OVERVIEW:

flexible & large-area electronics back to focus areas

Flexible electronics are lightweight, rugged, bendable, rollable, and potentially foldable. PARC's expertise in large-area electronics extends back to the 1970s, when we began researching and developing amorphous silicon (a-Si). Much of our current work involves thin film transistors (TFT) and p-i-n photodiodes for flat panel display and image sensor backplanes, and solar cells.

To enable practical development of portable systems, PARC has studied the bending limits of different flexible devices, identifying the carrier mobility changes with stress, and the stress limits that result in cracking or delamination of one of the layers.

Our a-Si, low temperature polysilicon (LTPS), and organic semiconductor TFTs also are applied to various radiation detectors, including x-ray, ultrasound, and neutron imaging.

Organic semiconductors have the advantage of low temperature deposition and a low elastic modulus, making them suitable for flexible substrates.

Low temperature a-Si on plastic: To build a-Si backplanes on most plastics, the substrate temperature must be reduced to 180 degrees Centrigrade or less. PARC has developed LTPS TFTs and photodiodes with performance closely approaching the high-temperature material.

Laser-crystallized p-Si on metal foil and quartz: A high-performance approach involves laser recrystallized poly-silicon fabricated on steel foil or quartz. The image to the left shows an OLED backplane that PARC designed and fabricated. PARC has invented several key p-Si devices and circuits for medical imaging and biometrics.

Hemispherical image sensor array: Bending allows only limited opportunities to make conformal electronics. PARC is investigating methods to produce curved arrays, such as the spherical shaped image sensor, shown in the image here. We cut the substrate so it can be bent into a close approximation of the required shape, while still allowing the matrix-addressed array to be made on a flat surface.

Innovative fabrication: We fabricate devices by photolithography in our versatile prototyping line, and also by digital lithography, an innovative mask-less patterning technique using jet-printing.

Pictured, left to right: PARC's Sensor Tape innovation, an all-printed disposable blast dosimeter now in development under a U.S. Defense Advanced Research Projects Agency program; a-Si backplane on plastic; flexible polySi OLED backplane; printed e-paper backplane on plastic

enabling technologies for industry applications

Backplanes
PARC’s flexible electronics team develops a wide variety of a-Si TFT backplanes on glass, plastic, and metal foil substrates, and uses them to build prototype displays and image sensors, using both conventional photolithography and printing techniques.

PARC has fabricated TFT backplanes on free-standing 8x8" PEN substrates to demonstrate the a-Si TFTs can be deposited at low temperature and with low mechanical stress, compatible with the physical properties of PEN.

Processing on flexible substrates is an essential step toward the goal of roll-to-roll manufacturing of displays, and other devices:

Reflective electrophoretic displays ("electronic paper")
Organic light emitting diode (OLED) backplanes
Curved focal plane image sensors
Hybrid image sensors with a-Si TFTs and organic sensors

Photodiodes
For x-ray imagers, PARC developed p-i-n photodiodes with high quantum efficiency and low reverse leakage. We have demonstrated photodiodes on plastic with only slightly increased leakage.

video: PARC Services for Flexible Electronics

contact

Jennifer Ernst
Director of Business Development
+1 650 812 4916

fundamentals

low-temperature a-Si on flexible substrates

Amorphous silicon backplanes on most plastic substrates require a deposition temperature of 180 degrees C or lower, compared to the usual deposition temperature of >250C. Meanwhile, the internal mechanical stress in a-Si can distort a plastic substrate preventing accurate alignment of TFTs.

PARC has demonstrated successful solutions to both problems. We fabricate high-quality TFTs at 180C and photodiodes at 150C, and we control the growth conditions to minimize mechanical stress. This enables backplanes to be made on free-standing plastic films with 5-micron alignment accuracy.

fact sheets

Printed Electronics Services: Application Development [overview]

Flexible Electronics Application Development [case study]

related milestones

1980s

foundational research on doping and hydrogenation of a-Si for large area electronics

1990s

pioneered development of flat panel x-ray imaging
dpiX spun out to commercialize a-Si circuits for ultra-high resolution displays & medical x-ray imagers
Laser crystallization of a-Si for low temperature polysilicon TFTs

2000s

developed first a-Si and polymer semiconductor transistor arrays entirely patterned using jet printing
poly TFT/OLED on flexible stainless steel substrates (with Universal Display Corp.)
first demonstration of all-additive printed polymer TFTs
demonstrated 100V LTPS array for controlling MEMs displays