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.

Thin-film transistors (TFTs) based on ultra-thin amorphous indium gallium zinc oxide (a-IGZO) semiconductors down to 4 nm were studied motivated by the increasing cost of indium. At and below 5 nm, it was found that the field-effect mobility was severely degraded, the threshold voltage increased, and the output characteristics became abnormal showing no saturated current. By encapsulating a layer of polymethyl methacrylate on the IGZO TFTs, the performance of the 5-nm-thick device was effectively recovered. The devices also showed much higher on/off ratios, improved hysteresis, and normal output characteristic curves as compared with devices not encapsulated. The stability of the encapsulated devices was also studied over a four month period.

The discovery of twisted bilayer graphene with tunable superconductivity has diverted great focus at the world of twisted van der Waals heterostructures. Here we propose a paradigm for bilayer materials, where covalent bonding replaces the van der Waals interaction between the layers. On the example of germanene-stanene bilayer, we show that such systems demonstrate fascinating topological properties and manifest giant capacitance effects of the order of C = 10²μ F as well as dipole-like charge densities of q = 1 − 2 × 10⁻⁴μ C cm⁻², showing promise for 2D ferroelectricity. The observed unique behaviour is closely linked to transverse strain-induced buckling deformations at the bilayer/substrate interface. In alternative GeSn bilayer structures with low twist angles the strain distortions trigger rich topological defect physics. We propose that the GeSn bilayer topology may be switched locally by a substrate-strain-induced electric fields. We demonstrate an approach to fabricate covalent bilayer materials, holding vast possibilities to transform applications technologies across solar, energy and optoelectronic sectors.

The piezoelectric thin-film traveling-wave micro-motor based on the microelectromechanical systems (MEMS) process has the advantages of compact size, easy integration and batch production. However, the piezoelectric thin-film micro-motor still exits a serious shortcoming of very small output torque. This paper proposes a novel lead zirconate titanate (PZT) piezoelectric thin-film motor with stator teeth to improve the output torque. Firstly, theoretical analysis and finite element simulations were performed to determine the design parameters of the stator teeth. The device preparation is completed by combining with wafer-scale MEMS fabrication techniques, in which the base Si layer of PZT-SOI wafer is thinned and etched to form the stator tooth structure based on the deep reactive ion etching (DRIE) process. Finally, the performance testing results showed that the novel motor achieved a large output torque of 39.4 $\mu$ N $\cdot$ m under a low driving voltage of 4.5 Vpp. The large output torque is 2.65 times higher than that of the previously reported piezoelectric thin-film motor with a much higher driving voltage of 11 Vpp. 2023-0099

The terahertz (THz) frequency range is incredibly important as it covers electromagnetic emissions typical for biological and molecular processes. All molecules emit THz waves in a unique fingerprint pattern, although the intensity of such signals is usually too weak to be detected. To address the efficiency gap in existing THz devices it is extremely important to create surfaces with perfect anti-reflection properties. Although metals are absolutely reflective, here we show both theoretically and experimentally that by constructing meta-surfaces made of a superposition of ultra-thin metallic nano-films (a couple of nanometres thick) and oxide layers a unique property of perfect transmission and impedance matching may be realised. The perfect transmission rates can be as high as 100% and it may be achieved in both optical and THz regimes. The predicted effect has been observed for numerous meta-surfaces of different compositions. The effect found here is expected to impact the renewable energies sectors, optoelectronic and telecommunication industries, accelerating the arrival of the sensors for the new 6G-technology. The phenomenon is highly relevant to all scientific fields where minimising electromagnetic losses through reflection is important.