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.

High-performance AlGaN/GaN lateral Schottky barrier diodes (SBDs) with recess structure and dual metal nitride anodes were demonstrated. With high work-function and nonrecess structure, a NiN anode enhances the breakdown voltage (BV), while a TiN anode reduces the turn-on voltage (V _ON ) due to its low work-function and contact to the two-dimensional electron gas (2DEG) layer directly on a recess structure. As the length of the NiN anode ( L _r ) on the nonrecess region decreases from 75 to 3 μm, V _ON is reduced from 0.56 to 0.30 V, while the reverse leakage current slightly increases from 3 ×10 ^-4 to 2 ×10 ^-3 A/cm ² at the bias of -10 V. The lateral AlGaN/GaN SBD with a L _r of 3 μm at a distance of cathode-anode ( L _AC ) of 20 μm achieves a high BV of 1.62 kV, an ultralow V _ON of 0.30 V and a small capacitance of 6.0 pF at zero bias with little degradation on ON-resistance, indicating superior potential application in high-frequency and high-power devices.

In this article, a gallium nitride (GaN) Schottky barrier diode (SBD)-based microwave rectifier with high efficiency, current, and power bandwidth is proposed for wireless strain sensing and monitoring. Solutions including semiconductor devices, rectification circuits, and sensing mechanisms are discussed. A microwave rectifier working at 928 MHz is designed for wireless rectification strain sensing, with a measured power efficiency over 85% and a load resistance lower to 40 $\Omega $ based on a customized quasi-vertical GaN SBD. The finger layout and TiN anode make the SBD series resistance reduced to 1.81 $\Omega $ , but saturation current enhanced to 11.8 nA, which significantly reduces rectification loss when the load resistance is small. Finally, a rectification strain sensor (RSS) is proposed by dielectric coupling the rectifier and a piezo-permittivity liquid metal elastomer foam (LMEF), with a measured relative output power variation and wireless working distance over 437%/mm and 3 m, respectively.

In this article, a novel equivalent current model of Schottky diode loss is proposed to guide the design of microwave rectifiers and semiconductor devices. The model employs an equivalent forward current equation based on charge conservation and Kirchhoff’s voltage law to achieve an accurate calculation of the diode’s turn-on period and losses under the influence of current harmonics. The estimation from the proposed model is compared with the results from harmonic balance simulation and the resultant error is within 1%. Once the diode’s SPICE parameters, working frequency, load resistance, and input power are given, the maximum efficiency of the rectifier circuit can be accurately predicted. Guided by the proposed model, a GaN diode and a rectifier were designed and fabricated to operate at 915 MHz. The measured maximum conversion efficiency reaches 92.3% when the input power is 23 dBm. The high-efficiency power range (efficiency $\ge$ 80%) and the load bandwidth (efficiency $\ge $ 50%) are extended from 16.5 to 25 dBm and from 700 to 7400 $\Omega$ , respectively. The consistency between the test and the calculated results validates the effectiveness of the proposed model.

In this article, a novel lateral Schottky barrier high-low impact-ionization-avalanche-transit-time (IMPATT) diode, i.e., the high-electron mobility transistor (HEMT)-like IMPATT (HIMPATT) diode, is proposed based on the AlGaN/GaN 2-D electron gas (2-DEG). Numerical simulation demonstrated that the HIMPATT diode shows better characteristics than the conventional vertical IMPATT diode because of a superior property of the AlGaN/GaN 2-DEG. Comparing with the vertical IMPATT diode, the optimum frequency of HIMPATT diode rises from 260 to 380 GHz, the maximum RF output power ${P}_{RF}$ rises from 2.30 to 3.06 MW/cm ² , and the maximum conversion efficiency $\eta $ rises from 14.7% to 18.5%. In addition, simulation results reveal that the trench length ${L}_{r}$ and depth ${D}_{r}$ of the 2-DEG channel significantly influence the output performances of HIMPATT diode, where the frequency characteristic is more sensitive to the trench length ${L}_{r}$ and the RF power characteristic is more sensitive to the trench depth ${D}_{r}$ . By designing the pattern shape of the trench area, a monolithic integrated HIMPATT diode oscillator array can be implemented on one chip to generate a wider frequency band with great RF performances than the vertical IMPATT diode. It provides more variable designing options for the applications of the HIMPATT diode in the terahertz regime.