High-Reliability Miniature RF-MEMS Switched Capacitors

This paper presents a radical departure from the standard RF microelectromechanical systems (MEMS) devices and introduces novel miniature MEMS switched capacitors for RF to millimeter-wave applications, which are around 150 times smaller in lateral dimensions than standard MEMS designs. The measured capacitance of a single device (l,w,t of 20, 9.5, 0.37 mum), suspended 0.25 mum above the pull-down electrode, is 3.9 and 11.7-12.1 iF (Cr = 3.0-3.1) in the up- and down-state positions, respectively. The measured capacitance ratio of a 4 X 4 array fabricated on quartz substrates and in a coplanar waveguide (CPW) configuration is 3.0 with an electrical Q > 90 at 20 GHz. The miniature MEMS spring constant is very high, and is much less sensitive to residual stress or temperature variations than standard MEMS devices. Dielectric charging simulations show that these devices can withstand a charge density 6.25 times higher than the standard MEMS devices. The mechanical resonant frequency for a gold device is 2.6 MHz and results in a switching time of 200 ns under a 32-V actuation voltage. Preliminary reliability tests at 13 GHz using bipolar actuation (plusmn30 V) and hot power switching have been performed on five 4 times 4 devices at 100 mW for 20 billion cycles, and at 500 mW for 5 billion cycles with no failures. A 4 times 4 array has also been used in the design of a tunable CPW resonator at 19.3 GHz with a 21% tuning range and 1.6-dB insertion loss. The authors believe that miniature MEMS devices will be very useful in the future for high-reliability MEMS and reconfigurable networks.