Measuring and testing – Speed – velocity – or acceleration – Angular rate using gyroscopic or coriolis effect
Reexamination Certificate
2003-02-06
2004-09-28
Kwok, Helen (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Angular rate using gyroscopic or coriolis effect
C073S504120
Reexamination Certificate
active
06796178
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a MEMS gyroscope. More particularly, the present invention relates to a rotation-type decoupled MEMS gyroscope that allows mutually independent motion of a drive body and a sensing body.
2. Description of the Related Art
Micro Electro Mechanical System (MEMS) is a technology embodying the fabrication of mechanical and electrical elements using semiconductor processing. A gyroscope for measuring angular velocity is an example of a device that may incorporate MEMS technology. A gyroscope is able to measure an angular velocity by measuring the Coriolis force that occurs when an angular velocity is applied to an object moving at a certain velocity. The Coriolis force is proportional to the cross product of the moving velocity and the angular velocity due to an external force. In order for the gyroscope to generate and sense the Coriolis force, the gyroscope has a mass body vibrating therein.
FIG. 1
illustrates a view for schematically viewing a MEMS gyroscope, in particular, a rotation-type gyroscope. A driving direction (A), an input direction (&OHgr;), and a sensing direction (S) are set in space in directions perpendicular to one another. Generally, in a gyroscope using MEMS technology, three coordinate axes are established. The first two axes, an X-axis and a Y-axis are parallel to a surface of the substrate and perpendicular to each other. The third axis, a Z-axis, is normal to the surface of the substrate. In
FIG. 1
, the driving direction (A) is set in the direction of the X-axis direction, the input direction (&OHgr;) is set in the direction of the Y-axis, and the sensing direction (S) is set in the direction of the Z-axis.
The mass body (“body”) is rotatably mounted about the X-axis, and is driven to move about the X-axis by a driving electrode (not shown). If an angular velocity is applied in the rotation direction about the Y-axis while the body moves, the Coriolis force in the rotation direction about the Z-axis is applied. When the force causes the body to rotate in the Z-axis, a sensing electrode (not shown) measures a displacement rotated, so the magnitude of the angular velocity may be calculated.
FIG. 1
shows, for the convenience of the following description, an example in which one body carries out all of the functions of the drive body, driven by the driving electrode, the sensing body, moving by the Coriolis force, and the sensing by the sensing electrode. Recently, the drive body and the sensing body have been manufactured separately, thus resulting in a gyroscope called a decoupled gyroscope. An advantage of a decoupled gyroscope is that it avoids a problem of driving the drive body using resonance while moving the sensing body nearly at a resonance frequency of the driving body.
Some conventional decoupled gyroscopes, however, may have only the drive body in a decoupled structure or only the sensing body in the decoupled structure, rather than completely separating the drive body and the sensing body. In a case where only the drive body is in the decoupled structure, the drive body performs only the driven motions and the sensing body performs all of the driven motions and the sensed motions. Accordingly, a problem occurs in that the sensed motions of the sensing body appear together with the driven motions.
On the contrary, in a case where only the sensing body is in the decoupled structure, the drive body performs all the driven motions and the sensed motions and the sensing body performs only the sensed motions. Accordingly, a problem occurs in that the driven motions of the drive body may affect a direction in which the Coriolis force is applied.
Some conventional gyroscopes are able to measure only the angular velocity inputted about the Z-axis being normal to the substrate, which causes a problem in that a two-axis angular velocity is not able to be measured on one plane. Accordingly, in a case of manufacturing a gyroscope for sensing a multi-axis angular velocity, an additional assembly process for vertically arranging devices is required.
In order to measure an input angular velocity relative to the axes of the horizontal directions, i.e., the X-axis or the Y-axis, the driving electrode must be equipped for vertically driving the body or the sensing electrode must be equipped for sensing a vertical displacement of the body. In order to manufacture the driving electrode or the sensing electrode having the above-described vertical direction, a fixed electrode, which is fixed to the substrate, and a moving electrode, which is spaced apart from the fixed electrode and positioned at an upper portion of the fixed electrode, have been previously manufactured. In a case where such an electrode is used as a driving electrode, the moving electrode is driven by applying a varying voltage between the moving electrode and the fixed electrode. In a case where such an electrode is used as a sensing electrode, an angular velocity is measured by sensing an electrostatic force varying with respect to a distance between the fixed electrode and the moving electrode.
An electrode having a structure as described above has a drawback in the difficulty of the manufacture thereof since the moving electrode is positioned at an upper portion of the fixed electrode. Consequently, the moving electrode is first formed to have a stacked structure on the upper portion of the fixed electrode. That is, in order to manufacture the aforementioned electrode, a multi-step process must be performed. First, the fixed electrode is formed on the substrate. Then, a sacrificial layer is deposited on the fixed electrode. Subsequently, the moving electrode is formed on the sacrificial layer, and then the sacrificial layer is removed. As mentioned above, several process steps must be performed to form a moving electrode floating over a fixed electrode.
Further, in order to measure precisely a displacement of the moving electrode in a vertical direction, a distance between the moving electrode and the fixed electrode should be small. Accordingly, a problem exists in that an adherence phenomenon may occur between the moving electrode and the fixed electrode.
Referring back to
FIG. 1
, there is shown a gyroscope for sensing an angular velocity applied to one arbitrary axis existing on a surface of a substrate. In this example, the drive body moves relative to one arbitrary axis of the substrate, for example, the X-axis, using a levitation force, so that a sensing motion rotating about the Z-axis normal to the surface of the substrate is generated.
However, such a gyroscope has a problem in that space consumption increases due to a ring-type structure and a circular arrangement of electrodes for rotational motions. Accordingly, in a case of manufacturing a plurality of gyroscopes on a single wafer, wasted space occurs where parts for gyroscopes are not mounted, thereby decreasing the number of gyroscopes to be manufactured on a unit area wafer.
Further, such a conventional gyroscope has a structure wherein the sensing electrodes for sensing the rotation of the sensing body are arranged in a radial direction, which creates a problem in that a distance between the moving electrode and the fixed electrode increases. Since the distance between the moving electrode and the fixed electrode inside the sensing electrode must be small, as well as uniform, for precise sensing, the increase in the distance between the moving electrode and the fixed electrode causes a deterioration in sensing performance.
SUMMARY OF THE INVENTION
It is a feature of an embodiment of the present invention to provide a rotation-type MEMS gyroscope capable of enhancing sensing of an angular velocity and having both the drive body and the sensing body having a decoupled structure.
It is another feature of an embodiment of the present invention to provide a rotation-type MEMS gyroscope being easily driven in a vertical direction, having a simplified manufacture process, and requiring decreased space consumption.
It is yet another feature of an
Jeong Hee-moon
Kim Jun-o
Lee Byeung-leul
Lee Sang-woo
Kwok Helen
Lee & Sterba, P.C.
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