CPI’s Flexible OTFT device array for AMOLED displays
The Centre for Process Innovation (CPI) has developed novel backplane fabrication processes to allow the bending of Organic Thin Film Transistors (OTFT) arrays to small radii (1 mm) without a significant reduction in device performance. The work undertaken demonstrates progress towards optimum Organic Semiconductor (OSC)/OTFT processing and performance to enable their integration into ultra-flexible active matrix organic light emitting diode AMOLED backplanes. High performance OSC materials with charge mobility suitable for OLED driving were used in the tests on 50 micron thick PEN film. A demonstration video of the bend testing of the array can be viewed below.
In order to achieve the tight bend radius, the multiple interfaces present in the device stack were optimised to allow good adhesion under the strains experienced in the bending test. Using patterned OSC layers and additional passivation layer processing, display pixel size OTFTs were fabricated and these were repeatedly bent (up to 10,000 times) to a radius of 1 mm, which equates to a strain of 2.5%. Minimal change in the turn on voltage and on current were observed for the elongated cycle test.
This demonstration of bend resistance in high performance OTFT devices is part of ongoing work to integrate these materials into active matrix backplanes for AMOLED. It is expected that within 2014 the first plastic based display demonstrators will be completed using OTFT in project ROBOLED, which has received funding through the Technology Strategy Board.
A paper describing the bend testing and device processing work was delivered at the recent International Display Workshop (IDW) in Sapporo, Japan – see paper number OLED3‑2.
CPI is the UK’s National Centre for Printable Electronics. Focused on the development, scale-up and commercialisation of printable electronics applications, CPI is equipped with an extensive range of assets specifically chosen and developed to allow clients to understand how their products and processes perform under pilot manufacturing conditions.