Stability in Electrical Properties of Ultra Thin Tin Oxide Films
- PDF / 246,490 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 100 Downloads / 272 Views
Stability in Electrical Properties of Ultra Thin Tin Oxide Films Yuji Matsui1, Yuichi Yamamoto and Satoshi Takeda R&D Center , Asahi Glass Co., Ltd. 1150 Hazawa-cho, Kanagawa-ku, Yokohama-shi, Kanagawa 221, Japan 1 New Products Development Center, Fabricated Glass General Div., Asahi Glass Co., Ltd. 426-1 Sumida, Aikawa-cho, Aikou-gun, Kanagawa, 243-0301 Japan ABSTRACT Tin Oxide films of less than 30nm in thickness were developed as transparent conductive electrodes. The films were deposited onto glass substrates by APCVD. Fluorine was used as a doping component. Stability to heat treatments in air at more than 500• was studied. Carrier concentration decreased and Hall mobility increased by the heat treatments. It was found relations between carrier concentration and mobility exhibited an exponential relation in extremely low fluorine concentration films. The exponent of the relation was close to –1.5. Resistivity decreased for the films, while it increased for films with high fluorine concentration. It was also found migration of sodium from the substrates into the films increased with increase of fluorine concentration in the films. Results suggest the sodium migration would affect grain growth and electrical properties of the films. INTRODUCTION Several kinds of materials, such as tin oxide(SnO2), indium tin oxide (ITO) and zinc oxide(ZnO), are known as Transparent Conductive Oxide (TCO). Among these materials, tin oxide shows unique characteristics in chemical inertness, stability to heat treatment and mechanical hardness. In addition, tin oxide has industrial advantages about deposition processes. Atmospheric Chemical Vapor Deposition (APCVD) system is usually used as a production system [1]. Its instrument cost is lower and productivity is higher than vacuum evaporation or sputtering systems. Many studies have been reported about tin oxide films deposited by APCVD, especially as substrates for a-Si solar cells [2][3][4][5][6][7][8][9]. Almost all studies are about the films thicker than 100nm. In recent years, industrial application of TCO substrates for what is called a pen touch screen is growing year by year. It is required the substrates show sheet resistance as high as 1k ohm/sq. and high optical transmission. In order to satisfy these requirements at the same time, film thickness of the tin oxide films is usually less than 30nm. We call the films ultra thin tin oxide films because electrical properties of the films in relation to deposition conditions are clearly different from those of bulk films. Another requirement is stability to heat treatment, because manufacturing processes of pen touch screens sometimes include sintering of a silver paste at more than 500•. In this paper we report about the stability in electrical properties of ultra thin tin oxide films in relation to deposition conditions.
Q4.9.1
EXPERIMENTS APCVD apparatus of an in-line type horizontal furnace is used for deposition. Heating up, film deposition and cooling down processes are done successively for moving substrates carried on
Data Loading...
