Development of a spring-less RF MEMS switch

Abstract

This thesis reports on the development of a novel 77GHz low loss MEMS switch with a mechanically unrestrained armature, over a RF transmitting coplanar waveguide. Electrostatic actuation is used during the switching operation. The attractive force from the electrostatic field is generated by a pair of the actuation electrodes on both sides of the armature, depending on the direction of the movement.

A Simulink model is employed to simulate the mechanical response of the switching armature. Different damping models are deployed into the Simulink model, yielding different actuation time for the switch. This model is also employed to design the dimensions of the MEMS switch in the mechanical domain. The effect of Van der Waal force between the dielectric layer and designed armature is also discussed. An electrical model of the RF MEMS switch is represented using lumped RLC components and characteristic impedance of the transmission line. The relationship between the electrical model and the scattering parameters is explained with the effects of the individual component on the S-Parameter being studied. Electromagnetic simulations have shown that the designed switch has potential of being employed in automotive collision avoidance system or in Doppler radar application. The proposed design is also capable of operating in lower frequency bands after some tuning, through different armature design.

A clean room fabrication flow is described as part of the development process of this novel switch. This is based on two Pyrex wafers and a SOI wafer utilising a double bonding and DRIE processes. RF characterisation of the coplanar waveguide and the micron-scale prototype at DOWN state is also discussed.

An alternative rapid prototyping technique based on high-frequency PCB and microscopic glass slide has been developed. This process is cheaper and requires shorter turnover time as compared to the clean room prototype. Electromechanical and SParameter measurements of the rapid prototype device are reported. These results are verified through simulations. The minimum actuation voltage of the prototype is 93V, with a rise and fall time of 165ms and 180ms. Switching is possible for frequencies from 2.8-5.5GHz and 6.6-10GHz, with the optimum frequency at 3.3GHz and 6.9GHz. The insertion loss and isolation of the prototype are -26.5dB and -38.5dB at 6.9GHz respectively. Although this is far from the state of the art for RF MEMS switches, it nevertheless proves the fundamental concept of a MEMS switch with an unrestrained armature by a prototype realised using a rapid prototype methodology.

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Identifiers

ORCID for Kian Shen KIANG: orcid.org/0000-0002-7326-909X

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