Significant Performance and Stability Improvements of Low-Temperature IGZO TFTs by the Formation of In-F Nanoparticles on an SiO2 Buffer Layer

Critical Effect of Oxygen Pressure in Pulsed Laser Deposition for Room Temperature and High Performance Amorphous In-Ga-Zn-O Thin Film Transistors

The aspects of low processing temperature and easy running in oxygen atmosphere contribute to the potential of pulsed laser deposition (PLD) in developing a-IGZO TFTs for flexible applications. However, the realization of low-temperature and high-performance devices with determined strategies requires further exploration. In this work, the effect of oxygen pressure and post-annealing processes and their mechanisms on the performance evolution of a-IGZO TFTs by PLD were systematically studied. A room-temperature a-IGZO TFT with no hysteresis and excellent performances, including a μ of 17.19 cm²/V·s, an I_on/I_off of 1.7 × 10⁶, and a SS of 403.23 mV/decade, was prepared at the oxygen pressure of 0.5 Pa. Moreover, an O₂ annealing atmosphere was confirmed effective for high-quality a-IGZO films deposited at high oxygen pressure (10 Pa), which demonstrates the critical effect of oxygen vacancies, rather than weak bonds, on the device's performance.

Ultraviolet-Assisted Low-Thermal-Budget-Driven α-InGaZnO Thin Films for High-Performance Transistors and Logic Circuits

Developing a low-temperature fabrication strategy of an amorphous InGaZnO (α-IGZO) channel layer is a prerequisite for high-performance oxide-based thin film transistor (TFT) flexible device applications. Herein, an ultraviolet-assisted oxygen ambient rapid thermal annealing method (UV-ORTA), which combines ultraviolet irradiation with rapid annealing treatment in an oxygen atmosphere, was proposed to realize the achievement of high-performance α-IGZO TFTs at low temperature. Experimental results have confirmed that UV-ORTA treatment has the ability to suppress defects and obtain high-quality films similar to high-temperature-annealing-treated samples. α-IGZO/HfAlO TFTs with high-performance and low-voltage operating have been achieved at a low temperature of 180 °C for 200 s, including a high μ_sat of 23.12 cm² V^-1 S^-1, large I_on/off of 1.1 × 10⁸, small subthreshold swing of 0.08 V/decade, and reliable stability under bias stress, respectively. As a demonstration of complex logic applications, a low-voltage resistor-loaded unipolar inverter based on an α-IGZO/HfAlO TFT has been built, demonstrating full swing characteristics and a high gain of 13.8. Low-frequency noise (LFN) characteristics of α-IGZO/HfAlO TFTs have been presented and concluded that the noise source tended to a carrier number fluctuation (ΔN) model from a carrier number and correlated mobility fluctuation (ΔN-Δμ) model. As a result, it can be inferred that the low-temperature UV-ORTA technique to improve α-IGZO thin film quality provides a facile and designable process for the integration of α-IGZO TFTs into a flexible electronic system.

Influence of Oxygen Flow Rate on Channel Width Dependent Electrical Properties of Indium Gallium Zinc Oxide Thin-Film Transistors

The effects of various oxygen flows on indium gallium zinc oxide (IGZO) based thin-film transistors (TFTs) with different channel width sizes have been investigated. The IGZO nano-films exhibited amorphous phase while the bandgap energy and sheet resistance increased with increasing oxygen flow rate. The electrical characteristics were evaluated with different sizes in channel width using fixed channel length. The distributions in terms of threshold voltage and current on–off level along the different channel width sizes have been discussed thoroughly. The minimum distribution of threshold voltage was observed at an oxygen flow rate of 1 sccm. The TFT electrical properties have been achieved, using an oxygen flow rate of 1 sccm with 500 µm channel width, the threshold voltage, ratio of on-current to off-current, sub-threshold swing voltage and field effect mobility to be 0.54 V, 10⁶, 0.15 V/decade and 12.3 cm²/V·s, respectively. On the other hand, a larger channel width of 2000 µm could further improve the ratio of on-current to off-current and sub-threshold swing voltage to 10⁷ and 0.11 V/decade. The optimized combination of oxygen flow and channel width showed improved electrical characteristics for TFT applications.

Effects of Capping Layers with Different Metals on Electrical Performance and Stability of p-Channel SnO Thin-Film Transistors

In this study, the effects of capping layers with different metals on the electrical performance and stability of p-channel SnO thin-film transistors (TFTs) were examined. Ni- or Pt-capped SnO TFTs exhibit a higher field-effect mobility (μ_FE), a lower subthreshold swing (SS), a positively shifted threshold voltage (V_TH), and an improved negative-gate-bias-stress (NGBS) stability, as compared to pristine TFTs. In contrast, Al-capped SnO TFTs exhibit a lower μ_FE, higher SS, negatively shifted V_TH, and degraded NGBS stability, as compared to pristine TFTs. No significant difference was observed between the electrical performance of the Cr-capped SnO TFT and that of the pristine SnO TFT. The obtained results were primarily explained based on the change in the back-channel potential of the SnO TFT that was caused by the difference in work functions between the SnO and various metals. This study shows that capping layers with different metals can be practically employed to modulate the electrical characteristics of p-channel SnO TFTs.

Impact of Photo-Excitation on Leakage Current and Negative Bias Instability in InSnZnO Thickness-Varied Thin-Film Transistors

InSnZnO thin-film transistors (ITZO TFTs), having high carrier mobility, guarantee the benefits of potential applications in the next generation of super-high-definition flat-panel displays. However, the impact of photo-excitation on the leakage current and negative bias stress (NBIS) of ITZO TFTs must be further explored. In this study, the ITZO thickness (T_ITZO) is designed to tailor the initial performance of devices, especially for the 100 nm T_ITZO TFT, producing excellent electrical properties of 44.26 cm²V^-1s^-1 mobility, 92 mV/dec. subthreshold swing (SS), 0.04 V hysteresis, and 3.93 × 10¹⁰ ON/OFF ratio, which are superior to those of the reported ITZO TFTs. In addition, incident light coupled with tunable photon energy is introduced to monitor the leakage current of various T_ITZO devices. The OFF-current results demonstrate that under the identical photon energy, many more electrons are photo-excited for the thicker T_ITZO TFTs. NBIS-induced V_th shift and SS deterioration in all TFTs are traced and analyzed in real time. As the T_ITZO thickens to near Debye length, the degree of degradation is exacerbated. When the thickness further increases, the notorious instability caused by NBIS is effectively suppressed. This study provides an important research basis for the application of ITZO-based TFTs in future displays.