Study of Self-Heating and High-Power Microwave Effects for Enhancement-Mode p-Gate GaN HEMT

The self-heating and high-power microwave (HPM) effects that can cause device heating are serious reliability issues for gallium nitride (GaN) high-electron-mobility transistors (HEMT), but the specific mechanisms are disparate. The different impacts of the two effects on enhancement-mode p-gate AlGaN/GaN HEMT are first investigated in this paper by simulation and experimental verification. The simulation models are calibrated with previously reported work in electrical characteristics. By simulation, the distributions of lattice temperature, energy band, current density, electric field strength, and carrier mobility within the device are plotted to facilitate understanding of the two distinguishing mechanisms. The results show that the upward trend in temperature, the distribution of hot spots, and the thermal mechanism are the main distinctions. The effect of HPM leads to breakdown and unrecoverable thermal damage in the source and drain areas below the gate, while self-heating can only cause heat accumulation in the drain area. This is an important reference for future research on HEMT damage location prediction technology and reliability enhancement.

Comprehensive Schottky Barrier Height Behavior and Reliability Instability with Ni/Au and Pt/Ti/Pt/Au on AlGaN/GaN High-Electron-Mobility Transistors

The reliability instability of inhomogeneous Schottky contact behaviors of Ni/Au and Pt/Ti/Pt/Au gate contacts on AlGaN/GaN high-electron-mobility transistors (HEMTs) was investigated via off-state stress and temperature. Under the off-state stress condition, Pt/Ti/Pt/Au HEMT showed abruptly reduced reverse leakage current, which improved the Schottky barrier height (SBH) from 0.46 to 0.69 eV by suppression of the interfacial donor state. As the temperature increased, the reverse leakage current of the Pt/Ti/Pt/Au AlGaN/GaN HEMT at 308 K showed more reduction under the same off-state stress condition while that of the Ni/Au AlGaN/GaN HEMT increased. However, with temperatures exceeding 308 K under the same off-state stress conditions, the reverse leakage current of the Pt/Ti/Pt/Au AlGaN/GaN HEMT increases, which can be intensified using the inverse piezoelectric effect. Based on this phenomenon, the present work reveals the necessity for analyzing the concurrent SBH and reliability instability due to the interfacial trap states of the MS contacts.

Dual-Band, Dual-Output Power Amplifier Using Simplified Three-Port, Frequency-Dividing Matching Network

This study presents a dual-band power amplifier (PA) with two output ports using a simplified three-port, frequency-dividing matching network. The dual-band, dual-output PA could amplify a dual-band signal with one transistor, and the diplexer-like output matching network (OMN) divided the two bands into different output ports. A structure consisting of a λ/4 open stub and a λ/4 transmission line was applied to restrain undesired signals, which made each branch equivalent to an open circuit at another frequency. A three-stub design reduced the complexity of the OMN. Second-order harmonic impedances were tuned for better efficiency. The PA was designed with a 10-W gallium nitride high electron mobility transistor (GaN HEMT). It achieved a drain efficiency (DE) of 55.84% and 53.77%, with the corresponding output power of 40.22 and 40.77 dBm at 3.5 and 5.0 GHz, respectively. The 40%-DE bandwidths were over 200 MHz in the two bands.

Scaling Behavior of InAlN/GaN HEMTs on Silicon for RF Applications

Due to the low cost and the scaling capability of Si substrate, InAlN/GaN high-electron-mobility transistors (HEMTs) on silicon substrate have attracted more and more attentions. In this paper, a high-performance 50-nm-gate-length InAlN/GaN HEMT on Si with a high on/off current (Ion/Ioff) ratio of 7.28 × 106, an average subthreshold swing (SS) of 72 mV/dec, a low drain-induced barrier lowing (DIBL) of 88 mV, an off-state three-terminal breakdown voltage (BVds) of 36 V, a current/power gain cutoff frequency (fT/fmax) of 140/215 GHz, and a Johnson’s figure-of-merit (JFOM) of 5.04 THz∙V is simultaneously demonstrated. The device extrinsic and intrinsic parameters are extracted using equivalent circuit model, which is verified by the good agreement between simulated and measured S-parameter values. Then the scaling behavior of InAlN/GaN HEMTs on Si is predicted using the extracted extrinsic and intrinsic parameters of devices with different gate lengths (Lg). It presents that a fT/fmax of 230/327 GHz can be achieved when Lg­ scales down to 20 nm with the technology developed in the study, and an improved fT/fmax of 320/535 GHz can be achieved on a 20-nm-gate-length InAlN/GaN HEMT with regrown ohmic contact technology and 30% decreased parasitic capacitance. This study confirms the feasibility of further improvement of InAlN/GaN HEMTs on Si for RF applications.