Thin-Film Aluminum RF MEMS Switched Capacitors With Stress Tolerance and Temperature Stability

This paper presents an RF microelectromechanical system switched capacitor which is based on a thin-film alu minum circular beam geometry that exhibits reduced sensitivity to both initial residual stress and stress changes versus ambient temperature. This novel design results in a pull-in voltage slope of -55 mV/°C from -5°C to 125°C, a capacitance ratio of 20 (C
_u
=50 fF, C
_d
= 1 pF), a down-state quality factor of 85 at 3127 MHz (Z
_d
= -j50 Ω), and a switching time of <; 10 μs from 25°C to 95°C. The device symmetry also facilitates low-series-inductance compact device arrays for high-value capac itances. Both 2×2 and 3×2 device arrays are demonstrated with down-state capacitances of 3.95 and 5.89 pF, which result in switched impedances of 135-4 Ω and 91-3 Ω at 0.3-10 GHz, respectively. The array impedances vary as 1/ω over a 33:1 frequency range, with down-state quality factors of 50-60 at 541-806 MHz (Z
_d
= -j50 Ω). The application areas are in high-linearity RF/microwave switches, phase shifters, and tunable matching networks and filters.