Normally-off GaN HEMTs with InGaN p-gate cap layer formed by polarization doping

Narrow gate margin has been the critical limiting factor for the p-gate normally-off GaN HEMTs, imposing significant challenges in both gate-drive design and gate reliability. In this work, by developing dopant-free p-type polarization doping technique in composition-graded InGaN layer, high-quality Schottky contact between the gate metal and cap layer was demonstrated, achieving excellent gate current blocking performance (10-6 mA/mm) after the turning-on of the gate heterojunction structure. Resultantly, normally-off GaN HEMTs with enhanced gate breakdown voltage up to 15.2 V was realized, being especially beneficial for the simplification of gate drive design and the safe operation of gate terminal.

Compact Slot Antenna Integrated with a Photovoltaic Cell

This paper presents a compact low-profile slot antenna integrated with a photovoltaic cell. The photovoltaic cell consists of a top metal grid, gallium arsenide substrate, and metallic bottom contact. The metallic bottom contact was used as a ground plane where the slot was etched for resonance. A second substrate was placed under the ground plane, and a 50 Ω microstrip line was printed on its bottom side to excite the slot. A chip inductor was used as a radio frequency (RF) choke in the alternating current blocking circuit to suppress RF current leakage towards the photovoltaic cell. Hence, the proposed antenna has a unique feature of functioning simultaneously as a photovoltaic cell and an antenna. The overall dimensions––25 mm × 31.75 mm × 0.893 mm (0.48λo × 0.61λo × 0.017λo at 5.77 GHz)––of the photovoltaic cell-integrated slot antenna structure can be used effectively with Internet of Things devices.

Processes associated with ionic current rectification at a 2D-titanate nanosheet deposit on a microhole poly(ethylene terephthalate) substrate

Films of titanate nanosheets (approx. 1.8-nm layer thickness and 200-nm size) having a lamellar structure can form electrolyte-filled semi-permeable channels containing tetrabutylammonium cations. By evaporation of a colloidal solution, persistent deposits are readily formed with approx. 10-μm thickness on a 6-μm-thick poly(ethylene-terephthalate) (PET) substrate with a 20-μm diameter microhole. When immersed in aqueous solution, the titanate nanosheets exhibit a p.z.c. of − 37 mV, consistent with the formation of a cation conducting (semi-permeable) deposit. With a sufficiently low ionic strength in the aqueous electrolyte, ionic current rectification is observed (cationic diode behaviour). Currents can be dissected into (i) electrolyte cation transport, (ii) electrolyte anion transport and (iii) water heterolysis causing additional proton transport. For all types of electrolyte cations, a water heterolysis mechanism is observed. For Ca2+ and Mg2+ions, water heterolysis causes ion current blocking, presumably due to localised hydroxide-induced precipitation processes. Aqueous NBu4+ is shown to ‘invert’ the diode effect (from cationic to anionic diode). Potential for applications in desalination and/or ion sensing are discussed.

Multimodal vibration damping using a simplified current blocking shunt circuit

The tuning of a simplified current blocking shunt circuit able to mitigate the vibration amplitude of multiple structural resonances is addressed in this article. The proposed strategy exploits the two-port network formalism in combination with physically motivated approximations to tune sequentially the electrical elements of the different branches of the shunt circuit. The resulting tuning method does not resort to optimization algorithms and requires only the knowledge of quantities that are easy to measure experimentally. It is demonstrated both numerically and experimentally using a piezoelectric beam.