Low-Temperature Poly-Si TFT by Excimer Laser Annealing
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Low-Temperature Poly-Si TFT by Excimer Laser Annealing
Tohru Nishibe LCD R&D Center ,Toshiba Corp. 1-9-2 Hatara-cho,Fukaya-shi, Saitama,366-8510, Japan ABSTRACT Poly-Si TFT-LCD has begun its way to an advanced display by integrating the driver circuits onto the glass substrate. Improvement of poly-Si TFT is essential in order to achieve value-added display where circuits for various functions are integrated on one substrate. This report the concept of poly-Si TFT display from present state to future scope, and required technologies for each generation. It will also focus on technologies such as crystallization and gate insulator formation at low temperature process.
INTRODUCTION Since low-temperature poly-Si (p-Si) TFT LCD panels first entered the market in the mid-1980s, the technology has been applied successfully to not only small displays, but also medium- and large-screen products[1]. P-Si TFT technology now has matured to the point of mass production. The yields are coming near those of a-Si TFT LCD. The greatest advantage of p-Si TFT LCD is various applications using p-Si circuits because they attain a field effect mobility of 100 cm2/V s or more for both n-type and p-type devices. For instance, we can incorporate the peripheral circuits directly onto the glass substrate, with no need for external mounting around the display panel. Eliminating the need for external IC’s to drive the pixels yields a drastic drop in the number of connection pins. It improves LCD panel reliability and allows the use of the small pixels necessary for fine-definition displays. In this paper, the concept of p-Si TFT display from the present state to the future scope will be presented. The required process for each generation will be shown. Then, we describe the stage for full-integrated display especially focussing on crystallization and gate insulator technologies. CONCEPT OF P-Si TFT DISPLAY
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Conventional technology involves mainly the X driver(signal line) and Y driver(scanning line) , which drive the pixel TFT. Technologies for the next wave of display devices will attempt to integrate the digital-analogue conversion circuit, time control circuit and other elements that previously required external IC’s. Collectively, these circuit form the display circuit. Any display panel with this display circuit will have to offer a high field mobility of 300 cm2/Vs, control of fluctuation in threshold voltage and 1.5um-class hyperfine processing. This will support rapid digital signal image processing, circuit margin for operation, and reasonable periphery area where p-Si circuits are integrated. As is shown in table 1, generations are divided into 4 stages: 1st stage is present state where simple digital circuits such as the sift registers and analogue switches, 2nd and 3rd stage are full-integration stage including the function of outer sophisticated IC’s such as D/A converters, timing control circuits and so on. Small size display for 2nd stage will be developed to large-scale display for 3rd stage. Functions of addition
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