Jann Kaminski

Low-temperature amorphous-silicon backplane technology development for flexible displays in a manufacturing pilot-line environment

— A low-temperature amorphous-silicon (a-Si:H) thin-film-transistor (TFT) backplane technology for high-information-content flexible displays has been developed. Backplanes were integrated with frontplane technologies to produce high-performance active-matrix reflective electrophoretic ink, reflective cholesteric liquid crystal and emissive OLED flexible-display technology demonstrators (TDs). Backplanes up to 4 in. on the diagonal have been fabricated on a 6-in. wafer-scale pilot line. The critical steps in the evolution of backplane technology, from qualification of baseline low-temperature (180°C) a-Si:H process on the 6-in. line with rigid substrates, to transferring the process to flexible plastic and flexible stainless-steel substrates, to form factor scale-up of the TFT arrays, and finally manufacturing scale-up to a Gen 2 (370 × 470 mm) display-scale pilot line, will be reviewed.

30.2: Active Matrix Electrophoretic Displays on Temporary Bonded Stainless Steel Substrates with 180 °C a‐Si:H TFTs

A low temperature, 180 °C, amorphous Si (a-Si:H) process on bonded stainless steel substrates is discussed and a 3.8-inch QVGA active matrix (AM) electrophoretic display as well as a 64×64 electrophoretic display with integrated column drivers are demonstrated. The n-channel thin-film transistors (TFTs) exhibited saturation mobilities of 0.7 cm2/V-sec, median drive currents of 26.2 μA and low defectivity.

65.4: Active Matrix PHOLED Displays on Temporary Bonded Polyethylene Naphthalate Substrates with 180 °C a-Si:H TFTs

A low temperature, 180 °C, amorphous Si (a-Si:H) process on bonded polyethylene naphthalate substrates is discussed and a 4.1-inch QVGA active matrix (AM) phosphorescent OLED display is demonstrated. The n-channel thin-film transistors (TFTs) exhibited saturation mobilities of 0.773 cm2/V-sec, layer to layer registration distortion less than 10ppm and low defectivity. The efficiency of the OLED display is 39 cd/A at 500 nits.

Direct Fabrication of a-Si:H Thin Film Transistor Arrays on Flexible Plastic Film and Metal Foil Substrates: Critical Challenges and Enabling Solutions

In this paper we describe solutions to effectively address critical challenges in direct fabrication of amorphous silicon thin film transistor (TFTs) arrays for active matrix flexible displays. For both metal foil and plastic flexible substrates a manufacturable handling protocol in automated display-scale equipment is required. We have successfully demonstrated a temporary bonding protocol that required development of new enabling materials, tools and processes. For metal foil substrates, the principal challenges are planarization and electrical isolation, and management of stress (CTE mismatch) during TFT fabrication. For plastic substrates, the principal challenges are dimensional instability management in conjunction with manufacturing-ready temporary adhesives. Solutions required a systems-level approach to address the challenges of the substrates and their handling simultaneously.

Principal Pilot Line Manufacturing Challenges and Solutions in Direct Fabrication of a-Si:H TFT Arrays on Flexible Substrates

Principal challenges to direct fabrication of high performance a-Si:H transistor arrays on flexible substrates include automated handling through bonding-debonding processes, substrate-compatible low temperature fabrication processes, management of dimensional instability of plastic substrates, and planarization and management of CTE mismatch for stainless steel foils. In collaboration with our industrial and academic partners, we have developed viable solutions to address these challenges, as described in this paper.