JP2010025898A - Mems sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small MEMS sensor which can detect three dimensional angular velocity and three dimensional acceleration. <P>SOLUTION: The MEMS sensor comprises a support part of frame form, an inner flexible part mounted inside of the support part, an inner suspension part combined with a center part of the inner flexible part, an excitation means to be mounted at the inner flexible part and to excite the inner flexible part, an angular velocity detection means for being mounted at the inner flexible part and for detecting the angular velocity component of three shafts according to deformation of the inner flexible part, three or more pieces of the outer flexible part which are beams projected to the outside of the support part, each of three or more pieces of the outer suspensions parts combined with a free end of each of the outer flexible parts, and an acceleration detection means for being mounted each of the outer flexible parts and for detecting acceleration component of three shafts according to deformation of each of outer flexible parts. The support part, the inner flexible part, the inner suspension part, the excitation means, the angular velocity detection means, the outer flexible part, the outer suspension part, and the acceleration detection means are formed in one die. The outer flexible part is projected from the support part to a corner part of the die. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a MEMS (Micro Electro Mechanical System) sensor, and more particularly to a MEMS sensor for detecting a three-dimensional angular velocity and a three-dimensional acceleration.

2. Description of the Related Art Conventionally, a MEMS sensor that functions as an acceleration sensor or a vibration gyroscope by detecting deformation of a beam or a diaphragm with a piezoelectric body or a piezoresistor is known (see, for example, Patent Documents 1-8). Patent Document 9 discloses a MEMS sensor in which two vibration gyroscopes and one acceleration sensor are arranged on one die.
JP 2006-177823 A JP 2006-308325 A JP 2007-3211 A JP-A-8-285883 JP 2004-294450 A JP 2007-24864 A JP 2007-256046 A JP 2007-33309 A Japanese Patent Laid-Open No. 10-10148

  As disclosed in Patent Document 9, the configuration in which the vibration gyroscope and the acceleration sensor are arranged on one die is more space efficient than the configuration in which these two types of sensors are arranged on a plurality of packages and dies. Rise. However, since the deformation of the flexible part due to the Coriolis force is generally smaller than the deformation of the flexible part due to excitation, the vibration gyroscope becomes larger than the acceleration sensor. Therefore, as disclosed in Patent Document 9, in a configuration in which a plurality of vibrating gyroscopes are arranged around the periphery of one die to detect angular velocity components of two or more axes, there is a problem that the die becomes large. is there.

  An object of the present invention is to provide a small MEMS sensor capable of detecting a three-dimensional angular velocity and a three-dimensional acceleration.

  (1) A MEMS sensor for achieving the above object includes a frame-shaped support portion, an inner flexible portion erected inside the support portion, and an inner weight portion coupled to a central portion of the inner flexible portion. And an excitation means arranged in the inner flexible part for exciting the inner flexible part, and an angular velocity detecting means for detecting a triaxial angular velocity component corresponding to the deformation of the inner flexible part arranged in the inner flexible part, Three or more outer flexible portions that are beams protruding from the support portion to the outside of the support portion; and three or more outer weight portions that are respectively coupled to the free ends of the respective outer flexible portions; And an acceleration detecting means for detecting a triaxial acceleration component corresponding to the deformation of each of the outer flexible portions. The support portion, the inner flexible portion, the inner weight portion, and the excitation are provided. The means, the angular velocity detection means, the outer flexible part, the outer weight part, and the acceleration detection means are formed in an integrated die, and the outer flexible part is formed from the support part to the die. Projects toward the part.

  The region remaining after placing the mechanical elements for detecting the three-dimensional angular velocity on the die is biased to the corners of the die. The flexible part for detecting the three-dimensional acceleration is composed of three or more beams, and the three-dimensional angular velocity is detected by connecting the weight part to the free end of each beam extending toward the corner of the die. Therefore, the mechanical element for detecting the three-dimensional acceleration can be efficiently arranged in the region of the die that remains after the mechanical element for arranging is arranged. Therefore, according to the present invention, the MEMS sensor that can detect the three-dimensional angular velocity and the three-dimensional acceleration can be downsized.

  (2) In the MEMS sensor for achieving the above object, the excitation means and the angular velocity detection means preferably include a plurality of piezoelectric elements, and the acceleration detection means preferably includes a plurality of piezoresistive elements.

  In this configuration, it is possible to detect an angular velocity corresponding to a weak Coriolis force with a higher sensitivity than when detecting an angular velocity using a piezoresistive element, and it is possible to detect an acceleration having a lower frequency than when detecting an acceleration using a piezoelectric element.

  (3) In the MEMS sensor for achieving the above object, the inner flexible portion is preferably a diaphragm.

  In this configuration, since the piezoelectric element having a larger area can be arranged on the diaphragm as compared with the case where the inner flexible portion is a beam, the angular velocity corresponding to the weak Coriolis force can be detected with high sensitivity.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the corresponding component in each figure, and the overlapping description is abbreviate | omitted.

  A motion sensor 1 as a first embodiment of the MEMS sensor of the present invention is shown in FIG. 2, and its die 10 is shown in FIG. The motion sensor 1 includes a die 10 which is a solid element housed in a package 20. The die 10 is formed with a diaphragm 11 for detecting a three-axis angular velocity component, an inner weight portion 12, a plurality of detection piezoelectric elements 13 and an excitation piezoelectric element 14. The die 10 is formed with four beams 15 for detecting triaxial acceleration components, four outer weight portions 16, and a plurality of piezoresistive elements R. Only the support portion 17 of the die 10 is fixed to the package 20. In FIG. 1B, FIG. 1C, and FIG. 2, the boundary of these functional elements is shown as the continuous line, and the interface of a layer structure is shown with the broken line.

  The die 10 has a substantially square shape in plan view, and is a laminated structure including a glass layer 170, a thick silicon layer 100, a stopper insulating layer 110, a thin silicon layer 120, an insulating layer 130, an electrode layer 140, a piezoelectric layer 150, and an electrode layer 160. Is the body. The outer dimensions of the die 10 are approximately 3 mm on a side of a substantially square and approximately 1 mm in height.

  The frame-shaped support portion 17 includes a glass layer 170, a thick silicon layer 100, a stopper insulating layer 110, a thin silicon layer 120, and an insulating layer 130. When viewed from a direction perpendicular to the diaphragm 11 (hereinafter, viewing from this direction is referred to as a plan view), the outer contour of the support portion 17 is an octagon and the inner contour is a circle. A diaphragm 11 is installed inside the support portion 17. Four beams 15 protrude outward from the support portion 17. Both the inner weight portion 12 connected to the center portion of the diaphragm 11 and the outer weight portion 16 connected to the free end of the beam 15 are supported by the support portion 17 in a state of floating from the package 20.

  The diaphragm 11 as the inner flexible portion is a thin film having a circular shape in plan view provided on the support portion 17. The diaphragm 11 is composed of a thin silicon layer 120 and an insulating layer 130.

  In the vicinity of the center where the stress of the diaphragm 11 is concentrated, four detection piezoelectric elements 13 are arranged in a substantially annular shape. An angular velocity detecting means for detecting a triaxial angular velocity component corresponding to the deformation of the diaphragm 11 is constituted by four detection piezoelectric elements 13. Four excitation piezoelectric elements 14 are arranged in a substantially annular shape at the peripheral edge of the diaphragm 11. Excitation means for exciting the diaphragm 11 so as to vibrate three-dimensionally includes four excitation piezoelectric elements 14. Each of the detection piezoelectric element 13 and the excitation piezoelectric element 14 includes electrode layers 140 and 160 and a piezoelectric layer 150 constituting electrodes. The material of the electrode layers 140 and 160 is platinum (Pt), for example. The material of the piezoelectric layer 150 is, for example, PZT (lead zirconate titanate).

  The plan view of the inner weight portion 12 coupled to the center portion of the diaphragm 11 is circular. The inner weight portion 12 includes a glass layer 170, a thick silicon layer 100, and a stopper insulating layer 110. Since the moment acting on the diaphragm 11 is increased by setting the center of gravity of the inner weight portion 12 far from the diaphragm 11, the plan view of the inner weight portion 12 becomes smaller as it approaches the diaphragm 11. A gap is formed between the support portion 17 and the inner weight portion 12 for the inner weight portion 12 to move relative to the support portion 17.

  By applying an excitation electrical signal to the excitation piezoelectric element 14, the inner weight 12 together with the diaphragm 11 is two-dimensionally vibrated. When the angular velocity is generated, a Coriolis force corresponding to the angular velocity and the speed of the inner weight portion 12 is generated in the inner weight portion 12. When the deformation of the diaphragm 11 caused by the Coriolis force is detected by a plurality of detecting piezoelectric elements 13, a triaxial angular velocity component can be detected. By using a piezoelectric element as the Coriolis force detection means, the angular velocity corresponding to the weak Coriolis force can be detected with higher sensitivity than when detecting the Coriolis force by piezoresistance.

  The four beams 15 as the outer flexible portions are thin films protruding from the support portion 17 toward the corner portion of the die 10 and having free ends coupled to the outer weight portion 16. The four beams 15 protrude from the support portion 17 in four directions at intervals of 90 degrees, that is, in four directions from the center of the cross to the end. The beam 15 is composed of a thin silicon layer 120 and an insulating layer 130.

  The four outer weight portions 16 are respectively coupled to the free ends of the beams 15. The four outer weight portions 16 are arranged at the corners of the die 10 which are also positions corresponding to the four end portions of the cross with the center of gravity overlapping the center of gravity of the inner weight portion 12. More specifically, the distance from the center of gravity of each outer weight part 16 to the center of gravity of the inner weight part 12 is equal, and the projection onto the diaphragm 11 of a straight line connecting the center of gravity of the outer weight part 16 and the center of gravity of the inner weight part 12 is Cross at 90 degree intervals. Each outer weight portion 16 includes a glass layer 170, a thick silicon layer 100, a stopper insulating layer 110, a thin silicon layer 120, and an insulating layer 130.

  A piezoresistive element R is formed in the vicinity of the interface between the thin silicon layer 120 of each beam 15 and the insulating layer 130. By using the piezoresistive element R as the acceleration detecting means, it is possible to detect acceleration having a lower frequency than when using a piezoelectric body as the acceleration detecting means. By detecting the deflection of the two beams 15 aligned in a straight line by the piezoresistive element R, the acceleration component of the axis parallel to the straight line (x-axis or y-axis) and the z-axis (axis parallel to the thickness direction of the beam) Can be detected. In order to individually detect the acceleration component of each axis, three or four bridge circuits in which four piezoresistive elements R are connected for each axis are configured. By forming the piezoresistive element R into a U shape that is long in the direction in which the beam 15 protrudes, the sensitivity can be increased.

(Action / Effect)
When the still to have the beam 15 is an acceleration a _x, as shown in FIG. 3A in a direction projecting from the support portion 17 occurs, the acceleration a _x beams 15a arranged in the direction of, and is formed on the surface of one of the beams 15b stretch piezoresistive elements R _a, shrinks piezoresistive elements R _b which is formed on the other surface. Therefore, when a difference in resistance value of the piezoresistive elements R arranged in the two beams 15 protruding in the opposite directions from the support portion 17 is detected by a bridge circuit, an acceleration component in the direction in which the two beams 15 are arranged. Can be detected. Since the four beams 15 are arranged at an interval of 45 degrees when viewed from the support portion 17, biaxial acceleration components can be detected from the resistance values of the piezoresistive elements R arranged on the four beams 15. When acceleration _az occurs in a direction perpendicular to the plane in which the four outer weight portions 16 are arranged as shown in FIG. 3B, all the piezoresistive elements R provided on the surface layer of the four beams 15 contract. That is, when the sum of the resistance values of the piezoresistive element R is detected by a bridge circuit, an acceleration component in a direction perpendicular to the plane in which the four outer weight portions 16 are arranged can be detected.

  In the present embodiment, a diaphragm 11 and an inner weight portion 12 used for detecting a three-dimensional angular velocity are arranged at the center portion of the die 10, and four beams 15 and an outer weight portion 16 are provided at the corner portions of the die 10. And three-dimensional acceleration is detected using each of the four beams 15 and the outer weight portion 16. Therefore, a function as a three-dimensional angular velocity sensor having the same sensitivity and a function as a three-dimensional acceleration sensor can be imparted to the die 10 having the same area as a die that functions only as a three-dimensional angular velocity sensor. As a result, the motion sensor that detects the three-dimensional acceleration and the three-dimensional angular velocity can be downsized. Further, by correcting the angular velocity using the detected acceleration, it is possible to improve the angular velocity detection accuracy. Furthermore, since the center of gravity of the four outer weight portions 16 for detecting acceleration overlaps the center of gravity of the inner weight portion 12 for detecting angular velocity in the z direction, it is accurate as the acceleration used for correcting the angular velocity. Acceleration can be detected.

(Production method)
First, as shown in FIG. 4, a piezoresistive element R is formed on the thinner silicon layer 120 of an SOI (Silicon On Insulator) wafer 1000. Specifically, first, a mask (not shown) made of a photoresist having a pattern corresponding to the piezoresistive element R is formed on the surface of the thin silicon layer 120. Next, the piezoresistive element R is formed by implanting impurities into the surface layer of the thin silicon layer 120 exposed from the mask. As an impurity, for example, boron (B) ions are implanted at a concentration of 2 × 10 ¹⁸ / cm ³ . Then, it activates by annealing. As the SOI wafer 1000, for example, a thick silicon layer 100 having a thickness of 625 μm, a silicon dioxide (SiO ₂ ) layer serving as a stopper insulating layer 110 having a thickness of 1 μm, and a thin silicon layer 120 having a thickness of 10 μm. Use.

Next, as shown in FIG. 5, the contact resistance reducing portion 121 is formed on the thin silicon layer 120, and the insulating layer 130 is formed on the surface of the thin silicon layer 120. Specifically, first, a mask (not shown) made of a photoresist having a pattern corresponding to the contact resistance reduction unit 121 is formed on the surface of the thin silicon layer 120. Subsequently, an impurity is implanted into the surface layer of the thin silicon layer 120 exposed from the mask, thereby forming the contact resistance reducing portion 121. As an impurity, for example, boron (B) ions are implanted at a concentration of 2 × 10 ²⁰ / cm ³ . Thereafter, the insulating layer 130 made of silicon dioxide is formed on the surface of the thin silicon layer 120 while being activated by annealing.

  Next, a contact hole H is formed in the insulating layer 130 as shown in FIG.

  Next, as shown in FIG. 7, the electrode layer 140, the piezoelectric layer 150, and the electrode layer 160 are laminated in this order on the surface of the insulating layer 130. For example, a platinum (Pt) film having a thickness of 0.1 μm is formed by sputtering as the electrode layers 140 and 160, and a PZT (lead zirconate titanate) film having a thickness of 3 μm is formed by the magnetron sputtering method, for example. To do.

  Next, as shown in FIG. 8, the detection piezoelectric element 13 and the excitation piezoelectric element 14 are formed by etching the electrode layer 140, the electrode layer 160, and the piezoelectric layer 150 by, for example, a milling method using argon (Ar) ions. To do. At this time, the wiring of the piezoresistive element R composed of the electrode layer 140 is also formed at the same time.

Next, the thin silicon layer 120 and the insulating layer 130 are etched to form the contour of the beam 15 shown in FIG. Specifically, first, a mask made of a photoresist having a pattern corresponding to the beam 15 is formed on the surface of the insulating layer 130. Subsequently, by patterning the insulating layer 130 by reactive ion etching using CHF ₃ gas, the patterning of the thin silicon layer 120 by reactive ion etching using CF ₄ gas, the contour of the beam 15 is formed.

  Next, as shown in FIG. 9, the lower surface of the work is temporarily fixed to the sacrificial substrate 99 with the thick silicon layer 100 facing upward. As the fixing means B, for example, wax, photoresist, double-sided pressure-sensitive adhesive sheet or the like is used.

Next, as shown in FIG. 10, the thick silicon layer 100 is etched to form the inner weight portion 12, the outer weight portion 16, and the portion made of the thick silicon layer 100 of the support portion 17. Specifically, for example, as follows. A photoresist mask P having a pattern corresponding to the inner weight portion 12, the outer weight portion 16 and the support portion 17 is formed on the surface of the thick silicon layer 100. Subsequently, the inner weight part 12, the outer weight part 16 and the support part are carried out by Deep-RIE (Reactive Ion Etching), in which reactive ion etching using SF ₆ gas and passivation using C ₄ F ₈ gas are alternately repeated. A portion composed of 17 thick silicon layers 100 is formed.

  Next, as shown in FIG. 11, the stopper insulating layer 110 is wet etched with buffered hydrofluoric acid using the etched thick silicon layer 100 as a mask. Thereafter, the sacrificial substrate 99 is removed from the workpiece.

  Next, as shown in FIG. 12, a glass wafer to be the glass layer 170 is anodically bonded to the thick silicon layer 100. As a material of the glass layer 170, for example, a Pyrex glass (registered trademark) wafer having a thickness of 500 μm is used. In the glass wafer, a groove N serving as a gap between the inner weight portion 12, the support portion 17, and the outer weight portion 16 is formed by cutting with a dicer, etching, sandblasting, or the like.

  Next, when the glass layer 170 is cut into the inner weight part 12, the support part 17, and the outer weight part 16, and then the work is cut for each die by a dicer, the die 10 of the motion sensor 1 shown in FIG. 1 is completed. In this step, the workpiece can be cut into an arbitrary shape by cutting with a dicer, etching, or sandblasting.

  Thereafter, when a post-process such as packaging is performed, the motion sensor 1 shown in FIG. 2 is completed.

(Other embodiments)
It should be noted that the technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention.

For example, as shown in FIG. 13, the outer peripheral surface of the support portion 17 and the inner peripheral surface of the outer weight portion 16 may be curved surfaces that are bent in an arc shape. Further, as shown in FIG. 14, each outer weight portion 16 may be supported by two beams 15 _α and 15 _β that are parallel to each other. In this case, a piezoresistive element R is disposed on each of the beams 15 _α and 15 _β . Further, the two beams 15 _α and 15 _β supporting one outer weight portion 16 may not be parallel to each other as shown in FIG.
For example, the inner flexible portion may be in the form of a cross beam.
The materials, dimensions, film forming methods, and mask pattern forming methods shown in the above embodiments are merely examples, and descriptions of addition and deletion of steps and replacement of the order of steps that are obvious to those skilled in the art are omitted. ing.

1A is a plan view according to an embodiment of the present invention, FIG. 1B is a cross-sectional view taken along line BB in FIG. 1A, and FIG. 1C is a cross-sectional view taken along line CC in FIG. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention. Sectional drawing concerning embodiment of this invention. The top view concerning embodiment of this invention. The top view concerning embodiment of this invention. The top view concerning embodiment of this invention.

Explanation of symbols

1: motion sensor, 10: die, 11: diaphragm, 12: inner weight part, 13: piezoelectric element for detection, 14: piezoelectric element for excitation, 15: beam, 16: outer weight part, 17: support part, 20: Package: 99: Sacrificial substrate, 100: Thick silicon layer, 110: Stopper insulating layer, 120: Thin silicon layer, 121: Contact resistance reduction part, 130: Insulating layer, 140: Electrode layer, 150: Piezoelectric layer, 160: Electrode Layer: 170: glass layer, 1000: wafer, B: fixing means, H: contact hole, N: groove, P: photoresist mask, R: piezoresistive element

Claims (3)

A frame-shaped support,
An inner flexible part erected inside the support part;
An inner weight part coupled to the central part of the inner flexible part;
An excitation means disposed in the inner flexible portion for exciting the inner flexible portion;
Angular velocity detection means for detecting a triaxial angular velocity component according to the deformation of the inner flexible portion, which is disposed in the inner flexible portion;
Three or more outer flexible parts that are beams protruding from the support part to the outside of the support part;
Three or more outer weight portions respectively coupled to the free ends of the respective outer flexible portions;
Acceleration detection means for detecting a triaxial acceleration component according to deformation of each of the outer flexible portions, which is disposed in each of the outer flexible portions;
With
The support portion, the inner flexible portion, the inner weight portion, the excitation means, the angular velocity detection means, the outer flexible portion, the outer weight portion, and the acceleration detection means are formed in an integrated die,
The outer flexible portion protrudes from the support portion toward the corner of the die,
MEMS sensor. The excitation means and the angular velocity detection means comprise a plurality of piezoelectric elements,
The acceleration detecting means includes a plurality of piezoresistive elements,
The MEMS sensor according to claim 1. The inner flexible portion is a diaphragm.
The MEMS sensor according to claim 2.

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