Flexible electronic components like resistors, capacitors, memories, amplifiers, and batteries are being developed that can operate on flexible substrates. Transferable silicon nanomembranes provide advantages for flexible electronics due to their high speed and mobility. Researchers have demonstrated circuits like SRAM memory and ring oscillators on flexible plastic substrates using extremely thin silicon layers. Flexible lithium ion batteries and supercapacitors have also been developed using carbon nanotubes and organic electrolytes. Flexible electrophoretic displays are being commercialized for applications like signs, mobile phones, and automobiles by leveraging their strong contrast, low power usage, and potential for large areas. Further progress is needed in areas like higher refresh rates and full color capabilities.

1. Chapter 3
Flexible Electronic Components
Fast flexible electronics operating at radio frequencies (>1 GHz) are more attractive
than traditional flexible electronics because of their versatile capabilities, dramatic power
savings when operating at reduced speed and broader spectrum of applications. Transferrable
single-crystalline Si nanomembranes (SiNMs) are preferred to other materials for flexible
electronics owing to their unique advantages. Further improvement of Si-based device speed
implies significant technical and economic advantages. While the mobility of bulk Si can be
enhanced using strain techniques, implementing these techniques into transferrable singlecrystalline SiNMs has been challenging and not demonstrated.
3.1 Resistors and Capacitors
The past approach presents severe challenges to achieve effective doping and desired
material topology. Here we demonstrate the doping techniques with self-sustained strain
sharing by applying a strain-sharing scheme between Si and SiGe multiple epitaxial layers, to
create strained print-transferrable SiNMs. We demonstrate a new speed record of Si-based
flexible electronics without using aggressively scaled critical device dimensions.
Fig. 3.1.1Structure of resistor
Fig. 3.1.2Structure of capacitor

2. Flexible electronic components
The given figureaboves shows the structures of thin flim resistors and capacitors
which are constructed on flexible substrate and the conductive paths are made up of flexible
materials such as silicon nanomembranes, grapheme, carbon nanotubes etc. Nanotechnology
is to a large extent for the manufacturing of electronic components
3.2 Memory, Amplifiers and Ring Oscillators
At the International Electron Devices Meeting (IEDM) last fall IBM researchers
demonstrated CMOS circuits —including SRAM memory and ring oscillators—on a flexible
plastic substrate. The extremely thin silicon on insulator devices had a body thickness of just
60 angstroms. IBM built them on silicon and then used a room-temperature process called
controlled spalling, which essentially flakes off the Si substrate. Then they transferred them
to flexible plastic tape.The devices had gate lengths of <30 nm and gate pitch of 100 nm. The
ring oscillators had a stage delay of just 16 ps at 0.9 V, believed to be the best reported
performance for a flexible circuit.
In a recent edition of the journal Nature Communications a team of researchers from
the University of Pennsylvania showed that nanoscale particles, or nanocrystals, of the
semiconductor cadmium selenide can be "printed" or "coated" on flexible plastics to form
high-performance electronics. Because the nanocrystals are dispersed in an ink-like liquid,
multiple types of deposition techniques can be used to make circuits, wrote the researchers. In
their study, the researchers used spin coating, where centrifugal force pulls a thin layer of the
solution over a surface, but the nanocrystals could be applied through dipping, spraying or
ink-jet printing as well, they report.
Using this process, the researchers built three kinds of circuits to test the nanocrystal’s
performance for circuit applications: an inverter, an amplifier and a ring oscillator. All of
these circuits were reported to operate with a couple of volts, according to the researchers an
important point since If you want electronics for portable devices that are going to work with
batteries, they have to operate at low voltage or they won’t be useful.
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3. Flexible electronic components
Fig. 3.2.1Flexible memories
3.3 Batteries
One of the things seemingly hampering advances in bendable electronics research is
uncertainty surrounding a product’s power source. At the University of Delaware, Bingqung
Wei and his colleagues are researching energy sources that are scalable and stretchable. In a
report published in Nano Letters, a journal of the American Chemical Society, Wei’s research
team reported significant progress in developing scalable, stretchable power sources using
carbon nanotube macrofilms, polyurethane membranes and organic electrolytes. According to
Wei, the supercapacitor developed in his lab achieved excellent stability in testing and the
results will provide important guidelines for future design and testing of this leading-edge
energy storage device.
Also in Nano Letters researchers from the Korea Advanced Institute of Science and
Technology (KAIST) in Daejeon, South Korea published a study on a new bendable Li-ion
battery for fully flexible electronic systems.
Although the rechargeable lithium-ion battery has been regarded as a strong candidate
for a high-performance flexible energy source, compliant electrodes for bendable batteries are
restricted to only a few materials, and their performance has not been sufficient for them to
be applied to flexible consumer electronics including rollable displays.
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4. Flexible electronic components
Fig. 3.3.1Flexible lithium ion battery
The researchers presented a flexible thin-film lithium ion battery that enables the
realization of diverse flexible batteries regardless of electrode chemistry. The result is a
flexible Li-ion battery that can be made with almost any electrode material. Here, the
researchers used lithium cobalt oxide as the cathode material, which is currently the most
widely used cathode in non-flexible Li-ion batteries due to its high performance. For the
anode, they used traditional lithium.
3.4 Flexible Displays
The desire for a display that has the flexibility and even “foldability” of paper, but
with the capability to update the information on the page almost instantly is what drives the
interest and commercial funding of flexible electrophoretic devices. Though the electronic
paper application is probably in our near future, with some prototypes already available, it is
likely that other applications will be more interesting from a commercialization and social
acceptance point of view. Large area displays,smart cards, mobile phones, and automotive
applications will be some of the targets for flexible electrophoretic displays.
For large area signage and displays, flexible elecrtrophoretic display technology holds
promise for several reasons. First, for applications where flexibility or even conformability is
desired or useful, the strong optical contrast at nearly all viewing and illumination angles is of
interest. The compartmentalization of the ink and the drive electronics into physically
separated pixels also allows for greater flexibility than polycrystalline or polymeric materials.
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5. Flexible electronic components
Additionally this technology holds promise for remote or mobile display applications due to
its low power usage and relative toughness when built with polymeric substrates. The slow
refresh time in these applications is a minimal issue because most signs are updated on much
longer time scales. At the same time, companies are making significant strides towards higher
refresh rates, nearing video speed.
Finally, the electrophoretic display technology is the only technology with which
large area (up to 30 inches wide) flexible displays have already been realized and are in the
process of commercialization, giving this technology a market lead. With a higher refresh
rate, electrophoretic displays will be able to break into the low end automotive and mobile
phone markets.
Fig. 3.4.1Illusion of flexible display
Fig. 3.4.2flexible display by Sony
While stability and environmental sensitivity are of much lower concern than for
organic display materials, the addition of color capabilities, either through novel multi-filter
stacking or through novel colored particle technology is more challenging than with the
organic display materials. The automotive and mobile phone markets are likely to fully
embrace the electrophoretic display when color becomes widely available due to its wide
viewing angles, robustness and flexibility as well as the fact that the displays may be made in
large volume with large active areas and have relatively low weight. Color capabilities will
be the largest challenge for electrophoretic displays, requiring innovative approaches to
overcome the inherent bi-color, bi-stable paradigm that the display technology has grown to
embrace. E-Ink has already made some progress toward this end by partnering with the
Toppan Printing Company to make color filters to overlay the electrophoretic display layer.
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6. Flexible electronic components
Roll to Roll Processing and the Future of Electrophoretic Display Technology:
Electrophoretic display sheets may already be made in a roll-to-roll format using
polymer sheets as the front planes with back planes of metal foil or polymeric sheets with
organic-semiconductor for the electronics. E-Ink Corporation began selling conventionally
produced electrophoretic displays on Mylar in 2001.As early as 2002 SiPix reported that it
already produces its electrophoretic display material on a roll-to-roll synchronized
lithographic process capable of handling up to 30 feet per minute, while the fully assembled
flexible panels may be produced at greater than 10 feet per minute.A schematic of their
Microcup sealing technology, using a predispersed sealing material that floats to the top of
each Microcup and then hardens.
For typical roll-to-roll production of the Microcup electrophoretic display material,
the SiPix process starts with a radiation curable coating on an ITO/PET film. It then
continues with embossing the coating with a prepatterned male mold to produce the
individual Microcups, filling the arrayed Microcups with a premixed electrophoretic fluid and
then top-sealing the filled Microcups via either a pre-emulsified sealing composition that
separates out from the electrophoretic fluid or using a top-sealing material that is overcoated
after filling. Either way, after sealing the array, it must be laminated with a second
conducting substrate film to form the top (or bottom) electrodes.The high volume production
capacity and the capability to remove defective display materiafrom a roll by the simple act
of cutting it away ensures a bright future for flexible electrophoretic display production. The
technical challenges that remain to be overcome for these types of flexible displays to be
widely accepted by industry are inexpensive full color capability, higher refresh or update
rates, the refinement of the electronics including drive electronics and power storage, and
ultra low cost production. The final, and perhaps most formidable, hurdle for flexible displays
in general may be finding a compelling first application for business or consumer
applications where flexible displays will be better than conventional displays. Overall,
though, flexible electrophoretic display materials are at the forefront of the flexible displays
movement with a promising future in many areas of application.
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