Defense: H. Pourzand
May 22, 2014
UNIVERSITY OF UTAH
ELECTRICAL AND COMPUTER ENGINEERING DEPARTMENT
THESIS DEFENSE FOR THE DEGREE OF
MASTER OF SCIENCE
Advisor: Massood Tabib-Azar
Microelectromechanical gyroscopes are readily used in cars and cell phones. Tactical gyroscopes are readily available inexpensively and they offer 0.01 to 0. 1 percent scale factor in accuracy. On the other hand, strategic gyroscopes with much better performance are 100,000 more expensive. The main objective of this work is to explore the possibility of developing in-expensive strategic grades gyroscopes using MEMS.
Most of the available gyroscopes are surface micro machined due to fabrication issues and misalignment problems that are involved in multistep fabrication processes necessary to use the bulk of the wafer as the proof mass in the MEMS gyroscope. It can be shown that the sensitivity of the gyroscope is inversely proportional to the natural frequency; so if bulk micromachining technique is used it is possible to decrease the natural frequency further than current limits in order to increase sensitivity. This thesis is focused on proposing a way to use bulk of the silicon wafer in the gyroscope to decrease the natural frequency to very low levels such as sub kilohertz regime that cannot be achieved by single mask surface micromachining processes and then proposing a solution for solving the misalignment problem caused by using multiple fabrication steps and masks instead of using only one mask in surface micro machined gyroscopes.
In our design discrete proofmasses are linked together around a circle by compliant structures to insure highest effective mass and lowest effective spring constant. By using a proposed double sided fabrication technology the effect of misalignments on frequency mismatch can be reduced. ANSYS simulations show that 20 µm misalignment between the masks causes a frequency shift equal to 0.3% of the natural frequency, that can be compensated using electrostatic frequency tuning. Acceleration parasitic effects can also be a major problem in a low natural frequency gyroscope. In our design a multiple sensing electrode configuration is used that cancels the acceleration effects completely. The sensitivity of the gyroscope with 3126 Hz natural frequency is simulated to be 574 mV/(Deg/sec) or about four times higher than 132 mV/(Deg/sec) , which was used as a benchmark for a sensitive gyroscope.
Monday, June 2, 2014
The public is invited