The effects of an O2 plasma-treated SiNX-based insulator on the interfacial property and the device performances of amorphous indium gallium zinc oxide thin-film transistors (a-IGZO TFTs) were investigated. We tried to improve the interfacial characteristics by reducing the trap density between the SiNX gate insulator and a-IGZO channel by the O2 plasma treatment. The plasma treated-device performances were remarkably improved. The drastic improvements obtained for the O2 plasma-treated a-IGZO TFTs included excellent bias stability as well as a high field effect mobility (μFE) of 19.4 cm2/V s, an on/off current (ION/IOFF) of 108, and a subthreshold value (S) of 0.5 V/decade.
Since the report by Nomura et al. [1] thin film transistors (TFTs) based on amorphous oxide semiconductors (AOSs) have emerged as a promising technology, particularly for active-matrix TFT-based backplanes, due to their superior electrical performance when compared with conventional amorphous silicon and polycrystalline silicon TFTs. Among the various AOSs, amorphous indiumgallium-zinc-oxide (a-IGZO) TFTs have high field-effect mobilities exceeding that of a-Si by a factor of 10 2 , a small subthreshold swing, good uniformity attributed to the amorphous structure, a low off current, good stability under electrical stress, and can be processed at low temperatures. Several research groups have already presented a-IGZO based working devices with remarkable electrical and optical properties. We have recently demonstrated high performance a-IGZO TFTs which exhibited a field effect mobility µ FE of 19.4 cm 2 /Vs, a subthreshold swing S of 0.5 V/decade, and a ratio of on and off current I ON /I OFF of 10 8 , respectively [2].Despite recent successes, some outstanding issues related to the a-IGZO TFT electrical performance still remain to be resolved, such as obtaining good electrical contact between source/drain (S/D) electrodes. A previous report [3] on contact resistance of candidate metal electrodes and a-IGZO showed the trend that the contact resistance decreases with the work function of the metallic electrode. High work function electrodes showed Schottky contacts, while reactive electrodes did ohmic contact. However, using reactive metals for an electrical contact require a high reproducibility of the process.We focus here on an investigation of Cu electrodes to obtain good ohmic characteristics in a-IGZO based TFTs. Specifically, we discuss the S/D series resistances and their effects on the TFT performance. The TFT S/D series resistance, the intrinsic field effect mobility µ FE-i , transfer length L T , and effective contact resistance R C-eff were extracted by the well-known transmission line method (TLM) using a series of TFTs with different channel lengths.The bottom gate type a-IGZO TFTs with staggered structure were prepared on heavily doped n-type silicon substrates having a LPCVD SiN x layer of 100 nm. Thin films of a-IGZO (80 nm thick) were deposited using DC magnetron sputtering with sintered InGaZnO 4 (99.999% purity) as the target material. Sputtering was performed at room temperature in an argon atmosphere with an oxygen partial pressure of 4%. A 4 inch diameter ceramic target, This paper focuses on the viability of low-resistivity electrode material (Cu) for source/drain electrodes in thin film transistors (TFTs). The effective resistances between Cu source/drain electrodes and amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors were examined. Intrinsic TFT parameters were extracted by the transmission line method (TLM) using a series of TFTs with different channel lengths measured at a low source/drain voltage. The TFTs fabricated with Cu source/drain electrodes showed good transfe...
This is the first report demonstrating that InGaZnO (IGZO) thin films deposited using DC magnetron sputtering can be used for the active channel layer of a thin film transistor (TFT) device. We have determined the process conditions at which dc magnetron sputtering provides a high growth rate and smooth surface for IGZO thin films using an InGaZnO 4 ceramic target. The effect of the oxygen content on the electrical properties of the IGZO thin films was examined. The field effect mobility of the TFT device fabricated with the IGZO thin film deposited at an optimum oxygen partial pressure of 6% was 9.2 cm 2 V À1 s À1 . The operation mechanism of IGZO-TFT was explained on the basis of the band diagram with flat band voltage. Moreover, we evaluated the effects of bias stress on transistor performance and showed that device instability appears to be a result of the carrier trapping and releasing in the gate insulator layer under high gate voltage stress.
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