Structural and electrical characteristics of high-κ Er2O3 and Er2TiO5 gate dielectrics for a-IGZO thin-film transistors

In this letter, we investigated the structural and electrical characteristics of high-κ Er₂O₃ and Er₂TiO₅ gate dielectrics on the amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) devices. Compared with the Er₂O₃ dielectric, the a-IGZO TFT device incorporating an Er₂TiO₅ gate dielectric exhibited a low threshold voltage of 0.39 V, a high field-effect mobility of 8.8 cm²/Vs, a small subthreshold swing of 143 mV/decade, and a high I_on/I_off current ratio of 4.23 × 10⁷, presumably because of the reduction in the oxygen vacancies and the formation of the smooth surface roughness as a result of the incorporation of Ti into the Er₂TiO₅ film. Furthermore, the reliability of voltage stress can be improved using an Er₂TiO₅ gate dielectric.     

Sputtered oxides used for passivation layers of amorphous InGaZnO thin film transistors

Four sputtered oxide films (SiO₂, Al₂O₃, Y₂O₃ and TiO₂) along with their passivating amorphous InGaZnO thin film transistors (a-IGZO TFTs) were comparatively studied in this paper. The device passivated by an Al₂O₃ thin film showed both satisfactory performance (μ_FE=5.3 cm²/V s, I_on/I_off>10⁷) and stability, as was probably related to smooth surface of Al₂O₃ thin films. Although the performance of the a-IGZO TFTs with a TiO₂ passivation layer was also good enough (μ_FE=3.5 cm²/V s, I_on/I_off>10⁷), apparent V_th shift occurred in positive bias-stress tests due to the abnormal interface state between IGZO and TiO₂ thin films. Sputtered Y₂O₃ was proved no potential for passivation layers of a-IGZO TFTs in this study. Despite unsatisfactory performance of the corresponding a-IGZO TFT devices, sputtered SiO₂ passivation layer might still be preferred for its high deposition rate and excellent transparency which benefit the mass production of flat panel displays, especially active-matrix liquid crystal displays.     

Amorphous InGaZnO thin film transistors with sputtered silver source/drain and gate electrodes

The amorphous InGaZnO (a-IGZO) thin film transistors (TFTs) with sputtered silver source/drain (S/D) and gate electrodes were investigated and developed. The sputtered single-film Ag was confirmed to be unfit for the electrodes of a-IGZO TFTs because of its bad contact with a-IGZO and atom diffusion into insulators. Accordingly the sputtered Mo films were proposed to serve as the capping layers, indicating that the 20-nm-thick Mo could effectively form ohmic contact with the a-IGZO, prevent the Ag diffusion into the SiO_x, and make good adhesion to the glass substrates. The devices with multi-layer S/D and gate electrodes (Mo/Ag/Mo) were successfully fabricated, exhibiting the reasonably good performance and thus proving the application of the sputtered silver electrodes into a-IGZO TFTs was possible.     

Advances in understanding of transparent conducting oxides

The band structures of some transparent conducting oxides are calculated using the screened exchange hybrid functional. The optical properties and band gaps of the CuAlO₂ defossalite family follow the expected chemical trends. The limits to the doping of n- and p-type oxides are examined in terms of the dopant compensation by native defects. The accessible range of the Fermi energy under doping is that for which compensating native defects have a positive formation energy. These energy limits are aligned on a band offset diagram. N-dopable oxides have a conduction band minimum that lies deep below the vacuum level, while p-dopable oxides have a valence band top that lies high towards the vacuum level. The nature of electron conduction in amorphous InGaZnO_x type oxides is discussed, in terms of the nature of localisation and the density of states at the mobility edge.     

Substantially Improving Device Performance of All‐Inorganic Perovskite‐Based Phototransistors via Indium Tin Oxide Nanowire Incorporation

All‐inorganic halide perovskites (IHPs) have attracted enormous attention due to their intrinsically high optical absorption coefficient and superior ambient stabilities. However, the photosensitivity of IHP‐based photodetectors is still restricted by their poor conductivities. Here, a facile design of hybrid phototransistors based on the CsPbBr₃ thin film and indium tin oxide (ITO) nanowires (NWs) integrated into a InGaZnO channel in order to achieve both high photoresponsivity and fast response is reported. The metallic ITO NWs are employed as electron pumps and expressways to efficiently extract photocarriers from CsPbBr₃ and inject electrons into InGaZnO. The obtained device exhibits the outstanding responsivity of 4.9 × 10⁶ A W^?1, which is about 100‐fold better than the previous best results of CsPbBr₃‐based photodetectors, together with the fast response (0.45/0.55 s), long‐term stability (200 h in ambient), and excellent mechanical flexibility. By operating the phototransistor in the depletion regime, an ultrahigh specific detectivity up to 7.6 × 10¹³ Jones is achieved. More importantly, the optimized spin‐coating manufacturing process is highly beneficial for achieving uniform InGaZnO‐ITO/perovskite hybrid films for high‐performance flexible detector arrays. All these results can not only indicate the potential of these hybrid phototransistors but also provide a valuable insight into the design of hybrid material systems for high‐performance photodetection.     

Investigation of the gate-bias induced instability for InGaZnO TFTs under dark and light illumination

Mechanism of the instability for indium–gallium–zinc oxide thin film transistors caused by gate-bias stress performed in the dark and light illumination was investigated in this paper. The parallel V_t shift with no degradation of subthreshold swing (S.S) and the fine fitting to the stretched-exponential equation indicate that charge trapping model dominates the degradation behavior under positive gate-bias stress. In addition, the significant gate-bias dependence of V_t shift demonstrates that electron trapping effect easily occurs under large gate-bias since the average effective energy barrier of electron injection decreases with increasing gate bias. Moreover, the noticeable decrease of threshold voltage (V_t) shift under illuminated positive gate-bias stress and the accelerated recovery rate in the light indicate that the charge detrapping mechanism occurs under light illumination. Finally, the apparent negative V_t shift under illuminated negative gate-bias stress was investigated in this paper. The average effectively energy barrier of electron and hole injection were extracted to clarify that the serious V_t degradation behavior comparing with positive gate-bias stress was attributed to the lower energy barrier for hole injection.     

Comparative study of quasi-static and normal capacitance–voltage characteristics in amorphous Indium-Gallium-Zinc-Oxide thin film transistors

Capacitance-voltage (C-V) characteristics of amorphous Indium-Gallium-Zinc-Oxide (a-IGZO) thin film transistors (TFTs) are comparatively investigated with two different measurement configurations. Normal gate-to-source/drain (S/D) C-V and quasi-static C-V curves are employed to characterize physical mechanisms with equivalent circuit models for a-IGZO TFTs. The difference between the normal C-V and the quasi-static C-V (QSCV) characteristics is investigated by the dependence on the gate voltage (V_G), measurement configuration, and optical illumination. The discrepancy is analyzed to be due to a high hole barrier in the S/D contact region and a slow response of active bulk charges (Q_loc and Q_free) in the a-IGZO active layer.     

A study on the electrical characteristics of InGaZnO thin-film transistor with HfLaO gate dielectric annealed in different gases

The effects of dielectric-annealing gas (O₂, N₂ and NH₃) on the electrical characteristics of amorphous InGaZnO thin-film transistor with HfLaO gate dielectric are studied in-depth, and improvements in device performance by the dielectric annealing are observed for each gas. Among the samples, the N₂-annealed sample has a high saturation carrier mobility of 35.1 cm²/V s, the lowest subthreshold swing of 0.206 V/dec and a negligible hysteresis. On the contrary, the O₂-annealed sample shows poorer performance (e.g. saturation carrier mobility of 15.7 cm²/V s, larger threshold voltage, larger subthreshold swing of 0.231 V/dec and larger hysteresis), which is due to the decrease of electron concentration in InGaZnO associated with the filling of oxygen vacancies by oxygen atoms. Furthermore, the NH₃-annealed sample displays the lowest threshold voltage (1.95 V), which is attributed to the increased gate-oxide capacitance and introduced positive oxide charges. This sample also reveals a change in the dominant trap type due to the over-reduction of acceptor-like border and interface traps, as demonstrated by a hysteresis phenomenon in the opposite direction. Lastly, the low-frequency noise of the samples has also been studied to support the analysis based on their electrical characteristics.