Stretchable electronics: near term commercial success stories

Stretchable
electronics: near term commercial success stories 
IDTechEx

Cambridge,
UK Stretchable electronics: near term commercial success stories

Stretchable
electronics is a diverse umbrella term including numerous technologies, each
targeting a different market, each having different technology readiness level,
and each facing a different
market prospect.  In the
IDTechEx Research report, Stretchable and Conformal Electronics
2017-2027 (www.IDTechEx.com/stretchable), we offer a comprehensive assessment of
the emerging industry.

In this article we highlight one stretchable
electronics technology with the potential
to become a near-term success
story: interconnects. For more information, please refer to Stretchable andConformal Electronics 2017-2027.

Connectors
are a simple essential component in all electronic system. Their simplicity
means that they can be made stretchable. This is in contrast to complex
multi-layer interfacial devices like transistors whose stretchable versions are
commercially years away despite numerous laboratory proof-of-concept results or
prototypes. They are also essential. Indeed, they can even be the only
stretchable component in stretchable systems made using the rigid
island-stretchable interconnect approach.

A
variety of approaches have been developed to produce stretchable interconnects.
Some are shown in the figure below. In one approach, PCBs are made stretchable.
Here, ICs and other rigid electronic components are mounded a standard PCB
‘island’. These islands are then interconnected using a thinned meandering PBC
lines, introducing stretchability. This technique is not yet easy to scale with
good yields, but is also serving high-value low-volume applications.

In
another approach, cables are arranged in a specific way to impart
stretchability. One example is shown below. Here, stretching does not change
the total length of the wire and thus causes no resistance change. Note that
this approach often require introducing a separate distinct cable onto the
e-textile systems, and whilst robust it is not structurally embedded. Note that
conductive cables are themselves not intrinsically stretchable. Many approaches
are however being developed, most at the early-stage prototyping level, to
create truly stretchable conductive fibres/yarns.
An example is shown here below. Here, carbon nanotubes were employed.

Yet
another approach is based on stretchable conductive inks. This approach enables the use of
post-production processes steps such as transfer or screen printing to
introduce the stretchable interconnect onto the textile. It therefore requires no alternation
to standard textile production lines. It
can also be used in stretchable circuits, particularly acting as stretchable
interconnects on long stretchable substrates for use in, for example, medical
electronics.

This approach is trendy all around the world:
whilst only three years ago only
two or three companies offered such inks, but now most players have either
launched a product or demonstrated capability. The application pipeline is also
gathering momentum with many products in late-stage prototyping phases and some
even in the early commercial phase sales. Some examples are demonstrated below.

Stretchable
conductive inks are still a young technology. Indeed, performance progress is
highly visible when tracking the last few generations of inks launched by any
given company in quick succession. Stretchable inks today can tolerate higher
elongation levels and suffer less resistance change. These improvements have
been achieved thanks to changes in resins, binders and even at times filler
size distribution.

There
is still a long way to go though. Currently, the printed lines are encapsulated
using a material such as TPU. This is not an elegant solution and the
encapsulant is not ideal (e.g., issues with comfort, breathability, etc). Direct on-textile printing
remains a long-term challenge as numerous textile substrates exist each with
different properties and almost none offering a good printing surface.

Critically,
the market requirements are yet fully known, and may even remain diverse and
fragmented. For example, today suppliers receive enquiries for conductivity and
stretchability levels at opposite ends of the performance spectrum. This is an
opportunity for competent suppliers to offer customized solutions before
slightly more standard product groups emerge. In fact, the ability to address
varying cost-performance needs represents an opportunity for the entire
category of ink-based stretchable interconnects compared to its rivals.

In
addition to wearable and medical application, in-mold electronics (IME)
applications are also emerging as a market for stretchable conductive inks. IME
has previously got off to a false start, but, as stated in Stretchable andConformal Electronics 2017-2027, we
believe that its time has come.

In IME,
functional and graphical inks are printed on a flat sheet then formed into a 3D
shape. Consequently, the inks will have to withstand at one-off elongation even
(30-50% original length). Whilst similar to the previously-discussed
stretchable inks, IME inks have different requirements:  (a) they
experience a one-off elongation, (b) they need to adhere well to the substrates
used (e.g., polycarbonate), and (c) they must be compatible with the stack of
other materials used in IME, e.g. layers graphical, insulating, transparent
conducting, and other inks.

Here
too, the industry has responded. Today, most suppliers have launched products
or demonstrated capability. Today, many are engaged with major end users in
either the automotive or while appliance industries. The trend is reflected in
the increasing number of porotypes launched on the market (figure below shows
some examples). In fact, in our ten-year market forecasts in Stretchable andConformal Electronics 2017-2027, we
expect success stories in the next two years.

Interestingly,
the materials toolkit for this technology is expanding beyond conductive inks.
For example, several stretchable transparent conductive film technologies have
been developed, and some are close to product launches. This technology enablebringing
capacitive touch technology to 3D-shaped surface in high-volume application. More detailed information on the
technologies, applications and players can
be found in Stretchable andConformal Electronics 2017-2027.