Themistokles Afentakis

Design and fabrication of high-performance polycrystalline silicon thin-film transistor circuits on flexible steel foils

This paper discusses in detail the design and fabrication process for the realization of high-performance polycrystalline silicon thin-film transistors and digital CMOS circuitry on thin flexible stainless steel foils. A comprehensive approach to substrate preparation is first presented. For transistor fabrication, distinct processing approaches are examined, such as solid-phase and excimer laser crystallization for the active semiconductor region, thermal growth and chemical vapor deposition for the gate insulator, and others. It is shown that process optimization has resulted in the fabrication of CMOS transistors with field-effect mobility values in the region of 200 cm/sup 2//V/spl middot/s and I/sub ON//I/sub OFF/ current ratios of at least seven orders of magnitude. The design and performance of high-speed digital CMOS is addressed, and the effects of the conductive foil through parasitic capacitive coupling are examined. CMOS inverter blocks in ring oscillator circuits operating with delay times as low as 1.12 ns are reported, as well as static and dynamic shift registers operating in the megahertz regime.

3.3: Display Driver Circuits Fabricated on Flexible Stainless Steel Foils

This paper discusses the design and fabrication of digital circuits (primarily shift registers) for display and other active-matrix driving applications on flexible substrates. The unique advantages of the substrate material and their relation to circuit performance are indicated. A high temperature fabrication process for laser annealed polycrystalline silicon MOS transistors on stainless steel foils is outlined, resulting in effective mobility values up to 267cm2/Vs for n-channel and 88cm2/Vs for p-channel devices. Transistor CMOS inverters with a minimum propagation delay of 1.02ns per inverter stage are reported. Both static and dynamic register designs with a high degree of integration are reported, having maximum operating frequencies up to 1.5MHz and 2.5MHz respectively, at supply voltages of 10V or less. These results constitute the first realization of this level of performance and complexity on flexible substrates, and demonstrate the feasibility of high-speed digital circuitry on thin foils suited for - but not limited to- active matrix array driving.

A Novel Agglomerated-Silicon Thin-Film Transistor

This letter discusses the fabrication and electrical characteristics of a novel thin-film transistor (TFT) architecture based on intentionally agglomerated silicon for the active (island) region. Although the agglomeration of irradiated semiconductor is undesirable during the laser crystallization of polycrystalline-silicon TFTs, it is shown that precisely controlled wirelike structures can be obtained for certain conditions. Their width and pitch are maintained over very long distances, and their crystal structure is almost single crystal. Fabricated n- and p-channel TFT characteristics with maximum effective mobility values of 360 and 70 cm2/V ·s, respectively, are presented, with on/off current ratios exceeding ten decades.