A road map has been proposed for the design methodology of a RF MEMS switch. The design methodology for RF
MEMS is often an interactive process which involves continuous adjustments for the specifications, structure and the
fabrication steps. This helps in defining and obtaining the required RF microwave specifications. A novel RF MEMS D
shape capacitive shunt switch is proposed. The switch structure is fabricated on a high resistive silicon substrate. This
structure consists of coplanar waveguide transmission line, a D shape lower electrode with thin dielectric layer on top
and suspended membrane bridge. The lower electrode of the switch is fabricated in D shape using high viscosity and
high conductive adhesives. The switch RF path is fabricated on top of silicon dioxide using a thick coplanar waveguide
transmission line. The thick transmission line metal connects to the lower electrode and the dielectric material to form
the through path of a shunt switch. The suspended metal membrane spans the two coplanar ground lines. With no applied
actuation voltage the residual tensile stress keeps the membrane suspended above the RF path. By applying an
electrostatic field between membrane and the lower electrode an attractive force causes the floating membrane to pull
down and make contact with the lower electrode and dielectric surface to form a low impedance RF path to ground.
Main area to which the development aims is lowering the actuation voltage to levels compatible with mainstream IC
technologies, while maintaining the RF performance. Proposed switch has shown satisfactory performance between 0-40
GHz frequency range. Paper will present simulation and theoretical results. Experimental results of conductive epoxy
fabrication are also presented. This switch could have an important application in the telecommunication network like
switching networks.
This paper will report on the design and fabrication of a novel 3D electrostatic RF MEMS switch, which uses two movable electrodes. The concept of two movable electrodes represents a unique feature of this device and is introduced to the RF MEMS community for the first time. Since the operating principle of the switch is based on electrostatic actuation, this unique feature results in a lower operating voltage. Combining the special bulk and surface micromachining techniques has enabled the realization of this new 3D RF MEMS switch. There are two main configuration for the device structure: 1) in the first device structure all parts are made up of bulk-micromachined free-structures. 2) In the second device structure the lower part is made up of a movable bulk-micromachined cantilever and the upper section is made up of surface micromachined movable thin film structures. By applying a DC voltage between movable plates, they come in touch and provide a pass for the RF signal (on-state of the switch) and as the DC voltage is removed, electrodes will be separated and disconnect the RF signal (off-state). The substrate can be used as a third electrode to separate beams in case of stiction. The monolithic nature of this switch technology makes it possible to develop various switch configurations like SPNT, C-type, and R-type switches, and switch matrices monolithically. This switch can be used as the basic building blocks for microwave switch matrices, multiplexers / demultiplexers, and phase shifters operating at microwave frequencies. The aim is to use the new features of this switch to achieve an acceptable low switching voltage, a better RF performance and particularly reliable switching operation. In this paper design considerations, HFSS simulation and the preliminary fabrication results of the switch are demonstrated.
Characteristics of a monolithic microvalve using a curved electrode electrostatic actuator and an integrable valve orifice are described. The valve is a normally open electrostatic microvalve with a 83 volts switching voltage. The curved electrode is a curled up cantilever structure with few hundred micrometers out of plane displacement. Lateral buckling of the actuator is overcome by using a mesh type or finger strip type metalization pattern. Cantilever with curvatures angle ranging 0 to more than 360 degrees have been achieved by changing the thickness ratio of composite layers of the cantilever. A valve channel consisting of three inverted pyramids in tandem have been sued. The flow rate of the valve linearly depends on the pressure difference across the valve. Thickness variation of the standard wafers has minimal effect on the final orifice sizes of the valve. The surface micromachining processes used to fabricate actuators and bulk micromachining process used to fabricate the valve channel, have been integrated in a set of processes to fabricate a monolithic normally open microvalve.
The suitability of refractory metal, molybdenum, as a material for microstructures in MEMS is explored in this paper. This paper describes the effects of dc magnetron sputtering conditions on the residual stress of the film. The effects of post deposition annealing as a means of stress relief are also reported. Post deposition annealing also addresses the problems of film adhesion. An example of the application of Mo is given in the form of a cantilever structure suspended over a silicon gap which involves both surface and bulk micromachining.
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