Mechanically flexible mobile phones have been long anticipated due to the rapid development of thin-film electronics in the last couple of decades. However, to date, no such phone has been developed, largely due to a lack of flexible electronic components that are fast enough for the required wireless communications, in particular the speed-demanding front-end rectifiers. Here Schottky diodes based on amorphous indium–gallium–zinc–oxide (IGZO) are fabricated on flexible plastic substrates. Using suitable radio-frequency mesa structures, a range of IGZO thicknesses and diode sizes have been studied. The results have revealed an unexpected dependence of the diode speed on the IGZO thickness. The findings enable the best optimized flexible diodes to reach 6.3 GHz at zero bias, which is beyond the critical benchmark speed of 2.45 GHz to satisfy the principal frequency bands of smart phones such as those for cellular communication, Bluetooth, Wi-Fi and global satellite positioning.

A high-performance solar-blind photodetector based on Cr-doped gallium oxide (Ga ₂ O ₃ ) has been fabricated. A 140-nm-thick Ga ₂ O ₃ layer was mechanically exfoliated from bulk crystal. The photodetector was based on a field-effect transistor structure, which showed a very high photo-to-dark current ratio larger than 10 ⁶ and excellent current saturation. When the photodetector was tested with a 254-nm ultra-violet light, the ratio of drain current with and without the UV light reached nearly six orders of magnitude. The dark current was as low as 5 pA. Furthermore, the current rise time and decay time were both about 25 ms. High responsivity of ${4.79} \times {10}^{{5}}$ A/W and external quantum efficiency of ${2.34} \times {10}^{{6}}$ also have been achieved at the same time.

High-performance thin-film transistors (TFTs) with amorphous indium gallium zinc oxide (IGZO)/Ga $_\text{2}$ O $_\text{3}$ heterojunction and the reference TFTs with single-layer IGZO, Ga $_\text{2}$ O $_\text{3}$ , and stacked IGZO/Al $_\text{2}$ O $_\text{3}$ layers are fabricated by sputtering. The as-deposited IGZO/Ga $_\text{2}$ O $_\text{3}$ TFT shows high ON current of 0.97 $\mu $ A $\cdot$ $\mu $ m $^{-\text{1}}$ at a drain voltage of 1 V, which is $\text{7}$ orders of magnitude higher than that of the reference single layer TFTs and high mobility of 22.2 cm $^{\text{2}}{\cdot}$ V $^{-\text{1}}{\cdot}$ s $^{-\text{1}}$ , which is twice of that of the reference as-deposited IGZO/Al $_\text{2}$ O $_\text{3}$ TFT (11.5 cm $^{\text{2}}{\cdot}$ V $^{-\text{1}}{\cdot}$ s $^{-\text{1}}$ ). Combining such superior conductivity of the IGZO/Ga $_\text{2}$ O $_\text{3}$ TFT with the energy-level alignment, it indicates quasi-two-dimensional electron gas existed at the interface originated from the electrons confined in the potential well of IGZO. After annealing in air atmosphere, the IGZO/Ga $_\text{2}$ O $_\text{3}$ TFT shows an effective gate modulation with high current ON/OFF ratio of 1.2 $\times$ 10 $^{\text{7}}$ and high mobility of 15.8 cm $^{\text{2}}{\cdot}$ V $^{-\text{1}}\cdot$ s $^{-\text{1}}$ comparing with that of the reference annealed IGZO/Al $_\text{2}$ O $_\text{3}$ TFT (11.5 cm $^{\text{2}}{\cdot}$ V $^{-\text{1}}{\cdot}$ s $^{-\text{1}}$ ). In addition, the bias stability of the annealed IGZO/Ga $_\text{2}$ O $_\text{3}$ TFT is enhanced due to the interface passivation. Our results indicate that amorphous IGZO/Ga $_\text{2}$ O $_\text{3}$ heterostructure is an effective way to achieve high-mobility and stable TFTs, which have great potential in low-cost, large-area, and flexible high-definition displays.

Amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs) enabled by an ultrathin, 5 nm, HfO₂ film grown by atomic-layer deposition were fabricated. An ultra-low operation voltage of 1 V was achieved by a very high gate capacitance of 1300 nF/cm². The HfO₂ layer showed excellent surface morphology with a low root-mean-square roughness of 0.20 nm and reliable dielectric properties, such as low leakage current and high breakdown electric field. As such, the a-IGZO TFTs exhibit desirable properties such as low power devices, including a small subthreshold swing of 75 mV/decade, a low threshold voltage of 0.3 V, and a high on/off current ratio of 8 × 10⁶. Furthermore, even under an ultralow operation voltage of 0.5 V, the on/off ratio was also up to 1 × 10⁶. The electron transport through the HfO₂ layer has also been analyzed, indicating the Poole-Frenkel emission and Fowler-Nordheim tunneling mechanisms in different voltage ranges.

Oxide semiconductors are regarded as promising materials for large-area and/or flexible electronics. In this work, a ring oscillator based on n-type indium-gallium-zinc-oxide (IGZO) and p-type tin monoxide (SnO) is presented. The IGZO thin-film transistor (TFT) shows a linear mobility of 11.9 cm²/(V∙s) and a threshold voltage of 12.2 V. The SnO TFT exhibits a mobility of 0.51 cm²/(V∙s) and a threshold voltage of 20.1 V which is suitable for use with IGZO TFTs to form complementary circuits. At a supply voltage of 40 V, the complementary inverter shows a full output voltage swing and a gain of 24 with both TFTs having the same channel length/channel width ratio. The three-stage ring oscillator based on IGZO and SnO is able to operate at 2.63 kHz and the peak-to-peak oscillation amplitude reaches 36.1 V at a supply voltage of 40 V. The oxide-based complementary circuits, after further optimization of the operation voltage, may have wide applications in practical large-area flexible electronics.