Inverse‐staggered polycrystalline silicon thin‐film transistors fabricated by excimer laser irradiation

Abstract

AbstractFundamental device performance, mobility distribution, and threshold voltage shift characteristics of inverted staggered polycrystalline thin‐film transistors (TFTs) are discussed. The present TFT uses a polycrystalline silicon (p‐Si) crystallized by excimer laser as semiconductor layer and SiN prepared by CVD method as gate insulator. The TFT was fabricated onto glass substrate of 100 mm2 at a maximum temperature of 300°C. Measurements of the distribution of mobility were carried out with devices placed at every 0.3 mm pitch. As a result, the mobility μ of TFT made at laser intensity of 200 mJ/cm2 is 20.9 cm2/V · s and the off‐current is 2 × 1011 A. TFT was found to be very uniform except for a region where a superposition of 200 mJ/cm2 laser irradiation over a weak laser intensity was made.The analysis indicates that the region for low micrometer is the area irradiated by a laser intensity 110 to 170 mJ/cm2. The region irradiated with laser intensity of this range also was found to be in a mixed state of amorphous silicon of depleted hydrogen atoms and crystalline consisting of fine grains. A shift voltage at 20 V gate dc voltage at 104 s after the application of the voltage is 0.2 V, 1/25 time smaller compared to a‐Si TFT. The present p‐Si TFT is demonstrated to exhibit high‐device performance for liquid crystal display.