The Study of Thin Film Transistor with Micro An-tenna Structure for Wireless Signal Transmission

Abstract

Wearable and flexible devices have been widely studied. In the flexible display system, thin film transistors (TFTs) are applied as an important building block such like electrical switch, rectifier or amplifier due to its relatively lower process temperature than field effect transistor using single crystal material. Wire connection is employed to supply an electrical power or a driving signal to TFTs. However, the contact electrodes, gen-erally formed by metal thin film, is one of the weakest part, so that it is easily broken in bending or folding situation, since the electrode shape is narrow (~ um level) and long (cm ~ m level) in a row or a column di-rection. Wireless power and signal transfer (WPST) can be a good candidate to solve this problem. Therefore, wireless thin film transistor (TFT) structure has been studied to apply to various flexible or wearable devices. One of the enabling technologies is the near-field magnetic induction coupling [1]. To apply the WPST connection system to TFT for the flexible system, it is essential to realize a receiving antenna with micro-meter level size structure to withstand the bending situation. The side effect of this micro size antenna is the decrease of transmission efficiency as scaling down the size of antenna. To compensate this side effect for employing micro antenna structure to TFT, the magnetic core (MC) is added to the micro antenna structure to increase the magnetic flux without the size change of antenna structure due to the decrease of the power efficiency as the scale down of antenna size. The MC is consisted of zinc oxide nano-wires (ZnO NWs) and nikel (Ni), a ferromagnetic material, which is coated on the vertical ZnO NWs. Due to the increase of self-resonance frequency with decreasing antenna size, we chose an amorphous indium gallium zinc oxide (a-IGZO) TFT, which showed higher mobility than a-Si TFT and optimized the TFT structure for high frequency driving. Then, WPST system is adopted to the a-IGZO TFT and the charancteristics are analyzed. To improve the wireless a-IGZO TFT sysem, various MC structures and a-IGZO TFT designs are studied and applicability of wireless TFT is estimated for the flexible and wearable system in this paper. ⓒ 2015 DGIST