Modeling and Designing of RF MEMS Switch using
ANSYS
Aamir F. Malik, M. Shoaib, S. Naseem
*
, S. Riaz
Microelectronics Research Center
University of the Punjab
Lahore, Pakistan
malik_merc@hotmail.com shoaib!shafi@hotmail.com
*
director@merc.pu.edu.pk saira@cssp.pu.edu.pk
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I. Introduction
Electrostatically actuated MEMS structure for radio
frequency (RF) applications has been recently developed. Low
power consumption, small dimensions, low insertion loss and
excellent performance compared to their conventional
counterparts made them a promising building block for future
[1]. It is one of the devices that are interested to be compatible
with integrated circuits. The RF mobile switches to be
compatible with integrated circuits (IC) must fulfill the three
following conditions [2!4].
• Very small size,
• Low actuation voltage,
• Low power consumption.
MEMS switches were first demonstrated in 1979 as electro
statically actuated cantilever switches [5]. This type of switch
was small in size and consumed low power. The main
disadvantage of this type of the switch was high actuation
voltage [6, 7]. The actuation mechanisms of other types are
based on electromagnetic, electrostatic and thermal principles
[8]. The micro!switches based on electromagnetic actuation
have low actuation voltage but consume high power and have
difficult manufacturing process. Where as, thermally actuated
micro!switches have high power consumption. If the actuation
voltage of the electro!statically switches is lowered, then this
type of switches will be the best candidate for RF applications.
In recent years so many attempts have been set on to reduce
the actuation voltage of the electrostatic type of micro!
switches. For example using a variety of hinges and materials
to lessen the spring constant of the beam, raise area of the
electrostatic field, decrease the gap and increase the dielectric
constant between two plates of the switch. Most of these
parameters are directly linked to each other. As an example, if
we decrease the gap or raise the area of the electrostatic field,
this results in increase of off capacitance, leading to a poor
isolation. The reduced actuation voltage of our proposed
structure is due to the decreased equivalent spring constant of
the system. Therefore we do not lose any other parameters as
well as the lifetime of the micro!switch is increased.
II. Mechanics of MEMS Switches
Devices capable of motion greatly broaden the
potential applications for MEMS. Desirable characteristics of
MEMS actuators include
• Force generation in millinewton range
• Displacement of 10 =m or more
• Linear response to input signals
• Fabrication compatible with standard surface
micromachining
• Reliable, with long life time
Actuation methods can be broadly classified by physical
stimulus that under lies the actuation. Most common physical
stimuli are electric fields, magnetic fields and thermal effects.
Actuation methods induced by electric fields include
electrostatic and piezoelectric. The common magnetic field!
induced actuation methods are magneto static and
magnetostrictive. For thermally driven actuation, methods
include difference in thermal coefficients of expansion between
two materials, shape memory materials and liquid!to!vapor
phase change.
Shape memory alloy (SMA) materials posses the ability to
repeatedly return to a shape ‘learned’ at a high temperature
when deformed at a low temperature. The most common shape
memory alloy is made from titanium and nickel (also known as
Nitinol). SMA actuators can generate forces of millinewtons
and larger, and can have large displacements [9]. Integration
with standard MEMS fabrication processes is not difficult.
2008 International Conference on Emerging Technologies
IEEE-ICET 2008
Rawalpindi, Pakistan, 18-19 October, 2008
978-1-4244-2211-1/08/$25.00 ©2008 IEEE