CN111190126B - Preparation method of MEMS magnetic field sensor adopting folded beam structure - Google Patents
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Abstract
The invention relates to an MEMS magnetic field sensor adopting a folded beam structure, a preparation process and application thereof. The electrode formed by the folded beam and the electrode on the substrate form a variable capacitor. The principle of the invention is that after the metal coil processed on the T-shaped folding beam structure is electrified, the Lorentz force makes the beam generate bending deformation, thereby changing the distance between the two electrodes and realizing the change of the capacitance value. The magnitude of the magnetic field can be measured by detecting the capacitance change. The folding beam structure can realize effective support of the movable polar plate, provides smaller equivalent elastic coefficient compared with the traditional structure, and can reduce various residual stress in the processing process of the sensor, improve the sensitivity of the sensor and reduce the power consumption of the sensor compared with the traditional torsion beam structure. The T-shaped folding beam structure of the sensor can release stress, so that the service life of the sensor is prolonged.
Description
Technical Field
The invention relates to a structure and a manufacturing method of a torsional high-sensitivity MEMS magnetic field sensor, belonging to the field of MEMS sensors and the field of micro-nano processing, and specifically comprising the following steps: an MEMS magnetic field sensor adopting a folded beam structure, a preparation process and application.
Background
The magnetic field sensor is one of a number of sensors. Magnetic field sensors play an important role in the fields of physics, machinery, military and the like. A magnetic field sensor is placed in a magnetic field, the sensor being able to identify the direction and strength of the magnetic field. When the permanent magnet is combined with the permanent magnet, non-contact measurement of the variation of current, speed, angle and the like can be realized; the magnetic field sensor can be used for detecting and controlling the manufacturing process in real time in industrial production; meanwhile, the method is widely applied to the fields of mineral resource development, medical electronics and the like.
An MEMS magnetic field sensor is a novel magnetic field sensor which is designed and processed by utilizing a micro-nano processing technology including an integrated circuit process since the appearance of an MEMS technology. The sensor has the characteristics of diversified sensing mechanisms, greatly improved sensitivity, greatly reduced power consumption, miniaturized device size, high-precision batch manufacturing and monolithic integration with an integrated circuit.
The research on the MEMS magnetic field sensor at home and abroad and the mature magnetic field sensor products in the market mainly comprise: u-shaped beam magnetic field sensor, torsional pendulum type magnetic field sensor, micro fluxgate sensor and the like based on Lorentz force detection. The U-shaped beam magnetic field sensor based on the Lorentz force detection utilizes the U-shaped beam to deform under the action of the Lorentz force to change resistance or capacitance to complete the magnetic field detection, but the magnetic field resolution is not high enough generally, and the U-shaped beam magnetic field sensor is not suitable for occasions needing high sensitivity and resolution. The torsional pendulum type sensor is fixed by anchor areas at two sides, a torsion flat plate is arranged in the middle, metal wires are plated on the edge of the torsion flat plate, and current is conducted in the wires and is driven by Lorentz force to generate torsional pendulum in a magnetic field. But the rotating shaft part is stressed greatly, so that the problems of easy damage and short service life exist. The micro fluxgate sensor can be suitable for detection in a wide weak magnetic field range and has high sensitivity, but the micro fluxgate sensor has the defects of high power consumption and large volume of a device.
The problems of low resolution, short lifetime and large power consumption of the existing MEMS magnetic field sensors limit their application range, so that further development of sensor structures with high resolution, long lifetime and low power consumption is required. Especially, due to the existence of mechanical movable parts, the reduction of internal stress, the improvement of fatigue resistance of devices and the increase of service life of the sensor are the prerequisites and key problems for optimizing other performances of the sensor.
Disclosure of Invention
The invention aims to provide a novel MEMS magnetic field sensor structure aiming at the defects of complex manufacturing process, poor stability and low sensitivity of the existing magnetic field sensor so as to realize a magnetic field sensor with high resolution, low power consumption, high sensitivity and long service life. In the invention, the folding beam with the T-shaped structure can effectively release the stress applied when the beam deforms, and the service life of a device is prolonged. The folding beam has a hollow structure, so that a smaller elastic coefficient can be provided, and the sensitivity can be improved. Because the motion of the symmetrical T-shaped beam generates differential capacitance, the resolution ratio is improved and the measurement error is reduced. The folded beam reduces the mass of the beam and is beneficial to reducing power consumption.
The invention provides a preparation method of an MEMS magnetic field sensor based on a folded beam structure.
In order to achieve the purpose, the invention adopts the following technical scheme:
the MEMS magnetic field sensor adopting the folded beam structure consists of the folded beam structure and a substrate; the folding beam structure is made of metal and is T-shaped; the folded beam structure itself becomes an electrode, and the electrode is arranged on the substrate; the electrode of the folded beam structure and the electrode on the substrate form a variable capacitor; an insulating layer is arranged on the upper surface of the folding beam structure, and a metal coil is arranged on the insulating layer; after the metal coil is electrified, the folded beam structure is bent and deformed under the action of Lorentz force in a magnetic field, so that the electrode distance between the folded beam structure and the substrate is changed, and the capacitance value is changed; the capacitance change trends at the two ends of the folding beam structure are opposite, and a differential capacitor is formed; the magnitude of the magnetic field is obtained by the feedback of the change amount of the differential capacitance.
Furthermore, the MEMS magnetic field sensor consists of a folded beam structure B and a substrate S;
a substrate S rectangular block; a groove is arranged in the middle of the top surface of the substrate S; a folding beam structure B is arranged on the bottom surface of the groove of the substrate S;
the folding beam structure B consists of an upper rectangular block body and a lower rectangular column body 2 part; the upper rectangular block is an upper electrode of the MEMS magnetic field sensor; the center of the bottom surface of the upper rectangular block body is connected with the top end of the lower rectangular column body, and the horizontal contour area of the upper rectangular block body is larger than that of the lower rectangular column body; the folding beam structure B is T-shaped;
The top surface of the upper rectangular block body is covered with an insulating layer I; 2 groups of coils W are arranged on the top surface of the insulating layer I; the coils W are positioned on two sides of the lower rectangular cylinder and are symmetrical with each other;
a through hole is formed in the substrate S groove at the joint of the substrate S groove and the lower rectangular cylinder, and metal is filled in the through hole; a folded beam structure electrode 1 is arranged on the substrate S at the bottom opening of the through hole; the lower rectangular column body is connected with the folded beam structure electrode 1 through metal in the through hole;
a substrate electrode 2 is arranged on the surface of the groove of the substrate S below the coil W; namely 2 groups of substrate electrodes 2 are arranged; the substrate electrode 2 is a lower electrode of the MEMS magnetic field sensor; a through hole is formed in the substrate S at the joint of the substrate electrode 2, the bottom of the substrate electrode 2 extends downwards and penetrates out of the corresponding through hole;
the upper electrode and the lower electrode form a variable capacitor of the MEMS magnetic field sensor;
the coil W is a magnetic induction coil that causes the upper electrode to bend and deform in a magnetic field environment.
The preparation process of MEMS magnetic field sensor with folded beam structure includes independent preparation process or IC circuit integrated preparation process;
the independent preparation is directly prepared on a wafer or an SOI (silicon on insulator) wafer;
the IC circuit integrated preparation method comprises the steps of depositing a passivation layer on a silicon chip which is finished with an IC circuit structure to protect the circuit structure, then preparing a sensor, and finally removing the passivation layer on the IC circuit;
The direct preparation method or the multi-step preparation method comprises the following processes: taking a round crystal silicon wafer, an SOI wafer or a silicon wafer for completing the deposition of a passivation layer and protecting the IC circuit structure of the circuit structure; firstly, depositing a lower electrode on a substrate, wherein the lower electrode can be formed by depositing copper or gold material or by a P-type heavy doping process; depositing a first conductive layer metal 1 on the surface of the substrate, preferably, the first conductive layer metal is metal aluminum; performing spin coating of photoresist, patterning the first metal layer by using the photoresist, and electroplating a layer of second conductive layer metal, wherein the second conductive layer metal is preferably metal nickel or chromium; and patterning is realized by adopting auxiliary processes such as photoetching and the like to obtain the upper electrode. On the upper surface of the upper electrode metal layer, a layer of silicon nitride or silicon dioxide is deposited to serve as an insulating layer. And simultaneously, patterning the insulating layer, corroding and removing two rectangular areas in a top view, and taking the patterned insulating layer as a mask, and corroding and removing the corresponding upper electrode metal rectangular area. And etching the back surface of the device, and finishing the extraction of the upper electrode and the lower electrode in modes of deposition and the like. And depositing and etching to form a ring-shaped copper, gold or aluminum electrode on the upper surface of the insulating layer to serve as a conductive coil. And finally, carrying out subsequent packaging.
The MEMS magnetic field sensor adopting the folded beam structure has the following purposes/performances:
when the magnetic field B is 100mT, 50mA current is introduced to the magnetic field sensor to the induction coil, and the displacement of the top end of the beam reaches 3 mu m;
the measuring range of the magnetic field sensor reaches 0.5-1T;
when the external magnetic field changes by 1mT, the differential capacitance difference variation of the magnetic field sensor is 50fF, namely the sensitivity is about 50fF/mT, and the resolution is 20 nT;
the power of the magnetic field sensor is 50mW-100 mW.
The sensor has the characteristics of wide range and high sensitivity, can be used in various measurement fields such as geomagnetic fields, general industrial equipment magnetic fields, medical equipment magnetic fields and the like, and has higher applicability compared with special magnetic field sensors in the fields.
The T-shaped folded beam structure greatly releases various material stresses in the processing process, and the maximum stress in the working process is about 5MPa and is far smaller than the maximum stress standard value of a general design structure, namely 500 MPa.
For use in the range of turndown, the lifetime is greater than 10 hundred million times.
To better explain the structural and technological features of the present invention, the present invention will now be explained with the following changed angles:
the MEMS magnetic field sensor adopts an n-type (100) silicon wafer to prepare a sensor structure. The overall structure is shown in fig. 1, the total length of the device is suggested to be 1000um-4000um, but not limited to, a plane symmetric flat plate structure. The distance from one end of the flat plate to the hollow of the T-shaped folding beam is 1/3 which suggests but is not limited to the total length of the flat plate. The anchor region is centered on the center of the overall structure and may be a planar rectangular structure having a width suggested by, but not limited to 1/3 the overall width of the structure. The gap of the flat plate structure has two symmetrical positions as shown in fig. 1, and the width is 1/4 which is suggested but not limited to the total structure width. The thickness of the plate structure is recommended to be, but not limited to, 10-30 um.
The center of the beam is fixed by adopting an anchor area. The metal wire is plated on the beam structure, and the metal wire with current is acted by Lorentz force in the magnetic field, so that the structure is stressed to be bent and deformed. When the lorentz force F experienced by the beam structure and the stress generated by the bending deformation of the cantilever beam are equal, the beam reaches a stable state. At the moment, the displacement generated by the beam changes the capacitance between the beam polar plate and the substrate electrode, and the magnetic field intensity can be calculated by measuring the capacitance change through the detection circuit.
The sensor structure is realized by the following method:
a. as shown in "2-1" of fig. 2, a deep reactive ion etching process is used to etch a cavity with a certain depth on the n-type silicon wafer, the depth is recommended but not limited to 30-40um, and the area of the cavity should be larger than that of the sensor, depending on the size of the sensor area. The process can also be performed on the basis of an SOI substrate.
b. As shown in fig. 2 as "2-2", a metal layer 1 is deposited and patterned in the chamber to form a bottom electrode, which may be rectangular and symmetrically disposed on both sides of the anchor region, with a size of 1000 x 500um, but not limited thereto, and a thickness of 1um, one on each side as shown.
c. As shown in fig. 2 "2-3," fig. 2 "2-4, a sacrificial layer metal 2 is deposited. The total thickness of the sacrificial layer to the substrate is suggested but not limited to 15-25 um. Wherein the thickness deposited in the "2-4" step of fig. 2 is preferably, but not limited to, 1-2um, which is equal to the thickness of the subsequent upper electrode.
d. As shown in "2-4" of fig. 2, a metal such as nickel is electroplated on the sacrificial layer metal 2 to form a movable flat plate, and the thickness of the flat plate, i.e. the thickness of the upper electrode, is suggested to be, but not limited to, 1-2 um.
e. As shown by "2-5" in FIG. 2, SiO is deposited on the upper electrode surface2Or Si3N4The insulating layers are patterned using a process such as photolithography, including forming void structures. This layer forms a flat plate with the upper electrode and isolates the lower electrode from the metal coil on the flat plate.
f. As shown at "2-5" in fig. 2, a metal layer 3 is deposited and patterned on the top surface of the insulating layer, preferably but not limited to 0.5um, to form a magnetic induction coil, which may be rectangular, circular or other irregular shape.
g. As shown in fig. 2 "2-6", the back of the silicon substrate is subjected to patterned deep reactive ion etching and deposition of metal Au, Cu, etc., and the process is used for completing the extraction of the upper and lower electrodes.
h. As shown at "2-7" in fig. 2, sacrificial layer etching is performed to release the beam structure.
"2-1", "2-2", "2-3", "2-4", "2-5", "2-6" and "2-7" in fig. 2 refer to schematic representations of the 7 main steps of a lithographic process implementing the method of the invention.
Advantageous effects
The supporting beam bears the maximum stress in the torsion of the beam, and compared with the traditional double-end free beam/plate structure, the folded beam structure greatly releases the stress of the connection between the supporting beam and the flat plate, so that the flat plate can obtain larger displacement freedom degree, and the integral sensitivity of the structure is improved. The invention has the advantages of reduced stress level, ensured mechanical property stability in the working process of the sensor, and less possibility of material fatigue fracture.
By setting typical sensor geometric parameters, the device structure working process is simulated by ANSYS software, and the result shows that when the applied magnetic field is increased to B120 mT, the displacement of the top end of the beam can reach 3.28 micrometers. When the applied magnetic field is changed by 1mT, the capacitance difference has a change of 23.5fF, i.e. the sensitivity is about 23.5fF/mT, and the resolution can reach 42.55 nT.
Drawings
Fig. 1 is a schematic structural diagram of a main body of a magnetic field sensor according to the present invention.
FIG. 2 is a schematic diagram of a photolithography process according to the method of the present invention.
Fig. 3 is a top view of the present invention with the cover plate P removed.
Fig. 4 is a cross-sectional view AA of fig. 3.
Detailed Description
The structural features and technical details of the present invention will now be described in detail with reference to the accompanying drawings.
Referring to fig. 1, 3 and 4, the MEMS magnetic field sensor using the folded beam structure is composed of a folded beam structure and a substrate; the folding beam structure is made of metal and is T-shaped; the folded beam structure itself becomes an electrode, and the electrode is arranged on the substrate; the electrode of the folded beam structure and the electrode on the substrate form a variable capacitor; an insulating layer is arranged on the upper surface of the folding beam structure, and a metal coil is arranged on the insulating layer; after the metal coil is electrified, the folded beam structure is bent and deformed under the action of Lorentz force in a magnetic field, so that the electrode distance between the folded beam structure and the substrate is changed, and the capacitance value is changed; the capacitance change trends at the two ends of the folding beam structure are opposite, and a differential capacitor is formed; the magnitude of the magnetic field is obtained by the feedback of the change amount of the differential capacitance.
Referring to fig. 3 and 4, further, the MEMS magnetic field sensor is composed of a folded beam structure B and a substrate S;
a substrate S rectangular block; a groove is arranged in the middle of the top surface of the substrate S; a folding beam structure B is arranged on the bottom surface of the groove of the substrate S;
the folding beam structure B consists of an upper rectangular block body and a lower rectangular column body 2 part; the upper rectangular block is an upper electrode of the MEMS magnetic field sensor; the center of the bottom surface of the upper rectangular block body is connected with the top end of the lower rectangular column body, and the horizontal contour area of the upper rectangular block body is larger than that of the lower rectangular column body; the folding beam structure B is T-shaped;
the top surface of the upper rectangular block body is covered with an insulating layer I; 2 groups of coils W are arranged on the top surface of the insulating layer I; the coils W are positioned on two sides of the lower rectangular cylinder and are symmetrical with each other;
a through hole is formed in the substrate S groove at the joint of the substrate S groove and the lower rectangular cylinder, and metal is filled in the through hole; a folded beam structure electrode 1 is arranged on the substrate S at the bottom opening of the through hole; the lower rectangular column body is connected with the folded beam structure electrode 1 through metal in the through hole;
a substrate electrode 2 is arranged on the surface of the groove of the substrate S below the coil W; namely 2 groups of substrate electrodes 2 are arranged; the substrate electrode 2 is a lower electrode of the MEMS magnetic field sensor; a through hole is formed in the substrate S at the joint of the substrate electrode 2, the bottom of the substrate electrode 2 extends downwards and penetrates out of the corresponding through hole;
The upper electrode and the lower electrode form a variable capacitor of the MEMS magnetic field sensor;
the coil W is a magnetic induction coil that causes the upper electrode to bend and deform in a magnetic field environment.
Furthermore, an annular block body C is arranged at the opening of the top of the groove of the substrate S; and a cover plate P is arranged on the top surface of the insulating layer I. Furthermore, the annular block body C is a rectangular ring; the coils W are divided into 2 groups, each group has 2 end points, and the 2 groups of end points are respectively led out from the two longer sides of the annular block C nearby;
further, the top surface of the upper rectangular block and the top surface of the substrate S are flush with each other.
Referring to fig. 3, further, two long sides of the insulating layer I are provided with bumps, and the bumps extend horizontally until being connected with the insulating layer I.
Furthermore, the material of the folded beam structure B is metal or P-type heavily doped silicon;
the substrate S is made of an n-type silicon wafer with a crystal face of (100), an SOI wafer or glass;
the insulating layer I is made of silicon dioxide or silicon nitride;
the folded beam structure electrode 1 is made of metal or P-type heavily doped silicon;
the substrate electrode 2 is made of metal;
the annular block body C is made of an insulator, and further made of packaging glue;
the cover plate P is made of an insulator, and is further made of a polymer material such as resin;
Furthermore, the total length of the substrate S is 1000 μm-4000 μm, the total width is 600 μm-1000 μm, and the total length is larger than the total width, and the substrate S is of a plane-symmetrical flat plate structure;
2 groups of hollow areas are arranged on the upper rectangular block body on two sides of the lower rectangular column body, each hollow area is a rectangular through hole, the distance from one end of each rectangular block body to the hollow part of the T-shaped folding beam is 1/4-1/3 of the total length of the flat plate, and the width of each hollow area is 1/6-1/4 of the width of the upper rectangular block body;
the sum of the thicknesses of the folded beam structure B and the insulating layer I is 10-40 mu m; the thickness of the upper rectangular block, inclusive.
The preparation method of the MEMS magnetic field sensor adopting the folded beam structure is a single preparation method or an IC circuit integrated preparation method;
the independent preparation is directly prepared on a wafer or an SOI (silicon on insulator) wafer;
the IC circuit integrated preparation method comprises the steps of depositing a passivation layer on a silicon chip which is finished with an IC circuit structure to protect the circuit structure, then preparing a sensor, and finally removing the passivation layer on the IC circuit;
the processes of the independent preparation method or the integrated preparation method of the IC circuit are as follows: taking a round crystal silicon wafer, an SOI wafer or a silicon wafer for completing the deposition of a passivation layer and protecting the IC circuit structure of the circuit structure; firstly, depositing a lower electrode on a substrate, wherein the lower electrode can be formed by depositing copper or gold materials or by a P-type heavy doping process; depositing a first conductive layer metal 1 on the surface of the substrate, preferably, the first conductive layer metal is metal aluminum; performing spin coating of photoresist, patterning the first metal layer by using the photoresist, and electroplating a layer of second conductive layer metal, wherein the second conductive layer metal is preferably metal nickel or chromium; and patterning is realized by adopting auxiliary processes such as photoetching and the like to obtain the upper electrode. On the upper surface of the upper electrode metal layer, a layer of silicon nitride or silicon dioxide is deposited to serve as an insulating layer. And simultaneously, patterning the insulating layer, corroding and removing two rectangular areas in a top view, and taking the patterned insulating layer as a mask, and corroding and removing the corresponding upper electrode metal rectangular area. And etching the back surface of the device, and finishing the extraction of the upper electrode and the lower electrode in modes of deposition and the like. And depositing and etching to form a ring-shaped copper, gold or aluminum electrode on the upper surface of the insulating layer to serve as a conductive coil. And finally, carrying out subsequent packaging.
Referring to fig. 2, further, the method for manufacturing the MEMS magnetic field sensor using the folded beam structure according to the present invention is specifically performed according to the following steps, taking the preparation based on the silicon substrate as an example:
step 3, continuously depositing and patterning a second metal layer of the sacrificial layer to obtain an opening serving as the sacrificial layer for corrosion; in addition, the pattern obtained from step 2 is different from the pattern obtained from step 3. To obtain a stepped sacrificial layer, this must be and can only be achieved by a multi-step deposition process.
Step 4, electroplating and patterning a third metal layer, wherein the third metal layer is an upper electrode;
step 5, depositing an insulating layer and patterning;
step 6, carrying out deep reactive ion etching on the back surface of the device, and carrying out metal deposition on the etching hole to complete the leading-out of the upper electrode and the lower electrode;
step 7, corroding the sacrificial layer and releasing the folded beam structure; then, depositing and patterning coils on the released folded beam structure to obtain a finished product; the material of the coil is the same as that of the first metal layer.
Preferably, taking the preparation based on the silicon substrate as an example, the preparation of the MEMS magnetic field sensor with the folded beam structure is performed according to the following steps:
step 1:
1.1 cleaning an n-type double-sided polished silicon wafer with a (100) crystal face;
1.2 performing DRIE (deep reactive ion) etching on the cleaned silicon wafer, wherein the etching depth is 30-40 mu m, the cavity is a rectangle with 1000 x 600 mu m, and the area of the cavity is larger than the projection area of the sensor folding beam on the substrate;
1.3 depositing a first metal with a thickness of 1 μm by LPCVD (low pressure chemical vapor deposition) process; preferably, the first metal is copper;
1.4, patterning the first metal by utilizing a photoetching and corrosion process to form a lower electrode, wherein the shape of the lower electrode is rectangular, and the area of the lower electrode is not larger than the projection area of the folding beam on the substrate;
step 2:
2.1 depositing a second metal, wherein the deposition thickness of the second metal is 20 mu m; the structure obtained by deposition in this step is referred to as a second metal first layer; the first layer of the second metal is a sacrificial layer; preferably, the second metal is aluminum;
2.2 patterning the first layer of the second metal obtained in the step 2.1 by using the photoresist as a mask to form a central columnar anchor area;
and 3, step 3:
3.1 continuing to deposit a second metal with the thickness of 10 mu m and level with the upper edge of the substrate; the structure obtained by deposition in this step is referred to as a second metal second layer
3.2, patterning the second metal layer obtained in the step 3.1, wherein a product obtained after patterning is called an annular frame; the outline of the annular frame is a rectangular frame body with the width of 5 mu m;
and 4, step 4:
4.1 electroplating with a third metal to a thickness greater than 10 μm; preferably, the third metal is nickel;
4.2, using photoresist as a mask plate, removing the region which does not need to be electroplated by corrosion, and simultaneously realizing two symmetrical hollowed-out regions; the area of each hollow-out area is 300 x 100 mu m, and the long edges of the hollow-out areas are flush with the edge of the anchor area;
4.3 adopting chemical mechanical polishing to enable the upper surface formed by the step 4.1 to be flush with the upper edge of the silicon substrate;
and 5:
5.1 depositing an insulating layer, wherein the thickness of the insulating layer is 5 mu m; preferably, the insulating layer is made of silicon dioxide;
5.2, corroding the insulating layer by using the photoresist as a mask to ensure that the coverage area of the insulating layer is consistent with that of the third metal layer;
and 6:
6.1 carrying out deep reactive ion etching on the back of the silicon wafer, wherein the etching through region is respectively connected with the substrate electrode and the anchor region of the upper electrode; the substrate electrode is made of copper, and the upper electrode is made of nickel;
6.2 depositing metal copper in the etched through hole, and connecting the metal copper with the anchor areas of the substrate electrode and the upper electrode in the 6.1;
And 7:
7.1 depositing a first metal on the insulating layer;
7.2, etching the first metal formed in the step 7.1, forming a coil in a graphical mode, and finishing leading out the coil to the two sides of the long edge so as to facilitate processing of the packaged pin;
7.3, corroding the sacrificial layer, and releasing the second metal to obtain a finished product.
Use/performance of MEMS magnetic field sensors employing folded beam structures:
when the magnetic field B is 100mT, 50mA current is introduced to the magnetic field sensor to the induction coil, and the displacement of the top end of the beam reaches 3 mu m;
the measuring range of the magnetic field sensor reaches 0.5-1T;
when the external magnetic field changes by 1mT, the differential capacitance difference variation of the magnetic field sensor is 50fF, namely the sensitivity is about 50fF/mT, and the resolution is 20 nT;
the power of the magnetic field sensor is 50mW-100 mW.
The sensor has the characteristics of wide range and high sensitivity, can be used in various measurement fields such as geomagnetic fields, general industrial equipment magnetic fields, medical equipment magnetic fields and the like, and has higher applicability compared with special magnetic field sensors in the fields.
The T-shaped folded beam structure greatly releases various material stresses in the processing process, and the maximum stress in the working process is about 5MPa and is far smaller than the maximum stress standard value of a general design structure, namely 500 MPa.
For use in the range of turndown, the lifetime is greater than 10 hundred million times.
Claims (3)
1. The preparation method of the MEMS magnetic field sensor adopting the folded beam structure is characterized in that the preparation method of the magnetic field sensor is a single preparation method or an IC circuit integrated preparation method;
the independent preparation method is directly prepared on a wafer or an SOI (silicon on insulator) wafer;
the IC circuit integrated preparation method comprises the steps of depositing a passivation layer on a silicon chip which is finished with an IC circuit structure to protect the circuit structure, then preparing a sensor, and finally removing the passivation layer on the IC circuit;
the processes of the independent preparation method or the IC circuit integrated preparation method are as follows: taking a round crystal silicon wafer, an SOI wafer or a silicon wafer for completing the deposition of a passivation layer and protecting the IC circuit structure of the circuit structure; firstly, depositing a lower electrode on a substrate, wherein the lower electrode can be formed by depositing copper or gold materials or by a P-type heavy doping process; depositing a first conductive layer metal on the surface of a substrate, carrying out spin coating of photoresist, patterning a first metal layer by using the photoresist, then electroplating a layer of second conductive layer metal, and carrying out patterning by adopting a photoetching auxiliary process to obtain an upper electrode, depositing a layer of silicon nitride or silicon dioxide on the upper surface of the upper electrode metal layer to be used as an insulating layer, simultaneously patterning the insulating layer, corroding and removing two rectangular areas in a top view, etching and removing the corresponding upper electrode metal rectangular area by taking the patterned insulating layer as a mask, carrying out back etching on a device, leading out the upper electrode and the lower electrode in a deposition and other modes, depositing and etching on the upper surface of the insulating layer to form an annular copper, gold or aluminum electrode to be used as a conductive coil, and finally carrying out subsequent packaging.
2. The method for preparing the MEMS magnetic field sensor using the folded beam structure according to claim 1, comprising the steps of:
step 1, taking a silicon wafer, etching a cavity by utilizing a deep reactive ion etching process, and depositing and patterning a first metal layer;
step 2, depositing and patterning a second metal layer, wherein the second metal layer is a sacrificial layer and is different from the first metal layer in material;
step 3, continuously depositing and patterning a step-shaped sacrificial layer second metal layer in order to obtain an opening serving as the sacrificial layer corrosion;
step 4, electroplating and patterning a third metal layer, wherein the third metal layer is an upper electrode;
step 5, depositing an insulating layer and patterning;
step 6, carrying out deep reactive ion etching on the back surface of the device, and carrying out metal deposition on the etching hole to complete the leading-out of the upper electrode and the lower electrode;
step 7, corroding the sacrificial layer and releasing the folded beam structure; and then depositing and patterning coils on the released folded beam structure to obtain a finished product.
3. The method for preparing the MEMS magnetic field sensor using the folded beam structure according to claim 1, comprising the steps of:
step 1:
1.1 cleaning an n-type double-sided polished silicon wafer with a (100) crystal face;
1.2 performing DRIE etching on the cleaned silicon wafer, wherein the etching depth is 30-40 μm, the cavity is a rectangle with 1000 x 600 μm, and the area is larger than the projection area of the sensor folding beam on the substrate;
1.3 depositing a first metal with the thickness of 1 μm by using an LPCVD process;
1.4, patterning the first metal by utilizing a photoetching and corrosion process to form a lower electrode, wherein the shape of the lower electrode is rectangular, and the area of the lower electrode is not larger than the projection area of the folding beam on the substrate;
step 2:
2.1 depositing a second metal, wherein the deposition thickness of the second metal is 20 mu m; the structure obtained by deposition in this step is referred to as a second metal first layer; the first layer of the second metal is a sacrificial layer;
2.2 patterning the first layer of the second metal obtained in the step 2.1 by using the photoresist as a mask to form a central columnar anchor area;
and step 3:
3.1 continuing to deposit a second metal with the thickness of 10 mu m; the structure obtained by deposition in the step is called a second metal second layer; the second metal second layer is a corrosion opening of the sacrificial layer;
3.2, patterning the second metal layer obtained in the step 3.1, wherein a product obtained after patterning is called an annular frame;
and 4, step 4:
4.1 electroplating with a third metal to a thickness greater than 10 μm;
4.2, removing the area which does not need to be electroplated by corrosion by using photoresist as a mask plate, and simultaneously realizing two symmetrical hollowed-out areas; the areas of the hollow areas are all 300 x 100 mu m, and the long edges are flush with the edges of the anchor areas;
4.3 adopting chemical mechanical polishing to enable the upper surface formed by the step 4.1 to be flush with the upper edge of the silicon substrate;
and 5:
5.1 depositing an insulating layer, wherein the thickness of the insulating layer is 5 mu m;
5.2, corroding the insulating layer by using the photoresist as a mask to ensure that the coverage area of the insulating layer is consistent with that of the third metal layer;
step 6:
6.1 carrying out deep reactive ion etching on the back of the silicon wafer, wherein the etching through region is respectively connected with the substrate electrode and the anchor region of the upper electrode;
6.2 depositing metal copper in the etched through hole, and connecting the metal copper with the substrate electrode and the anchor area of the upper electrode in the step 6.1;
and 7:
7.1 depositing a first metal on the insulating layer;
7.2, etching the first metal formed in the step 7.1, forming a coil in a graphical mode, and finishing leading out the coil to the two sides of the long edge so as to facilitate processing of the packaged pin;
7.3, corroding the sacrificial layer, and releasing the second metal to obtain a finished product.
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| CN111190126B (en) * | 2017-06-09 | 2022-06-07 | 温州大学 | Preparation method of MEMS magnetic field sensor adopting folded beam structure |
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| CN111573615B (en) * | 2020-05-19 | 2023-09-05 | 上海集成电路研发中心有限公司 | Inertial sensor and manufacturing method thereof |
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| CN113562687B (en) * | 2021-07-23 | 2024-04-09 | 中国科学院空天信息创新研究院 | Manufacturing method of low-frequency MEMS (micro-electromechanical systems) magneto-resistive sensor modulated by magneto-resistive motion |
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