Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Physical deformation
Reexamination Certificate
2002-08-14
2004-06-22
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Physical deformation
C310S306000, C310S307000
Reexamination Certificate
active
06753582
ABSTRACT:
TECHNICAL FIELD
A microelectromechanical systems (MEMS) switch, and in particular a MEMS switch that operates using low actuation voltage.
BACKGROUND
A microelectromechanical system (MEMS) is a microdevice that integrates mechanical and electrical elements on a common substrate using microfabrication technology. The electrical elements are typically formed using known integrated circuit fabrication techniques. The mechanical elements are typically fabricated using lithographic and other related processes to perform micromachining, wherein portions of a substrate (e.g., silicon wafer) are selectively etched away or added to with new materials and structural layers. MEMS devices include actuators, sensors, switches, accelerometers, and modulators.
MEMS switches (i.e., contacts, relays, shunts, etc.) have intrinsic advantages over their conventional solid-state counterparts (e.g., field-effect transistor (FET) switches), including superior power efficiency, low insertion loss and excellent isolation. However, MEMS switches are generally much slower than solid-state switches. This limitation precludes applying MEMS switches in certain technologies where sub-microsecond switching is required, such as switching an antenna between transmit and receive in high-speed wireless communication devices.
There are antenna applications where MEMS switches are critically important because of the relatively low insertion loss. One such application is in a smart antenna application that relates to switching between a plurality of antennas within a wireless communication device. Smart antenna switching applications typically require switching speeds ranging from milliseconds to seconds depending on the systems.
One type of prior art MEMS switch includes a connecting member called a “beam” that is electro-thermally deflected or buckled. The buckled beam engages one or more electrical contacts to establish an electrical connection between the contacts.
FIGS. 1 and 1A
illustrate a prior art MEMS switch
10
that includes a beam
12
which is electro-thermally buckled. Beam
12
is formed of a high thermal expansion conductor
14
and a low thermal expansion dielectric
16
. Conductor
14
and dielectric
16
are restrained at opposing ends by anchors
18
A,
18
B.
Activation of MEMS switch
10
is illustrated in
FIG. 1A. A
voltage is applied across beam
12
such that current travels through beam
12
with much more of the current passing through low resistance conductor
14
. As current passes through beam
12
(indicated by arrows A in FIG.
1
A), there is resistive heating generated within beam
12
that causes beam
12
to thermally expand. The large differential between the thermal expansion of conductor
14
and dielectric
16
causes beam
12
to buckle outward toward the side of conductor
14
. As beam
12
buckles, a contact stud
20
mounted on beam
12
engages contacts
22
A,
22
B so that signals (indicated by arrows B in
FIG. 1A
) can be passed between contacts
22
A,
22
B.
One benefit of using an electro-thermally deflected beam is that the switch requires a relatively low actuation voltage during operation. However, when the MEMS switch is in the actuated position, power is being consumed continuously in order to maintain the resistive heating within the beam.
FIG. 2
illustrates another prior art MEMS switch
30
that includes a beam
32
which is secured at opposite ends to anchors
34
A,
34
B. Beam
32
is secured to anchors
34
A,
34
B in a manner that places beam
32
under compressive stress. The compressive stress causes beam
32
to buckle. Beam
32
needs to remain in a buckled state for MEMS switch
30
to operate appropriately.
A lateral actuation electrode
36
is positioned adjacent to beam
32
at the level beam
32
would occupy were it not buckled from the compressive stress. This level of beam
32
is referred to as the neutral position and is indicated in
FIG. 2
with line
38
. A voltage is applied to lateral actuation electrode
36
to generate an electrostatic force that pulls beam
32
up or down toward its neutral position. The inertia of beam
32
carries it past the neutral position to the other side where beam
32
electrically connects contacts (not shown) to allow signals to pass between the contacts.
MEMS switch
30
does not require any power to maintain beam
32
in either the up or down position. One drawback associated with MEMS switch
30
is that large actuation voltages are required with electrostatic actuation in general, and in particular when electrostatic actuation is used to maneuver a buckled beam.
REFERENCES:
patent: 6310419 (2001-10-01), Wood
patent: 6407478 (2002-06-01), Wood et al.
Qiu, Jin.,et al. ,“A Centrally-Clamped Parallel-Beam Bistable MEMS Mechanism”,IEEE 2001,352-356.
Nelms David
Schwegman Lundberg Woessner & Kluth P.A.
Tran Mai-Huong
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