Etching a substrate: processes – Gas phase etching of substrate – Application of energy to the gaseous etchant or to the...
Reexamination Certificate
1999-02-22
2001-10-02
Gulakowski, Randy (Department: 1746)
Etching a substrate: processes
Gas phase etching of substrate
Application of energy to the gaseous etchant or to the...
C216S002000, C438S014000, C073S504160
Reexamination Certificate
active
06296779
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to microfabricated sensors, and more particularly to microfabricated gyroscopic sensors.
Multi-axis sensors are highly desirable for inertial sensing of motion in three dimensions. Previously, such sensors were constructed of relatively large and expensive electromagnetic devices. More recently, micromechanical sensors have been fabricated using semiconductor processing techniques. Specifically, micromechanical accelerometers and gyroscopes have been formed from silicon wafers by using photolithographic techniques. Such microfabricated sensors hold the promise of large scale production and therefore low cost.
One objective in the construction of microfabricated sensors is to increase the sensitivity and improve the signal to noise ratio of the device. Another objective is to simplify the fabrication steps so as to reduce the cost and complexity and to increase the yield in the manufacturing process.
The integration of three gyroscopic sensors to measure the rotation rates about the three separate axes coupled with three accelerometric sensors to measure the acceleration along the three axes on a single chip would provide a monolithic, six degree-of-freedom inertial measurement system capable of measuring all possible translations and orientations of the chip.
It would be useful to provide a gyroscopic sensor to measure rotation about axes parallel to the surface of a substrate on which the gyroscopic sensor was fabricated. It would also be useful to provide a gyroscopic sensor with reduced noise.
SUMMARY OF THE INVENTION
In one aspect, the invention is directed to a microfabricated gyroscopic sensor for measuring rotation about an input axis. The gyroscopic sensor includes a substrate, a mass, and a suspension system connecting the mass to the substrate. A drive system causes the mass to oscillate substantially about a drive axis, and a position sensor measures a rotation of the mass about a sense axis. Rotation of the mass about the input axis and oscillation of the mass about the drive axis generates a Coriolis force to oscillate the mass about the sense axis. A voltage source to apply a voltage between a plurality of electrodes associated with the substrate to cause the mass to oscillate, in the absence of the Coriolis force, more precisely about the drive axis.
Implementations of the invention include the following. A processor may be coupled to an output of the position sensor to generate a signal varying with the rate of rotation of the mass about the axis of rotation. A second voltage source may apply a second voltage between electrodes connected to the mass and the electrodes connected to the substrate to adjust a resonant frequency of oscillations of the mass about the sense axis. The drive axis may be substantially perpendicular to the surface of the substrate and the axis of rotation and sense axis are substantially parallel to a surface of the substrate. The mass may be substantially ring-shaped. First and second pluralities of electrode fingers may project from the mass, and third and fourth pluralities of electrode fingers projecting from the substrate and be interdigitated with the first and second pluralities of electrode fingers. The fourth plurality of electrode fingers may be positioned opposing the first plurality of electrode fingers. Fifth, sixth, seventh and eighth pluralities of electrode fingers may be similarly disposed, and the pluralities of electrode fingers are substantially co-planar. The voltage source may apply a first DC voltage between the third plurality and the fourth plurality of electrode fingers and second DC voltage, which is substantially equal in magnitude and opposite in sign, between the seventh plurality and the eighth plurality of electrode fingers.
In another aspect, the invention is directed to a method of sensing rotation with a gyroscopic sensor including a mass connected to a substrate by a suspension system. The method includes rotating the mass about an input axis and causing the mass to oscillate substantially about a drive axis. The rotation of the mass about the input axis and the oscillation of the mass about the drive axis generates a Coriolis force to oscillate the mass about a sense axis. An oscillation of the mass about the sense axis is measured, a voltage is applied between electrodes associated with the substrate to cause the mass to oscillate, in the absence of a Coriolis force, more precisely about the drive axis.
In another aspect, the invention is directed to a microfabricated gyroscopic sensor. The gyroscopic sensor includes a substrate having a first plurality of electrode teeth, a vibratory structure including a second plurality of electrode teeth and a suspension system connecting the second plurality of electrode teeth to the substrate, the second plurality of electrode teeth interdigited with the first plurality of electrode teeth, a drive system to cause the vibratory structure to oscillate relative to the substrate, and a position sensor to measure a deflection of the mass caused by a Coriolis force. The first and second pluralities of electrode teeth have thicknesses substantially greater than their widths.
Implementations of the invention include the following. The suspension system may include a plurality of flexures having an aspect ratio of at least about 10:1. The first and second pluralities of electrode teeth may have an aspect ratio of at least 5:1 and may be separated by gaps having an aspect ratio of at least 10:1.
In another aspect, the invention is directed to a method of fabricating a gyroscopic sensor. An insulative layer is formed on a first substrate, a recess is formed in a first surface of a second substrate, and the first surface of the second substrate is bonded to the first substrate so that the recess defines an enclosed cavity between the first and second substrates. Circuitry for the gyroscopic sensor is formed on a second surface of the second substrate, and a plurality of trenches are etched in the second substrate from the second surface to the cavity, the plurality of trenches defining a vibratory structure connected to the first substrate.
Implementations of the invention include the following. The vibratory structure may have a thickness of at least 25 microns and the recess may have a depth of about 1 micron. The etching step may comprise a deep reactive ion etch.
Advantages of the invention include the following. The gyroscopic sensor measures rotation about an axis parallel to the surface of the substrate. The gyroscopic sensor has reduced quadrature error. The gyroscopic sensor may include a vibratory structure and interdigited electrodes with a high aspect ratio. The gyroscopic sensor has a significantly reduced noise level.
Other advantages and features of the invention will be apparent from the description which follows, including the drawings and claims.
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Y. Gianchandani, et al., “Micron-sized, High Aspect Ratio
Clark William A.
Howe Roger T.
Juneau Thor
Ahmed Shamim
Fish & Richardson P.C.
Gulakowski Randy
The Regents of the University of California
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