Junctionless Fully Transparent Low-voltage Thin-film Transistors Based On Indium-tin-oxide

Recently, a novel type of field effect transistors named junctionless nanowiretransistors attracts much attention. Without the necessity to form junctions betweensource/drain electrodes and channel layer, the device structure is greatly simplifiedand the fabrication cost is thus reduced. This junctionless device is a potentialcandidate for future logic and memory electric circuits.Oxide semiconductor has attracted much attention in the application ofthin-film transistors （TFTs） because of its high mobility, optical transparency andsimple deposition process. In this paper, we manufacture bottom-gate junctionlessfully transparent thin-film transistors based on indium-tin-oxide （ITO）. Thesource/drain electrodes and channel layer are the same ITO thin film, no traditionaljunction between source/drain electrodes and channel is formed. Thus, themanufacturing process is greatly simplified. First, we deposit SiO₂dielectric throughplasma enhanced chemical vapor deposition （PECVD）. The SiO₂dielectric showslarge capacitance as a result of the electric double layer （EDL）. Secondly, ITO thinfilms with various thicknesses （20nm,40nm and80nm） are deposited by radiofrequency magnetron sputtering and patterned by Ni mask. The whole fabricationprocess is performed at room temperature. When the ITO channel layer is reduced toabout20nm, the gate bias of the TFTs can effectively modulate the output current.These junctionless TFTs show excellent electrical performance with a low operatingvoltage of1.5V, a small subthreshold swing of0.13V/dec, a high mobility of21.56cm2/Vs and a large on/off ratio of1.3×106. The performance of these devicesshows excellent stability. They show no significant performance degradation evenafter4-month aging in air ambient, the subthreshold swing remains0.13V/dec, thefield effect mobility decreases slightly to18.99cm2/Vs and the on/off ratio is stilllarger than106. The devices are fully transparent; the average optical transmittance inthe visible light spectrum is79%.Such low-voltage, simple-process and stable-performance junctionless TFTshave great potential for the application of novel sensors, low-cost low-power portableelectronic products and transparent electronics.