2282 IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 46, NO. 12, DECEMBER 1999 Low-Temperature Polysilicon Thin-Film Transistor Driving with Integrated Driver for High-Resolution Light Emitting Polymer Display Mutsumi Kimura, Ichio Yudasaka, Sadao Kanbe, Hidekazu Kobayashi, Hiroshi Kiguchi, Shun-ichi Seki, Satoru Miyashita, Tatsuya Shimoda, Tokuro Ozawa, Kiyofumi Kitawada, Takashi Nakazawa, Wakao Miyazawa, and Hiroyuki Ohshima Abstract—A high-resolution low-temperature polysilicon thin- film transistor driven light emitting polymer display (LT p-Si TFT LEPD) with integrated drivers has been developed. We adopted conductance control of the TFT and optimized design and voltage in order to achieve good gray scale and simple pixel circuit. A p-channel TFT is used in order to guarantee reliability in dc bias. An inter-layer reduces parasitic capacitance of bus lines. Because of the combination of the LT p-Si TFT and LEP, the display is thin, compact, and lightweight, as well as having low power consumption, wide viewing angle, and fast response. I. INTRODUCTION L OW-TEMPERATURE polysilicon thin-film transistors (LT p-Si TFT’s) have been utilized to drive liquid crystal displays (LCD’s) [1]–[3]. There are many candidates for active matrix devices, i.e., single-crystal Si MOS FET, amorphous Si TFT, high-temperature p-Si TFT, LT p-Si TFT, other semiconductor devices, etc. Among the candidates, only the LT p-Si TFT has performance high enough to compose integrated driver circuits and the capability of being fabricated on a large transparent substrate simultaneously. Additionally, it has already been reported that the LT p-Si TFT can also be fabricated on a plastic substrate [4]. These advantages of the LT p-Si TFT allow the present great successes to come true in LCD’s, not only in research and development, but also in the market. However, the LT p-Si TFT is not only for LCD’s. The LT p-Si TFT’s have great potential even for other displays which have integrated driver circuits and are large sizes [5]. On the other hand, light emitting polymers (LEP’s) [6]–[8] promise to achieve thin, compact, lightweight, and inexpen- sive displays. Moreover, the display can have low power consumption, wide viewing angle, and fast response. Until now, for LEP displays (LEPD’s), mainly static and passive matrix driving methods have been utilized. However, for high- resolution displays consisting of many pixels, needless to say, the static method cannot drive the LEP. The passive matrix Manuscript received October 1, 1998; revised June 1, 1999. The review of this paper was arranged by Editor J. Hynecek. M. Kimura, I. Yudasaka, S. Kanbe, H. Kobayashi, H. Kiguchi, S. Seki, S. Miyashita, and T. Shimoda are with Base Technology Research Center, Seiko Epson Corporation, Owa Suwa 392-8502, Japan (e-mail: kimura.mutsumi@exc.epson.co.jp). T. Ozawa, K. Kitawada, T. Nakazawa, W. Miyazawa, and H. Ohshima are with L Project, Seiko Epson Corporation, Owa Suwa 392-8502, Japan. Publisher Item Identifier S 0018-9383(99)09015-2. method cannot drive the LEP, either [9], because the high- resolution display demands high voltage in the short scanning period in order to achieve the required average brightness, and this high voltage results in a lower power efficiency of the light emitting. Accordingly, instead of the static or passive matrix driving method, an active matrix driving method is better for high-resolution display as the pixels may be driven close to their best power efficiency point. Since the LEPD is not a cell structure, i.e., liquid layer and two sandwiching substrates, it does not need the second substrate. Moreover, the LEPD does not need a backlight, light guide, polarizer, diffuser, etc., which are used in the LCD. Therefore, the display consists of one substrate, peripheral drivers, and many contacts between them. The next target is to eliminate the peripheral drivers and contacts. If the peripheral drivers are replaced by monolithic drivers integrated on the substrate, not only can the peripheral drivers be eliminated, but the number of contacts can also be decreased. The display is dramatically reduced to only one substrate. As a result, the display will be exceedingly thin, compact, lightweight, and inexpensive. Because of the advantage of the wide viewing angle, the LEPD is suitable for direct view applications. Most applica- tions such as these are large size displays. In the case of the current LEPD structure, since the polymers and cathode metal are serially stacked on the substrate and light emits through the substrate, the substrate must be transparent. Therefore, for the device to drive the LEPD, the capability of fabrication on a large transparent, i.e., glass or plastic, substrate is needed. In conclusion, in order to drive the high-resolution LEPD, the active matrix device is needed and it must have enough performance to compose integrated drivers and have the ca- pability to be fabricated on the large transparent substrate, simultaneously. Only the LT p-Si TFT can satisfy these demands. Therefore, the objective of our development in this paper is to confirm how the LT p-Si TFT is suitable to drive the high-resolution LEPD. A high-resolution LT p-Si TFT LEPD with integrated drivers is designed, fabricated, and evaluated [10]. We adopted conductance control of the TFT and optimized design and voltage in order to achieve good gray scale and simple pixel circuit. A p-channel TFT is used in order to guarantee reliability in dc bias. An inter-layer reduces 0018–9383/99$10.00  1999 IEEE