Copper source/drain electrode contact resistance effects in amorphous indium–gallium–zinc‐oxide thin film transistors

Abstract

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...

Effects of Metal Electrode on the Electrical Performance of Amorphous In–Ga–Zn–O Thin Film Transistor

“…19) In the case of Cu, it was reported that good ohmic contact was formed between Cu and a-IGZO in the TFT annealed in ambient air. 12) However, inter-diffusion or interfacial reaction between Cu and a-IGZO during annealing may cause a change in device performance. There is a report on the contact resistance change between a metal electrode and a-IGZO, including Cu and Al in the TFT.…”

Photoelectron spectroscopy study of thin Ag films deposited on to amorphous In–Ga–Zn–O surface

“…The electrical property changes of the a-IGZO based TFT are closely related to the contact materials, and electrical property changes with various S/D electrode materials (Mo, Ti, Al, Au/Ti, Au-Mn, Ti/Cu, Ag, Ti/Al/Ti, Cu/Ti, Pt) have been intensively studied [9][10][11][12][13][14][15][16][17]. These results can be understood in terms of work function values, the amount of charge transfer between the electrode and the channel layer, and other factors associated with semiconductor physics [18].…”

A study of contact properties between molybdenum and amorphous silicon tin oxide thin film transistors

“…The requirement of low contact resistance between electrode and semiconductor is contributed to achieve high device performance. Traditional electrode materials such as Al, Ti, ITO, Cu, and Mo have been widely used as S/D electrode . Usually, there is an interfacial reaction between oxide thin film and electrodes such as Al, Ti, and Cu, which inevitably influence device performance.…”