Paul Wickboldt

Polysilicon thin film transistors fabricated on low temperature plastic substrates

We present device results from polysilicon thin film transistors (TFTs) fabricated at a maximum temperature of 100 °C on polyester substrates. Critical to our success has been the development of a processing cluster tool containing chambers dedicated to laser crystallization, dopant deposition, and gate oxidation. Our TFT fabrication process integrates multiple steps in this tool, and uses the laser to crystallize deposited amorphous silicon as well as create heavily doped TFT source/drain regions. By combining laser crystallization and doping, a plasma enhanced chemical vapor deposition SiO2 layer for the gate dielectric, and postfabrication annealing at 150 °C, we have succeeded in fabricating TFTs with ION/IOFF ratios >5×105 and electron mobilities >40 cm2/V s on polyester substrates.

6.4: Crystallization of Ultra-low Temperature ITO by XeCl Excimer Laser Annealing

The effect of excimer laser (XeCl, λ=308nm) annealing on ITO films deposited at 25°C using DC magnetron sputtering has been studied. With increasing laser fluence, the film crystallinity is improved while retaining the as-deposited texture. Electrical conductivity, optical transparency, and surface roughness are all significantly enhanced by the laser annealing.

Poly-Si thin film transistors fabricated on plastic substrates

Summary form only given. We report the thin film transistor (TFT) fabrication and laser-doping processes for different low-temperature gate dielectrics and doping techniques. Electrical properties of both TFT and test/calibration devices are presented.

Polycrystalline thin-film transistors on plastic substrates

Flat panel displays made on plastic substrates are envisioned for use in certain commercial and military systems because they are more rugged and lightweight than displays made on glass substrates. High information content can be attained for such displays using an active matrix array of thin film transistors (TFTs) for the pixels and high current TFTs for the drivers. In this work the fabrication of high performance polysilicon TFTs on flexible plastic substrates is presented along with corresponding electrical characteristics. Plastic substrates pose severe temperature constraints on the fabrication process. To overcome electrical characteristics. Plastic substrates pose sever temperature constraints on the fabrication process. To overcome these constraints, our group at LLNL has used low temperature silicon, oxide, and aluminum thin film deposition steps and pulsed excimer laser processing to perform the TFT channel crystallization and the source/drain doping. Sheet resistance values below 1k(Omega) /

Polycrystalline silicon thin film transistor technology for flexible large-area electronics

DAL are obtained using our laser doping technique for 900 angstrom thick polysilicon films. Our n-channel polysilicon TFT electrical performance on plastic shows mobilities up to 50 cm2/V-sec and ON current to OFF current ratios of up to 1 X 106 for gate voltages from -1 to +35 V.

Applications of pulsed lasers in low-temperature thin film electronics fabrication

The burgeoning number of mobile consumer electronics has created a demand for lightweight, low-cost, portable displays. The development of a polycrystalline-silicon thin film transistor (TFT) technology compatible with plastic substrates will enable displays and large-area electronics that are low power, rugged and flexible. Significant challenges exist in the development of a polysilicon TFT fabrication process that is compatible with plastic substrates, since plastic has a much lower thermal budget than glass substrates. In general, superior polysilicon TFT performance is achieved with higher temperature fabrication processes because the quality of the polysilicon and gate- dielectric films are very sensitive to process temperature. In this work, an ultra-low-temperature process for fabricating high-quality self-aligned polysilicon TFTs on flexible plastic substrates is described. All fabrication steps are performed at or below 100 degrees C. Polysilicon is formed by crystallizing sputtered amorphous Si films using a XeCl excimer laser with a pulse duration of approximately 35 ns. Gate oxide deposition is formed using high-density plasma CVD, and metal films are deposited by sputtering.

Room temperature indium tin oxide by XeCl excimer laser annealing for flexible display

For the past several years, our group has focused on the development of polysilicon thin film transistor (TFT) processes having maximum allowable substrate temperatures between 100 degree(s) to 350 degree(s)C. These processes are based on excimer laser crystallization of low temperature deposited a-Si thin films combined with low temperature deposited dielectrics and self-aligned gate TFT structures. We have also developed a laser-based, source-drain-gate doping/annealing process. Typical n-channel TFT mobilities found are (mu) napproximately 150 cm2/V-s for the 100 degree(s)C process and approximately 400 cm2/V-s for the 350 degree(s)C process. In this paper we describe the basic processes and process physics. We then show results for TFTs fabricated at a variety of maximum substrate temperatures and a-Si deposition techniques.