From Electronics Manufacture & Test – 27 May 2010
Sony has developed a super-flexible 80µm-thick 4.1in 121ppi 432 x 240 x RGB (FWQVGA) pixels OTFT-driven full colour OLED display that can be wrapped around a pencil.
An OTFT (Organic Thin-Film Transistor) is a thin-film transistor with organic (carbon-based compound) semiconductor. The OTFT can be directly made on a flexible substrate at low temperature below typically 180°C.
To create the display, Sony developed OTFTs with an original organic semiconductor material (a PXX derivative) with eight times the current modulation of conventional OTFTs. That figure is according to internal comparisons between OTFTs with pentacene (C22H14) and OTFT with a PXX (peri-Xanthenoxanthene) derivative. The OTFT with a PXX derivative shows hole mobility four times higher than an OTFT with pentacene and better switching performance, resulting in current density at a certain gate voltage of eight times higher than conventional pentacene OTFT.
In order to achieve this, it was necessary to develop the integration technologies of OTFTs and OLEDs on an ultra-thin 20μm thick flexible substrate (a flexible on-panel gate-driver circuit with OTFTs which is able to get rid of conventional rigid driver IC chips interfering roll-up of a display) and soft organic insulators for all the insulators in the integration circuit.
By combining these technologies, Sony successfully demonstrated the world’s first OTFT-driven OLED panel capable of reproducing moving images while being repeatedly rolled-up and stretched around a cylinder with a radius of 4mm. Even after 1000 cycles of repeatedly rolling-up and stretching the display, there was no clear degradation in the display’s ability to reproduce moving images.
Sony has announced that it will proceed with the development of the solution / print based process which manufactures display devices from organic materials that can be dissolved in common solvents. This process requires fewer steps, and consumes materials and energy more efficiently compared to the conventional high temperature vacuum semiconductor process which use inorganic, silicon materials.
Images courtesy of Sony