Engineering topics
Publications and source records attributed to Si, Mengwei.
Magnetoacoustic waves generated in piezoelectric and ferromagnetic coupled nanocomposite films through magnetically driven surface acoustic waves present great promise of loss-less data transmissions.
The van der Waals layered material CuInP 2 S 6 features interesting functional behavior, including the existence of four uniaxial polarization states, polarization reversal against the electric field through Cu ion migration, a negative-capacitance regime, and reversible extraction of Cu ions. At the heart of these characteristics lies the high mobility of Cu ions, which also determines the spontaneous polarization. Therefore, Cu migration across the lattice results in unusual ferroelectric behavior. Here, we demonstrate how the interplay of polar and ionic properties provides a path to ionically controlled ferroelectric behavior, achieved by applying selected DC voltage pulses and subsequently probing ferroelectric switching during fast triangular voltage sweeps. Using current measurements and theoretical calculations, we observe that increasing DC pulse duration results in higher ionic currents, the buildup of an internal electric field that shifts polarization loops, and an increase in total switchable polarization by ~50% due to the existence of a high polarization phase which is stabilized by the internal electric field. Apart from tuning ferroelectric behavior by selected square pulses, hysteretic polarization switching can even be entirely deactivated and reactivated, resulting in three-state systems where polarization switching is either inhibited or can be performed in two different directions.
Nano-membrane tri-gate β-gallium oxide (β-Ga 2 O 3 ) field-effect transistors (FETs) on SiO 2 /Si substrate fabricated via exfoliation have been demonstrated for the first time. By employing electron beam lithography, the minimum-sized features can be defined with the footprint channel width of 50 nm. For high-quality interface between β-Ga 2 O 3 and gate dielectric, atomic layer-deposited 15 nm thick aluminum oxide (Al 2 O 3 ) was utilized with tri-methyl-aluminum (TMA) self-cleaning surface treatment. The fabricated devices demonstrate extremely low subthreshold slope (SS) of 61 mV dec –1 , high drain current (I DS ) ON/OFF ratio of 1.5 × 10 9 , and negligible transfer characteristic hysteresis. Furthermore, we also experimentally demonstrated robustness of these devices with current–voltage (I–V) characteristics measured at temperatures up to 400 °C.
Polarization in ferroelectrics can be switched in the direction of an applied electric field by dipole reorientation, enabling numerous applications and fundamental phenomena. In this study, we demonstrate that, in the van der Waals (vdW) layered ferrielectric Cu In P 2 S 6 , a unique mechanism exists where polarization aligns against the direction of the applied electric field, seemingly in violation of the fundamental properties of a dipolar solid. The mechanism is the result of the electric field driving the Cu atoms unidirectionally across the vdW gaps, which is distinctively different from dipole reorientation. The crossing of Cu atoms is the fundamental process of ionic conductivity, yet it is compatible with the existence of polarization. These phenomena are confirmed by nanoscale imaging and spectroscopy of ferroelectric capacitors, coupled with dynamic density-functional-theory simulations. The symbiotic relationship of ferroelectric and ionic phenomena enables alternative approaches to control polarization and necessitates a change in perspective on nucleation, domain-wall dynamics, and other ferroelectric and electromechanical characteristics in material systems where ionic and ferroelectric phenomena manifest.