Electrostatic actuators with expanded tuning range due to biaxial intrinsic stress gradients

A stress gradient was induced in two directions (through the plane of the beam and along its length) to produce a beam deflection of varying curvature. The stress gradient in the through-plane direction was produced by altering the conditions during electroplating and in the in-plane direction through lithographic patterning. The pull-down characteristics of four electrostatic actuator designs were analyzed. The in-plane stress gradient, along the length of the beam, significantly improved the tuning range compared with devices containing spatially uniform stress. This advance has greatly eased the instability problem of electrostatically actuated beams. The tuning range of a device with two hinges and a square front improved from less that 33% to 70%. Devices with two hinges and elliptical front improved to 45% tuning range and those with rectangular shape improved to 65% stability. This advance has been applied to actuators for RF tuners. Voltage cycling impacted only the initial cycling of the actuator.