In this work, the dual junction-high-electron-mobility-transistor (DJ-HEMT) was investigated. The thin AlGaN was grown between the p-GaN gate and gate metal. In the TCAD simulations, the band gap and electric field were shown in this letter, proving the dual junction forming. Moreover, DJ-HEMT shows the high gate voltage swing due to the dual junction at the gate region of device, which enhance gate performance. By contrast with standard p-GaN HEMT (ST-HEMT), DJ-HEMT shows higher $\text{V}_{\text {TH}}$ of 2V, saturation current of 187mA/mm, $\text{I}_{\text {ON}}/\text{I}_{\text {OFF}}$ ratio of $5.1\times 10^{{8}}$ and gate swing voltage which is higher than 20V. In addition, DJ-HEMT also shows the lower device leakage current and superior life time measurement due to the thicker and higher barrier of AlGaN cap layer.

A normally-OFF p-GaN gate AlGaN/GaN high-electron-mobility transistor with high ON-state resistance ( ${R}_{ \mathrm{\scriptscriptstyle ON}}$ ) uniformity was realized using a self-terminated digital etching technique. ${R}_{ \mathrm{\scriptscriptstyle ON}}$ uniformity control was improved by simultaneously using an AlN etching stop layer in an epitaxial design and a novel digital etching procedure. Digital etching includes the multiple-cycle oxidation and the wet etching of p-GaN layers and provides easy control of p-GaN removal depth and surface damage reduction at the gate-to-drain and gate-to-source spacing areas. Low-frequency noise and pulse measurements indicated that device surface traps and current collapse phenomena were suppressed.

A 36-38-GHz monolithic microwave integrated circuit (MMIC) single-pole double-throw (SPDT) switch employing a traveling-wave concept with absorptive characteristic is presented. The switch uses absorptive sections for better impedance matching in all ports. The switch obtained good linearity with the insertion loss of 3.2 dB, more than 28-dB isolation, and the return losses at all the ports are larger than 8.1 dB within the bandwidth of interest (36-38 GHz). The switch was fabricated by using GaAs 0.15-μm process. The chip area is very compact, just about 1 mm x 1.1 mm, including all the pads. To our best knowledge, this is the first GaAs MMIC traveling-wave switch type that has the absorptive characteristic.

Normally-off p-GaN gated AlGaN/GaN high electron mobility transistors (HEMTs) were developed. Oxygen plasma treatment converted a low-resistive p-GaN layer in the access region to a high-resistive GaN (HR-GaN); that oxygen plasma treatment used an AlN layer as an oxygen diffusion barrier layer to prevent further oxidizing of the underlying AlGaN barrier layer, and to ensure that the low-resistive p-GaN layer in the access region was fully oxidized. Relative to conventional p-GaN gated AlGaN/GaN HEMTs, these AlGaN/GaN HEMTs with HR-GaN layers achieved a lower drain leakage current of 4.4 $\times 10^{-7}$ mA/mm, a higher drain current on/off ratio of 3.9 $\times 10^{9}$ , a lower on-state resistance of 17.1 ${\Omega }\cdot $ mm, and less current collapse.

A 60-GHz differential frequency tripler with broadband performance was implemented in 90-nm CMOS technology. A Gm-boosted topology and notch filter were used in a fully differential cascode configuration to improve the performance of broadband and harmonic suppression. The proposed frequency tripler exhibits a measured 3-dB bandwidth ranging from 51.3 to 70.2 GHz, with a minimum conversion loss of 5.24 dB at 60 GHz. Compared with the third-harmonic frequency, the fundamental frequency and second-harmonic frequency are suppressed by more than 29.2 and 33.7 dBc, respectively.