Dual-Gate D.C. Sputtered Staggered Amorphous Indium-Gallium-Zinc Oxide Thin-Film Transistor

Alex Kuo, Gwanghyeon Baek, and Jerzy Kanicki

Recently, amorphous indium-gallium-zinc-oxide thin-film transistor (a-IGZO TFT) has shown promises as an alternative to amorphous silicon TFT due to its higher field-effect mobility, lower leakage current, and superior opto-electronic characteristics. These favorable characteristics open up the possibilities of using a-IGZO TFTs in the pixel electrode circuits for displays and sensors. It is common to include light shields (LS) for TFTs used in opto-electronic applications to screen the transistor channel from photons, maximize the sensor’s dynamic range, or prevent electrostatic discharge damage during processing. It is well known that for disordered semiconductor TFTs, (e.g. amorphous silicon and CdSe), a light shield structure acts as an additional gate to a TFT as the voltage present on the shield can vary with the application, and this LS voltage alters the electrical performance of the transistor. We present the a-IGZO TFT structure with a light shield in the back channel. It has a field effect mobility of 12.79 cm²V^-1s^-1, threshold voltage of 0.21 V, and subthreshold swing of 179 mV/dec. The transistor’s light shield does not alter any of its electrical characteristics, while effectively protects the channel region from photo-generated carriers. By applying a voltage on the light shield, we can alter the TFT’s V_T; the relationship between the threshold and light shield voltages is linear with a slope of -0.5, and is independent of the transistor’s channel dimension. Aside from the transistor’s threshold voltage, its field-effect mobility, subthreshold swing, and off-current all remain invariant to the applied light shield voltage. This device is very desirable for high resolution displays and detectors. This study was supported by Canon Research Center, Canon, Inc., Japan.

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