THE MICROMECHANICAL RESONANT SWITCH ("RESOSWITCH")

A micromechanical switch, dubbed the “resoswitch”, has been demonstrated that harnesses the resonance and nonlinear dynamical properties of its mechanical structure to 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. The device comprises a wine-glass mode disk resonator 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 <4ns, which is more than 200 times faster than the μs-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. INTRODUCTION 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 μs 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. Indeed, the benefits afforded to switched-mode power applications that would ensue if the transistors they presently employ were replaced by switches with FOM’s on the order of those exhibited by RF MEMS switches would be enormous. For example, switched-mode power amplifiers that ideally should be able to achieve 100% drain efficiency presently cannot attain such values in practical implementations, in part because the transistors they use for switching exhibit large input capacitors (for small “on” resistances) and are often limited in the voltages they can support. MEMS switches, being made of metal, have very small “on” resistances and would be able to support higher voltages. However, if they are to be used in switched-mode power applications, their actuation voltages would need to be lowered substantially (from >50V down to the single-digit volt range), their speeds would need to be much higher (e.g., ns switching times), and their reliability enhanced substantially, since typical power amplifier and converter applications would require cycle counts in the 100’s of quadrillions. Pursuant to achieving a switch suitable for power amplifier and converter applications, this work demonstrates a micromechanical switch, dubbed the “resoswitch”, that harnesses the resonance and nonlinear dynamical properties of its mechanical structure to 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. The device comprises a wine-glass mode disk resonator 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 <4ns, which is more than 200 times faster than the μs-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 observable degradation. RESOSWITCH STRUCTURE AND OPERATION Fig. 1 presents schematics describing the structure and operation of one simple rendition of a resoswitch that comprises a capacitively-transduced wine-glass disk micromechanical resonator [2] (c.f., Fig. 2) made in a conductive material (preferably, a metal) and surrounded by four electrodes, two of which are situated along an indicated input axis having larger electrode-to-resonator gaps than their counterparts along an orthogonal switch axis. To operate the switch, an ac input voltage at the wine-glass mode disk resonance frequency is applied to the input electrodes (along the input Control Electrodes Switch Contact Electrodes D