Design, fabrication, testing and packaging of a silicon micromachined radio frequency microelectromechanical series (RF MEMS) switch

RF characterization and packaging of a single pole single throw (SPST) direct contact microelectromechanical (MEMS) series radio frequency (RF) switch is reported. Precise thickness of the silicon MEMS structure is achieved using a specially developed silicon Deep Reactive Ion Etching (DRIE) thinning process. A stress free release process is employed which ensures a high yield of released microstructures. The design of the device is based on stiffness equations derived from first principles. Displacement of the actuator under applied field is measured to confirm electrostatic pull in, which occurs in the 30–50 V range. The variation of contact resistance with time has been measured and is found to have a power law decay, in agreement with theoretical models. At the bare die level the insertion loss, return loss and the isolation of the switch were measured to be ?0.43 dB, ?25 dB and ?21 dB, respectively at 10 GHz. The devices were packaged in commercially available RF packages and mounted in alumina boards for post package characterization. Due to the presence of bond wires in the signal path of the packaged devices, the RF performance was found to degrade at high frequencies. However, losses were measured to be at acceptable levels up to 2 GHz. Factors contributing to insertion loss at the die and package device levels are discussed in detail with possible solutions.     

Interfacial Layers in Brittle Cracks

A study has been made of interfacial layers that form within cracks in mica and silicate glass. The layers are the result of interactions with environmental species behind the crack tip. Deposition processes are associated with precipitation from aqueous solutions and corrosion of the crack walls. The level of precipitation depends on such factors as "impurity" content, temperature, etc. It is demonstrated that the layers can bridge the interface and thereby significantly increase the apparent toughness and the strength. These retardation effects are modeled as an "internal"(negative) contribution to the net stress intensity factor on the crack from closure tractions over a near-tip area of the interface. The results highlight the potential importance of surface chemistry as a determinant of both equilibrium and kinetic fracture properties.