Zhizhe Wang

The parameter degradation and failure mechanisms of 1200 V asymmetric trench-type (AT) silicon carbide (SiC) metal oxide semiconductor field-effect transistors (MOSFETs) under various single and repetitive surge currents, with various gate bias voltages (V_GS) of 0 V, −5 V, and −10 V, are systematically investigated in this work. It is indicated that V_GS has no impact on the single surge reliability, with the same maximum single surge current (SSC_max) under different V_GS. However, during repetitive surge stress (90% and 60% SSC_max), the maximum surge cycles have increased as V_GS increases from −10 V to 0 V. It may be caused by the enhancement of channel-assisted leakage conduction, allowing more surge current to flow through the channel. It is concluded from gate capacitance (Cg-Vg) and low-frequency noise (LFN) characterizations that lower V_GS increases SiC/SiO₂ interface defect density, accelerating parameter degradation during single and repetitive surge stress. Both chip and package failures are observed for single and repetitive surge stress. For single surge stress, the device failure has resulted from the melted source Al as the metal erodes and penetrates through the interlayer dielectric and the ohmic contact layer between the source metal and the SiC-doped region, respectively, leading to a three-terminal short circuit. For repetitive surge stress, the device failure has been caused by the penetration of Al metal into the interlayer dielectric, leading to a gate-source short circuit. This comprehensive research provides valuable guidance for enhancing the surge reliability of SiC MOSFETs.

This article proposes a novel dual-sheet-beam (DSB) flat-roofed sine waveguide (FRSWG) slow wave structure (SWS) designed for terahertz-band operation. Analysis of the novel structure’s slow wave characteristics revealed flat dispersion properties within the 210230 GHz bandwidth. The transmission characteristics of a DSB FRSWG circuit were calculated and demonstrated relatively low transmission loss, with a unit loss of 1.35 dB/cm, and minimal reflection, characterized by a reflection coefficient below −22 dB, across the 210–250 GHz frequency band. A W-band DSB FRSWG was fabricated using nano-CNC machining technology and subjected to cold-test measurements. Experimental results showed S ${}_{21} \gt -3$ dB and S ${}_{11} \lt -18$ dB in the 90–100 GHz range, closely matching simulation results and validating the structure’s favorable transmission characteristics. A DSB FRSWG traveling-wave tube (TWT) was designed based on this novel structure. Beam-wave interaction simulations indicate an output power exceeding 200 W within the 210–230 GHz band, achieving a maximum power of 307.5 W, with a 3-dB bandwidth greater than 20 GHz.

AlN back-barrier thickness physically governs ultrathin-channel GaN high-electron-mobility transistor (HEMT) performance by dictating a competition between material states. At 440 nm, the AlN back barrier effectively relaxes strain while maintaining two-dimensional growth, yielding high mobility and a trap profile favorable for robust short-channel breakdown and high-frequency operation—resulting in fT/fmax = 34.32/70.95 GHz and 69% power-added efficiency at 3.6 GHz. For a thicker 1-μm layer, three-dimensional island growth with deep-level traps dominates, providing superior vertical blocking to achieve 1.78 kV breakdown voltage for high-voltage operation. By linking the AlN back-barrier thickness to these underlying physical mechanisms, this work establishes a physics-based design framework for deterministically tailoring GaN HEMTs toward high-frequency or high-voltage operation, thereby opening a viable pathway to advance the performance limits of nitride electronics.

Wide-band-gap semiconductors have brought about a revolution in the speed of power electronic switching, but electromagnetic interference has become a new burden. In this paper, we present a tangential electric field probe dedicated to the diagnosis of power electron electromagnetic noise. The proposed probe adopts four-layer printed circuit board technology and can measure the E_x or E_y of the tangential electric field. The detection structure adopts enhanced dipole and differential amplifier with a 20 dB gain to improve the detection sensitivity. Through the measurement results, the proposed probe can operate from 100 kHz to 4.6 GHz, which is just right for power circuits. Its unwanted field suppression is above 10 dB, and maximum frequency response reach -25.8 dB at 0.65 GHz. The measurement results of a typical GaN power module demonstrate the effectiveness of the proposed probe.

A novel slow wave structure (SWS) called the rectangular groove sine waveguide (RGSWG) SWS is proposed. The proposed structure incorporates a rectangular groove inside the sine waveguide (SWG), which runs parallel to the $H$ -plane of the waveguide. The high-frequency characteristics of this innovative SWS have been simulated. The calculations reveal that the average impedance of the RGSWG SWS is approximately twice that of the conventional SWG SWS. In addition, high-frequency transmission systems for both the RGSWG and the conventional SWG have been designed and analyzed. The results demonstrate that the RGSWG slow wave circuit exhibits superior reflection characteristics. The beam–wave interaction of RGSWG traveling-wave tube (TWT) was analyzed using particle simulation software. In the operating frequency range from 90 to 98 GHz, the RGSWG TWT can produce an output power of over 52 W, given an input power of 150 mW, an operating voltage of 9.3 kV, and a beam current of 200 mA. This RGSWG TWT attains a maximum output power of 77 W at the typical frequency of 94 GHz, with a corresponding gain of 27.1 dB. In comparison, under the same conditions, the conventional SWG TWT can only produce an output power of 36 W in the operating frequency range of 90–98 GHz. The RGSWG has been fabricated and tested, with the test results largely consistent with the calculated outcomes. The test results indicate that the insertion loss is greater than −3.4 dB within the frequency range of 89–100 GHz, and the return loss is below −15 dB.

The calibration of the four-port three-component probe, measuring ${H}_{x}$ , ${H}_{y}$ , and ${E}_{z}$ , is interesting for near-field measurement. At high frequency, calibration errors caused by the frequency response are very distressing. These error reasons include the multiple refection caused by embedded part of the calibrator (first error term) and the single reflection caused by the probe approaching the calibrator (second error term). The first error term has been proven to be eliminated through de-embedding calibration method of two-port probe. However, the second error term cannot be removed by this method, which will cause the impedance discontinuity of calibration process. In this article, a middle underfill L-standard as a calibrator is proposed for a four-port three-component probe de-embedding calibration. The new L-standard design can increase the inductive reactance of transmission structure to resist the capacitive effect of the probe when approaching the calibrator. The results of simulation or measurement show that the new L-standard can improve the impedance continuity by nearly 75.6% with a suitable height. Compared with traditional embedding calibration method of four-port three-component probe, the frequency response after using the new calibrator can improve about $0.7\sim 2.2$ dB, and the ripples caused by embedded part can be eliminated.

This paper presents the design and investigation of a two-stage flat-roofed sine waveguide (SWG) traveling-wave tube (TWT) incorporating a novel coupling structure. Initially, the slow-wave structure (SWS) of a 220 GHz flat-roofed SWG was optimized, and the output performance of the corresponding TWT was thoroughly analyzed. Subsequently, a specialized coupling structure was designed and fabricated, with the experimental results demonstrating an excellent agreement with the simulation predictions. The coupling structure exhibits low reflection and is easily manufacturable, making it highly suitable for energy coupling in two-stage TWTs. Finally, a two-stage TWT, integrating both the optimized flat-roofed SWG structure and the coupling structure, was developed and characterized. Under operating conditions of a 20.8 kV beam voltage, 150 mA current, and 150 mW input power, the proposed TWT achieved remarkable performance metrics: a maximum output power of 160 W within the frequency range 210–230 GHz and a 3 dB bandwidth exceeding 20 GHz. This research provides a valuable reference solution for the realization of high-power, broadband terahertz radiation sources, contributing significantly to the advancement of terahertz vacuum electronic devices.

This work investigates the threshold voltage ( V _th ) instability in Schottky-type p-GaN gate HEMTs subjected to positive/negative gate switching stress. Under the gate switching stress, a characteristic “M”-shaped V _th curve with elevated V _{GS, ON} is revealed. This pattern is ascribed to the competitive transport of electrons and holes. Considering the condition of reduced V _{GS, OFF} , an increasing V _th has also been observed, which is attributed to the curtailed electron emission while the promoted hole release. Further, with the increasing of the duty cycle, a positive V _th shift at the lower V _{GS, ON} and a negative shift at higher V _{GS, ON} are needs to be taken seriously, and it also confirm the competitive mechanism in the abnormal “M”-shaped V _th instability. The research highlights that the impact of positive/negative gate switching stress on V _th instability are significant and cannot be neglected.