Scott Ageno

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.

Temporary bond-debond process for manufacture of flexible electronics: Impact of adhesive and carrier properties on performance

Manufacturing of microelectronics on flexible substrates is challenged by difficulties in maintaining alignment and conformity of the substrate through deposition, patterning, and etch processes. To address these difficulties, a temporary bond-debond method has been developed for effective automated handling of flexible substrate systems during electronics fabrication. The flexible substrate is temporarily bonded to a rigid carrier, which provides structural support and suppresses bending during processing. The photolithographic alignment of the bonded system is strongly dependent upon the viscoelastic properties of the bonding adhesive. An additional challenge is to control the stress developed during processing; these stresses evolve predominately through thermomechanical property mismatches between the carrier and flexible substrate. To investigate the role of the thermomechanical properties of the carrier and adhesive, the stress, and subsequent bowing of bonded systems (flexible substrate-adhesive-ca...

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.

Flexible reflective and emissive display integration and manufacturing

The U.S. Army, Arizona State University (ASU) and commercial industry have joined forces to create the Flexible Display Center (FDC) at Arizona State University, a large-scale collaborative venture designed to rapidly advance flexible display technology to the brink of commercialization. The Center has completed its startup phase and is now engaged in an intensive and aggressive applied research and development program that will produce high quality, high performance active matrix reflective and emissive flexible display technology demonstrators (TDs). Electrophoretic ink and cholesteric liquid crystals have been selected as Center reflective imaging layer technologies; these technologies are attractive because they are fully reflective and bistable (extremely low power) and because the materials are environmentally robust and intrinsically rugged. Organic light emitting devices (OLEDs) have been chosen as the emissive imaging layer technology. These three electro-optic subsystems will be integrated with a flexible a-Si thin film transistor active matrix backplane platform. We have created the integrated design, backplane fabrication, display assembly, test and evaluation capability to enable rapid cycles of learning and technology development. Backplane fabrication is currently accomplished on a 6” wafer scale pilot line linked to a Manufacturing Execution System and supported by a comprehensive suite of in-fab metrology tools. We are currently installing a GEN II pilot line, with qualified operation slated for 2006. This line will be used to demonstrate process and display form factor capability, while providing high yield low volume manufacturing of pilot-scale levels of technology demonstrators for the Army and our commercial partners.

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.

12.2: Solution Processable Passivation Layer for Active Matrix Thin Film Transistors on Rigid and Flexible Substrates

Organosiloxane based spin on planarizing dielectrics (PTS-E and PTS-R) were developed for application in flat panel displays as a replacement to conformal chemical vapor deposited SiNx. Here we demonstrate the successful use of siloxane-based material as a passivation layer for active matrix α-Si thin film transistors (TFT) on both rigid and flexible substrates.

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.