Jiro Kasahara

A high-performance short-channel bottom-contact OTFT and its application to AM-TN-LCD

We have demonstrated an organic thin-film-transistor (OTFT)-driven active-matrix twisted-nematic liquid crystal display (AM-TN-LCD) on a glass substrate, with a resolution of 160/spl times/120 pixels, 79 ppi. Substrate temperature was kept below the plastic-compatible temperature of 180/spl deg/C throughout the fabrication process. In order to realize an OTFT-driven display with fine resolution, we employed short-channel bottom-contact (BC) pentacene OTFTs. It has been known that their drivability is limited by contact resistance at source/drain (S/D). We found that the S/D contact resistance was markedly reduced when the thickness of the nonohmic Ti adhesion layer for ohmic Au S/D electrodes was reduced less than /spl sim/3 nm. We elucidate that this 3 nm corresponds to the thickness of the accumulating layer in a pentacene channel. When we use a self-assembled monolayer of mercapto-silane-coupling agent as the adhesion layer, the contact resistance becomes negligibly small and BC OTFTs scalable below 10 /spl mu/m were obtained. In addition to this OTFT-cell technology, we developed a low-damage pentacene patterning technique for integration of OTFTs and introduced low-temperature panel assembly process to suppress thermal-stress degradation of pentacene OTFTs, which are the key technologies to achieve OTFT-driven AM-TN-LCD.

A flexible full‐color AMOLED display driven by OTFTs

Abstract— Organic thin-film-transistor (OTFT) technologies have been developed to achieve a flexible backplane for driving full-color organic light-emitting diodes (OLEDs) with a resolution of 80 ppi. The full-color pixel structure can be attained by using a combination of top-emission OLEDs and fine-patterned OTFTs. The fine-patterned OTFTs are integrated by utilizing an organic semiconductor (OSC) separator, which is an insulating wall structure made of an organic insulator. Organic insulators are actively used for the OTFT integration, as well as for the separator, in order to enhance the mechanical flexibility of the OTFT backplane. By using these technologies, active-matrix OLED (AMOLED) displays can be driven by the developed OTFT backplane even when they are mechanically flexed.

Solution-processed organic thin-film transistors with vertical nanophase separation

We have found that spin coating a solution of 6,13-bis(triisopropyl-silylethynyl)-pentacene (TIPS-pentacene) blended with poly(α-methylstyrene) (PαMS) induces vertical nanophase separation, which results in a trilayer film: a TIPS-pentacene layer, a mixed layer of TIPS-pentacene/PαMS, and a TIPS-pentacene layer. Organic thin-film transistors (TFTs) made from this TIPS-pentacene/PαMS solution have remarkably improved uniformity and thermal stability without degradation of electrical characteristics compared to organic TFTs with a conventional TIPS-pentacene sole channel layer.

Reduction of contact resistance in pentacene thin-film transistors by direct carrier injection into a-few-molecular-layer channel

We found an abrupt reduction of contact resistance, Rc, in pentacene bottom-contact thin-film transistors (TFTs) with Au/Ti source/drain (S/D) electrodes when Ti thickness is below ∼3nm. Our results suggest that the direct ohmic contact with a few molecular layer channel is a key to reduce the Rc of the S/D electrodes. We propose a Au/self-assembled monolayer electrode structure enabling direct ohmic contact with these few molecular layer channels, and achieved high-performance bottom-contact TFTs with an extrinsic mobility of 1.1cm2∕Vs, an on/off ratio of 106, and a subthreshold swing of 0.3 V/decade.

Capless anneal of ion-implanted GaAs in controlled arsenic vapor

GaAs wafers were implanted with sulfur or silicon ions and annealed at temperatures from 800 to 950 °C under arsenic partial pressure controlled by arsine (AsH3) flow. Electrical characteristics obtained in this method were nearly identical or superior to those obtained with dielectric films. No sign of surface deterioration was observed even after annealing at 950 °C. The implantation into a Cr‐doped epitaxial layer resulted in better characteristics than into semi‐insulating substrates from a vender. The best doping efficiency of 89% was obtained with a dose of 1×1013 Si+/cm2. The method is simple and reproducible, and suitable for the annealing process in production.

63.2: Distinguished Paper: A Full-Color, Top-Emission AM-OLED Display Driven by OTFTs

We have developed an integration architecture for high-resolution organic-TFT (OTFT) arrays with top pixel electrodes on a plastic film. In this architecture, no damage isolation method of organic semiconductor (OSC) in a photolithographically defined resolution is employed. All the insulators in the backplane consist of organic polymers, enhancing both the mechanical flexibility of the backplane and the manufacturing throughput. These technologies have been successfully applied to produce a flexible, full-color and top-emission active-matrix organic light-emitting diode (AM-OLED) display on a plastic substrate with a resolution of 80 ppi.

Out‐diffusion of Ga and As atoms into dielectric films in SiOx /GaAs and SiNy/GaAs systems

Residual Ga and As atoms in SiOx and SiNy dielectric films deposited on GaAs were investigated by Rutherford backscattering spectroscopy and particle‐induced x‐ray emission techniques. Both Ga and As atoms were detected in the films after high temperature heat treatment, and even in the films as‐deposited. The magnitude of the residual atoms presumably out‐diffused from GaAs substrates was of the order of 1×1019 /cm3. The concentration of Ga atoms prevails over that of As atoms in SiOx/GaAs systems as is generally known, and vice versa in SiNy/GaAs systems after heat treatment. Dynamic behavior of Ga and As atoms in the films as functions of annealing temperature and annealing time cannot be explained by a simple diffusion mechanism. A model is proposed that the damaged layer around the interface of the systems is responsible for the anomalous out‐diffusion phenomena.

10.5L: Late-News Paper: All-Organic TFT-Driven QQVGA Active-Matrix Polymer-Dispersed LCD with Solution-Processed Insulator, Electrodes, and Wires

A high-performance pentacene organic-TFT backplane with a solution-processed novel poly(4-vinylphenol)-based dielectric and a solution-processed organo-silver electrode/wire has been developed below 150°C. The all-organic-TFT backplane has been successfully applied to drive a QQVGA active-matrix (AM) polymer-dispersed (PD) LCD with a resolution of 79 dpi and a display size of 2.5 inches.

Monolithic integration of 5-Gb/s optical receiver block for short distance communication

The authors developed an optical receiver block for applications such as board-to-board or chip-to-chip data communications. They implemented the optical receiver block with an interdigit metal-semiconductor-metal (MSM)type photodetector and 0.35- mu m gate junction FETs which were monolithically integrated on a GaAs substrate. High-speed operation of 5 Gb/s was observed with a relatively low power consumption of 8.2 mW. >

Improvement of V th control for GaAs FET's by shallow-channel ion implantation

Fluctation of a net electrical activity of implanted impurities is thought to be the main origin of fluctuation of the threshold voltage (Vth) of GaAs FETs which have a channel layer formed by ion implantation directly into semi-insulating substrates. Net electrical activity is affected by several factors such as implantation damage and the nature of the substrate. Calculation of Vthpredicts that a shallow channel is advantageous to reduce the fluctuation of Vthwhen the fluctuation of the net activity of implantated impurities predominates in that of Vth. The advantage of the shallow channel was verified experimentally by a through-film implantation technique, which was one of the ways to realize the shallow-channel FET.