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In this work, effect of gamma irradiation on chemical vapor deposition grown ReS2 thin films vis‐a‐vis change in its structure, morphology, chemical composition, and memristive behaviour is reported to assess its radiation hardness for space applications. High‐resolution transmission electron micrographs and selected area electron diffraction pattern infer polycrystalline to amorphous phase transition and increase in the number of grain boundaries (GBs) after exposure to 25 kGy of gamma radiation. X‐ray photoelectron spectroscopy and low‐temperature photoluminescence measurements reveal the formation of sulfur vacancies (SV) accompanied with partial oxidation of film. Memristors are then fabricated on the as‐grown film using different metal electrodes, which are Ag, Pt, and Ti in lateral geometry, and their resistive switching (RS) mechanism is studied along with the impact of gamma irradiation. RS is attributed to the formation of conducting filaments due to GB‐mediated migration of metal ions, SV, and oxygen ions from the partially oxidized film. Furthermore, irradiation is found to increase current in the high resistance state of the device, which subsequently reduces the memory window. This impact is observed to be consistent across all the devices which validates the effect of irradiation irrespective of the nature of the metal electrode used. [ABSTRACT FROM AUTHOR]

This Letter pioneers an investigation into the influence of temperature on threshold voltage (VTH) instability under negative bias in ferroelectric charge trap gate stack (FEG) high electron mobility transistors. Based on the experimental stress condition, i.e., gate bias of −20 V and temperature (T) range from 30 to 150 °C, our findings reveal a unidirectional VTH shift with 30 °C < T < 90 °C, and transitioning to a bidirectional VTH shift at 90 °C ≤ T ≤ 150 °C. The observed VTH < 0 V can be ascribed to the emission of electrons from the trapping layer, prompted by the pre-poling of the ferroelectric (FE) layer and the presence of interface traps. In contrast, under high-temperature stress, where VTH > 0 V, it indicates the depletion of the two-dimensional electron gas electrons due to de-poling and saturation of the polarization in the reverse direction. Moreover, this phenomenon is consistent with extracted activation energies (Ea) of 0.55 ± 0.01 and 0.79 ± 0.01 eV. Additionally, the recovery characteristics validate the trapping/detrapping process. [ABSTRACT FROM AUTHOR]

In this study, AlGaN/GaN HEMTs with Au-free Ti/Al/Ni/Ti ohmic contacts were fabricated. The device presents a contact resistance (R c) of 0.64 Ω·mm and high linearity characteristics. The two-tone measurement at 28 GHz shows that the 2 × 50 μ m device exhibits an excellent third-order intercept point (OIP3) value of 41.64 dBm at V DS = 28 V, and an OIP3/ P DC of 24.2. An OIP3 of 46.59 dBm was achieved when the device's gate width was increased to 8 × 50 μ m at V DS = 48 V. These results demonstrate that AlGaN/GaN HEMTs with Ti/Al/Ni/Ti ohmic contacts have potential for Ka-band applications. [ABSTRACT FROM AUTHOR]

In this paper, AlGaN/GaN high-electron-mobility transistors (HEMTs) with ohmic etching patterns (OEPs) "fabricated to improve device radio frequency (RF) performance for Ka-band applications" are reported. The fabricated AlGaN/GaN HEMTs with OEP structures were used to reduce the source and drain resistances (Rs and Rd) for RF performance improvements. Within the proposed study using 1 μm hole, 3 μm hole, 1 μm line, and 3 μm line OEP HEMTs with 2 × 25 μm gate widths, the small signal performance, large signal performance, and minimum noise figure (NFmin) with optimized values were measured for 1 μm line OEP HEMTs. The cut-off frequency (fT) and maximum oscillation frequency (fmax) value of the 1 μm line OEP device exhibited optimized values of 36.4 GHz and 158.29 GHz, respectively. The load–pull results show that the 1 μm line OEP HEMTs exhibited an optimized maximum output power density (Pout, max) of 1.94 W/mm at 28 GHz. The 1 μm line OEP HEMTs also exhibited an optimized NFmin of 1.75 dB at 28 GHz. The increase in the contact area between the ohmic metal and the AlGaN barrier layer was used to reduce the contact resistance of the OEP HEMTs, and the results show that the 1 μm line OEP HEMT could be fabricated, producing the best improvement in RF performance for Ka-band applications. [ABSTRACT FROM AUTHOR]

A new power receiving unit (PRU) is proposed in this paper for resonant wireless power transfer (WPT), which is characterized by the capability of attracting high power from the power transmitting unit (PTU). The resonant WPT is designed for delivering the electrical power to the PRU attached on an electrical vehicle (EV) chassis 50 cm away from a PTU installed on the ground. The proposed PRU uses only the passive elements such as inductors, diodes, and capacitors, which need no initial power from the EV. It is then applicable for charging a battery to several hundred volts for even a first-time charging battery. For a resonant WPT at a switching frequency of 4 MHz, the proposed PRU behaves as a negative impedance converter (NIC) itself in the subharmonics of 4 MHz. The NIC effect plus the subharmonic oscillation causes an instability current charging the battery connected to the PRU. In this paper, we simulated the PRU and performed the experiment. The experiment demonstrated a battery charging of 150 W from 50 cm away using three D-mode GaN HEMT transistors via the instability current ramp. The power transfer efficiency (PTE) improved as the power delivered to the load (PDL) increased. The peak PTE was 65% in the present findings. The simulation analysis showed that the circuit allowed itself be used to much higher power transfer when it is implemented with more GaN HEMT transistors connected in parallel. The theoretical derivation of the PRU circuit is also used to support both the experimental and simulation results. [ABSTRACT FROM AUTHOR]

The effect of different SiNx thicknesses on the performance of AlGaN/GaN high-electron-mobility transistors (HEMTs) was investigated in this paper. The current, transconductance (Gm), cut-off frequency (fT), maximum oscillation frequency (fmax), power performance, and output third-order intercept point (OIP3) of devices with three different SiNx thicknesses (150 nm, 200 nm, and 250 nm) were measured and analyzed. The DC measurements revealed an increase in both the drain-source current (IDS) and Gm values of the device with increasing SiNx thickness. The S-parameter measurement results show that devices with a higher SiNx thickness exhibit improved fT and fmax. Regarding power performance, thicker SiNx devices also improve the output power density (Pout) and power-added efficiency (PAE) in the Ka-band. In addition, the two-tone measurement results at 28 GHz show that the OIP3 increased from 35.60 dBm to 40.87 dBm as the SiNx thickness increased from 150 nm to 250 nm. The device's characteristics improved by appropriately increasing the SiNx thickness. [ABSTRACT FROM AUTHOR]

Aluminum gallium nitride/gallium nitride (AlGaN/GaN) heterostructure devices have proven to be highly effective for high‐frequency power amplifiers and power switching applications with improved performance compared to those made with traditional silicon technology and other advanced semiconductor technologies. The development of enhancement‐mode (E‐mode) AlGaN/GaN high electron mobility transistors (HEMTs) and metal–insulator–semiconductor HEMTs (MIS‐HEMTs) has been a focus in recent years due to their potential applications. Arising from the concept of a flash‐memory‐like hybrid ferroelectric charge storage structure, the high‐performance hybrid ferroelectric charge storage gate (FEG) GaN HEMT has gradually gained a great deal of attention due to the concept being a useful and versatile tool to realize E‐mode operations. This article attempts to review the latest progresses in this technology, including alternative improvements and device characteristics. Future challenges for the E‐mode FEG‐HEMT are also discussed. [ABSTRACT FROM AUTHOR]

This paper presents a 250 kHz bidirectional battery charger circuit using a GaN HEMT. The charger is subjected to a high-/low-side constant voltage at 200 V/20 V. The charger circuit is a hybrid of the LLC and flyback circuit topologies. Both the power output analysis and efficiency control of this circuit are simplified when the magnetization current is minimized using the low-resistance GaN HEMT. The switching frequency is controlled to match the series resonance in a way that is analogous to conventional LLC circuit controls, while the duty ratio that determines the power output and the dead time, which determines the zero voltage switching, is controlled in an analogous manner to the flyback circuit control. The charging and discharging modes were altered by applying a double-throw relay that changes the transformer turn ratio, which is different from conventional LLC designs using the switching frequency adjustment. A nominal turn ratio with Np = 35 and Ns = 3.5 for a 200 V/20 V converter can only produce an internal series resonance with no current flowing in any charging direction. The proposed circuit using a transformer with multiple windings (Np = 35, Ns,F = 4, and Ns,R = 3) was fabricated to deliver 125 W output power from the power grid battery to the vehicle battery in the forward (charging) mode and 90 W in the reverse (discharging) mode. The conversion efficiency was calculated to be as high as 97% in the forward mode and 95% in the reverse mode. The high conversion efficiency is due to the characteristics of the GaN HEMT, including low resistive and switching losses. The equations derived in this paper associate these losses with the series resonant frequency and power conversion rate, which highlight the advantages of using a GaN HEMT in this CLLC design. [ABSTRACT FROM AUTHOR]

An inversion-mode In0.53Ga0.47As FinFET exhibiting a transition frequency (fT) of 271 GHz and a maximum oscillation frequency (fmax) of 78 GHz at Vds = 0.5 V is reported in this work. Simultaneously, the transconductance (gm) of 2056 (μS/μm) and drain induced barrier lowering (DIBL) of 121 (mV/V) obtained were also exhibited. Moreover, a subthreshold swing (SS) of 86 and 97 (mV/dec) was obtained at Vds = 0.05 and 0.5 V, respectively. These exceptional properties are the result of employing N2 remote plasma treatment, enhancing the quality of high-k/III-V interface and carrier mobility. The fin structure contributes to good suppression of short channel effects (SCEs), and the superior transfer characteristics are due to the improved gate controllability. We also extracted an effective electron velocity (νeff) of 2.18 × 107 (cm/s) by delay time analysis, providing a probable explanation for the obtained fT performance. This work explicitly exhibits the potential of high-performance inversion-mode InGaAs FinFETs, positioning them as promising candidates for future high-frequency system applications. [ABSTRACT FROM AUTHOR]