tri axis micro gyroscope
DESCRIPTION
mems fabricationTRANSCRIPT
Design and Analysis of a Tri-Axis Gyroscope Micromachined by Surface Fabrication
Outline
Motivation
Introduction
Background
Applications
Design
Principle of Operation
Fabrication of the Gyroscope
Experimental Setup
Results
Conclusion
Motivation
Recent Progress in microfabrication techniques.
Tri-axis Gyroscope
Miniature size and low cost.
Reliable batch fabrication techniques and reduction of production cost gradually become the focus of evolution of this device.
Various applications.
Introduction
What is Gyroscope?
A gyroscope is a device for measuring or maintaining orientation, based on the principle of preserving angular momentum. Mechanical gyroscopes typically comprise a spinning wheel or disc in which the axle is free to assume any orientation.
Background
In 1991, Greiff et al. designed conventional macroscale gyroscope with detective resolution of 4deg/sec and 1Hz bandwidth.
In 2006, Vinay et al. proposed a micro tri-axis gyroscope in which a single proof mass is embedded.
However, accuracy, bandwidth and decoupling efficacy of measurements are insufficient.
Applications
Image stabilization
Inertial Navigation Systems(INS).
Rollover detection
Active suspension for advanced vehicles
Satellite posture control.
Design
The microgyroscope mainly consists of four key components
Seismic inertial mass modules
Flexure pivots
Sensing differential capacitor sets
Rotational comb-drive electrodes
Design
The proposed tri-axis microgyroscope is schematically shown in below.
Design
The seismic inertial mass modules includes: Inner disk, outer-ring, distributed translational proof mass(DTPM)
In fact, the seismic inertial mass modules are nothing but the angular rate detection elements whose responding motions are induced by Coriolis effect in three axes.
1- Outer-ring2- DTPM3- Inner-disk
Design
Flexure pivots include four spring sets.
Spring#1(marked as S1),which is used to suspend the outer-ring(used for detection of angular rate about Y-direction).
The inner-disk(used for detection of angular rate about x-direction) is suspended by a set of torsion spring, named as Spring#2(marked as S2).
Spring #3(marked as S3) and Spring #4 are, respectively, used to resist the radial and tangential acceleration of DTPM due to external angular excitations about z-direction.
11- S112- S213- S314- S4
Design
The sensing capacitor sets include two pairs of differential capacitor and four pairs of comb electrodes.
The comb electrode pairs by the DTPM are used to measure the induced radial displacement of DTPM if any regular excitation about Z axis is present.
4,6,7 – Sensing electrodes5,8,9 – Comb electrodes
Operation
Operation
Change in o/p voltage ~ Measure of angular rates
Operation
Suspension flexure(S1)
Fabrication
Cleaning of waferInsulation layer 4μm and Structure layer 40μmAll mechanical components are micro machined on bottom layer.
Fabrication
Al material deposited (mask#1)
Fabrication
Spin Coat Photo Resist (mask#2) The glass photomask(mask#2) is used to pattern the desirable PR by photolithography.
Fabrication
PR patterned and layer of Al partially removedIt is noted that the hard etching mask is concurrently patterned with the glass photo mask, by photolithography process.
Fabrication
PR removed and structure layer then etched by DRIEThe mechanical structure is formed by DRIE
Fabrication
Al removed and insulation then etched by the BOEThe purpose of deposited Al is to resist DRIE so that Geometry of structure layer by SOI wafer can be defined.
Fabrication
Wafer cleanedPyrex has high optical transmittance over wide range wave length.
Fabrication
Spin coat PR
Fabrication
PR patterned
Fabrication
HF (Hydrogen Fluoride) etchingBy standard liftoff process after the corresponding trenches to house
Fabrication
PR removed and Au deposited as electrode
Fabrication
Bonding of Dual layers
Fabrication
A couple of scanning electron microscope(SEM) Images
Experimental Setup
Driving circuit Sensing Circuit
Results
As the External angular velocity about x axis or y axis is exerted, the inner-disk or outer ring responds to tilt owing to Coriolis effect.
Hence the air gap between the corresponding mass module and differential capacitors is altered so that the voltage across capacitors is accordingly changed, as shown in results.
Results
The relation between capacitance variation and the corresponding induced voltage is found to be fairly linear.
In other words, it can be conveniently used for measure of detected angular rate,
Results
Conclusion
Capability of detecting tri-axis angular motions.
Designed in geometry such that the stress of proposed microgyroscope is considerably reduced but the resolution for angular displacements is increased.
The mass production cost has been considered at the design stage but the resolution, bandwidth and decoupling capability of tri axis detection can be expected to be much upgraded .
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