No abstract

No abstract

No abstract

We have developed a high-mobility and high-processability oxide semiconductor using amorphous In2O3–SnO2–ZnO (a-ITZO) as the channel material. An a-ITZO thin-film transistor (TFT) was fabricated by a back-channel-etch process. Its field effect mobility was more than 20 cm2 V-1 s-1 and its subthreshold swing was 0.4 V s-1, which makes it a promising candidate for next-generation TFTs.

Thin-film transistors (TFTs) with transparent amorphous indium-tin-zinc-oxide (a-ITZO) channel were fabricated. The field effect mobility (μ) of the a-ITZO TFT was more than 15.0 cm 2 V −1 s −1 , which is higher than the generally reported value of amorphous indium-gallium-zinc-oxide (a-IGZO) TFT. However, μ deteriorated with a decreasing channel length of the a-ITZO TFT due to the annealing process after patterning of the ITZO. We studied the effects of the annealing process on the contact resistance between the a-ITZO film and the source/drain electrodes. A transmission line method (TLM) chart indicated that the parasitic resistances between the source/drain electrode and the back-channel region of the a-ITZO was 2 × 10 4 .Amorphous silicon thin-film transistors (a-Si:H TFTs) are widely used for active-matrix liquid crystal displays. However, a performance limit remains because the mobility of a-Si:H TFTs is at most 0.5 cm 2 V −1 s −1 , which is not enough to drive the next generation of flat panel displays. Therefore transparent amorphous oxide semiconductors (TAOS), whose mobility (μ) is over 10 times higher than the a-Si:H TFT, are considered prime candidates for practical use.In fact, several TAOS materials like zinc oxide, 1,2 indium-galliumzinc-oxide (a-IGZO), 3,4 zinc-tin oxide 5,6 and zinc-indium-oxide 7,8 have been studied for use in TFTs. In particular, a-IGZO is the most promising material and has been widely researched. Among the TAOS, we have also reported on amorphous indium-tin-zinc-oxide (a-ITZO) 9 as satisfying the demand for a higher μ TFT. This material is not only useful for high resolution displays, but also for driver circuits, memory devices and charge coupled devices. Since such applications require a shorter channel length to enhance their electrical properties, the contact resistivity between the back-channel of the a-ITZO and source/drain electrodes would be significant. 10 As for TFT fabrication, an annealing process is essential to stabilize the oxygen vacancies of the a-ITZO channel. However, the effect of the timing of the annealing process during the TFT fabrication on the contact resistivity is not yet clear. Due to the above reason, we fabricated two kinds of a-ITZO TFTs, with and without the annealing process, after patterning the ITZO channel, and compared their performance by measuring the contact resistance between the ITZO channel and source/drain electrodes. Experimental ProcedureTFT fabrication.-The 50-nm-thick a-ITZO films were deposited on a non-alkaline glass substrate by the RF magnetron sputtering of an ITZO ceramic target. Each concentration of In, Sn, Zn is under 50%. The deposition was performed at 150 • C in a mixed gas of Ar and O 2 at a deposition pressure of 1 Pa. The RF sputtering power was maintained at 100 W. The bottom-gate and etch-stopper type a-ITZO TFT was fabricated as follows. A 50-nm-thick Cr gate electrode was formed on a glass substrate. A 150-nm-thick SiOx film was deposited by plasma-enhanced chemical vapor deposition (PECVD) as a gate insulato...