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1250-G13-07

Fabrication of IGZO and In2O3-Channel Ferroelectric-Gate Thin Film Transistors Eisuke Tokumitsu and Tomohiro Oiwa Precision and Intelligence Laboratry, Tokyo Institute of Technology 4259-R2-19 Nagatsuta, Midori-ku Yokohama 226-8503, Japan

ABSTRACT We have fabricated and characterized ferroelectric-gate TFTs using In-Ga-Zn-O (IGZO) or In2O3 as a channel material. The ferroelectric gate insulator used in this work is (Bi,La)4Ti3O12 (BLT). We observed normal n-channel transistor operation for both IGZO and In2O3-channel TFTs. However, a charge injection type hysteresis was observed for IGZO channel TFTs in drain current – gate voltage (ID-VG) characteristics. Post fabrication anneal at 300oC reduced the charge-injection-tyoe hystereesis and the subthreshold swing was also improved from 0.27 to 0.19 V/decade. On the other hand, when the In2O3 was used as a channel, hysteresis due to the ferroelectric gate insulator was clearly observed in ID-VG characteristics. A memory window of 2V, a subthreshold voltage swing of 0.35V/decade, a field-effect mobility of 1.6 cm2/Vs, and a on/off drain current ratio of more than 106 were obtained.

INTRODUCTION Oxide-channel thin film transistors (TFTs) have attracted much attention for flat-paneel display applications. In particular, ZnO[1,2] and amorphous In-Ga-Zn-O (IGZO)[3,4] are the most mromising candidates as channel materials, because TFTs with such oxides exbihit a channel mobility of more than 10 cm2/Vs, which is much higher than amorphous silicon TFTs. Hence, it will be possible to implement driver and peripheral logic circuits by IGZO-based TFTs. In addition, it would be interesting if we can realize high-density nonvolatile memories as well as logic circuits and driver TFTs by all-oxide TFTs on a single substrate for future system-on-panel or system-on film applications. In our previous work, we reported excellent electrical properties of indium-tin-oxide (ITO) channel ferroelectri-gate TFTs using (Bi,La)4Ti3O12 (BLT) gate insulator, where we demonstrated that the ferroelectric gate insulator can control large channel charges of the conductive ITO film[5,6]. In this work, we have fabricated and characterized ferroelectric-gate TFTs using IGZO or In2O3 as a channel material, because lower carrier concentration can be expected for these films than ITO. EXPERIMENTAL PROCEDURE Bottom-gate structure TFTs were fabricated on SiO2/Si substrates using IGZO or In2O3 as a channel and BLT as a gate insulator. First, Pt/Ti or ITO layer was deposited by sputtering and patterned to form the bottom gate electrodes. Next, the ferroelectric BLT thin film was formed by the sol-gel technique. Bi3.35La0.75Ti3O12 source solution was spin-coated and consolidated at 400 oC for 10 min in O2, and then crystallized at 750oC for 30 min in O2 ambient.

The thickness of the BLT film is approximately 200 nm. Then, thin (10-20 nm) IGZO or In2O3 channel layer was deposited by sputtering at room temperature. The carrier concentration of the sputtered IGZO film is sensitive to the O2/Ar ratio