Evaluation Engineering - 20

MEMS

company calls Ideal Switch technology,
and its first new products targeted for test
and measurement applications became
available in 2018.

Time for a switch
EMRs and other mechanical switches are
large, have limited channel density, suffer
from relatively rapid contact wear, and
are susceptible to environmental stresses
like shock and vibration. As the size of the
cantilever in an EMR is large and heavy
(in relay terms), the time required for it
to reach the contact to make or break
the circuit is long, limiting its potential
switching speed. While a MEMS switch
also uses a mechanical approach, it is a
microelectromechanical device fabricated
in a wafer-level manufacturing process in
a semiconductor fab. Its cantilever weighs
almost nothing, and can switch in 10 µs
rather than the 10 ms or so required
by EMRs. This 1000-times reduction in
switching time has major positive benefits
for switch matrices, such as reducing the
cost-of-test, which is primarily limited by
test time.

Figure 3: The
basic unit cell of
a Menlo Micro
switch measures
only 50x50 ¬µm.
Menlo Micro

20

EVALUATION ENGINEERING JULY 2019

Menlo Micro switching elements are
smaller than the width of a human hair
(Figure 3), so hundreds of them can be
fit into a small package. Seeing as they
are fabricated using a wafer-level process on 8-inch wafers, manufacturing is
easily scalable like other semiconductor
products. From a size perspective when
compared to a typical EMR, a 100-switch
matrix using a series of Menlo Micro
6-channel switches consumes 85% less
space, weighs 120 grams less, reduces
board height by 75%, and given the lowpower electrostatic drive, reduces total
power consumption by 20W.
One of the more remarkable characteristics of MEMS switch technology is
that even though the components within
the devices are incredibly small and light,
they can nevertheless be arranged to handle hundreds of volts and tens of amperes,
while requiring just a few picoamps for
actuation.
With advances in electrodeposited alloys and other material innovations, the
reliability and longevity issues that have
plagued MEMS switch developments in

the past have been eliminated. Menlo
Micro's current devices, for example,
can operate for a minimum lifetime of 3
billion operations and typically greater
than 10 billion. With future advances in
materials and processing, this metric
will be increased to greater than 25 billion operations in the next few years. In
contrast, EMRs have operating lifetimes
typically less than a few million operations while reed relays can last for a few
hundred million operations. While a few
hundred million switching cycles might
seem enormous, switch matrices in many
ATE applications operate at hundreds of
cycles per second, so the ability of MEMS
switches to operate far longer means they
will likely long outlive the system itself.
To help designers become familiar with
MEMS switches in a matrix environment,
Menlo Micro developed an evaluation board
based on its MM1200 6-channel SPST device (Figure 4). The MM1200 can handle
current of 1 A per channel or 3 A in total,
has an AC signal frequency range of DC to 1
GHz, on-state resistance of less than 1 ohm,
and a switching speed of less than 10 µs.
Evaluation Engineering

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