an insulating layer laid on the resistor strip and the lead, and a functional film layer formed on the insulating layer. And the projection of the functional film layer on the substrate is staggered from the resistor strips. The resistance strips and the functional film layer are arranged in a staggered manner, so that the resistance strips are prevented from being interfered by deformation of the functional film layer, and the detection accuracy and sensitivity of the piezoresistive sensor are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of microelectromechanical system sensors, and more particularly, relates to a piezoresistive sensor for a microelectromechanical system and a preparation method thereof. Background Art

[0002] A Micro-Electro-Mechanical System (MEMS), also called a microelectronic mechanical system, refers to a tiny device with dimensions of several millimeters or even smaller. Its internal structure is generally in the micrometer or even nanometer scale and is an independent intelligent system. In a MEMS scanning control system, in order to stabilize the operation of a micromirror, a sensor needs to be integrated on the micromirror to feedback the motion state of the micromirror and control its scanning angle, frequency, and laser modulation time. Common sensors use optical, capacitive, or piezoresistive methods to detect the motion state of the micromirror.

[0003] A piezoresistive sensor is doped in a silicon substrate by ion implantation. When the doped region deforms, i.e., is subjected to stress, the resistivity of the doped region will change. In a MEMS micromirror, the piezoresistive sensor has been widely used due to its high sensitivity and high integration. As Figure 1 shown, the piezoresistive sensor is integrated into the torsion shaft. When the micromirror twists, the torsion shaft generates deformation stress, and the resistivity of the piezoresistor changes. By detecting the change in the output voltage, the motion state of the MEMS micromirror is monitored.

[0004] The principle of a common piezoresistive sensor on the torsion shaft of a MEMS micromirror is as Figure 2 shown. Regions 1, 2, 3, and 4 are the connection regions between the piezoresistive sensor and the external circuit, and regions R1, R2, R3, and R4 are resistor bar regions. Usually, regions 1 and 3 are used as voltage input terminals, and regions 2 and 4 are used as voltage output terminals. As Figure 3 shown, regions 2 and 4 are on the axis of the torsion shaft, and regions 1 and 3 are symmetrically distributed on both sides of the axis. When the torsion shaft twists around the center line, the resistor bars distributed at different positions on the torsion shaft are subjected to inconsistent stresses, and the resistance values change. The voltage at the output terminal will reflect the torsion angle of the torsion shaft, thereby realizing the monitoring of the motion state of the micromirror.

[0005] In order to achieve other functions, multiple functional thin films are usually formed above the resistor strip. Therefore, the resistance change of the resistor strip in the piezoresistive sensor is not only caused by the stress change induced by the rotation of the torsion shaft, but also affected by the stress of each functional thin film on the piezoresistor. Among them, during the operation of the micromirror, the stress of some functional thin films will change greatly, some functional thin films may undergo irreversible deformation and peeling, the stress on the piezoresistive sensor may change greatly, and the voltage output by the piezoresistive sensor will not be able to reflect the motion state of the micromirror, which will affect the control accuracy at least and may even cause the micromirror to fail to work seriously. Summary of the Invention

[0006] The technical problem solved by the present invention is: how to avoid the stress influence of the functional thin film on the resistor strip in the piezoresistive sensor.

[0007] The present application discloses a piezoresistive sensor for a microelectromechanical system. The piezoresistive sensor includes a substrate, a resistor strip formed on the substrate, a lead wire electrically connected to the resistor strip, an insulating layer laid on the resistor strip and the lead wire, and a functional film layer formed on the insulating layer. The projection of the functional film layer on the substrate is offset from the resistor strip.

[0008] Optionally, the substrate is a silicon substrate, and a part of the silicon substrate is doped to form the resistor strip.

[0009] Optionally, the number of the resistor strips is four. The four resistor strips are symmetrically distributed on the center line of the substrate, and the four resistor strips are electrically connected to form a Wheatstone bridge. When the substrate is installed on the torsion shaft of the microelectromechanical system, the center line coincides with the torsion axis of the torsion shaft.

[0010] Optionally, the projection of the functional film layer on the substrate covers the center line, and the four resistor strips are symmetrically distributed on both sides of the projection.

[0011] Optionally, the functional film layer has four hollow areas, and the four hollow areas correspond to the four resistor strips one by one.

[0012] The present application also discloses a preparation method for a piezoresistive sensor for a microelectromechanical system. The preparation method includes:

[0013] Preparing and forming a resistor strip on the substrate;

[0014] Preparing and forming a lead wire connecting the resistor strip on the substrate;

[0015] Preparing and forming the insulating layer on the resistor strip and the lead wire;

[0016] A functional film layer is formed on the insulating layer, and the projection of the functional film layer on the substrate is offset from the resistor strip.

[0017] Optionally, the method for forming the resistor strip on the substrate includes:

[0018] The substrate is a silicon substrate, and doping is performed on a partial area of the silicon substrate to form the resistor strip.

[0019] Optionally, the number of the resistor strips is four, and the four resistor strips are symmetrically distributed on the center line of the substrate, and the four resistor strips are electrically connected to form a Wheatstone bridge. When the substrate is mounted on the torsion axis of the microelectromechanical system, the center line coincides with the torsion axis of the torsion axis.

[0020] A piezoresistive sensor for a microelectromechanical system and a preparation method thereof disclosed by the present invention have the following technical effects:

[0021] By arranging the resistor strip and the functional film layer in an offset manner, the deformation of the functional film layer is avoided from interfering with the resistor strip, and the detection accuracy and sensitivity of the piezoresistive sensor are improved. Description of the Drawings

[0022] Figure 1 Schematic diagram of the position of the piezoresistive sensor on the micromirror structure of the prior art;

[0023] Figure 2 Schematic diagram of the principle of the piezoresistive sensor on the micromirror structure of the prior art;

[0024] Figure 3 Schematic diagram of the regional distribution of the resistor strips of the piezoresistive sensor on the micromirror structure of the prior art;

[0025] Figure 4 Cross-sectional schematic diagram of the piezoresistive sensor for a microelectromechanical system according to Embodiment 1 of the present invention;

[0026] Figure 5 Another cross-sectional schematic diagram of the piezoresistive sensor for a microelectromechanical system according to Embodiment 1 of the present invention;

[0027] Figure 6 Schematic diagram of the resistor strip distribution of the piezoresistive sensor for a microelectromechanical system according to Embodiment 1 of the present invention.

[0028] The corresponding relationship between the reference numerals and the component names is as follows:

[0029] 10 - Substrate, 20 - Resistor strip, 30 - Lead, 31 - Internal lead, 32 - External lead, 40 - Insulating layer, 50 - Functional film layer, 51 - Hollowed-out area, 100 - Torsion axis, 101 - Torsion axis line. Detailed Description of the Invention

[0030] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0031] Before describing the various embodiments of the present application in detail, the technical concept of the present application will be briefly described first: In the piezoresistive sensor of the current MEMS mirror, the resistance strip is easily affected by the stress of the functional film layer, which affects the measurement accuracy and may even cause the sensor to malfunction. For this reason, the piezoresistive sensor for a microelectromechanical system provided in the present application designs the resistance strip to be offset from the functional film layer, reducing the influence of the deformation of the functional film layer on the resistance strip, so that the resistance change of the resistance strip can accurately reflect the torsion angle of the MEMS mirror. The specific principle of the piezoresistive sensor for a microelectromechanical system of the present application will be described below with more embodiments.

[0032] Specifically, as Figure 4 and Figure 5 shown, a piezoresistive sensor for a microelectromechanical system in this Embodiment 1 includes a substrate 10, a resistance strip 20 formed on the substrate 10, a lead 30 electrically connected to the resistance strip 20, an insulating layer 40 laid on the resistance strip 20 and the lead, and a functional film layer 50 formed on the insulating layer 40. The projection of the functional film layer 50 on the substrate 10 is offset from the resistance strip 20. Among them, "offset" means that there is no functional film layer 50 directly above the resistance strip 20, so that the resistance strip 20 is avoided from the functional film layer 50, reducing the influence of the stress change of the functional film layer 50 on the resistance strip 20.

[0033] In one implementation, the substrate 10 is a silicon substrate, and a part of the silicon substrate is doped to form the resistance strip 20. By using a part of the substrate 10 as the resistance strip 20, when the stress of the substrate 10 changes, it can be directly conducted to the resistance strip 20, improving the sensitivity and accuracy of detection.

[0034] Further, as Figure 6As shown, the number of resistor bars 20 is four. The four resistor bars 20 are symmetrically distributed along the center line of the substrate 10, and the four resistor bars 20 are electrically connected to form a Wheatstone bridge as a detection circuit. When the substrate 10 is mounted on the torsion axis 100 of the microelectromechanical system, the center line coincides with the torsion axis 101 of the torsion axis 100. An electrical connection area is provided between two adjacent resistor bars 20 for use as a voltage input terminal and a voltage output terminal. Exemplarily, the electrical connection area C1 between resistor bars R1 and R4 and the electrical connection area C3 between resistor bars R2 and R3 serve as voltage input terminals to connect to an external power supply; one of the electrical connection areas C21 and C22 between resistor bars R1 and R2 and one of the electrical connection areas C41 and C42 between resistor bars R3 and R4 serve as voltage output terminals to connect to a voltmeter. When the stress generated by the rotation of the torsion axis 100 is transmitted to the resistor bar 20, it causes a change in the resistance value of the resistor bar 20, and the voltage at the voltage output terminal changes, thereby reflecting the magnitude of the torsion angle of the torsion axis.

[0035] For the convenience of distinction, the lead 30 is divided into an internal lead 31 and an external lead 32. The electrical connection areas C21 and C22 between resistor bars R1 and R2 are electrically connected through the internal lead 31, and the electrical connection areas C41 and C42 between resistor bars R3 and R4 are electrically connected through the internal lead 31; the electrical connection area C1 between resistor bars R1 and R4 and the electrical connection area C3 between resistor bars R2 and R3 are connected to the external power supply through the external lead 32, and the electrical connection area C22 between resistor bars R1 and R2 and the electrical connection area C41 between resistor bars R3 and R4 are connected to the voltmeter through the external lead 32. An insulating layer 40 can also be provided between the lead 30 and the substrate 10 to avoid leakage on the substrate 10.

[0036] In one embodiment, as Figure 4 shown, the projection of the functional film layer 50 on the substrate 10 covers the center line, and the four resistor bars 20 are symmetrically distributed on both sides of the projection, that is, the functional film layer 50 is entirely located between the four resistor bars 20. The functional film layer 50 covers the internal lead 31 and avoids the resistor bars 20, so that the resistor bars 20 are as far away from the functional film layer 50 as possible, reducing the interference of the deformation of the functional film layer 50 on the resistor bars 20.

[0037] In one embodiment, as Figure 5 shown, the functional film layer 50 has four hollow areas 51, and the four hollow areas 51 correspond to the four resistor bars 20 one by one, that is, the functional film layer 50 "exposes" the resistor bars 20, and the part of the functional film layer 50 above the resistor bars 20 is etched away, thereby reducing the interference of the deformation of the functional film layer 50 on the resistor bars 20.

[0038] This second embodiment also discloses a preparation method for a piezoresistive sensor for a microelectromechanical system. The preparation method includes:

[0039] Step S10: Prepare and form a resistor strip 20 on the substrate 10;

[0040] Step S20: Prepare and form a lead 30 connecting the resistor strip 20 on the substrate 10;

[0041] Step S30: Prepare and form an insulating layer 40 on the resistor strip 20 and the lead 30;

[0042] Step S40: Prepare and form a functional film layer 50 on the insulating layer. The projection of the functional film layer 50 on the substrate 10 is offset from the resistor strip 20.

[0043] Exemplarily, in step S10, the substrate 10 is a silicon substrate. By doping local areas of the silicon substrate, multiple resistor strips 20 are formed. Exemplarily, the number of resistor strips 20 is four, and the four resistor strips 20 are electrically connected to form a Wheatstone bridge. During the doping process, multiple electrical connection areas are also formed between the resistor strips 20. For example, the electrical connection area C1 between resistor strips R1 and R4, the electrical connection area C3 between resistor strips R2 and R3, the electrical connection areas C21 and C22 between resistor strips R1 and R2, and the electrical connection areas C41 and C42 between resistor strips R3 and R4.

[0044] Next, in step S20, the lead 30 is formed by a sputtering process. The lead 30 is a metal lead. The lead 30 electrically connects each resistor strip 20 and the electrical connection areas. At the same time, the lead 30 inputs an external voltage into the Wheatstone bridge and outputs the output voltage of the Wheatstone bridge to a voltmeter for detection. The lead 30 is divided into an internal lead 31 and an external lead 32. Each resistor strip 20 and the electrical connection areas are connected through the internal lead 31. Among them, two electrical connection areas are connected to an external power supply through the external lead 32, and the other two electrical connection areas are connected to a voltmeter through the internal lead.

[0045] Further, in step S30, the insulating layer 40 is deposited on the resistor strip 20 and the lead 30 by a deposition process. In step S40, the functional film layer 50 is deposited on the insulating layer 40 by a deposition process. Among them, in one implementation, when depositing on the insulating layer 40, the functional film layer 50 is formed in the area between the resistor strips 20, which can avoid the functional film layer 50 covering the resistor strip 20; in another implementation, the functional film layer 50 is first deposited on the insulating layer 40, and then the part of the functional film layer 50 opposite to the resistor strip 20 is etched off to avoid the resistor strip 20 being covered by the functional film layer 50.

[0046] The piezoresistive sensor for a microelectromechanical system and its preparation method disclosed in this embodiment avoid the deformation of the functional film layer interfering with the resistor strip by arranging the resistor strip and the functional film layer offset from each other, thereby improving the detection accuracy and sensitivity of the piezoresistive sensor.

[0047] The specific embodiments of the present invention have been described in detail above. Although some embodiments have been shown and described, those skilled in the art should understand that these embodiments can be modified and perfected without departing from the principles and spirit of the present invention defined by the claims and their equivalents, and these modifications and improvements should also be within the protection scope of the present invention.

Claims

1. A piezoresistive sensor for a microelectromechanical system, characterized in that, The piezoresistive sensor includes a substrate, a resistor strip formed on the substrate, a lead wire electrically connected to the resistor strip, an insulating layer laid on the resistor strip and the lead wire, and a functional film layer formed on the insulating layer. The projection of the functional film layer on the substrate is offset from the resistor strip.

2. The piezoresistive sensor for a microelectromechanical system according to claim 1, characterized in that, The substrate is a silicon substrate, and a part of the silicon substrate is doped to form the resistor strip.

3. The piezoresistive sensor for a microelectromechanical system according to claim 2, wherein The number of the resistor strips is four. The four resistor strips are symmetrically distributed on the center line of the substrate, and the four resistor strips are electrically connected to form a Wheatstone bridge. When the substrate is mounted on the torsion axis of a microelectromechanical system, the center line coincides with the torsion axis of the torsion axis.

4. The piezoresistive sensor for a microelectromechanical system according to claim 3, characterized in that, The projection of the functional film layer on the substrate covers the center line, and the four resistor strips are symmetrically distributed on both sides of the projection.

5. The piezoresistive sensor for a microelectromechanical system according to claim 3, characterized in that, The functional film layer has four hollow areas, and the four hollow areas correspond to the four resistor strips one by one.

6. A method for fabricating a piezoresistive sensor for a microelectromechanical system according to any one of claims 1 to 5, characterized in that, The preparation method includes: Preparing and forming a resistor strip on the substrate; Preparing and forming a lead wire connecting the resistor strip on the substrate; Preparing and forming the insulating layer on the resistor strip and the lead wire; Preparing and forming a functional film layer on the insulating layer. The projection of the functional film layer on the substrate is offset from the resistor strip.

7. The preparation method according to claim 6, characterized in that, The method for preparing and forming a resistor strip on the substrate includes: The substrate uses a silicon substrate, and a part of the silicon substrate is doped to form a resistor strip.

8. The preparation method according to claim 7, characterized in that, The number of the resistor strips is four. The four resistor strips are symmetrically distributed on the center line of the substrate, and the four resistor strips are electrically connected to form a Wheatstone bridge. When the substrate is mounted on the torsion axis of a microelectromechanical system, the center line coincides with the torsion axis of the torsion axis.

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