Research Projects

A Micromechanical Power Converter

Yang Lin and Clark Nguyen

Defense Advanced Research Projects Agency

RF MEMS switches operating at RF to millimeter-wave frequencies substantially outperform p-i-n diode and field-effect transistor (FET) counterparts in insertion loss, isolation, and switch figure of merit (FOM). Unfortunately, their much slower switching speeds (e.g., 1-15 us versus the 0.16-1ns [1] of FET’s) and cycle lifetimes on the order of 100 billion cycles (for the good ones) relegates them mainly to antenna switching, reconfigurable aperture, and instrumentation applications, and precludes them from much higher volume applications, such as switched-mode power amplifiers and power converters. The resonant switches introduced by this project, on the other hand, harness the resonance and nonlinear dynamical properties of micromechanical resonators to overcome the problems of conventional RF MEMS while still retaining their inherent advantages. To data, a polysilicon micromechanical switch shown in Figure 1(a) and (b), dubbed the “resoswitch”, has been demonstrated that can greatly increase switching speed and cycle count (even under hot switching), and lower the needed actuation voltage, all by substantial factors over existing RF MEMS switches[2]. The device comprises a wine-glass mode disk resonator [3] driven hard via a 2.5V amplitude ac voltage at its 61-MHz resonance frequency so that it impacts electrodes along an orthogonal switch axis, thereby closing a switch connecting a 10V source to the switch electrode. The 61-MHz operating frequency corresponds to a switching period of 16ns with an effective rise time of less that 4ns, which is more than 200 times faster than the us-range switching speeds of the fastest RF MEMS switches. Furthermore, since the voltage source is on during switching, the switch essentially hot switches with a demonstrated lifetime exceeding 16.5 trillion cycles without failure, but with some observed degradation. The frequency response and time domain output waveform of this resoswitch are shown in Figure 1 (c) and (d) respectively. To address the resistance issue of polysilicon version resoswitch, a nickel metal resoswitch has been designed and fabricated. The testing and characterization are ongoing.

Figure 1: Schematics showing (a) the physical structure of the micromechanical resoswitch, identifying its ports and equating it to a functional equivalent circuit; and (b) illustrating the “off” and “on” states of the micromechanical resoswitch. (c) Frequency response (in vacuum) as measured by a network analyzer of the direct contact version of the resoswitch for varying resonance input ac voltage amplitudes and (d) Oscilloscope (i.e., time domain) waveform of the resoswitch output node when driven by a resonance input signal with 2.5V amplitude.

[1]

H. Kamitsuna, et al., “A fast low-power 4×4 switch IC using InP HEMTs for 10Gbit/s system,” Proceeding, IEEE CSIC, Jul. 2004, pp. 97–100.

[2]

Y. Lin, et al., “The micromechanical resonant wwitch (“Resoswitch”)”, Tech. Digest, 2008 Solid-State Sensor, Actuator, and Microsystems Workshop, Hilton Head, South Carolina, June 1-5, 2008, pp. 40-43.

[3]

Y.-W. Lin et al., “60-MHz wine glass micromechanical disk reference oscillator,” Tech. Dig., 2004 IEEE ISSCC, Feb. 15-19, 2004, pp. 322-323.