Zn and Ta oxide materials-based resistive and threshold switching devices

Abstract

This doctoral dissertation describes an experimental study on the electrical features and corresponding mechanisms of Zn and Ta Oxide material-based resistive and threshold switching devices by approaching various structural modifications. In the first place, solution-based synthesis of Li-doped ZnO TFTs was presented. In particular, my experiment adopted a carbon-free synthesis method without using hydrocarbon complexes that can easily degrade the electrical properties of TFTs. The structural and electrical properties of Li-doped ZnO TFTs were analyzed by varying the concentrations of Li dopants, together with those of undoped ZnO TFTs for comparison. Experimental observations suggest that the incorporation of Li dopants on the ZnO TFTs by using a carbon-free synthesis method was clearly enhanced the field effect mobility and electrical stabilities of TFTs. Secondly, the influence of a heavy Kr gas sputtering process on the electrical and structural features of amorphous indium-gallium-zinc-oxide (a-IGZO) thin film transistors (TFTs) was reported. Electrical observation revealed effective reduction of threshold voltage shifts by adapting a simple sputtering process with Kr gas during growth of a-IGZO TFTs. In addition, the application of Kr-gas resulted in a reduction of oxygen vacancies associated with defect sites in the a-IGZO active channel layer. Structural analyses including atomic force microscopy, X-ray reflectivity, Auger electron spectroscopy, and X-ray photoelectron spectroscopy depth profiling were carried out, along with electrical bias stability tests that convincingly confirm progress of heavy Kr gas process-induced features. Lastly, I examined the electrical characteristics of Ta2O5−x oxide-based bipolar resistive frames for various TaNx bottoms. Control of the nitrogen content of the TaNx electrode is a key factor that governs variations in its oxygen affinity and structural phase. I analyzed the composition and chemical bonding states of as-grown and annealed Ta2O5−x and TaNx layers and characterized the TaNx electrode-dependent switching behavior in terms of the electrode’s oxygen affinity. Our experimental findings can aid the development of advanced resistive switching devices with thermal stability up to 400 °C.