Patent Application
20180135984
The present invention relates to a MEMS gyroscope. More particularly, the present invention relates to a symmetrical z-axis MEMS gyroscope utilizing the principle of detecting the movement of a sensor mass body, in accordance with a Coriolis force generated by exciting the sensor mass body rotating in a first direction in a second direction.
MEMS (Micro Electro Mechanical excitation systems) is a technique for achieving mechanical and electrical components using a semiconductor process, and a MEMS gyroscope which measures angular velocity is a representative example of utilizing MEMS technique. The gyroscope measures an angular velocity by measuring a Coriolis force generated when a rotational angular velocity is applied to an object moving at a predetermined speed. At this time, the Coriolis force is proportional to the cross product of the moving speed and the rotational angular speed due to the external force.
Further, in order to detect the generated Coriolis force, the gyroscope is provided with a mass which vibrates inside. Normally, a direction in which the mass in the gyroscope is driven is referred to as an excitation direction, a direction in which the rotational angular velocity is input to the gyroscope is referred to as an input direction, and a direction of detecting the Coriolis force generated in the mass is referred to as a sensing direction.
The excitation direction, the input direction, and the sensing direction are set as mutually orthogonal directions on the space. Normally, in a gyroscope utilizing the MEMS technique, coordinate axes are sets in three directions including two directions (a horizontal direction or x, y-directions) parallel to a plane formed by a bottom wafer substrate and perpendicular to each other, and one direction (a vertical direction or a z-direction) perpendicular to the plate surface of the substrate.
Therefore, the gyroscope is divided into an x-axis (or y-axis) gyroscope and a z-axis gyroscope. The x-axis gyroscope is a gyroscope in which the input direction is the horizontal direction, and the y-axis gyroscope is based on the vertical axis on the plane but is substantially the same as the x-axis gyroscope in the principle aspect. Thus, the x-axis and y-axis gyroscopes are collectively referred to as x-y axis gyroscopes. Meanwhile, in order to measure the angular velocity applied in the vertical direction using the z-type gyroscope, excitation needs to be performed in one axial direction on the plane, and the sensing needs to be performed in the direction perpendicular to the one axis on the plane. Accordingly, all the excitation electrodes and the sensing electrodes are located on the same bottom wafer.
A vibrating sensor mass body ms is located inside the MEMS-based gyroscope. When an angular velocity is applied around the z-axis perpendicular to the excitation direction x from the outside, the Coriolis force (Fc=2 mΩ×ωA sin ωt) acts on the sensor mass body in a third direction y perpendicular to the plane formed by the excitation direction x and its vertical axis z, and the magnitude of the displacement of the sensor mass body ms which varies with the Coriolis force is detected. Here, ms is a mass of the sensor mass body, Ω is the external angular velocity, ω (=2πf) is the excitation frequency of the sensor mass body, A is the driving amplitude of the sensor, and t is time. Since the performance sensitivity of the MEMS-based gyroscope is defined by Coriolis force (Fc/Ω=2πmfA) in comparison with the unit angular velocity, it is required to increase the mass m of the sensor at the design stage or increase the excitation frequency f of the sensor or increase the driving amplitude A.
In the conventional z-axis gyroscope as illustrated in
On the other hand, the magnitude of the movement of the sensor mass body caused by the Coriolis force is calculated by measuring the variation of the electrostatic capacitance C between the sensor mass body and the fixed detecting electrode. It is not possible to avoid a parasitic capacitance generated by an excitation voltage relatively larger than the sensing signal from being included in the sensing signal which is output from the fixed sensing electrode, as the noise. Therefore, as in a z-axis gyroscope of
In conclusion, as the excitation resonance frequency fd of the sensor closely matches the sensing resonance frequency fs, the overall sensitivity of the angular velocity can be maximized. However, an attempt to obtain the maximum sensing amplitude As by bringing fd close to fs causes a result of an increase in deviation of the detected amplitudes As of individual chips in the wafer in the manufacturing process, due to a problem in which sensing resonance frequency fs and the excitation resonance frequency fd sensitively change because of a micro-fabrication process error of the MEMS-based gyroscope structure, which ultimately leads to a cause of significant reduction in production yield.
Meanwhile, since the ultra-small precision instruments such as MEMS gyroscopes are sensitive to external noise or manufacturing process errors, the toughness or stability of the system is a very important consideration factor. However, it is difficult to have these robust and stable structures when using a single mass as illustrated in
However, as mentioned above, even if the MEMS gyroscope is designed to have a perfect antiphase structure and antiphase oscillation, in fact, excitation of the excitation electrode does not have perfect antiphase, or even if excitation is performed to the perfect antiphase, it is not easy to secure perfect antiphase motion in the sensing mode, due to errors in various manufacturing processes, external noise, or the like.
Therefore, in a symmetric z-axis MEMS gyroscope with two masses, it is necessary to devise a structure that is easy to manufacture and can also ensure perfect antiphase in the excitation mode or the sensing mode.
An aspect of the present invention provides a symmetric z-axis MEMS gyroscope capable of ensuring perfect antiphase in the excitation mode or sensing mode.
Another aspect of the present invention provides a symmetric z-axis MEMS gyroscope that is easy to manufacture and is resistant to external noises.
The aspects of the present invention are not limited to those mentioned above and another aspect which is not mentioned can be clearly understood by those skilled in the art from the description below.
According to an aspect of the present invention, there is provided a z-axis MEMS gyroscope including: a sensor frame disposed parallel to a bottom wafer substrate; a sensor mass body which relatively moves to the sensor frame, and is excited at one degree of freedom in an excitation mode; and at least one sensing electrode which senses displacement of the sensor mass body at the one degree of freedom in a sensing mode by Coriolis force, when an external angular velocity is input to the sensor mass body, wherein the sensor mass body includes two mass units, the two mass units are arranged in line symmetry with each other, and the antiphase motion of the two mass units is maintained by an antiphase link mechanism directly or indirectly connected between the two mass units.
According to the symmetrical z-axis MEMS gyroscope according to the present invention, since a perfect antiphase is guaranteed in the excitation mode or the sensing mode, it is possible to provide some degree of robust performance against a micro process error or an external noise.
Since the provision of the toughness is provided using a simple MEMS structure that can be manufactured in an integrated gyro wafer processing process, there is an advantage that no special additional process or cost occurs.
Advantages and features of the present invention and methods of accomplishing them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. It should be understood, however, that the present invention is not limited to the embodiments disclosed below but may be embodied in various different forms, the embodiments are merely provided to make the disclosure of the present invention complete, and to completely inform the invention to a person having ordinary knowledge in the technical field to which the invention belongs, and the present invention is only defined by the scope of the claims. The sane reference numerals refer to the same constituent elements throughout the specification.
Further, the embodiments described herein will be described with reference to a perspective view, a cross-sectional view, a side view, and/or a schematic view, which are ideal illustrations of the present invention. Therefore, the form of the illustration can be modified by manufacturing technique and/or tolerance and the like. Therefore, the embodiments of the present invention are not limited to the specific forms illustrated, but also include a change in the form generated according to the manufacturing process. Also, in each drawing illustrated in the present invention, each constituent element may be slightly enlarged or reduced in view of the convenience of explanation.
Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.
Also, support springs 14a, 14b, 15a, and 15b for supporting the movement of the sensor mass bodies 10a and 10b and the sensor frames 20a and 20b in the y-direction are connected between anchors 50a and 50b and the sensor frames 20a and 20b in the y-direction. Between the two sensor frames 20a and 20b, at least one or more antiphase link mechanisms 20a and 20b are connected between the two sensor frames 20a and 20b in order to ensure perfect antiphase of the movement of the in the y-direction of the sensor frames 20a and 20b in the excitation mode. In
On the other hand, in an embodiment of the present invention, in order to guide the first sensor mass body unit 10a and the second sensor mass body unit 10b to move in opposite directions on the basis of the x-axis at the time of the sensing mode, at least two horizontal seesaw link structures 30a, 32a, 34a, and 36a or 30b, 32b, 34b, and 36b may be used. At this time, the horizontal seesaw link structure may be configured to include seesaw bodies 30a and 30b, rotation links 32a, 32b, and 34a which connect both ends of the seesaw bodies 30a and 30b to the sensor mass body 10a and 10b, and pivot links 36a and 36b which connect the center of the seesaw bodies 30a and 30b to the fixing anchor 50a and 50b.
For example, when the first sensor mass body unit 10a moves in the positive x-axis direction (rightward direction), while the upper rotating links 32a and 32b also move in the positive x-axis direction, the seesaw bodies 30a and 30b pivots in a clockwise direction. At this time, since the lower ends of the seesaw bodies 30a and 30b move in the negative x-axis direction (leftward direction) due to the center pivot links 36a and 36b, the lower rotation link 34a and 34b move to the left side. Finally, the movement of the second sensor mass body unit 10b is guided in the negative x-axis direction (leftward direction) opposite to the direction of the first sensor mass body unit 10a.
The antiphase link mechanism 40a includes two anchor connections 43a and 44a connected to a central anchor 45a having no movement to the gyro wafer, and two link arms 41a and 42a which are rotationally symmetrical with respect to each other by 180 degrees on the basis of the center of the antiphase link mechanism 40a and are connected to the two sensor frames 20a and 20b, respectively. Further, the antiphase link mechanism 40a includes a torsional stiffness support 47a which impart torsional stiffness to the antiphase link mechanism 40a, and is formed by closed curves passing through at least the intersection points between the two anchor connections 43a and 44a and the two link arms 41a and 42a. In addition to the torsional rigid support function, the torsional rigid support 47a includes a function of geometrically connecting a first structure including the first anchor connection 43a and the first link arm 41a, and a second structure including the second anchor connection 44a and the second link arm 42a.
In
In the z-axis MEMS gyroscope as illustrated in
(ms+mf)ÿ+kay=Fd(t) [Equation 1]
m
s
{umlaut over (x)}+k
b
X=2ms{dot over (y)}Ω [Equation 2]
Here, x is the displacement of the sensor mass bodies 10a and 10b in the x-direction, y is the displacement of the sensor mass bodies 10a and 10b in the y-direction, ms is the mass of the sensor mass bodies 10a and 10b, and mf is the mass of the sensor frames 20a and 20b. Further, ka is a stiffness of spring disposed in a vertical direction (sum of stiffness of the spring 14a or 14b and stiffness of the spring 15a or 15b in
Therefore, in the excitation mode, the sensor mass bodies 10a and 10b, and the sensor frames 20a and 20b are vibrated together in the y-direction. However, in the sensing mode, the sensor mass bodies 10a and 10b are vibrated in the x-direction with respect to the sensor frames 20a and 20b, and the sensor frames 20a and 20b does not substantially move in the x-direction.
Under the conditions in which the rotational angular velocity Ω in the z-axis direction is applied onto the gyro wafer, sensor mass bodies 10a and 10b and the sensor frames 20a and 20b are excited together in the y-direction by the excitation electrodes 62, 64, 66, and 68. The excitation electrodes 62, 64, 66, and 68 may be provided as a comb electrode, a plate electrode or other methods. The excitation electrodes 62, 64, 66, and 68 are attached and fixed to the side surfaces of the anchors 61, 63, 65, and 67 fixed to the wafer substrate, respectively. In the embodiment of
In the above-described excitation mode, substantially no relative displacement of the sensor mass body 10a and 10b and the sensor frames 20a and 20b occurs in the y-direction, and vibration caused by the excitation is supported by the support springs 14a, 14b, 15a, and 15b arranged in the vertical direction (y-direction). At this time, the two sensor frames 20a and 20b are connected in the y-direction by the two antiphase link mechanisms 150a and 150b.
The two antiphase link mechanisms 150a and 150b are arranged symmetrically axisymmetrically with respect to each other in the x-axis direction. In the antiphase link mechanisms 150a and 150b, the force acting on the end portion of the link arm is converted into a reaction force of the completely antiphase at the end portion of the other link arm due to the rotationally symmetric structure of the antiphase link mechanisms 150a and 150b. Therefore, when the first sensor frame unit 20a moves downward, the lower link arms of the antiphase link mechanisms 150a and 150b pull the second sensor frame unit 20b upward. Conversely, when the first sensor frame unit 20a moves upward, the lower link arms of the antiphase link mechanisms 150a and 150b push the second sensor frame unit 20b downward. Thus, even if the excitation force applied to the upper first sensor mass body unit 10a and the first sensor frame unit 20a by the excitation electrodes 62, 64, 66, and 68, and the excitation force applied to the lower second sensor mass body unite 10b and the second sensor frame unit 20b do not have completely antiphase, and in fact, completely antiphase due to the antiphase link mechanisms 150a and 150b can be guaranteed in the vibration of the sensor mass bodies 10a and 10b and the sensor frames 20a and 20b.
On the other hand, when the rotation angular velocity Ω in the z-axis direction and the excitation in the y-axis direction simultaneously act, the sensor mass bodies 10a and 10b vibrates in the x-direction by the Coriolis force as illustrated in the right side of the expression 2. Here, the sensor mass bodies 10a and 10b are connected to the sensor frames 20a and 20b by support springs 12a, 13a, 12b, and 13b arranged in the horizontal direction, respectively. These support springs 12a, 13a, 12b, and 13b may also be provided as folding type MEMS beam springs which can also be linearly deformed. Therefore, in the sensing mode, the sensor frames 20a and 20b do not substantially move in the x-direction, and the sensor mass bodies 10a and 10b may move in the x-direction with respect to the sensor frames 20a and 20b.
On the other hand, since the completely antiphase of the excitation direction of the two sensor mass bodies 10a and 10b is guaranteed with respect to the y-axis by the antiphase link mechanisms 150a and 150b at the time of excitation, Coriolis force acting on the two sensor mass bodies 10a and 10b is also completely opposite. Therefore, in the sensing mode, if the first sensor mass body unit 10a moves in the negative x-axis direction (leftward direction), the second sensor mass body unit 10b moves in the positive x-axis direction (rightward direction). In addition, if the first sensor mass body unit 10a moves in the positive x-axis direction (rightward direction), the second sensor mass body unit 10b moves in the negative x-axis direction (leftward direction). The reciprocal movement of the sensor mass bodies 10a and 10b in the sensing mode is naturally guided by the horizontal seesaw link structures 30a, 32a, 34a, and 36a or 30b, 32b, 34b, and 36b. The horizontal seesaw link structures include seesaw main bodies 30a and 30b, rotation links 32a, 32b, 34a, and 34b which connect both ends of the seesaw main bodies 30a and 30b to the sensor mass bodies 10a and 10b, and pivot links 36a and 36b which connect the center of the seesaw bodies 30a and 30b to the fixing anchors 50a and 50b. Therefore, if the first sensor mass body unit 10a moves in the x-axis direction (rightward direction), while the upper rotation links 32a and 3b also move in the x-axis direction, the upper seesaw bodies 30a and 30b pivot in the clockwise direction. At this time, the lower ends of the seesaw bodies 30a and 30b move in the negative x-axis direction (leftward direction) by the central pivot links 36a and 36b, and thus, the lower rotation links 34a and 34b move toward the left side. Finally, the movement of the second sensor mass body unit 10b is guided in the negative x-axis direction (leftward direction) which is a direction opposite to that of the first sensor mass body unit 10a.
The movement in the Coriolis force direction (x-direction) of the sensor mass body 10a and 10b may be determined by the interval between each of the sensor mass body 10a and 10b and each of the sensing electrodes 52, 54, 56, and 58 or may be detected by a change in electrostatic capacitance due to a change in area. These sensing electrodes 52, 54, 56, and 58 can also be provided as comb electrodes or flat plate electrodes, and may be attached to the side surfaces of the anchors 51, 53, 55, and 57 fixed to the wafer substrate, respectively. In the embodiment of
Anchors 53 and 57 for fixing the sensing electrodes are located inside the sensor mass bodies 10a and 10b, and below the sensor frames 20a and 20b and the sensor mass bodies 10a and 10b, i.e., below the gyro wafer 90, bottom wafers 110 are spaced apart at regular intervals. At this time, the anchors 50b, 53, and 57 extend to reach from the gyro wafer 90 to the bottom wafer 110 (50b′, 53′, and 57′). Therefore, even when the sensor frames 20a and 20b or the sensor mass body 10a and 10b in the gyro wafer 90 vibrate, the anchors 50b, 53, and 57 are fixed without being moved.
In
The z-axis MEMS gyroscope which is excited in the y-axis direction and performs sensing in the x-axis direction in connection with the embodiment described in
Referring to
Specifically, the sensors masses 10a and 10b are excited in the x-axis direction by the excitation electrodes 152, 154, 156, and 158. At this time, the first sensor mass body unit 10a and the second sensor mass body unit 10b are excited in the mutually opposite directions. Such an excitation in the opposite direction can be guided by the horizontal seesaw link structures 30a, 32a, 34a, and 36a or 30b, 32b, 34b, and 36b.
For example, if the first sensor mass body unit 10a is excited in the positive x-axis direction (rightward direction), while the upper rotating link 32a and 32b also move in the x-axis direction, the seesaw main bodies 30a and 30b pivot in a clockwise direction. At this time, since the lower ends of the seesaw bodies 30a and 30b move in the negative x-axis direction (leftward direction) due to the center pivot links 36a and 36b, the lower rotation link 34a and 34b move to the left side. Finally, the motion of the second sensor mass body unit 10b excited in the negative x-axis direction is guided in the negative x-axis direction (leftward direction) which is the direction opposite to that of the first sensor mass body unit 10a. Of course, when the first sensor mass body unit 10a is excited in the negative x-axis direction (leftward direction), the motion of the second sensor mass body unit 10b will be guided in the x-axis direction (rightward direction).
Excitation of the sensor mass bodies 10a and 10b in the x-direction of these causes the motion in the y-direction by the Coriolis force, under the external rotational angular velocity Ω. Here, since the excitation directions of the respective sensor mass bodies 10a and 10b are opposite to each other, the Coriolis force acting on the respective sensor mass bodies 10a and 10b also becomes opposite to each other. That is, when the first sensor mass body unit 10a moves in the positive y-direction, the second sensor mass body unit 10b moves in the negative y-direction, and when the first sensor mass body unit 10a moves in the negative y-direction, the second sensor mass body unit 10b moves in the positive y-direction. At this time, the sensor mass bodies 10a and 10b move integrally with the sensor frames 20a and 20b in the same sensing direction (positive y-direction or negative y-direction), and the movement thereof is detected by the sensing electrodes, 164, 166, and 168.
The antiphase link mechanisms 150a and 150b provide reaction force of the perfectly opposite phase with respect to the motion in the sensing direction of the sensor mass bodies 10a and 10b and the sensor frame 20a and 20b at the end portion of the link arm. Therefore, when the first sensor frame unit 20a moves downward, the lower link arm of the antiphase link mechanisms 150a and 150b pulls the second sensor frame unit 20b upward. Conversely, when the first sensor frame unit 20a moves upward, the lower link arm of the antiphase link mechanisms 150a and 150b push the second sensor frame unit 20b downward. Therefore, perfect antiphase can be guaranteed to the motion in the sensing direction of the sensor mass body 10a and 10b and the sensor frames 20a and 20b.
Although the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art to which this invention pertains will appreciate that the invention can be implemented in other concrete form without changing the technical spirit or essential characteristics. Accordingly, it is understood that the embodiments described above are illustrative rather than limited in all aspects.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2015-0066097 | May 2015 | KR | national |
This application is a continuation application of international application PCT/KR2016/004861, filed on May 10, 2016, now pending, which claims foreign priority from Korean Patent Application No. 10-2015-0066097 filed on May 12, 2015 in the Korean Intellectual Property Office, the disclosure of each document is incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/KR2016/004861 | May 2016 | US |
| Child | 15808185 | US |
