Performance enhancement for antipodal Vivaldi antenna modulated by a high-permittivity metasurface lens

A metasurface unit is designed operating at 2–20 GHz to enhance the gain and radiation performance of an antipodal Vivaldi antenna(AVA).The unit has a simple structure,stable ultra-wideband performance,high permittivity,and can independently modulate two polarization modes electromagnetic waves.We analyze the current distribution on the unit and extract equivalent characteristic parameters to verify the ability of independent modulation on two polarization modes electromagnetic waves.The designed metasurface unit is integrated into the aperture of the AVA and forms the metasurface lens(ML)for guiding the propagation of electromagnetic waves.Two types of ML are proposed and integrated into the AVA to design antennas Ant1 and Ant2.The modulation effect of the lens on the electromagnetic wave is analyzed from the perspective of electric field amplitude and phase,and the final design is obtained.From the optimized design results,the AVA and the proposed Ant2 are fabricated and measured,and the measurement results are in good agreement with the simulation ones.The impedance bandwidth measured by Ant2 basically covers the 2–18 GHz frequency band.Compared with the conventional AVA,the gain of the proposed Ant2 is increased by 0.6–3.7 d B,the sidelobe level is significantly reduced,and the directivity has also been clearly improved.

A novel high breakdown voltage and high switching speed GaN HEMT with p-GaN gate and hybrid AlGaN buffer layer for power electronics applications

A novel p-GaN gate GaN high-electron-mobility transistor(HEMT)with an AlGaN buffer layer and hybrid dielectric zone(H-HEMT)is proposed.The hybrid dielectric zone is located in the buffer and composed of horizontal arranged HfO2 zone and SiNx zone.The proposed H-HEMT is numerically simulated and optimized by the Silvaco TCAD tools(ATLAS),and the DC,breakdown,C-V and switching properties of the proposed device are characterized.The breakdown voltage of the proposed HEMT is significantly improved with the introduction of the hybrid dielectric zone,which can effectively modulate the electric field distribution in the GaN channel and the buffer.High breakdown voltage of 1490 V,low specific on-state resistance of 0.45 mΩ·cm2 and high Baliga's figure of merit(FOM)of 5.3 GW/cm2,small R onQ oss of 212 mΩ·nC,high turn-on speed 627 V/ns and high turn-off speed 87 V/ns are obtained at the same time with the gate-to-drain distance L gd of 6μm.

Dielectric thin films for GaN-based high-electron-mobility transistors

The effects of dielectric thin films on the performance of GaN-based high-electron-mobility transistors （HEMTs） were reviewed in this work. Firstly, the nonpolar dielectric thin films which act as both the surface passivation layers and the gate insulators of the high-frequency GaN-based high-electron-mobility transistors were presented. Furthermore, the influences of dielectric thin films on the electrical properties of two-dimensional electron gas （2DEG） in the A1GaN/GaN hetero-structures were ana- lyzed. It was found that the additional in-plane biaxial tensile stress was another important factor besides the change in surface potential profile for the device perfor- mance improvement of the A1GaN/GaN HEMTs with dielectric thin films as both passivation layers and gate dielectrics. Then, two kinds of polar gate dielectric thin films, the ferroelectric LiNbO3 and the fluorinated A1203, were compared for the enhancement-mode GaN-based HEMTs, and an innovative process was proposed. At last, high-permittivity dielectric thin films were adopted as passivation layers to modulate the electric field and accordingly increase the breakdown voltage of GaN-based HEMTs. Moreover, the polyimide embedded with Cr particles effectively increased the breakdown voltage of GaNbased HEMTs. Finally, the effects of high-permittivity dielectric thin films on the potential distribution in the drift region were simulated, which showed an expanded electric field peak at the drain-side edge of gate electrode.