The HARPSS process for fabrication of precision ... - Semantic Scholar
Mechatronics 12 (2002) 1185–1199
The HARPSS process for fabrication of precision MEMS inertial sensors Farrokh Ayazi
*
School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0250, USA
Abstract The high aspect-ratio combined poly- and single-crystal silicon micromachining technology (HARPSS) and its application to fabrication of precision MEMS inertial sensors are presented. HARPSS is a single wafer, all silicon, front-side release process which is capable of producing 10–100’s of microns thick, electrically isolated, 3-D poly- and single-crystalline silicon microstructures with various size air-gaps ranging from sub-micron to tens of microns. High aspect-ratio (>50:1) polysilicon structures are created by refilling 100’s of microns deep trenches with polysilicon deposited over a sacrificial oxide layer. This technology provides features required for precision micromachined inertial sensors. The all-silicon feature of this technology improves long term stability and temperature sensitivity while fabrication of large area, vertical electrodes with sub-micron gap spacing will increase the sensitivity by orders of magnitude. Ó 2002 Published by Elsevier Science Ltd. Keywords: Silicon micromachining; MEMS; Polysilicon micromachining; Deep reactive ion etching; Inertial sensors; Gyroscope
1. Introduction Next generation high performance MEMS inertial sensors, consisting of microaccelerometers and microgyroscopes [1], will require fabrication technologies that can combine high aspect-ratio deep dry etching of silicon with polysilicon surface micromachining to realize all-silicon, 100’s of microns thick microstructures which are electrically isolated from one another and separated by small capacitive gaps. The allsilicon feature of such a technology improves long-term stability and temperature
*
Tel.: +1-404-894-9496; fax: +1-404-894-4700. E-mail address: [email protected] (F. Ayazi).
0957-4158/02/$ - see front matter Ó 2002 Published by Elsevier Science Ltd. PII: S 0 9 5 7 - 4 1 5 8 ( 0 2 ) 0 0 0 2 3 - 5
1186
F. Ayazi / Mechatronics 12 (2002) 1185–1199
sensitivity. Hundreds of microns thick silicon structures have large mass (up to a few milligrams) with reduced Brownian displacement noise which make them suitable for inertial-grade devices. Fabrication of large area, vertical capacitors with sub-micron gap spacing will increase the sense capacitance and hence the sensitivity of MEMS devices by orders of magnitude. By shrinking the capacitive gaps to sub-micron levels, bias, actuation and control voltages will also shift down to CMOS acceptable levels (
The HARPSS process for fabrication of precision MEMS inertial sensors Farrokh Ayazi
*
School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0250, USA
Abstract The high aspect-ratio combined poly- and single-crystal silicon micromachining technology (HARPSS) and its application to fabrication of precision MEMS inertial sensors are presented. HARPSS is a single wafer, all silicon, front-side release process which is capable of producing 10–100’s of microns thick, electrically isolated, 3-D poly- and single-crystalline silicon microstructures with various size air-gaps ranging from sub-micron to tens of microns. High aspect-ratio (>50:1) polysilicon structures are created by refilling 100’s of microns deep trenches with polysilicon deposited over a sacrificial oxide layer. This technology provides features required for precision micromachined inertial sensors. The all-silicon feature of this technology improves long term stability and temperature sensitivity while fabrication of large area, vertical electrodes with sub-micron gap spacing will increase the sensitivity by orders of magnitude. Ó 2002 Published by Elsevier Science Ltd. Keywords: Silicon micromachining; MEMS; Polysilicon micromachining; Deep reactive ion etching; Inertial sensors; Gyroscope
1. Introduction Next generation high performance MEMS inertial sensors, consisting of microaccelerometers and microgyroscopes [1], will require fabrication technologies that can combine high aspect-ratio deep dry etching of silicon with polysilicon surface micromachining to realize all-silicon, 100’s of microns thick microstructures which are electrically isolated from one another and separated by small capacitive gaps. The allsilicon feature of such a technology improves long-term stability and temperature
*
Tel.: +1-404-894-9496; fax: +1-404-894-4700. E-mail address: [email protected] (F. Ayazi).
0957-4158/02/$ - see front matter Ó 2002 Published by Elsevier Science Ltd. PII: S 0 9 5 7 - 4 1 5 8 ( 0 2 ) 0 0 0 2 3 - 5
1186
F. Ayazi / Mechatronics 12 (2002) 1185–1199
sensitivity. Hundreds of microns thick silicon structures have large mass (up to a few milligrams) with reduced Brownian displacement noise which make them suitable for inertial-grade devices. Fabrication of large area, vertical capacitors with sub-micron gap spacing will increase the sense capacitance and hence the sensitivity of MEMS devices by orders of magnitude. By shrinking the capacitive gaps to sub-micron levels, bias, actuation and control voltages will also shift down to CMOS acceptable levels (
