Abstracts Engineering

High Performance RF MEMS Metal-Contact Switches and Capacitive Switches

by Chenhui Niu

This dissertation presents designs, fabrication processes and measurements of a series of high performance RF MEMS switches.Chapter 2 presents a miniature RF MEMS metal contact switch based on a tethered-cantilever structure. The miniature size and the use of tethers result in an excellent biaxial residual stress and stress gradient tolerance. The switch is built using thin metal process with a large biaxial stress and a high stress gradient (50 MPa and -105 MPa/um), and works well under these conditions. In the up-state, the switch capacitance is 9.4 fF and results in an isolation of 20 dB at 20 GHz. In the down-state, the switch resistance is 3.6 ohm for a gold-gold contact under 30 V actuation voltage. The switch is compatible with CMOS back-end processing. With its miniature size, the switch could be placed in arrays to achieve lower contact resistance and higher power handling.Chapter 3 presents a multi-contact mN-force RF MEMS metal-contact switchwith a pull-down voltage (Vp) of 45 V-50 V and an operation voltage of 60V-65V. The switch gets a contact force of s 2.0 mN under 65 V actuation voltage and a release force of s 1.2 mN (simulated). The switch gets an on-state resistance of s 1.8 with Ru-Au contact and an off-state capacitance of 13.5 fF, which results in a figure of merit of 24 fs. In the temperature stability measurement, the switch shows a change of 4V in pull-down voltage and a change of 2V in release voltage from 25 C to 125 C. In the high power handling measurement, the switch demonstrates a reliability of > 10 million cold switching cycles with 5 W RF power.Chapter 4 first presents a high capacitance ratio (Cr) capacitive switch with continuous tuning capability after pull-down. The measured up-state capacitance is 74 fF. The pull-down voltage of the switch is 30V -32V and there is an 8.4% linear tuning range from 33V to 40V actuation voltage. The measured down-state capacitance is 1296 fF under 40V actuation voltage, resulting in a Cr of 17.5. Next, a back-to-back switch using the high Cr switch is designed to improve IP2 without extra power supply. The back-to-back switch shows an up-state capacitance of 31fF, a Cr of 19.7 and a 6.8% continuous tuning range from 34V to 40V. The back-to-back switch shows a 14 dB higher OIP2 than the single switch does.