Fabrication of silicon-oxide thin film by using ionized physical vapor deposition and application to gate insulators in transparent thin-film transistors

Using an ionized physical vapor deposition (IPVD) apparatus, we formed a low-temperature silicon-oxide gate insulator (GI) for top-gate-type In-Ga-Zn oxide channel transparent thin-film transistors (IGZO-TTFTs) for the first time. IGZO-TTFTs with SiO_χ GIs (100 nm) showed a low gate leakage current of about 10^-12 A up to 30 V (gate voltage) comparable to an AlO_χ GI fabricated by atomic layer deposition (ALD). However, it had a high drain off-current (∼10^-8 A) with a low drain current on-off ratio of ∼10^-2 A due to the inductively coupled plasma (ICP) stream during the IPVD-GI process. In order to protect an IGZO channel layer from the plasma effect, we deposited a shallow AlO_χ (10 nm) layer on the IGZO by using ALD. Using this double-layered GI, a high mobility transistor (30.95 cm²/sV) with a drain current on-off ratio of ∼10⁶ could be achieved.