The Woodruff School

SUMMARY

Hemispherical resonator gyroscope (HRG) is one of the most successful designs for navigation grade gyroscope, which has been widely used in high value space missions. The physical principle of the HRG is based on the inertial properties of elastic waves propagating in a solid object. The undisputable advantage of these existing instruments is their high sensitivity, environmental stability, and robust operation over time. A disadvantage is their extremely high cost and large size. With the latest advances in micro-fabrication technology and the development of MEMS inertial sensors, there is a possibility that the conventional HRG can be miniaturized down to chip scale. Axisymmetric structures such as circular ring, cylinder and disk have been successfully used for MEMS gyroscopes. The curved three dimensional structure of μHRGs allows low resonance frequencies (< 10 kHz) at extremely small sizes compared to its planar counterparts. It also has the potential of higher mechanical quality factor and higher degree of symmetry compared to the prior arts. Furthermore, the structure is expected to demonstrate low stiffness, which would enable large reference vibration amplitudes with large capacitive gaps, resulting in an improved mechanical noise floor and sensitivity. A large electrostatic tuning range will be another outcome of the low stiffness of the μHRG structure. This work explores the design, fabrication and testing of microscale hemispherical resonator gyroscopes (µHRG). A monolithic process flow with co-fabricated and self-aligned polysilicon electrodes around hemispherical shell structure is developed. This 3D manufacturing technology combines the high aspect ratio trench-refill process and high aspect ratio hemispherical shell process. New fabrication technique is also developed for lithography with a three dimensional hemisphere surface topography. The most significant benefits of this process are that the electrode depth is scalable to hundreds of micrometers and large capacitive gap can be formed, allowing for large vibrational amplitude of the high-Q hemispherical shells.

SUBJECT:	Ph.D. Dissertation Defense

BY:	Peng Shao

TIME:	Monday, July 21, 2014, 10:00 a.m.

PLACE:	Pettit Building, 102 A

TITLE:	Microscale Hemispherical Shell Resonating Gyroscopes

COMMITTEE:	Dr. Farrokh Ayazi, Co-Chair (ECE) Dr. Olivier Pierron, Co-Chair (ME) Dr. Peter Hesketh (ME) Dr. Levent Degertekin (ME/ECE) Dr. Oliver Brand (ECE)

SUMMARY Hemispherical resonator gyroscope (HRG) is one of the most successful designs for navigation grade gyroscope, which has been widely used in high value space missions. The physical principle of the HRG is based on the inertial properties of elastic waves propagating in a solid object. The undisputable advantage of these existing instruments is their high sensitivity, environmental stability, and robust operation over time. A disadvantage is their extremely high cost and large size. With the latest advances in micro-fabrication technology and the development of MEMS inertial sensors, there is a possibility that the conventional HRG can be miniaturized down to chip scale. Axisymmetric structures such as circular ring, cylinder and disk have been successfully used for MEMS gyroscopes. The curved three dimensional structure of μHRGs allows low resonance frequencies (< 10 kHz) at extremely small sizes compared to its planar counterparts. It also has the potential of higher mechanical quality factor and higher degree of symmetry compared to the prior arts. Furthermore, the structure is expected to demonstrate low stiffness, which would enable large reference vibration amplitudes with large capacitive gaps, resulting in an improved mechanical noise floor and sensitivity. A large electrostatic tuning range will be another outcome of the low stiffness of the μHRG structure. This work explores the design, fabrication and testing of microscale hemispherical resonator gyroscopes (µHRG). A monolithic process flow with co-fabricated and self-aligned polysilicon electrodes around hemispherical shell structure is developed. This 3D manufacturing technology combines the high aspect ratio trench-refill process and high aspect ratio hemispherical shell process. New fabrication technique is also developed for lithography with a three dimensional hemisphere surface topography. The most significant benefits of this process are that the electrode depth is scalable to hundreds of micrometers and large capacitive gap can be formed, allowing for large vibrational amplitude of the high-Q hemispherical shells.