Shahin Jafarabadiashtiani

P-25: A New Driving Method for a-Si AMOLED Displays Based on Voltage Feedback

We present a new driving technique for active-matrix organic light-emitting diode displays using amorphous silicon backplanes. The technique uses voltage feedback to compensate for threshold voltage shift of TFTs. Measurement results show less than 3.5% change in OLED current over 2700 hours of bias stress.

A-Si Amoled Display Backplanes on Flexible Substrates

In view of its maturity and low-cost, the amorphous silicon (a-Si) technology is an attractive candidate for active matrix organic light emitting diode (AMOLED) display backplanes on flexible substrates. However, the a-Si material comes with significant intrinsic shortcomings related to speed (mobility) and stability of operation, requiring novel threshold-voltage-shift (δVT) compensated thin-film transistor (TFT) pixel circuits and architectures to enable stable OLED operation. But given the dramatic progress in efficiency of OLED materials over recent years, the drive current requirement has been significantly lowered, thus relaxing the constraints on a-Si TFTs. For compatibility to plastic substrates, the a-Si TFT process temperature must be reduced from the conventional 300°C to ∼150°C or below, which tends to compromise the integrity of thin-film materials and device performance. Hence, optimizing the TFT process for high device performance with limited thermal budget is a necessary step towards flexible AMOLEDs with a-Si backplanes. This paper reviews the design and process challenges, and specifically examines the performance of TFTs and δVT- compensated integrated pixel driver circuits on plastic substrates with respect to current driving ability and long term stability. More importantly, lifetime tests of circuit degradation behaviour over extended time periods demonstrate highly stable drive currents and its ability to meet commercial standards.

57.2: Extreme AMOLED Backplanes in a‐Si with Proven Stability

Instability has long been a barrier to the use of a-Si AMOLED backplanes. We present here the first demonstration of proven stability of a-Si AMOLED pixels. Over 7000h of stability data is shown for pixel circuits that compensate for threshold-voltage shift, temperature, and OLED degradation (extreme compensation). This demonstrates that stable AMOLED backplanes are achievable using well-established and proven a-Si TFT technology in mainstream use by the flat panel display industry.

A high-speed driver for current-programmed active-matrix OLED displays

This paper proposes a new driving technique for improving settling time in current-programmed active-matrix organic light-emitting diode (AMOLED) pixel circuits. Here, a current feedback along with a second generation current conveyer is employed as the driver to cancel the effect of parasitic line capacitances. Circuit-level simulation using a high-voltage CMOS process for external driver and a VerligA model for amorphous silicon thin film transistors shows more than 8 times reduction in programming time of a typical current programmed pixel circuit for programming current of 100nA.