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J. Micro/Nanolith. MEMS MOEMS 10(1), 011505 (Jan-Mar 2011)
Novel multicontact radio frequency
microelectromechanical system switch
in high-power-handling applications

Bo Liu
Abstract. We report a novel multicontact radio frequency (RF) micro-
Zhiqiu Lv
electromechanical system (MEMS) switch with mechanical independent
Xunjun He
switch elements and microspring contacts. The consistent contact
Yilong Hao
arrangement and the robust contact design can effectively increase
Zhihong Li
the contact area, reduce the current density, and therefore improve the
Peking University
power-/current-handling capability. The working mechanism of the switch
Institute of Microelectronics
with microspring contact is investigated by CoventorWare R simulation
National Key Laboratory of Science
tools. The switch, fabricated by the Cu-Ni dual-metallic-sacrificial-layer
and Technology on Micro/Nano Fabrication
surface micromachining, is actuated at 55 V for characterization. The
Cheng Fu Road, Haidian District
closing time is 11 s, and the opening time is 13.5 s. The isolation is
Beijing 100871 China
-30.9 dB at 2 GHz and -11.5 dB at 20 GHz; the insertion loss is -0.12 dB
E-mail:liubo@ime.pku.edu.cn
at 2 GHz and -0.22 dB at 20 GHz. The contact metal is Pt-Au, and the
measured switch resistance drops from 48 to 1.2
when the actuation
voltage increases from 40 to 65 V. The switch element handles a current
of 300 mA at 0.1 Hz. The switch is an excellent candidate for microwave
applications requiring high-power handling. C 2011 Society of Photo-Optical
Instrumentation Engineers (SPIE). [DOI: 10.1117/1.3564864]
Subject terms: radio frequency microelectromechanical system switches; ohmic
contacts; microsprings; power-handling ability; metallic sacrificial layers; surface
micromachining.
Paper 10081SSRR received Jul. 30, 2010; revised manuscript received Feb. 14,
2011; accepted for publication Feb. 21, 2011; published online Mar. 22, 2011.
1
Introduction
structures, it cannot be ensured that all pairs of contact
Radio frequency (RF) microelectromechanical system
structures fully contact to each other during operations (see
(MEMS) switches hold the promise of high isolation, high
Sec. 2 for more details). A novel multicontact RF MEMS
linearity, ultralow power consumption, and insertion loss,1
switch is presented in this work. The switch contacts are
which surpass the solid state devices in some extent and are
arranged in maximum uniformity by placing two switch ele-
called nearly ideal switches.2 Various designs of RF MEMS
ments face to face. Moreover, the contacts are applied as the
switches are demonstrated,3-5 and categorized, according to
microspring11 design to ensure the maximum contact area.
the contact type, as capacitive contact switches and ohmic
contact switches. Ohmic contact RF MEMS switches per-
2
Design
form well from direct current (dc) to tens of gigahertz, which
2.1
Conceptual Design
offers a broadband to the reconfigurable RF system appli-
cations, such as automatic test equipment systems, synthetic
The reported multicontact switches are those with a sin-
aperture radar, and cellular systems.
gle beam containing multiple contacts12. Figure 1(a) shows
The power-handling ability of switches is a critical factor
a schematic view of the reported four-contact RF MEMS
for practical application, and to date, it is largely increased.
switch. The movable part of the switch is the cantilever,
As reported, the switch developed by RadantMEMS
which can be actuated by applying voltage on the actuation
(Columbus, Ohio) handles an RF power of 40 dBm (10 W),6
pads. The current flows through the cantilever and passes the
and the switch from RFMD (Greensboro, North Carolina)
contacts when the switch is downstate. On upstate, the circuit
handles a power of 36 dBm (4 W).7 Platinum group metals8
is open. Because of the stress and stress gradient induced dur-
and gold alloys7 are introduced as contact materials. Obvi-
ing fabrication13 and/or the roughness of contact surface,14
ously, the characteristics of the contact material affect much
the contact surface is not ideally flat and the real contacts
of their power-handling ability.9 Nevertheless, good mechan-
cannot be made on the designed contact area. Suppose the
ical and electrical designs are also necessary for achieving
most protruding spots from the top and bottom contacts de-
the desirable performance. The multicontact8 and the switch
fine a face ABC, as shown in Fig. 1(b); thus, only those
array10 allow the RF power to be shared on multiple contacts
exact spots on the face ABC can make the contact, neglect-
and switches, and are reported as effective configurations
ing the local elastic or plastic deformation. The worst case
for the power-handling enhancement. However, owing to the
is that only these three spots make contact and all the other
three-point contact nature and the stiffness of the mechanical
designed contact parts hang around. Consequently, the finite
contacted spots make the current path and have to suffer
a high-temperature, high-current-density, and high-contact-
1932-5150/2011/$25.00 C 2011 SPIE
pressure process, which easily causes failures.15-17
J. Micro/Nanolith. MEMS MOEMS
011505-1
Jan-Mar 2011/Vol. 10(1)

Liu et al.: Novel multicontact radio frequency microelectromechanical system switch. . .
Fig. 1 Comparison of the reported four-contact ohmic contact switch with our designed switch: (a) Schematic of a prototype of a solid-four-
contact switch, (b) detailed contact part of the solid-four-contact switch, (c) schematic of a prototype of our designed switch with two mechanically
independent microspring-two-contact switch elements, and (d) detailed contact part of our designed switch.
To improve the reliability of the switch, our idea is to
Fig. 2(a). All these components were in lumped beam mod-
distribute the current with increasing the possible contact
els based on linear Bernoulli beam theory. The components
spots/area. The specific changes, as shown in Fig. 1(c), are
were connected with buses (x,y,z,rx,ry,rz), which meant the
described in detail as follows:
ends of each components were fixed together in six degreed
of freedom. The constructed model is shown in Figs. 2(b)
(1) The conventional four-solid-contact switch is sepa-
and 2(c), whose parameters are listed in Table 1. The contact
rated into two switch elements to decrease the influ-
was designed to take place on the pairs of dimples.
ence from the stress gradient of the cantilever. The
The pulse power with a step of 1 V was applied on the
two switch elements are mechanically independent,
actuation pads from 0 to 100 V. Eight integration points were
but electrically connected, which are actuated simul-
set on the contact to simulate the contact mechanism. The dis-
taneously.
placements of the ends (front tip and back tip) of the dimple
(2) All the contacts are placed closely together (face to
according to different actuation voltage were simulated by
face) to minimize the misalignment and the inconsis-
dc transfer analysis, presented in Fig. 3(a). The gap between
tency induced from the fabrication.
the contacts was 0.3 m. Therefore, if the displacement was
(3) The contacts are replaced by the microspring contacts
>0.3 m, the dimples were connected with the bottom con-
to increase the deformation and improve the possible
tacts. As the actuation voltage increased, the interaction first
contact area.
took place at the front tip. From 45 to 47 V, the switch was
partially contacted. At 47 V, the back tip also touched the
The stiffness of the microspring contact part is reduced
bottom contact. From 47 to 52 V, the contact was made on
by a thinner beam. The deformation of the contact is largely
the whole dimple area. Continually increasing the actuation
increased. Therefore, the contacts are more robust to the
voltage to 100 V, the switch was partially contacted again
uneven surface. The spots in each contact face of A1B1C1,
and the front tip was levered up. Figure 3(b) presented the
A2B2C2, A3B3C3, and A4B4C4 are all possible to make the
contact force and conductance, which were increased from
contact, as shown in Fig. 1(d).
the first partially contact status to the full contact status. The
conductance was not increased with the contact force linearly
2.2
Simulation
because it was also affected by the contact area. During the
The switch was made of a pair of mechanically independent
second partial contact status, the top actuation pad started to
microspring-to-contact switch elements. The mechanical
collapse on the dielectric layer at 56 V; therefore, the front
properties of the designed switch depended on the switch
tip stopped from levering up, and the contact force on the
element, which was simulated with a top-down system-level
dimple was reduced, and thus, the conductance also reduced
tool called ARCHITECT from CoventorWare R . It was
accordingly. Not until 85 V did the top actuation pad totally
abstracted into seven components: two anchor parts, two
collapse on the dielectric layer. The statuses of partial con-
cantilever beams, a pair of actuation pads, two microspring
tact, full contact, and actuation pad collapse were illustrated
beams, and two pairs of dimple contacts, as shown in
in Fig. 3(c).
J. Micro/Nanolith. MEMS MOEMS
011505-2
Jan-Mar 2011/Vol. 10(1)

Liu et al.: Novel multicontact radio frequency microelectromechanical system switch. . .
Fig. 2 System-level simulation schematic of the microspring-two-contact switch element: (a) System-level schematic designed in Saber Sketch
editor, (b) constructed model of the two-contact switch with microspring contact presented in Scene3D, and (c) detailed microspirng contact part.
3
Fabrication
the expected contact material can be realized after removing
The switch was fabricated on the SCHOTT BOROFLOAT R
the sacrificial layers.
33 (B33) glass substrate utilizing electroplated gold as the
3.1
Metallic Sacrificial Layer
structural material. The contacts were made from Pt-Au
combination (Pt was applied for the bottom contact, and
We had applied and compared both copper and nickel to
Au was applied for the top contact). The mechanical mov-
serve as the sacrificial layer. The metal was sputtered on the
able part was achieved from surface micromachining. The
substrate. The base pressure in the deposition chamber before
material and process of the sacrificial layer is crucial for
starting the sputter process was about 1 x 10 - 4 Pa. Argon
surface micromachining technology. In our case, it must be
gas was introduced with a flow rate of 15.5 sccm. Both of the
compatible with electroplating Au. Cross-linked polymethyl
targets were with a purity of 99.95%. The detailed sputtering
methacrylate,18 photoresist,19 or polyimide20 were reported
conditions are listed in Table 2. The thickness of copper was
as the sacrificial layer, and the obvious benefit of these or-
3065 A, and the thickness of nickel was 2895 A.
ganic sacrificial layers was that they could be diminished
Following the sacrificial layer deposition, the anchor
with oxygen plasma, and therefore, the structure could be
windows were opened by etching the sacrificial layer. After
released in a totally dry process. However, a seed layer has
this process, the surface of copper became rough, as shown in
to be sputtered on the top of the organic sacrificial layer be-
Fig. 4(a), compared to the surface of nickel, as shown in
fore electroplating, which was usually a combination of an
Fig. 4(b). The reason was probably that the copper was
adhesion layer and the metal layer to be electroplated. As a
dissolved into the developer solution. The interface of
result, after the dry-releasing process, the top contact would
electroplated gold on copper and nickel sacrificial layers
be left as the adhesion layer, rather than the intended contact
were compared after the structure was released, as shown in
material.18 Metal sacrificial layers are conductive and have
Fig. 5. Cantilevers were flipped over to take scanning
no such problems. The electroplating process can be directly
electron microscope (SEM) and atomic force microscopy
conducted on it, which means no seed layer is needed and
(AFM) images. The root-mean-square (rms) roughness of
J. Micro/Nanolith. MEMS MOEMS
011505-3
Jan-Mar 2011/Vol. 10(1)

Liu et al.: Novel multicontact radio frequency microelectromechanical system switch. . .
Table 1 Parameters of the switch dimension.
Table 2 Deposition conditions of the copper and nickel.
Parameters
Values (m)
Cu
Ni
Lbeam
39
Power (W)
500
300
Wbeam
18
Pressure (Pa)
0.96
0.98
Lpad
50
Deposition time (min)
22.5
57
Wpad
80
Wbp
15
and lower insertion loss. Therefore, it was better for gold
Lmicrospring
9
to be electroplated on nickel layer. However, nickel itself
could not be applied as the sacrificial layer, solely, because
Wmicrospring
12
of its large stress induced from sputtering. We proposed a
R
dual-metallic-sacrificial-layer surface micromachining21 to
dimple
2
fabricate the device, which resulted in a smooth structural
Hmicrospring
1
surface and an insignificant residual stress.
G
0.6
3.2
Fabrication Process
Hdltlayer
0.3
The fabrication process is shown in Fig. 6. The detailed
process flow is described as follows:
Hdimple
0.3
H
(1) A 3000-A deep trench was etched on the B33 glass
btmlayer
0.3
substrate to define the area of bottom actuation pad
Hbeam
6
and the anchors.
(2) A liftoff process of Ti/Pt with 100/3000 A in thick-
ness was followed to make the bottom layer consisting
gold surface released from copper was 9.45 nm, and that of
of the bottom actuation pad and bottom contacts.
gold surface released from nickel was 4.74 nm. Considering
(3) A 3000-A thick dielectric layer of SiO2 film was de-
the contact surface, the lower roughness of the surface in-
posited by the plasma-enhanced chemical vapor de-
dicated more possible contacted spots, higher conductance,
position and patterned with the advance oxide etch,
Fig. 3 Simulations of the operation mechanism of the microspring contact switch: (a) Simulation of displacement of the ends (the front and back
tips) of the dimple, (b) simulation of the contact force and conductance of a single dimple, and (c) displacement of the top contact, microspring,
and the top actuation pad at the actuation voltage of 46, 50, and 90 V, illustrating the partial contact status, full contact status, and actuation pad
collapse status.
J. Micro/Nanolith. MEMS MOEMS
011505-4
Jan-Mar 2011/Vol. 10(1)

Liu et al.: Novel multicontact radio frequency microelectromechanical system switch. . .
Fig. 4 Comparison of the sacrificial layer surfaces after opening the anchor window: (a) SEM image of copper sacrificial layer and (b) SEM
image of nickel sacrificial layer.
STS (Surface Technology Systems, Plc, Newport,
ple area with wet etching. The etchant of Cu was
UK) to open windows for anchors and bottom con-
CH3COOH:H2O2:H20 = 1:1:20, and the etch rate
tacts.
was 1918 A/min at room temperature.
(4) The first sacrificial layer of Cu was deposited with
(5) The second sacrificial layer of nickel was deposited
3000 A in thickness and patterned to define the dim-
with 3000 A in thickness, which followed the shape
Fig. 5 Comparison of the gold bottom surfaces, which were flipped over after releasing from the copper and nickel sacrificial layers, respectively:
(a) SEM image of the gold surface releasing from the copper sacrificial layer, (b) SEM image of the gold surface releasing from the nickel
sacrificial layer, (c) AFM image of the gold surface releasing from the copper sacrificial layer, and (d) AFM image of the gold surface releasing
from the nickel sacrificial layer.
J. Micro/Nanolith. MEMS MOEMS
011505-5
Jan-Mar 2011/Vol. 10(1)

Liu et al.: Novel multicontact radio frequency microelectromechanical system switch. . .
Fig. 8 Contact resistance versus actuation voltage of our fabricated
switch.
(8) The whole diced wafer was immersed into the fum-
ing nitric acid and followed with a deionized water
rinse. Finally, the wafer was baked on a hot plate to
Fig. 6 Fabrication process of the designed switch.
evaporate the water. The switch was released.
The fabricated switch is presented in Fig. 7, which was in
of the former process, and both sacrificial layers were
a coplanar waveguide (CPW) configuration. The thickness
wet etched to define the anchor windows. TFB from
of the beam and the microspring before releasing were mea-
Transene Company, Inc. (Danvers, Massachusetts)
sured with surface profiler AS500, and the mean values of
was applied to etch nickel, and the etch rate was 1200
which were 5.57 and 1.25 m, respectively. The cantilever
A/min at room temperature. Copper was etched by the
part was thicker, and the microspring part was thinner than
etchant mentioned before. After this step, the wafer
the design.
was tested to make sure the whole wafer was electri-
cally conducted.
4
Experimental Characterizations
(6) A 1 m thick Au was electroplated on the sacrifi-
4.1
Actuation Voltage and Contact Resistance
cial layer to fabricate the microspring top contact,
The primary contact was recorded by slowly increasing the
which followed the shape of dimples. The mold for
power supply voltage from zero until the contacts first be-
electroplating was made from AZ R 9260 photoresist
came conductive. The switch primarily contacted at 40 V.
with 9 m thick. Before electroplating, the wafer was
The contact resistance of our switch was measured with a
cleaned with oxygen plasma.
multimeter via two probes, which was stamped on the input
(7) A 6-m-thick Au layer was electroplated to make
and output pads. The measured data were subtracted by the
the beam and top actuation pad structures. Then, the
parasitic resistance formed by the probes and the wires. The
wafer was diced.
contact resistance of the switch decreased from 48 to 1.2
as
Fig. 7 SEM image of the fabricated switch: (a) Switch and switch element overview and (b) enlarged microspring contact part.
J. Micro/Nanolith. MEMS MOEMS
011505-6
Jan-Mar 2011/Vol. 10(1)

Liu et al.: Novel multicontact radio frequency microelectromechanical system switch. . .
Fig. 9 Switching time test of the fabricated switch: (a) Setup of the switching time test and (b) measurement of the switching time. The actuation
voltage was applied on 3 s and removed at 33 s. The closing time was 11 s, and the opening time was 13.5 s.
the actuation voltage increased from 40 to 65 V, as shown in
tually no bouncing. The switching time can be reduced by
Fig. 8. The primary contact voltage and the contact resistance
increasing the actuation voltage or testing in vacuum.
trend agree well with the simulation result. The difference
stemmed majorly from the lower thickness of the beam than
4.3
Radio Frequency Measurements
expected.
The RF characteristics of the designed switch were shown
in Fig. 10, which were compared to a test structure with a
single microspring-two-contact switch element implemented
4.2
Switching Time
in a CPW line. An RF source Agilent E8362B of 100 MHz
The test equipment was set up under atmosphere, as illus-
to 20 GHz was applied on the input and output pads. The
trated in Fig. 9(a). The switch was placed in series with a
switch was measured under atmosphere after the short-open-
20-k
resistor and a constant voltage source of 4 V; there-
load-through calibration. The shorted switch was tested as an
fore, the constant current was 0.2 mA. Experimental results
indication of the transmission line loss at the measuring band.
of the switching time were obtained by measuring the volt-
Below 2 GHz, the measurement setup induced a large fluctua-
age across the switch as a function of time with a Tektronix
tion on the insertion loss, which was not shown in Fig. 10. The
TDS 2014B oscilloscope. The actuation voltage was ampli-
isolation was -30 dB for our designed four-contact switch and
fied from a function generator, which was a 55 V square
-37 dB for the two-contact switch element at 2 GHz; and was
wave with a period of 30 s. As shown in Fig. 9(b), the
-11.5 dB for the four-contact designed switch and -17.5 dB
actuation started at 3 s and stopped at 33 s. The switch
for the two-contact switch element at 20 GHz. The fitted
responded at 14 and 42 s, respectively. The switching time
upstate capacitance was 22 fF for our four-contact designed
was determined by the mean value of the time respond-
switch and 10.3 fF for the two-contact switch element. The
ing of 90 and 10% of the constant voltage (4 V). There-
four-contact switch had a larger upstate capacitance because
fore, the closing time was 11 s, and the opening time was
the overlapping region was twice as much as that of the two-
13.5 s.
contact switch element. Larger contact area also induced a
The simulation of small-signal frequency analysis resulted
lower contact resistance in dc and less insertion loss in RF.
in the resonance frequency of 202.9 kHz. This mechanical
The insertion loss was -0.12 dB for our four-contact switch
resonant frequency resulted in a fast switching time and vir-
and -0.2 dB for the two-contact switch element at 2 GHz;
Fig. 10 Measured RF characteristics of our designed switch in upstate and downstate, compared to a two-contact switch element. (a) The
isolation of our designed switch and a two-contact switch element in upstate, the measured data were fitted with a capacitance, and (b) insertion
loss and reflection loss of our designed switch and a two-contact switch element in downstate, the measured data were fitted with a resistance
and an inductance connected in series.
J. Micro/Nanolith. MEMS MOEMS
011505-7
Jan-Mar 2011/Vol. 10(1)

Liu et al.: Novel multicontact radio frequency microelectromechanical system switch. . .
and was -0.22 dB for our four-contact switch and -0.25 dB
Fig. 1(a), and the highest current handled, which was only
for the two-contact switch element at 20 GHz. According to
200 mA. The microspring contact took effect in handling high
the downstate insertion loss and reflection loss, the switch
current. For our designed four-contact switch, the current was
was fitted as the series connected resistance and inductance.
split into two routes and passed through each mechanically
For our four-contact switch, the resistance was 1.5
and the
independent microspring-two-contact switch element; there-
inductance was 90 pH; for the two-contact switch element,
fore, the expecting current-/power-handling ability could be
the resistance was 2.4
and the inductance was 42 pH. The
higher.
fitted downstate resistance of our designed switch was much
lower than the two-contact switch element. The larger induc-
tance for four-contact switch was because of the fork-shaped
5
Conclusions
wave guide connecting the two two-contact switch elements.
A novel electrostatic actuated ohmic multicontact RF MEMS
switch is reported. With the improved structure design, four
4.4
Power Handling Capability
microspring contacts with maximum consistency were made
The failure mechanisms of the ohmic contact switch when
in the switch. The microspring contact switch operation
handling high power include melting/shorting and contact
mechanism was studied with simulation tools. As the ac-
erosion/material transport. Refractory materials can improve
tuation voltage increased, the contact part underwent three
the melting degree, but these materials have larger resistances
statuses, from partial to full contact, and back to partial con-
and a stiffer surface, which induce higher temperature on the
tact again. During the second partial contact statuses, the
contacts and limit the real contact area. A Pt-Au contact
top actuation pad also went through partial to full collapse
combination was applied in our design. A pair of soft-hard
status. The switch was fabricated with Cu-Ni dual-metallic-
bimetallic contacts can modify the topology of the contact
sacrificial-layer surface micromachining. The actuation volt-
surface and enhance the power-handling ability.22 The melt-
age and the contact resistance agree well with the simulation.
ing point of platinum is 2041.4 K, whereas that of gold is
The switch made a primary contact at 40 V, and the contact
1337.33 K. The Young's modulus of platinum is 168 GPa, and
resistance decreased to 1.2
when the actuation voltage in-
that of gold is 79 GPa. In the material respect, Pt-Au contact
creased to 65 V. The switching time was 13.5 s for open
guarantees a higher melting temperature and more contact
and 11 s for close. The isolation of the developed switch
area than Au-Au contact. Because of the limited number of
and the fitted upstate capacitive was twice as much as that
the fabricated microspring-four-contact switches, it was un-
of the two-contact ones, due to the double overlapping area.
able for us to implement the irreversible current-handling
The insertion loss and the fitted downstate resistance were
ability test on those switches. However, our switch was sym-
reduced, compared to the two-contact switch element. The
metrically designed and the main failure of the ohmic con-
two-contact switch element can handle a current of 300 mA,
tact MEMS switch for high-power handling stemmed from
which surpasses the current-handling ability of the conven-
the local high temperature on the contact surface.16 There-
tional solid-four-contact switch of 200 mA. Our switch is a
fore, the test was implemented on a test structure of a single
promising candidate for a high-power-handling application
microspring-two-contact switch element in a CPW configu-
in microwave system.
ration (the same as the former mentioned test structure for
RF test). To avoid contact erosion failure, the ohmic contact
Acknowledgments
MEMS switches normally work in cold-switch cycles. The
The authors thank all participants and contributors to this
test setup is shown in Fig. 11. The switches were pretreated
work, especially to the technicians of the National Key Lab-
first, and a current of 20 mA was applied on the actuated
oratory of Science and Technology on Micro/Nano Fabrica-
switch for 1 min. We applied a current of 12 pulses within a
tion in Peking University for their helpful assistance.
period of 10 s. The switch worked fine, until the current in-
creased to 300 mA. The switch was permanently connected.
In a 50-
transmission line, this corresponds to a high RF
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Computer Science from Peking University,
9. K. Hyouk, C. Dong-June, P. Jae-Hyoung, L. Hee-Chul, P. Yong-Hee,
China, in 2003 and 2007, respectively. His
K. Yong-Dae, N. Hyo-Jin, J. Young-Chang, and B. Jong-Uk, "Con-
research interests include RF MEMS and
tact materials and reliability for high power RF-MEMS switches,"
power MEMS.
in Proc. of IEEE 20th Int. Conf. on Micro Electro Mechanical Systems
(MEMS2007)
, pp. 231-234 (2007).
10. E. P. McErlean, J. S. Hong, S. G. Tan, L. Wang, Z. Cui, R. B. Greed,
and D. C. Voyce, "2x2 RF MEMS switch matrix," in IEE Proc. of
Microwaves, Antennas and Propagation, pp. 449-454 (2005).
11. B. Liu, Z. Lv, X He, and Z. Li, "Microspring contact for enhancement
of power handling and reliability in RF MEMS switch," in 5th Asia-
Pacific Conference on Transducers and Micro-Nano Technology Tech.
Digest
, July, Perth, Australia, p. 250 (2010).
Xunjun He received his BSc in electronic sci-
12. P. M. Zavracky, N. E. McGruer, R. H. Morrison, and D. Potter, "Mi-
ence and technology in 2000, MEng in mate-
croswitches and microrelays with a view toward microwave applica-
rials physics and chemistry in 2003, and PhD
tions," Int. J. RF Microwave Comput.-Aided Eng. 9, 338-347 (1999).
in electronic science and technology in 2008
13. H. Sedaghat-Pisheh, K. Jung-Mu, and G. M. Rebeiz, "A novel stress-
from Harbin University Science and Tech-
gradient-robust metal-contact switch," in IEEE 22nd Int. Conf. on Micro
Electro Mechanical Systems (MEMS 2009)
, pp. 27-30 (2009).
nology, China. His research interests include
14. L. Almeida, R. Ramadoss, R. Jackson, K. Ishikawa, and Q. Yu, "Study
microwave active circuits and RF MEMS de-
of the electrical contact resistance of multi-contact MEMS relays fab-
vices.
ricated using the MetalMUMPs process," J. Micromech. Microeng. 16,
1189-1194 (2006).
15. B. Jensen, K. Huang, L. Linda, and K. Kurabayashi, "Low-force contact
heating and softening using micromechanical switches in diffusive-
ballistic electron-transport transition," Appl. Phys. Lett. 86, 023507
(2005).
Yilong Hao is dean of the School of Micro-
16. B. D. Jensen, L. L. W. Chow, H. Kuangwei, K. Saitou, J. L. Volakis, and
electronics from Peking University and vice
K. Kurabayashi, "Effect of nanoscale heating on electrical transport in
president of Chinese Society of Micro-Nano
RF MEMS switch contacts," J. Microelectromech. Syst. 14, 935-946
Technology. His major research interest fo-
(2005).
17. H. Kwon, S. Jang, Y. Park, T. Kim, Y. Kim, H. Nam, and Y. Joo,
cuses on MEMS devices design and fabrica-
"Investigation of the electrical contact behaviors in Au-to-Au thin-film
tion. He has authored and coauthored over
contacts," J. Micromech. Microeng. 18, 105010 (2008).
100 publications in journals and conference
18. N. Nishijima, H. Juo-Jung, and G. M. Rebeiz, "Parallel-contact
proceedings.
metal-contact RF-MEMS switches for high power applications," in
Proc. of 17th IEEE Int. Conf. on Micro Electro Mechanical Systems
(MEMS2004)
, pp. 781-784 (2004).
19. Z. Cui and R. Lawes, "A new sacrificial layer process for the fabrication
of micromechanical systems," J. Micromech. Microeng. 7, 128-130
(1997).
Zhihong Li received his BS in the Depart-
20. A. Bagolini, L. Pakula, T. LMScholtes, H. TMPham, P. J. French,
ment of Computer Science and Technology,
and P. M. Sarro, "Polyimide sacrificial layer and novel materials for
Peking University, China, in 1992. He re-
post-processing surface micromachining," J. Micromech. Microeng. 12,
385-389 (2002).
ceived his PhD at the Institute of Microelec-
21. B. Liu, Z. Lv, Z. Li*, X. He, and Y. Hao, "A surface micromachining
tronics, Peking University, majoring in VLSI
process utilizing dual metal sacrificial layer for fabrication of RF MEMS
technology and reliability, in 1997. He joined
switch," in Proc. of 5th IEEE Int. Conf. on Nano/Micro Engineered and
in the MEMS group at this institute afterward.
Molecular System (NEMS 2010), pp. 620-623 (2010).
He was a visiting scholar at Cornell Univer-
22. A. Broue, J. Dhennin, F. Courtade, P. L. Charvet, P. Pons, X. Lafontan,
sity and University of California, Davis from
and R. Plana, "Thermal and topological characterization of Au, Ru and
2000 to 2004. Presently, he is a professor
Au / Ru based MEMS contacts using nanoindenter," in Proc. of IEEE
of MEMS Research Center, Institute of Mi-
23rd Int. Conf. on Micro Electro Mechanical Systems (MEMS 2010),
pp. 544-547 (2010).
croelectronics, Peking University. His research interests include de-
sign and fabrication of MEMS, especially Bio MEMS and RF MEMS.
He has published more than 100 peer-reviewed articles and given
Bo Liu received her BS in electrical sci-
more than 10 invited speeches at international conferences and work-
ence and technology from Harbin Institute
shops. He was the cochair of Technical Program Committee in IEEE
of Technology, China, in 2005. As a PhD
NEMS'09 and currently serves as the member of Technical Program
candidate in microelectronics at the Peking
Committee for the IEEE Sensors Conference and the IEEE MEMS
University, her main research area is the
Conference.
high-power handling RF MEMS switch. She
was a visiting student at Saarland Univer-
sity, Germany, in 2007. Her current research
interests include design, fabrication, packag-
ing, and test of MEMS devices.
J. Micro/Nanolith. MEMS MOEMS
011505-9
Jan-Mar 2011/Vol. 10(1)

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