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This article presents a 200-GHz phased-array wireless communication system featuring local oscillator beamforming using high-temperature cofired ceramic (HTCC) technology. The system is constructed using HTCC transmit (Tx) and receive (Rx) system-in-packages (SiPs), which are mounted on printed circuit boards and connected to parabolic antennas through waveguide feeders. These SiPs heterogeneously integrate all components of the front-end channels, achieving low-loss interconnection and 3-D integration through vertical hollow waveguides within the HTCC. The Tx SiPs incorporate integrated Schottky diode mixers with MoCu waveguide filters, performing single-sideband upconversion with high image rejection. Measured Tx channel gain ranges from 17 to 40 dB over 192.5 to 212.5 GHz, with channel saturated output power from 5.2 to 9.6 dBm over 193.5 to 211.5 GHz. Furthermore, the eight-element Tx array achieves an effective isotropic radiated power of 35.9–43.3 dBm across 196–213 GHz and supports a scanning capability of ±30° in the E-plane. The phased-array Tx-Rx wireless link is demonstrated over a 30-m distance using 16-quadrature amplitude modulation (QAM) and 64-QAM waveforms, supporting maximum data rates of 32 and 24 Gbps, respectively.

This article presents a 220-GHz wideband converter for terahertz (THz) applications, which facilitates the transition from the TE10 mode of the rectangular waveguide (RWG) to the TE20 mode of the substrate-integrated waveguide (SIW). This converter consists of waveguides, a dipole antenna, a grounded slotline, and a SIW. The dipole antenna effectively couples the TE10-mode guided wave from the RWG into the slotline. Due to the quasi-slotline mode and SIW TE20 mode being odd modes with similar electric field distributions, the longitudinal slotline effectively excites the TE20 mode within the SIW. This study elucidates the converter’s principles and propagation properties through electric field analysis and electromagnetic (EM) simulations. Besides, a back-to-back converter prototype was fabricated and measured, exhibiting an insertion loss of 2.1–5.0 dB from 198 to 238 GHz (18.3% bandwidth) and a return loss better than 6.1 dB. The estimated loss for a single converter is 1.1–2.5 dB, including the loss of a 1.4-mm-long SIW. Furthermore, based on the proposed mode converter, an SIW bandpass filter and a balun were designed and demonstrated, providing further evidence of the existence of the TE20 mode in SIW. To the best of our knowledge, this article presents the first 220-GHz converter from the RWG TE10 mode to the SIW TE20 mode, demonstrating its potential applications in THz planar integration.

In this article, the current collapse (CC) and current enhancement (CE) of the hydrogen-terminated diamond (H-diamond) MOSFET are found. The nonmonotonic variation of the drain current (DC) due to the long-term trapping effects is characterized by a proposed method, which involves the transient current measurements and the energy-level extractions. Based on the method, the measured transient current is utilized to infer that the abnormal phenomena are caused by the combined effect of the trapping near the gate and the absorption of atmospheric components on the surface of the device. With the extracted energy levels, the CC is deduced to be induced by the surface trap. The energy diagram for the surface trap in the H-diamond is given to make the trapping mechanism more clearly. By changing the test atmosphere, the CE is found to be caused by the component of the air. This work is useful for improving the performance of the H-diamond device.

This article presents a novel 200-GHz four-element phased-array receiver system-in-package (SiP) using high-temperature co-fired ceramic (HTCC) technology for wireless communications. The receiver employs a local oscillator (LO) phase-shifting architecture to realize sub-terahertz (THz) beamforming. All components of the front-end array are heterogeneously integrated within the HTCC. To achieve low-loss interconnection and 3-D integration, quartz substrates and vertical air-filled waveguides are incorporated within the HTCC. Meanwhile, an electromagnetic bandgap (EBG) structure is introduced in the vertical transitions to mitigate energy leakage caused by assembly gaps, thus reducing the sensitivity to assembly errors. Besides, a highly efficient parabolic reflector antenna array with a multilayered structure is designed for beam scanning. The overall size of the front-end package is 40.7 $\times $ 43 $\times $ 7.3 mm3. The measured channel gain is 8.2–23 dB from 194.5 to 234.5 GHz (18.6% bandwidth), and the measured lower-sideband noise figure is 7.5–9.4 dB, covering from 196 to 215 GHz. The phased-array receiver can achieve a scanning range of ±30° in the ${E}$ -plane. To evaluate its over-the-air (OTA) performance, a wireless link is demonstrated with 16-quadrature amplitude modulation (QAM) and 64-QAM waveforms, achieving a maximum data rate of 32 Gbps.

Diamond-based devices with high ON/ OFF ratio are promising candidates for power and sensor applications. However, the limited ON/ OFF ratio caused by relatively high leakage currents still remains to be a problem. Herein, we present hydrogen-terminated diamond metal–insulator–semiconductor field-effect transistors (MISFETs) with a 40-/100-nm aluminum oxide/hafnium dioxide stacked passivation layer to reduce leakage currents. Due to the stacked passivation layer, the fringing capacitances were introduced and the electric field at the drain edge of the gate was reduced. Encouragingly, the drain and gate leakage currents were reduced to the order of $10^{-{9}}$ mA/mm under OFF-state conditions at room temperature. Consequently, an ON/ OFF ratio of $\sim 1\times 10^{{11}}$ was achieved, which is the highest value among the previously reported diamond-based field-effect transistors (FETs). Moreover, a record ON/ OFF ratio of $\sim 5\times 10^{{9}}$ was obtained even at 200 °C. Results of this work can pave the way for diamond-based devices in power or sensor applications.

Drain current hysteresis phenomenon has been shown in hydrogen terminated diamond (H-diamond) metal-insulator-semiconductor field-effect transistors (MISFETs), in which the drain current varies with the sweep direction of the gate bias. This article aims to investigate the mechanism of this drain current hysteresis in the Al2O3/H-diamond MISFETs. Firstly, the drain current at a direct current (dc) bias is measured with a $100 ~\mu \text{s}$ sampling interval in 5 s. It is found that the dynamics of the drain current is opposite to that calculated using the trap model. Then, to reveal this anomalous phenomenon, an orientation polarization (OP) model accounting for adsorbates on the H-diamond surface is proposed. It shows that the relaxation induced by the orientational polarization results in a delay of the vertical electric field change in the channel under the gate, thus resulting in a drain current hysteresis at dc bias. The proposed model is verified by the combination of the measured gate capacitance versus frequency and the dynamic drain current measured at different biases and different temperatures. The activation energy calculated from the Arrhenius equation of the orientational polarization rather than traps is 0.0011 eV. The charging/discharging of the OP capacitance results in an overshoot of the drain current at the short pulse edges (PEs), which generates traps that lead to a drain current hysteresis at the pulse bias. The results of this article can be helpful for improving the reliability of H-diamond MISFETs.