Hideaki Kawakami

High performance low-temperature poly-Si n-channel TFTs for LCD

High-performance poly-Si TFTs were fabricated by a low-temperature 600 degrees C process utilizing hard glass substrates. To achieve low threshold voltage (V/sub TH/) and high field-effect mobility ( mu /sub FE/), the conditions for low-pressure chemical vapor deposition of the active layer poly-Si were optimized. Effective hydrogenation was studied using a multigate (maximum ten divisions) and thin-poly-Si-gate TFTs. The crystallinity of poly-Si after thermal annealing at 600 degrees C depended strongly on the poly-Si deposition temperature and was maximum at 550-560 degrees C. The V/sub TH/ and mu /sub FE/ showed a minimum and a maximum, respectively, at that poly-Si deposition temperature. The TFTs with poly-Si deposited at 500 degrees C and a 1000-AA gate had a V/sub TH/ of 6.2 V and mu /sub FE/ of 37 cm/sup 2//V-s. The high-speed operation of an enhancement-enhancement type ring oscillator showed its applicability to logic circuits. The TFTs were successfully applied to 3.3-in.-diagonal LCDs with integration of scan and data drive circuits. >

Transferred Charge in the Active Layer and EL Device Characteristics of TFEL Cells

The relationship between transferred charge in the active layer of a thin-film electroluminescent (TFEL) cell and EL device characteristics has been investigated electrically. Making use of a charge density-voltage characteristic measuring system based on a Sawyer-Tower circuit, a general formula for the input power density was found to be given by twice the product of the frequency, the threshold voltage of the active layer, and the transferred-charge density. From this formula, the luminous efficiency could be estimated, once the dependence of the luminance upon the frequency and the transferred charge density was found. At a frequency smaller than the inverse of twice the luminous decay time, e.g. 500 Hz in the ZnS:Mn case, the luminance was found to be proportional to the product of frequency and transferred charge density. Hence, the luminous efficiency becomes constant with a value 2–2.5 times larger than that for 5 or 1 kHz drive conditions.

Analysis of current-voltage characteristics in polysilicon TFTs for LCDs

An analytic model which can accurately calculate the characteristics of polysilicon TFTs was developed. The theoretical current-voltage curves were compared with measured data, and correlations with trap density in polysilicon film and device performance were investigated. Good agreement was obtained between theoretical and measured results. It was also found that on-current was improved by reducing the densities near the band edges in a forbidden gap. This effect was realized by optimizing the film deposition temperature or by using laser annealing. A hydrogenation effect reduced the density near the midgap, which improved off-current. The TFTs were successfully applied in grey-scale liquid-crystal displays (LCDs) with fully integrated drive circuits.<<ETX>>

26.1: Invited Paper: Materials and Components Optimization for IPS TFT‐LCDs

Materials and components for IPS (in-plane switching) -TFT-LCDS are optimized based on a basic analysis of the in-plane switching behavior of nematic liquid crystals. We have newly developed materials and components accessible for mass producible and commercially available IPS-TFT-LCDS. New phenomena unlike from that found in conventional TN-TFT-LCD cases, such as a higher holding ratio characteristic which is specific to the IPS mode, are found. An optimization procedure for a liquid crystal mixture and a color filter is reviewed. By using new materials and components, we have supplied an IPS-TFT-LCD module consisting of a common driver LSI whose driving voltage is 5 volts with a response speed of 60ms (rise+fall), almost comparable to that of conventional TN-TFT-LCDs. Finally, our recent development state toward a faster response speed of 25ms, which is applicable to a moving picture display, is discussed.

High-performance low-temperature poly-Si TFTs for LCD

High-performance low-temperature poly-Si TFTs were developed by a 600°C process so that a glass substrate could be utilized. To achieve low threshold voltage (V<inf>TH</inf>) and high field effect mobility (µ<inf>FE</inf>), effective hydrogenation using a thin poly-Si gate was employed. Furthermore, active layer poly-Si deposition conditions by LPCVD were optimized. Thinning the gate poly-Si was very effective in reducing V<inf>TH</inf>by hydrogenation. Crystallinity of poly-Si after therma annealing at 600°C depended closely on the poly-Si deposition temperature and was a maximum at 550-560°C. The developed TFTs, with poly-Si deposited at 550°C and a 1000 Å gate, had a V<inf>TH</inf>of 6.2 V and µ<inf>FE</inf>of 37 cm²/V.s. These TFTs were successfully applied to LCDs with fully integrated drive circuits.

Wide‐viewing‐angle 13.3‐in. XGA displays with in‐plane switching mode of nematic LCs addressed by TFTs

— We have developed a 13.3-in. TFT-LCD employing a new, wide-viewing-angle “super” TFT technology utilizing the in-plane switching mode of nematic liquid crystals. The new TFT-LCD has XGA resolution (1024 × RGB × 768 pixels), displaying 262,144 colors, providing vertical and horizontal viewing angles of 140°. This is far wider than that of a conventional TFT display, which is restricted to about 40° vertically and 90° horizontally.

A high-resolution active matrix using p-channel SOI TFTs

A high-quality silicon-on-insulator (SOI) layer with 3-in-diameter quartz substrate and connected silicon islands was fabricated by a radio-frequency-heated zone-melting-recrystallization method. The whole area was successfully recrystallized and 95% of the silicon layer had a

A 10×10 Polycrystalline-Silicon Thin-Film Transistor Matrix for Liquid-Crystal Display

A 10×10 thin-film transistor (TFT) matrix has been fabricated using a molecular beam deposited polycrystalline silicon film on a glass substrate by low-temperature (below 600°C) fabrication processes. The field-effect mobility of the TFT element is 40 cm2/Vs at a gate voltage of 10 V, and the response time is less than 10 ns. Combining the TFT matrix with a twisted-nematic liquid-crystal layer, a transmissive-type active matrix liquid-crystal display. It has been shown that the polycrystalline silicon TFT matrix is compatible with a liquid-crystal cell both from the viewpoint of device fabrication and of TFT characteristics.

White light emitting thin film electroluminescent cell with stacked SrS:Ce/Cas:Eu active layers

Abstract Optical properties of white electroluminescent (EL) cell with stacked SrS:Ce/CaS:Eu active layers are presented. Color changes from blue-green to white by changing voltage or frequency.

A Monochromatic Black and White Supertwisted Nematic Liquid Crystal Display with a Single Cell and a Birefringent Film

To achieve a monochromatic black-and-white (B/W) STN-LCD with a single cell and a birefringent plastic film, the optimum conditions of optical properties in the birefringent film are analyzed theoretically and experimentally. By optimizing the film retardation to minimize the transmission of a STN-LCD at 550 nm, optical retardation in a STN cell is canceled and a B/W STN-LCD is obtained. By selecting the suitable conditions for compensating retardation of the STN cell, a B/W STN-LCD is achieved with the contrast ratio of 10:1.