MEMS RF Switches with Ultra-High Switching Speeds

摘要

The objective of this program was to validate a new actuator for high-speed, radio-frequency (RF) switches and to develop methodologies for its fabrication. Special attention is placed on switch performance at frequencies between 12-18 GHz. The switch is predicated on thin-film microelectromechanical systems (MEMS) technology with piezoelectric actuation. In general, piezoelectric materials develop strain when an electric field is present, which allows mechanical expansion and contraction of the material to be controlled by an applied voltage. Unlike traditional electrostatic MEMS switches, the closing force between the metal-to-metal contacts can be significantly improved by increasing the bias voltage (electric field strength) across the piezoelectric material. Because the switch restoring force is large, in-use stiction is greatly mitigated with this architecture. The piezoelectric material lead zirconate titanate (PZT) proved to be a viable actuator for high-speed switches. Three strategies are suggested for lowering the switch time constant into the tens of nanoseconds range while preserving other important characteristics of the switch (e.g., high isolation, low resistive losses). These include a bimorph design, piezoelectric extensional bars, and flextensional actuators. Combinations of these strategies are likely to yield a high-performance switch.