CMOS/BICMOS Self-assembling and Electrothermal Microactuators for Tunable Capacitors
Abstract
Advanced RF systems on chip will benefit from microelectromechanical (MEMS) tunable capacitors integrated on a CMOS or BICMOS chip with high quality factor (Q) and large tuning range. RF circuits with on-chip CMOS/BICMOS MEMS tunable capacitors will have small footprints and will not have the reduction in tuning range coming from fixed capacitance between off-chip circuit parts. CMOS-MEMS micro-movers that use the principles of self-assembly and electrothermal actuation are successfully designed, modeled, fabricated and characterized for use in RF tunable capacitors, latch mechanisms and nanometer-scale gap-closing structures. The micro-movers exploit the lateral stress gradient setup by embedding metal layers into CMOS-MEMS beams that are offset from the centerline of the beam. Built-in residual stress in the aluminum and silicon dioxide layers creates a gradient driving self-assembly upon microstructural release. Electrothermal actuation generates a stress gradient from the different temperature coefficients of expansion of the offset materials. This actuation has relatively low driving voltage of around 12 V maximum, which is compatible with IC technology and silicon substrates. Various micro-mover designs in four different CMOS/BICMOS processes are characterized. The largest lateral displacement from self assembly is 11 micrometers in a 100 micrometer by 40 micrometer footprint. The largest lateral displacement from electrothermal actuation is 25.5 micrometers in an actuator with the same footprint. Frequency response of the micro-movers is limited by the thermal time constant with the fastest measured 3dB bandwidth of 178 Hz. The largest tuning range achieved among tunable capacitor designs is 352.4% with a Q of 52 at 1.5 GHz. For zero-power stand-by operation of RF MEMS capacitors, mechanical latch structures are developed by sequencing micro-movers.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 2003
- Accession Number
- ADA501052
Entities
People
- Altug Oz
Organizations
- Carnegie Mellon University