CMOS-compatible RF-MEMS tunable capacitors

Abstract

New CMOS-MEMS tunable capacitors have been designed, fabricated and tested. Large-tuning range and high quality factor, Q, are achieved. The structures were made from the CMOS interconnect stack using a maskless CMOS micromachining process. Our tunable capacitor designs can be classified into two categories based on their tuning schemes as gap&area tuning and gap-only tuning. The capacitors with gap&area tuning were fabricated using Austria Microsystems (AMS) 0.6 /spl mu/m and Agilent 0.5 /spl mu/m CMOS processes. These devices have a measured nominal capacitance of 209 fF and a measured Q of 28 at 1.5 GHz. The capacitance change is measured from 209 fF to 294 fF within a 24 V control voltage, and 72.4 mW power at 1.5 GHz. The capacitors with gap-only tuning were fabricated in the TSMC 0.35 /spl mu/m CMOS process and have larger tuning range and more power efficiency than the 1st generation designs. For these new designs, 3.52 to 1 tuning range has been measured with tuning from 42 fF to 148 fF within a 12 V control voltage and 34 mW power and Q of 52 at 1.5 GHz. The tuning mechanism uses electro-thermal actuation. The essential differences between this work and prior work are the CMOS compatibility and more area efficiency at several gigahertz.