J.-M. Huang

Mechanical design and optimization of capacitive micromachined switch

Abstract Design and optimization of a shunt capacitive micromachined switch is presented. The micromachined switch consists of a thin metal membrane called the “bridge” suspended over a center conductor, and fixed at both ends to the ground conductors of a coplanar waveguide (CPW) line. A static electromechanical model considering the residual stress effects is developed to predict the effective stiffness constant and the critical collapse voltage of the bridge for several typical bridge geometries. The deformation of the bridge and its contact behavior with the dielectric layer are analyzed using the finite element method (FEM) in order to explore a good contact field with different bridge geometries. Furthermore, a nonlinear dynamic model that captures the effects of electrostatic forces, elastic deformation, residual stress, inertia, and squeeze film damping is developed, and is used for predicting the switching speed (including the switching-down and the switching-up time) and the Q -factor. The effects of variation of important parameters on the mechanical performance have been studied in detail, and the results are expected to be useful in the design of optimum shunt capacitive micromachined switch. The results may also be useful in the design of actuators with membranes or bridges.

Mechanical characterization of micromachined capacitive switches: design consideration and experimental verification

The mechanical modeling and experimental study of radio frequency (RF) micromachined capacitive switches is presented in this paper. The micromachined capacitive switch, fabricated using bulk and surface micromachining techniques, consists of a thin metal membrane suspended over a center conductor, and fixed at both ends to the ground conductors of a coplanar waveguide (CPW) line. A static mechanical model considering complicated geometry and the residual stress effect of the bridge is established to demonstrate the pull-in instability phenomenon of the micromachined capacitive switch, and to predict the effective stiffness constant and critical collapse voltage of the bridge for several typical bridge geometries. An optoelectronic laser interferometric system, based on a modified Michelson interferometer incorporated with optoelectronic devices is developed to evaluate the membrane deformation characteristics of the micromachined capacitive switch with different applied dc bias voltages. It is illustrated that the analytical solution is well agreed with the numerical simulation and experiment.

Micromachined patch antenna and array using MEMS technology

Following the development of MEMS fabrication technique, novel patch antennas are developed to become reality using surface micromachining process. In this paper, surface micromachined patch antennas are investigated and fabricated to have an excellent RF performance. The square patch antenna is designed to operate in its dominant mode with the broad radiation pattern of approximately 6.5dB in directivity. The impedance bandwidth is approximately 1.5% and the radiation efficiency is approximately 53%. The radiation patterns of micromachined patch antennas are broad in nature, when operating from 13 to 22GHz. Since the radiation efficiency and directivity (gain) of the individual element is rather weak, arrays are designed to obtain better overall the radiation efficiency and directivity.

Micromachined capacitive switches at microwave frequencies

Both electrical and mechanical models, exemplified with a micromachined capacitive switch with simple bridge structure, accurately describing its electrical and mechanical characteristics are described in this paper. The electrical model is represented as a RLC circuit, while the mechanical model is represented as a fixed-fixed beam. The advantage of these models is that it is possible to pre-determine various characteristics, such as the switching time of micromachined capacitive switches, during the design stage. These models can be used to accurately design micromachined capacitive switches for microwave applications. An illustrated fabrication process is also discussed.

Characterization of high-isolation rf capacitive microswitches

With the recent growth of microelectromechanical systems (MEMS), RF capacitive microswitches are becoming popular. As such there is a need to accurately characterize the performance of the RF capacitive microswitches. To realize this goal, the paper proposes both electrical and static mechanical models to precisely extract the performance parameters of the RF capacitive microswitches. The electrical model proposed in this paper provides a means to represent the RF capacitive microswitches for use to determine the resistance, capacitance, and inductance. The static mechanical model predicts the effective stiffness constant and the pull-in voltage. Deformation of the bridge and its contact behavior with the dielectric layer are also precisely analyzed using Finite Element Method. Finally this paper discusses the fabrication of the RF capacitive microswitches.

Integrated add/drop multiplexer (ADM) using micromachined mirror

High speed, low insertion loss optical add/drop multiplexer (ADM) is designed and fabricated. The optical vertical micromirror is fabricated by deep dry etching, the aspect ratio reaches as high as 20. A thin aluminum film is deposited on the sidewall of the micromirror to increase the reflectivity. The anchors and pads are fabricated firstly, followed by the comb drive, micromirror and fiber grooves. Refilling technique is introduced to electrically insulate the anchors and pads from the substrate while still maintaining the mechanical support. The anchors and pads are strong enough to sustain the floating structures (micromirror and moving comb) and also assure good electrical connection to the electrostatic comb drive so that the external voltage can be applied. By improving dry etching, the finger width is only 2micrometers and the gap is only 2.5micrometers . A typical electrostatic comb drive is fabricated by the deep reactive ion etching (RIE) and underneath releasing. Folded suspension beams of 800micrometers long, 2.0 micrometers wide and 35micrometers deep are employed to support the movable micromirror. The stiffness along the desired lateral direction is 0.21N/m. Comb drive using three electrodes is employed. Its applied voltage is decreased by a ratio of 0.707 compared with that of the two electrodes system, and the switching speed is also increased. To simply the optical fiber assembly, fiber grooves are fabricated along with the other structures. This device has a typical of optical ADM that can be widely used in all optical networks. All of the processes are compatible with IC technology and can be integrated with control circuits in a single chip.

Large deflection of out-of-plane magnetic actuators using surface micromachining

A magnetic actuator with torsional-polysilicon flexures, capable of very large out-of-plane displacement (the order of 1mm), and individually controlled with integrated coils that will be discussed in this paper. Magnetic actuator uses coils to produce the magnetic field required for individual microactuator motion, while the off-chip magnetic actuates unclamped devices. The advantages of the actuators are exploited: large deflections are achieved using magnetic forces to actuate compliant microflexure structures; Actuation is achieved using magnetic fields generated by off-chip sources; The actuating force is applied in a conducting environment such as a saline fluid. Individually prototype- torsional actuators are deflected over 70

An approach to the coupling effect between torsion and bending for electrostatic torsional micromirrors

DEG out of the plane of the wafer, when a current of 100 mA flows through a twenty-turn coil integrated into each actuator. The magnetic actuator provides an interaction force of several tens (mu) N between the coil-driven and the off-chip magnetic field. The micro actuators are capable of achieving large deflections (100s of micrometers ) in stationary air and fluid dynamic flow. A completed model of static mechanical and magnetic is built up to characterize mechanical properties including angular deflection, vertical deflection, bending stresses of thin plate. Both the coil- driven and the actuator structure are constructed in polysilicon surface micromachinging process.