Microsoft Word - Vol 6-2p5V2-press.doc

IIUM Engineering Journal, Vol. 6, No. 2, 2005 Z. Dahari et al.

MEMS ELECTROMAGNETIC MICRO RELAYS
OVERVIEW AND DESIGN CONSIDERATIONS

ZURAINI DAHARI, THURAI VINAY AND DINESH SOOD
School of Electrical and Computer Engineering

RMIT University, GPO Box 2476V, Melbourne, Australia

s3047454@student.rmit.edu.au

Abstract : Miniature electromagnetic relay matrices capable of switching currents up to
one ampere range are widely used in commercial applications such as instrumentation
and telecommunication. Traditionally these devices have been fabricated from a number
of discrete components, however in recent years the emergence of Micro Electro
Mechanical System (MEMS) technology has opened up the possibility for batch
fabrication of microrelays at much reduced unit cost. While several electromagnetic
microrelay designs have been successfully developed and commercialized for use as
individual units, development work on electromagnetic microrelay matrices where
individual relays can be selectively switched on and off have been fewer and less
successful. Due to inherent limitations of the micromachining processes, significant
dimensional and material property variations occur among individual relays in a matrix.
These variations severely limit the tolerance window and hence the reliability of
operation of the device. After reviewing existing designs of electromagnetic microrelays,
a set of desirable design features that would make the electromagnetic microrelay more
robust are identified. A novel design incorporating these features is proposed and
preliminary results of ANSYS1 simulation studies are presented.

Keywords: MEMS, microrelay and electromagnetic

1. INTRODUCTION

Recent trend in the world market shows a continuing demand for the miniaturization of
devices. This trend has triggered the emergence of microelectromechanical systems
(MEMS) technology in the past few decades. MEMS technologies such as silicon
micromachining, bulk micromachining and LIGA (German Acronym for Lithographie,
Galvano-formung, Abformung) offer significant advantages in size reduction without
sacrificing device performance. Some of the motivating factors are reduced cost, weight
and power consumption. MEMS technology is multidisciplinary with its applications
ranging from optics, transportation, aerospace, robotics, chemical analysis, and
biotechnologies. Comprehensive details on MEMS technology could be referred to Madou
[1], Senturia [2] and Pelesko [3]. MEMS pressure sensors, accelerometers are now
established commercialized products [4]. Electromechanical microrelay is amongst the
predicted MEMS-based products to be commercialized in the next five years [5].

IIUM Engineering Journal, Vol. 6, No. 2, 2005 Z. Dahari et al.

The commercial need for relays up to 2A is projected to be 1 billion units annually.
Despite the rapid advances of the semiconductor, the electromechanical relays (EMR) still
serves about ninety percent (90%) of the market needs compared to ten percent (10%) by
solid state relays (SSR). The major reasons of the continuing use of electromechanical
relays are due to its robustness and reliability in harsh environments. In addition, they
have large switching range from µV and µA, could handle both DC and AC signals, have
low contact resistance (mΩ) and high insulation resistance (MΩ) [6]. Figure 1 shows the
miniaturization trend in manufacturing relays during the past 40 years. As can be seen
from Fig. 1, the predicted board space for the next generation would be about 30 mm2, the
volume about 100 mm2. Through MEMS technology, micro sized electromechanical relay,
termed microrelay which integrates the merits of both SSR and EMR could be
manufactured. MEMS technology offers possibility for exceptional miniaturization of
relays, extremely low power consumption and high shock resistance.

Fig. 1: Ongoing miniaturization of telecom relays during the past 40 years [6]

Pioneered by Petersen [7], realization of microrelay using MEMS technologies has
attracted interests of a number of researchers in both academic and industrial field. Relay
operation requires sufficient contact force to provide stable contact, reliable opening
which involves a lift-off force which exceeds the adherence of sticking contacts and the
highest possible breakdown voltage to assure electrical insulation between the open
contacts and driving circuit. The basic requirements for microrelay design can be derived
as 300 µN contact force to achieve contact resistance less than 100 mΩ, lift-off force
greater than 300 µN to overcome adherence, and contact gap in the range of 100 to 250
µm to have a breakdown voltage greater than 500 V [8]. These key parameters are
dependable on the contact material, actuation means and mechanical design. From a report
by Schimkat [8], AuNi5 is reported as a well suited contact material for microrelays due to
relatively high contact force and lower adhesion force. Table 1 summarized the
experimental results of the characteristics of several contact materials.

Various actuation methods have been demonstrated successfully; such as electrostatic
[9,10,11], thermal [12, 13,14] and electromagnetic [15,16]. The most typical method is
electrostatic due to its simplicity, small size and the versatility of integration with the
standard integrated circuit (IC) technologies. However, the basic design requirements
mentioned above are beyond the operating range of typical electrostatic microrelay.
Recently, electromagnetic actuation has generated considerable interest. The feasibility of

IIUM Engineering Journal, Vol. 6, No. 2, 2005 Z. Dahari et al.

magnetic materials in MEMS technologies are discussed thoroughly by Busch-Vishniac
[17], G. Reyne [18] and D. Niarchos [19].

Table 1: Characteristics Contact Data for Microrelays [8].

Au AuNi5 Rh

Minimum contact force for stable contact, Fmin
(mN)

<0.1 0.3 0.6

Maximum adherence force, Fad (mN) 2.7 0.3 < 0.1

Contact resistance, Rc at Fmin (mΩ) <30 <100 <1000

Though some improvement in magnetic materials properties and compatibility with IC
processing still remains a challenge, electromagnetic actuation has been the preferred
choice in microrelay applications where larger contact force (few millinewtons) is required
to achieve stable electrical contact [20]. Besides, it is also possible to achieve latching by
adding permanent magnet or semi-hard magnetic material thereby minimising power
consumption [21]. In the case of microrelay matrices, where individual relays will have to
be switched on and off selectively, reliability of operation remains an issue owing to the
difficulty in achieving sufficient dimensional uniformity among individual relays in the
matrix during their manufacture. Authors’ research is concerned with the development of a
robust design for the microrelay that will be more tolerant to MEMS fabrication
imperfections. A novel design of the electromagnetic microrelay is proposed and analysed
using ANSYS finite element analysis software.

2. ELECTROMAGNETIC MICRORELAYS

Traditionally electromagnetic relays have been fabricated from a number of discrete
components which include an armature made of soft magnetic material, elastic spring,
electromagnetic coil, a magnetic core, and special metal contacts [22]. For applications
requiring the switch to remain open or closed for relatively long periods of time, a
permanent magnet is incorporated into the magnetic circuit to maintain the switch in the
closed position even when the control signal is removed. Implementation of magnetic
actuation schemes at the micro scale is quite challenging. The most problematic is the
design and fabrication of the excitation coil that would provide sufficient ampere-turns.
Deposition of magnetic materials and their subsequent patterning and treatment to impart
desirable characteristics to them are also difficult in a micro fabrication environment [19].
Micromachined electromagnetic relays reported in early publications [23-26] are simply
adaptations of the conventional relay design to suit the microfabrication environment.
Planar magnetic coil and flat cantilever spring element have been common features in all
of them.

2.1 Principle of operation of the electromagnetic microrelay

Most magnetic microactuators that are reported in publications depend on the attractive
force that can be generated between an armature made of ferromagnetic material and a

IIUM Engineering Journal, Vol. 6, No. 2, 2005 Z. Dahari et al.

current-carrying coil [27], as shown in Fig. 2. Related to the above microactuators are
devices that use a permanent magnet instead of the magnetisable armature as shown in
Fig. 3. These devices have the advantage that the actuator can generate both attractive and
repulsive forces. More importantly, the relay could be held in its closed state even after the
control current is removed.

Fig. 2: Magnetization-type actuator. Fig. 3: Planar magnetic microactuator.

The operation of the latching electromagnetic microrelay can best be understood by
considering the variations in magnetic, and restoring spring forces with air gap. The
relative positions of the spring and magnetic force characteristics for three different states
of the relay, namely, unactuated (in either closed or open state), on the verge of closing
from the open state, and on the verge of opening from the closed state are shown in Fig. 4,
5 and 6 respectively. Here the spring characteristic is assumed to be linear. Previous
studies suggest that the dependence of the magnetic force on the air gap can roughly be
described by a power law F  gn with an exponent n in the range -1.4 to -2 [28]. When
there is no coil current, the magnetic force will be solely due to the permanent magnet.
Depending on the direction of current flow in the coil, the magnetic force can be either
enhanced or reduced by the electromagnet. In Fig 4, Fs0 = kg0, Fm0 = Rkg0 (say) are the
spring and magnetic forces respectively when the air gap, g is zero, k is the spring
stiffness, g1 and g2 are the air gaps corresponding to the two intersection points of the force
characteristics, g0 is the air gap when the spring is unstressed, and R is the ratio Fm0/ Fs0.
Note that g1 is a stable equilibrium point whereas g2 is an unstable equilibrium point. In
the unactuated case, either the relay remains open with air gap g1 or remains closed with
contact force Fm0 - Fs0.

Figure 5 shows the effect of increasing the magnetic force by applying a coil current.
The spring force line is shown to touch the magnetic force curve at the air gap, gt. Any
further increase in the coil current will cause the relay to close. Figure 6 shows the effect
of reducing the magnetic force by applying coil current in the opposite direction. Here the
magnetic force curve is shown to meet the spring force line at g = 0. Any further increase
in the coil current will cause the relay to open.

IIUM Engineering Journal, Vol. 6, No. 2, 2005 Z. Dahari et al.

Fig. 4: Spring and Magnetic Forces as functions of air gap.

Fig. 5: Relative position of force characteristics.

Fig. 6: Relative position of force characteristics of microrelay on the verge of latching
of microrelay on the verge on unlatching.

IIUM Engineering Journal, Vol. 6, No. 2, 2005 Z. Dahari et al.

When a current pulse of sufficient amplitude and duration is passed through the
electromagnetic coil, the induced magnetic field due to the permanent magnet and the
electromagnet in the relay will create sufficient force on the armature to pull the relay
closed. The relay will stay closed due to the field from the permanent magnet, which is not
strong enough to pull the relay closed by itself, but will hold it there when the air gap
becomes small and the flux becomes stronger. To reset the relay, current pulse is applied
in the opposite direction which will reduce the resultant flux in the air gap sufficiently so
that the beam can spring back to the open position.

Another important practical consideration is the ability of the microrelay to withstand
ambient shock and vibration [29]. It can be shown that greater the area of the closed region
between the spring and magnetic force characteristics (between g1 and g2) in Fig 4, the
greater will be the resistance of the microrelay to shock and vibration.

Thus the following four design rules can be formulated for the microrelay.

 For latching to occur, the entire magnetic force characteristics for the case of full
positive electromagnetic actuation should be below the spring force line.

 Minimum contact force requirement must be satisfied. That is, the magnitude at zero
air gap of the spring force must be less than the magnitude at zero air gap of the
magnetic force due to the permanent magnet alone by the minimum contact force
required.

 For the switch to unlatch, the magnitude at zero air gap of the spring force must be
greater than the magnitude at zero air gap of the magnetic force for the case of full
negative electromagnetic excitation.

 The area enclosed by the spring and magnetic force characteristics must be sufficiently
large so as to alleviate the detrimental effects of shock and vibration.

Parameters of the spring (k and g0), magnetic circuit (n), permanent magnet (Fm0), and
electromagnetic coil (ampere-turns) should be carefully matched to achieve optimum
performance. However, manufacturing imperfections associated with MEMS processes
are likely to result in significant variations in the values of these parameters and severely
limit the tolerance window of the final product.

2.2 Microrelay matrices

While several electromagnetic microrelay designs have been successfully developed
and commercialized for use as individual units, development work on electromagnetic
microrelay matrix arrays have been fewer and less successful although many commercial
applications await them. By combining such relay matrices with electronics, it would be
possible to perform multiplexing and to reduce the number of electrical lines required to
switch individual relays in the matrix; an 88 array for instance would require 16 control
lines, as opposed to 64 control lines when the relays are packaged separately without the
multiplexing electronics. Such relay arrays have great potential in the telecommunication
industry.

IIUM Engineering Journal, Vol. 6, No. 2, 2005 Z. Dahari et al.

While individual microrelays can be made to operate reliably, making micro relay
matrix arrays in which individual relays need to be selectively and reliably switched on
and off by an appropriate multiplexing scheme presents many challenges. The major
problem is the difficulty in achieving the degree of uniformity in the structural dimensions
among the individual relays in the matrix. It is difficult to achieve close dimensional
tolerances of micro relay structures when cost effective MEMS fabrication methods are
used. Due to the inherent limitations of the micromachining processes, significant
variations in the dimensions of the micro relay occur across the wafer. For example, each
individual microrelay may not have the same thickness of cantilever beam and the initial
air gap. Besides, stiction problem, which occurs when two nominally flat surfaces are
placed in contact also contribute to unreliability of the switching action [30]. Due to these
reasons, each individual relay in a matrix will have varying electrical, magnetic and
mechanical properties, and as a result the strength of the control signals required for
switching the relays on and off is bound to vary widely. A small variation of +5% in the
thickness of the cantilever, for instance, would result in +15% variation in the spring
parameter k. This could cause serious switching errors in the relay matrix. Experience of
two of the authors of this paper suggests that micro relay matrix arrays based on
microrelay designs outlined in section 2.2 is bound to have very narrow tolerance window
and hence very low reliability.

2.3 Alternative design concepts

The most interesting of all electromagnetic microrelay designs that have been reported
to date is MagLatchTM which has been commercialised by Magfusion [31]. The major
advantage of this relay is the latching mechanism to maintain the non-volatile state
without requiring constant current supply. The device is based on preferential
magnetization of a permalloy cantilever in a permanent external magnetic field. Switching
between two stable states is achieved by sending a short current pulse through an
integrated coil underneath the cantilever. However, suitability of this design for the
fabrication of integrated microrelay arrays with viable, cost effective row and column
addressing scheme is yet to be demonstrated.

A major drawback of the conventional design discussed in Section 2.1 is the variability
associated with the initial air gap and thickness of the cantilever. Any stress induced in the
cantilever beam during the electroplating process is likely to cause some initial deflection
in the cantilever and variable air gap. The stiffness of the cantilever spring varies as the
cube of its thickness, implying that the stiffness variation would be about three times the
thickness variation. As the heavier armature at the end of the cantilever is not fixed when
the relay is in the off state, resistance of the device to shock and vibration is bound to be
low.

To alleviate these problems, Roshen et al. [32] proposed a micromachined
electromagnetic switch with fixed on and off positions using two soft magnets and one
permanent magnet as shown schematically in Fig. 7(a). Two soft magnets situated in fixed
positions above and below a permanent magnet toggles between two fixed positions by the
application of current in an actuator coil for a brief period. The permanent magnet is
attached to a micromachined hinge or spring which moves under the action of a net force,
thereby opening or closing the switch. Current in the actuator coil changes the relative

IIUM Engineering Journal, Vol. 6, No. 2, 2005 Z. Dahari et al.

strength of the magnetic forces due to the soft magnets. In the absence of current in the
actuator coil, the switch is kept in the open or closed position by the attractive magnetic
force between the permanent magnet and either the upper or lower soft magnet, whereby
the stronger force is exercised between the permanent magnet and the nearest soft magnet.

In the conventional electromagnetic microrelay design, the strain energy stored in the
spring when the relay is in the closed state is not gainfully utilised. When the relay is
switched open from its closed state, the stored energy is transformed into kinetic energy
and manifests as oscillations which eventually dies down due to damping.

(a) Fixed on-off position switch (b) Bistable switch

Fig. 7: Schematic designs of bistable, latching, electromagnetic switch.

Tabat et al. [33] proposed a novel design, shown schematically in Fig. 7(b) that utilises
the stored energy in the switch for changing its state. Bistable operation is obtained using a
single coil and a magnetic core with a gap. A plunger having two magnetic heads is
supported for back and forth linear movement with respect to the gap in the core. The
single electrical coil is coupled to the core and is provided with electrical current to attract
one of the heads toward the core by reluctance action and drive the plunger to the limit of
travel in one direction. The current is then cut off and the plunger returns by spring action
toward the gap, where after the current is reapplied to the coil to attract the other head of
the plunger to its limit of travel. This process can be repeated at a time when switching of
the actuator is required.

While the above two novel concepts have significant merits and are worth pursuing,
one has to bear in mind the difficulties of micromachining such devices. To the authors’
knowledge, an economically viable design utilizing one or more of these two concepts that
is amenable to micromachining remains to be developed.

3. DISCUSSION OF ONGOING RESEARCH AT RMIT
UNIVERSITY

A group of researchers at RMIT University are attempting to develop a robust design
for an electromagnetic microrelay that can form the building block of microrelay array
matrices. The main focus is to develop a relay structure with the following features: easily
manufacturable by standard MEMS processes with minimum cost, has fixed on and off
positions so that resistance to shock and vibration can be enhanced, utilizes the strain

IIUM Engineering Journal, Vol. 6, No. 2, 2005 Z. Dahari et al.

energy stored in the spring for switching from one state to the other resulting in a more
positive switching action, uses a permanent magnet to achieve latching as well as push-
pull action during switching.

3.1 Proposed design of electromagnetic micro relay

The proposed design under study is shown schematically in Fig. 8(a) and (b). A
relatively thick and rigid beam is attached at two points to the free ends of two thin
cantilever beams as in Fig. 8(c). These can be made of Silicon or a low permeability
material such as electroplated Nickel. An important feature of this mechanical
arrangement is that the elastic support provided by the pair of cantilever beams is very stiff
for pure vertical movements of the rigid beam (due to axial stiffening of the cantilever
beams), but quite flexible for tilting movements as shown in Fig 8(d). Furthermore, in the
tilted position the mechanical system once again becomes quite stiff if the lower end of the
rigid beam is held against a mechanical stop, as in Fig. 8(e). Two permanent magnets are
attached to the ends of the rigid beam and magnetized in a vertical direction as shown. The
electromagnet is formed by a number of planar parallel wires all carrying current in the
same direction (normal to the plane of the paper). The Permalloy strip is placed
underneath the wires to increase the magnetic flux due to the current carrying wires. It is
to be noted that, even without the two permanent magnets, bistable operation similar to the
device of Fig. 8(b) is possible with this design.

When a current pulse is applied to the coil (in a direction along the outward normal to
the paper), the RHS permalloy pole piece will be polarized N and the other S, attracting
the LHS end of the rigid beam while repelling the RHS end, and causing the beam to tilt
counter clockwise. When the coil current is switched off, the magnetic attraction between
the LHS permanent magnet and the LHS permalloy pole piece will be able to hold the
rigid beam to remain in the tilted position. A current pulse in the opposite direction will
cause the rigid beam tilt to the opposite side.

Fig. 8: Schematic of the proposed mechanical system

IIUM Engineering Journal, Vol. 6, No. 2, 2005 Z. Dahari et al.

3.2 Finite Element Analysis (FEA)

To realistically study the mechanical system, a simple linear analysis will not suffice;
nonlinear effect of stiffening of the beam caused by deflection will have to be accounted
for. Using ANSYS software, a nonlinear finite element analysis is carried out to
determine the force-deflection characteristics of the proposed structure. Figure 9 gives the
normalized force – deflection characteristics of the LHS end of the rigid beam when the
RHS end of the beam is held down against a normalized dead stop distance, dn below the
undeflected position of the beam. At positive normalized forces (upward), the graph
demonstrates for higher values of dn, the characteristics display a very flat region which
implies the increasing stiffness of the system. However, beyond a certain threshold values
of the applied force, the deflection steadily increases with force. For example, for dn =
0.042, the graph is nearly constant between the normalized force of 0.00 to 0.02, but when
it reached the threshold value at around 0.03, the deflection increase significantly. It
appears that buckling of the cantilever beams occur beyond this threshold.

This trend repeats for the negative forces (downward forces) at small value of dn for
example, dn =0.008. Generally, the FEA results show flat regions in terms of normalized
deflection which demonstrates high degree of stiffness when downward forces are applied.
It can therefore be concluded that within the limits set be the threshold, the mechanism
offers significant disturbance immunity.

Some preliminary analysis of the magnetic circuit of the microrelay has also been done
performed to determine the force generated on the rigid beam by the electromagnet at
various positions of the rigid beam. The magnetic circuit simulated is shown in Fig. 10(a).
In this analysis the permanent magnets are left out and the rigid beam is assumed to be
made up of a high permeable material such as electroplated permalloy. The objective is to
see whether bistable operation is possible with such an arrangement. The element type
PLANE13 is used to model the magnetic circuit, cantilever beam, air gap and the coil,
while two-dimensional four node boundary elements, INFIN110, are used to simulate an
infinite extension of the surrounding air. The flux patterns for initial horizontal beam
position and for a tilted position are shown in Fig. 10(b) and Fig. 10(c). Effect of the tilt
angle on the resultant force and its point of application are analysed and the results
presented in Table 2.

It can be seen from Table 1 that as the angle of tilt of the rigid beam increases the point of
application of the resultant magnetic force moves further to the right of the beam centre.
The normalized force and the tilting moment also increase with the angle of tilt. Graph in
Fig. 11 demonstrates that bistable operation under electromagnetic excitation is feasible
provided the spring force line lies below the magnetic force line.

Table 1: Magnetic force on beam at tilted angle

Tilted angle,

Normalised force

(Fθ/F0)

Normalised offset

(e/l)

Normalised tilting moment

(Fθe/ F0l)

0 1.00 0.00 0

5 1.04 0.17 0.1768

10 1.22 0.33 0.4026

15 1.78 0.54 0.9612

IIUM Engineering Journal, Vol. 6, No. 2, 2005 Z. Dahari et al.

Fig. 9: Force – deflection characteristics of the LHS end when RHS end is pressed
down against a dead stop distance d below the undeflected position of rigid beam.

(a )

(b) (c)

Fig. 10: FEA of magnetic circuit and the magnetic flux patterns for horizontal and tilted
position

IIUM Engineering Journal, Vol. 6, No. 2, 2005 Z. Dahari et al.

Fig. 11: Tilting moment at different angle

4. SUMMARY

Because of their narrow tolerance window, existing designs of electromagnetic
microrelays are proving to be problematic for fabricating microrelay matrices where
individual relays are required to be selectively switched on and off by row and column
multiplexing. A novel design incorporating a number of desirable features to improve
switching robustness is proposed. ANSYS simulation studies are being pursued to
demonstrate the advantages of the proposed design. A prototype is to be built and
evaluated in the near future.

REFERENCES

[1] M. J. Madou, Fundamentals of Microfabrication: The Science of Miniaturization, CRC Press.
2nd Edition, 2002.

[2] S. D. Senturia, Microsystem Design, Springer, 2004.
[3] J. A. Pelesko and D. H. Bernstein, Modeling MEMS and NEMS, CRC Press, 2002.
[4] H. F. Schlaak, “Potential and Limits of Micro-electromechanical Systems for Relay and

Switches”, in Proc. 21st International Conference on Electrical Contacts, Zurich, pp. 19-30, 9-
12 Sep, 2002.

[5] R. H. Grace, “Commercialization Issues of MEMS/MST/Micromachines, An Updated Industry
Report Card on the Barriers to Commercialization”, in Proc. Of Sensors Expo & Conference,
Boston, 23-26 Sep, 2002.

[6] W. Johler, “ Switching Contacts for Low Level Applications-An Overview”, in Proc. 21st
International Conference on Electrical Contacts, Zurich, pp. 19-30, 9-12 Sep, 2002.

[7] K. E. Petersen, “Microelectromechanical Membrane Switches on Silicon. IBM J. Res. Dev., 24,
pp. 376-385, 1979.

[8] J. Schimkat, “Contact Materials for Microrelays” in Proc. The Eleventh Annual International
Workshop on MEMS 98, pp. 190-194, 25-29 Jan, 1998.

[9] G. B Chong et al., “Simulations Based Design for a Large Displacement Electrostatically
Actuated Microrelay”. Analog Integrated Circuits and Signal Processing, 32, pp. 37-46, 2002.

IIUM Engineering Journal, Vol. 6, No. 2, 2005 Z. Dahari et al.

[10] H. S. Lee, “Integrated Microrelays: Concept and Initial Results”, Journal of
Microelectromechanical Systems. Vol 11, No.2, pp. 147-153, 2002.

[11] J. Kim, “A Micromechanical Switch with Electrostatically Driven Liquid-Metal Droplet”.
Sensors and Actuators A , vol. 97-98, pp. 672-679, 2002.

[12] J. Qiu et al. “ A High-Current Electrothermal Bistable MEMS Relay”, n Proc. Of Micro
Electro Mechanical Systems, 2003. MEMS-03 Kyoto. IEEE The Sixteenth Annual
International Conference, pp. 64-67, 19-23 Jan. 2003.

[13] Y. Wang et al., “A micromachined RF microrelay with electrothermal actuation”, Sensors and
Actuators A: Physical, Vol. 103, Issues 1-2, pp. 231-236, 2003.

[14] T. Moulton and G. K. Ananthasuresh, “Micromechanical devices with embedded electro-
thermal-compliant actuation”, Sensors and Actuators A: Physical, Vol. 90, Issues 1-2, pp. 38-48,
2001.

[15] G. D. Gray, Jr. and P. A Kohl, “Magnetically bistable actuator: Part 1. Ultra-low switching
energy and modelling”. Sensors and Actuators A: Physical, Vol. 119, Issue 2, pp. 489-501,
2005.

[16] J. W. Judy, “Batch-Fabricated Ferromagnetic Microactuators With Silicon Flexures”. Doctoral
Dissertation, University of California, Berkeley, 1996.

[17] I. J. Busch-Vishniac, “The case of magnetically driven microactuators”, Sensor and Actuators,
vol 33, pp. 207-220, 1992.

[18] G. Reyne, “Electromagnetic actuation for MOEMS, examples, advantages and drawbacks of
MAGMAS”, Journals of Magnetism and Magnetic Materials, vol. 242-245, pp. 1119-1125,
2002.

[19] D. Niarchos, “Magnetic MEMS: key issues and some applications,” Sensors and Actuators A,
vol. 109, pp. 166-173, 2003.

[20] L. K. Lagorce, O. Brand and M. G. Allen, “ Magnetic Microactuators Based on Polymer
Magnets”, IEEE Journals of Microelectromechanical Systems, vol. 8, no.1, 1999.

[21] H. Hosaka, H. Kuwano and K. Yanagisawa, “Electromagnetic microrelays: Concept and
fundamental characteristics”, in Proc. IEEE Microelectromechanical Sys. Conf., Fort
Lauderdale, pp. 41-47, 1993.

[22] J.A Wright and Y. C. Tai, “ Micro-miniature Electromagnetic Switches Fabricated Using
MEMS Technology”, Proceedings: 46th Annual Relay Conference: NARM ’98, Illinois, pp.
13-1 to 13-4, April, 1998.

[23] H. Hosaka and H. Kuwano, “Design and fabrication of miniature relay matrix and investigation
of electromechanical interference in multi-actuator systems” MEMS '94, Proceedings, IEEE
Workshop, pp. 313 – 318, 25-28 Jan. 1994.

[24] W. P. Taylor and M.G. Allen, “Integrated Magnetic Microrelays: Normally Open, Normally
Closed, and Multi-Pole Devices”, in Transducers ’97, International Conference on Solid-State
Sensors and Actuators, Chicago, pp.1149-1152, 16-19 Jan, 1997.

[25] E. Fullin et al., “A New Basic Technology for Magnetic Micro-actuators”,
Micro Electro Mechanical Systems, 1998. MEMS 98. Proceedings., The Eleventh Annual
International Workshop , pp.143–147, 25-29 Jan.1998.

[26] H.A. C. Tilmans et al. “ Fully-Packaged Electromagnetic Microrelay”, Micro Electro
Mechanical Systems, 1999, Twelfth IEEE International Conference on MEMS '99, pp. 25 -
30, 17-21 Jan. 1999.

[27] T. Masood, “Microactuators : electrical, magnetic, thermal, optical, mechanical, chemical &
smart structures”, Boston : Kluwer Academic, 1998.

[28] W.P. Taylor, O. Brand and M.G. Allen, “Fully Integrated Magnetically Actuated Micromachined
Relays”, Journal of Microelectromechanical Systems, Vol. 7, No. 2, June 1998.

IIUM Engineering Journal, Vol. 6, No. 2, 2005 Z. Dahari et al.

[29] K. Persson, “Fundamental Requirements on MEMS Packaging and Reliability”, 8th
International Symposium on Advanced Packaging Materials”, 2002.

[30] A. Witrouw, H.A.C Tilmans and I.De Wolf, “Material issues in the processing, the operation
and the reliability of MEMS”, Microelectronic Engineering, vol. 76, pp. 245-257, 2004.

[31] http://www.magfusion.com
[32] US Patents, 05475353.
[33] US Patents, 5,808,384.