This paper presents a novel method to obtain high isolation for a wideband RF MEMS switch. The MIM shunt capacitive switch consists of two identical beams placed in parallel over floating metals of different lengths on the signal line of a CPW. With two beams in parallel, the effective resistance and inductance of the switch is lesser than a switch with only one beam. The decrease in resistance provides higher isolation at resonant frequency while the decrease in inductance provides higher isolation at frequencies beyond resonant frequency. While the increase in insertion loss due to two beams is insignificant, there is a substantial increase in isolation over a large band of frequency. A switch with two beams with isolation greater than 30 dB and insertion loss less than 0.5 dB in the range of 3 GHz to 30 GHz is demonstrated. © 2019 IOP Publishing Ltd.

Amitava Dasgupta

Department of Electrical Engineering

Deleep R. Nair

Electric switches

Inductance

Insertion losses

Microstrip lines

MIM devices

CAPACITIVE SWITCH

EFFECTIVE RESISTANCES

Fabrication and characterizations

High isolation

RF MEMS CAPACITIVE SWITCHES

RF-MEMS SWITCHES

SHUNT CAPACITIVE

WIDEBAND OPERATION

Natural frequencies

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Journal of Micromechanics and Microengineering

RF MEMS capacitive shunt switches with a dielectric-on-metal (DOM) capacitor, which are widely used for microwave applications in the communication field, suffer from some serious drawbacks. A significant shift is observed in the resonant frequency of these switches due to the reduction in the down-state capacitance caused by the surface roughness of the dielectric layer. In order to achieve accurate down-state capacitance, a thin layer of floating metal is deposited on the dielectric layer converting the DOM switch to a metal-insulator metal (MIM) switch. The MIM switch opens up interesting possibilities in the design, such as achieving flexibility in the operating frequency of the switch. This paper reports a novel method to achieve design flexibility for multi-frequency operation in switches, by effectively utilizing the equipotential nature of the floating metal in the MIM capacitor. Unlike in a DOM switch, the resonant frequency can be varied by changing merely the length of the floating metal, without having to make any other structural modifications. This enables to have switches operating at different frequency on the same wafer. The beams of the switches are also designed in such a way as to provide stress resilience, thereby preventing buckling. This paper presents the design, simulation, fabrication and characterization of a switch that operates in the X-band. The fabricated switches show excellent stress resilience. The characterized switch demonstrates a reduction in the resonant frequency in proportion to an increase in the length of the floating metal, hence validating the design flexibility proposed in this paper. © 2017 IOP Publishing Ltd.

Novel RF MEMS capacitive switches with design flexibility for multi-frequency operation

Surface roughness is an important factor that influences the reliability and performance of radio frequency microelectromechanical systems switches. The presence of surface roughness impedes a perfect contact in the down-state condition of the switch which in turn affects the following parameters - resonant frequency, down-state capacitance, and isolation at resonance. The result is a significant deviation from the electromagnetic characteristics simulated by assuming flat surfaces making a perfect contact. However, creating a rough topography manually is cumbersome. A Visual Basic Script code for generating rough surfaces of any average value and standard deviation has been developed. The code runs on High Frequency Structure Simulator platform. This paper focuses on the simulations that include the effect of surface roughness on both the beam and the dielectric layer using a 3-D geometric model by representing surface asperities as an array of pyramids, the heights of which follow a Gaussian distribution. This assumption takes into account of the statistical nature of surface roughness. The results of simulation indicate that the presence of surface roughness reduces down-state capacitance and isolation and shifts the resonant frequency from the X-band (8-12 GHz) for which it was originally designed. © 2016 IEEE.

Fulltext

IEEE Journal of the Electron Devices Society

Study of the Effect of Surface Roughness on the Performance of RF MEMS Capacitive Switches Through 3-D Geometric Modeling

A low-temperature wet-release process for low stiffness structures fabricated using material of low Young's modulus has been developed and presented. The release process Is described In the light of different forces that cause stiction during release. This technique is successfully demonstrated for different low stiffness structures with gold as the membrane material and positive photoresist or SiO2 as the sacrificial layer. © 2008 Society of Photo-Optical Instrumentation Engineers.

Journal of Micro/Nanolithography, MEMS, and MOEMS

Low-temperature wet-release process for low stiffness structures

2019 20th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems (EuroSimE)

Modelling, Simulations and Performance Analysis of MEMS vibrating Gyroscope in Coventor MEMS+ Environment

High on/off capacitance ratio RF MEMS capacitive switches

Design, fabrication and characterization of RF MEMS shunt switch for wideband operation of 3 GHz to 30 GHz

Journal	Journal of Micromechanics and Microengineering
Publisher	Institute of Physics Publishing
ISSN	09601317
Open Access	No