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Thick single crystal silicon MEMS with high aspect ratio vertical air-gaps
 

Summary: 138
Thick single crystal silicon MEMS with high aspect ratio
vertical air-gaps
Pejman Monajemi and Farrokh Ayazi
School of Electrical and Computer Engineering, Georgia Institute of Technology,
Atlanta, GA 30332
ABSTRACT
This paper presents recent advances in the HARPSS micromachining technology, which enables implementation of
movable Single Crystal Silicon (SCS) structures with high aspect ratio vertical air gaps on low-resistivity silicon
substrate. This is suitable for applications of micro-gravity accele rometers, low voltage tunable capacitors, and high-
resolution gyroscopes that require aspect ratios as large as 100:1 to achieve high sensitivity and wide tuning range. The
single-sided HARPSS process eliminates the need for double-sided processing, and wafer bonding to subsequently
package the device. The device thickness and gap spacing can be varied in a wide range, 30-150Ám and 0.2-2Ám
respectively, to select the performance range. The movable MEMS elements are made of bulk silicon substrate, resulting
in higher mass, higher quality factor (Q), and better shock resistance, compared to using polysilicon (poly) as the
movable structure. This process provides a mechanism for creating corrugation in SCS electrodes to reduce the
Brownian noise of sensors. This technique realxes the need to reduce the noise by using the maximum available mass
and through-wafer etch. The corrugations are created by a DRIE technique for etching poly surrounded by oxide inside
the isolation trenches. Also, uniform capacitive gap spacings are created by growing sacrificial oxide inside the trenches.
Keywords: Single Crystal Silicon (SCS), Polysilicon (poly), HARPSS, Accelerometer, Tunable capacitor, Tuning fork

  

Source: Ayazi, Farrokh - School of Electrical and Computer Engineering, Georgia Institute of Technology

 

Collections: Engineering