Electrostatic Actuators With Expanded Tuning Range Due to Biaxial Intrinsic Stress Gradients

Abstract

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.[921]

Numerical and analytical study on the pull-in instability of micro-structure under electrostatic loading

“…(12)- (14) indicate that the change of α 1 will change every coefficient of Eq. (12). Although the mechanical restoring force increases due to the increment of α 1 , the critical maximum beam displacement also changes.…”

“…For single DOF model, the stiffness of the continuous system is simplified as one spring constant. For structure like beam or plate, the stiffness is influenced by the axial loading, intrinsic stress gradient [12] and geometric nonlinearity due to large deflection [2]. At the same time, the electrostatic force is dependent on the deflection and this deflection dependence property is responsible for the pull-in instability.…”

High performance microshutter device with space-division modulation

“…The difference in the residual stress of two layers is commonly used in the fabrication of curl-shaped structures with many kinds of materials, such as silicon-based materials, metals and polymers [11][12][13][14]. We selected titanium and gold as the materials for fabrication of the microshutter because they can be easily formed at low temperature with physical deposition equipment such as a sputter and they have a relatively large difference in residual stress.…”

Stable zipping RF MEMS varactors

“…In our varactor, we retain the flexibility to tailor the shape of the bottom electrode in addition to the tailoring the shape of the cantilever. Gray et al demonstrated zipping actuators where the stiffness of the movable electrode was tailored to some degree [26,27]. However, their devices were designed to be actuators with extended travel range rather than varactors [27].…”

“…Gray et al demonstrated zipping actuators where the stiffness of the movable electrode was tailored to some degree [26,27]. However, their devices were designed to be actuators with extended travel range rather than varactors [27]. As such, no RF measurements were reported although some dc capacitance measurements were performed.…”