1 Consumer Electronics
Printable/flexible sensors add
new options for designers
Several P/F sensors currently available
open new opportunities in design and
manufacturing for wearables and IoT.
While several of these features are
shared by existing microelectromechanical systems (MEMS), MEMS
Fig. 1: Printable/flexible sensors offer new
are typically not flexible, cannot be
ith wearables and Internet of
capabilities well suited to wearables and IoT.
manufactured in an R-2-R process
Things (IoT) applications proShown is a temperature-sensing Smart Label from
(batch-mode only), and can require
liferating, potential suppliers
Thinfilm which uses technology from PST Sensors.
significant capital investments (unless
want to develop printable/flexible (P/F)
of course one uses a silicon foundry for
sensors (fig.1) that can fulfill applications
wafer processing).
conductive-carbon-based patterned circuit
requirements in unique ways. Accordingly,
In order of announcement date, the
configuration that serves as the sensor. A
Lux Research expects the P/F sensors marfollowing companies have brought P/F
electronics network is printed on the underket to grow from $17 million in 2014 to apsensors to market: Interlink
side of the next functional layer, which also
Electronics (www.iefsr.com),
serves as the encapsulant of the stack.
PST Sensors (www.pstsensors.
The Versa Pad is an excellent example of
com), Spec Sensors (www.
Interlink’s integration/systems solutions apspecsensors.com), and Brewer
proach, which solves customer application
Science (www.brewerscience.
requirements while simultaneously adding
com). While by no means an
value to their product offering. This touch
exhaustive list of today’s P/F
pad device uses FSR sensors along with
sensor suppliers, this group
discrete microprocessors that run propriprovides a solid survey of the
etary algorithms to provide sensor fusion.
Fig. 2: According to Lux Research, the market for P/F
types of sensors currently
Applications include computer mouse and
sensors is poised to grow very rapidly in a few years.
available.
touchpad pointing, hand-held consumer
devices, and human-to-machine (HMI)
proximately $400 million by 2024 — a 35%
interface touch solutions as well as analog
compounded annual growth rate (fig.2).
Force and displacement sensing
data capture for machines.
Roger Grace Associates believes this
P/F sensors became commercially available
Today, Interlink is delivering presgrowth will be driven not by a technology
in 1985, with Interlink Electronics’ introsure-sensitive touch sensors for vehicle
push, but by market pull from many signifi- duction of Force Sensing Resistor (FSR)
navigation panel control and door entry
cant applications in sports/wellness/medical technology. Interlink Electronics was a
control. Albert Lu, Interlink’s CTO, notes
wearable devices. These applications will
very early, if not the earliest, organization
that,” Our automotive touch-sensitive senexploit several inherent features of P/F
to successfully commercialize P/F sensors.
sors are unique, in that they can work under
sensors, including:
In 1985 when the company was founded, it
tough conditions, such as when users have
• Small size / low profile
began developing its proprietary FSR techmoist fingers or are wearing gloves, that
• Low manufacturing cost based on existing nology which is still a key part of their wide
others can’t. Ruggedized laptop computers
batch-mode processing, with the ability to sensor product line. Interlink has moved
manufactures have exploited this feature.”
be scaled to ultra-high volume, roll-to-roll from its original sensor supplier position to
(R-2-R) manufacturing
a “human-to-machine solutions provider”.
• Enhanced performance over discrete 3-D
The company has successfully satisfied
Temperature, humidity sensing
solutions due to size and geometry
customer application requirements by proMargit Harting and David Britton
• Device-to-device uniformity
viding sensors and discrete microcontrolco-founded PST Sensors as a spin-off of
• Ability to conform to the surfaces to
lers with proprietary, application-specific
their work on silicon nanoparticle- based
which they are attached
algorithms as part of their solution.
electronics, which started in 2002 at the
• Lower capital expenses for manufacturing
Interlink’s FSR technology consists of a
University of Cape Town, South Africa.
• Ease of integration with other functions
polymer, PET, or plastic substrate with its
Their work on P/F sensors began in 2010,
on the same or layered carriers.
first functional layer being a proprietary,
the company was founded shortly afterBY Roger H. Grace, President
Roger Grace Associates, www.rgrace.com
W
JUNE 2015 • electronicproducts.com • Electronic Products
Consumer Electronics 2
According to Robert Frueh, Brewer Sciwards, and their first thermistor was introence’s Director of New Business Developduced in the spring of 2011. In September
ment, “Brewer Science’s system integration
2014, PST Sensors moved to its indepencapabilities allow it to go well beyond just
dent premises where they are continuing
providing sensors. It is able to fully integrate
applications development and producing
sensors with hardware and software configP/F temperature sensors. These sensors
urations to network a full array of sensors
consists of silicon semiconductor and silver
across a wide area – wirelessly – while
conductor patterns that are applied to subcapturing the data in real time.”
strates of paper and plastic (PET and other
There is also some noteworthy work
polymer) films using silk screening.
going on with printed gas sensors. See
According to Britton, “Our printable/
sidebar, A printed, non-flexing sensor for
flexible temperature sensors … have a
electrochemical gas sensing. Although
well-known response to temperature. They
few companies are currently offering
perform better than discrete components
commercial P/F-based sensors, there’s
because of their low thermal mass, and
much research at several universities and
better thermal contact [which gives them]
a faster response time of
under a second, compared to
5 to 10s for discrete thermistors. Additionally, since
our technology is scalable,
we can easily create large-area thin sensors, enabling
higher sensitivity than discrete
components. The variable
form factor, ability to integrate Fig. 3: Brewer Science employs it proprietary, highly
purified, electronics-grade aqueous SWCNT ink to create
with any other electronics
the TH1022A101 temperature-humidity transducer.
technology, and a temperature
range of −267°C to above 100°C make them institutes. This will be addressed in an
upcoming article.
■
available for a wide range of applications.”
A major current application of their
temperature sensor is in the Smart Label
TO LEARN MORE...
(fig. 1) from Thinfilm (www.thinfilm.no)
About P/F sensor activity, Roger Grace Aswhere the sensor is integrated with other
sociates will present papers this year on the
functions realized with printed electronics,
topic at the Sensors Expo 2015 Pre-Conferto measure the condition of packaged goods, ence session on June 9 (www.sensorsexpo.
such as pharmaceuticals and food, in transit
com) and also at the Sensors Global Summit
or storage.
in La Jolla, CA on November 10 and 11
(www.sensorsglobalsummit.com).
Brewer Science is a new entrant into
the P/F sensor world, leveraging its 30
years’ experience in specialty materials
About the author
for semiconductor industries to develop a
Roger H. Grace (rgrace@rgrace.com) is
fully integrated temperature and humidity
president of Roger Grace Associates, a
sensor, the TH1022A101 transducer (fig.
Naples, FL–based strategic marketing
3). Employing Brewer Science’s proprietary,
consulting firm specializing in high tech,
highly purified, electronics-grade aquewhich he founded in 1982. His background
ous SWCNT ink, the sensor is capable of
includes over 45 years in high-frequency
providing real-time simultaneous measureanalog design, application engineering,
ment of temperature and rapidly fluctuating project management, marketing, and conhumidity in the surrounding environment.
sulting. Mr. Grace has specialized in sensors
Its ultrahigh-speed sensing capability posiand ICs for over 35 years, and his clients
tions it among the fastest sensors of its kind
include the international “Who’s Who” of
in the world: it senses within 10 ms, which
corporations, federal labs, and government
is fast enough to read the fluctuations in
agencies. He received his BSEE and MSEE
humidity due to someone speaking!
(as a Raytheon Fellow) from Northeastern
University and was its Engineering Alumni
of the Year in 2004.
A printed, non-flexing sensor for
electrochemical gas sensing
Hayward, CA-based Spec Sensors has been
developing screen-printed electrochemical gas sensors since 2009. Their current
product line, available in volume since
early 2014, includes sensors for CO, as well
as O3, H2S, NO2, SO2, NO and alcohol.
Their sensor (fig. S1) is constructed with a
plastic base layer, a conductive-ink-printed
gas sensitive layer, and a laminated plastic
top. Currently provided in a 15 x 15 x 3.5
mm format; a 10 x 10 x 2.5-mm version is
expected by the end of 2015.
Company founder Joe Stetter explains
that, “Our decision to develop printable/
flexible sensors was
greatly influ-
Fig. S1: A Spec Sensors’
screen-printed
electrochemical gas
sensor is constructed
with a base layer of
plastic, a conductiveink-printed gas sensitive
layer, and a laminated
plastic top layer.
enced by the printed electronics industry.
However, we had to create much of the
necessary design and manufacturing infrastructure in-house since we didn’t have
the luxury of using a production ‘foundry’
similar to what exists in the MEMS industry. This meant that we needed to develop
everything including the analytical models,
materials, inks and process development.
Additionally, there were no standards or
roadmaps to help guide the process.”
The result is P/F gas sensors that meet
or exceed the performance specifications
of 3-D approaches while providing less
cost, size, and power consumption — key
characteristics for wearables and the consumer market, especially in environmental-monitoring applications. Current applications include residential and commercial
indoor/outdoor air quality monitoring for
CO and NO2, and breathe monitoring for
alcohol consumption. Electronic Products • electronicproducts.com • JUNE 2015