Recess gate AlGaN/GaN millimeter-wave power high-electron-mobility transistors (HEMTs) with N ₂ O plasma treatment on access region have been fabricated. A thin oxide layer formed on the gate region leads to the gate leakage current at least three orders of magnitude lower than that of conventional recess gate HEMT, which results a ultralow off-state current of 9.4×10 ^-7 mA/mm accompanied by an on/off ratio of over 10 ⁸ , and a suppressed current collapse of about 4% due to a simultaneous plasma treatment on the gate-source and the gate-drain regions. The forward and the reverse gate-bias stress measurements show that the increment in gate current is within an order of magnitude, indicating an excellent stability of the thin oxide layer. The large signal measurement shows that the HEMT with SiN passivation can yield an output power density of 6 W/mm associated with a peak power-added efficiency (PAE) of 46.8% and a gain of 6.8 dB (V _ds = 25 V), and an output power density of 4.3 W/mm with a PAE of 59.4% and a gain of 6.6 dB (V _ds = 15 V), respectively, at 30 GHz. The small signal measurement shows that the HEMT without SiN passivation can yield f _T and f _max of 85 and 274 GHz, respectively.

In this paper, AlGaN/GaN Fin-HEMTs with different fin configurations are theoretically and experimentally investigated. A simple physical-based threshold voltage model for AlGaN/GaN Fin-HEMTs is built for qualitative analysis. It is shown that the threshold voltage of AlGaN/GaN Fin-HEMTs depends on the width and height of the fin structure. The peak value and linearity of transconductance and current gain cutoff frequency are improved by reducing the fin length. It is also found that the linearity of transconductance is sensitive to the fin height, which can be attributed to the capacitance control from sidewalls.

This article presents a finger-type gallium nitride (GaN) Schottky barrier diode (SBD)-based microwave rectifier with medium-power capacity and wide power bandwidth. A complete solution including SBD design and fabrication, model extraction, circuit optimization, and demonstration is proposed. The finger-type anode and critical thickness epitaxial layer techniques are adopted to reduce the GaN SBD resistance to 1.9 Ω (0.011 m · cm ² ) and achieve nearly constant junction capacitance over a wide range of voltages (17-25V). Revised equivalent models including the effects of large pads, critical thickness epitaxial layer, and finger-type layout are proposed to describe the new features of the SBD. A 2.45-GHz microwave rectifier based on the GaN SBD is designed and measured, having a maximum power and an efficiency of 1.91 W and 78.5%, respectively. The high-efficiency power range (≥70% and ≥75%) is significantly extended to 14 and 10.8 dB. Finally, a wireless clinical examination prototype constructed by a rectifier, antennas, biomedical sensors, and a signal processer is proposed for demonstration. The resulting wireless electrocardiogram shown in computer is clear and stable.

This paper proposes a novel electrical method for the determination of channel temperature in AlGaN/GaN high-electron mobility transistors. A test structure combining various device geometries has been utilized to achieve the temperature dependence of the channel resistance and then applied to detect the channel temperature under the gate instead of that at the gate edge on the drain side. A 2-D electrothermal model has been built, and the model demonstrates excellent agreement with the experimental data. Compared with gate resistance thermometry and micro-Raman spectroscopy, our method has advantages of high accuracy, easy positioning, and immunity to the gate head geometry. This facilitates its potential for temperature extraction, especially for short channel devices. Finally, we apply this method to different device structures to demonstrate its scalability, and the uncertainty caused by current collapse is also discussed.

In this paper, AlGaN/GaN high-electron mobility transistors (HEMTs) with different fin configurations are fabricated and analyzed. Through S-parameter measurements and modeling of the designed devices, a detailed RF investigation on small-signal model parameters is performed under different biasing conditions. Good agreements between measured and simulated scattering parameters up to 40 GHz illustrate the validity and accuracy of the model. The influence of different fin structures on model parameters and linearity improvement is examined, and this can help to improve the frequency characteristics of fin structure by optimizing the fin length, fin width, and trench width. The significant linearity of Fin-HEMTs is confirmed by the analysis of the model parameters, which is the first time to study the small-signal characteristic of AlGaN/GaN Fin-HEMTs in detail.