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The impact of embedded microfluidic cooling on the performance of Ku-band gallium nitride (GaN) microwave monolithic integrated circuit (MMIC) power amplifiers (PAs) has been studied in this work. The research demonstrates that embedded cooling can substantially lower junction temperatures, mitigate the self-heating effect, and thereby improve the electrical performance of GaN MMIC PAs. Using merely 10.4 mW of pumping power (Ppump), the technology reduces the maximum junction temperature (Tj,max) from 216.7 to 147.8 °C. Furthermore, the system enhances the saturation current by 13.8%, increases output power (Pout) and gain (Gain) by 1.8 dB, elevates the power added efficiency (PAE) by 5.9%, and improves the heat flux of last gate (Qgate) to 37.3 kW/mm2 and the heat flux of MMIC (QMMIC) over 2.6 W/mm2, while reducing the thermal resistance (Rj-c) from 2.13 to 1.26 °C/W. Additionally, there is a notable improvement of the small signal gain (S21) by 2.5 dB. Therefore, the achievements in this work indicate that embedded cooling offers a powerful technique to suppress the thermal effects on GaN MMIC PAs, consequently improving their electrical performance. [ABSTRACT FROM AUTHOR]

In this work, the effects of proton-induced trap evolution on the electrical performances of AlGaN/GaN metal–insulator–semiconductor (MIS) high-electron-mobility-transistors (HEMTs) have been investigated in detail. Contrary to observed proton-induced degradation in sheet electron density (ns), carrier mobility (μn), and sheet resistance (RSH), a significant improvement in gate leakage current (IG) and off-state drain–source breakdown voltage (BVDS) is found in irradiated devices. The low-frequency noise (LFN) results show that the density of traps in the AlGaN layer and AlGaN/GaN interface increases after irradiation, which leads to a degradation in ns, μn, and RSH and an improvement in BVDS due to enhanced electron trapping and depletion. Furthermore, the measurement results obtained from the frequency-dependent conductance technique show that irradiated devices exhibit decreased trap density (DT) at the insulator/semiconductor interface with hardly changed trap energy level (ET), which confirms the observed proton-induced decrease in IG. An increase in DT at the AlGaN/GaN interface is also found after irradiation, which is consistent with LFN results. These traps with deeper ET induce a serious Coulomb scattering effect. This work provides valuable information for the systematic understanding of the proton irradiation effect of AlGaN/GaN MIS-HEMTs. [ABSTRACT FROM AUTHOR]

• Decreased channel temperature and improved RF power performance in planar distributed channel device. • Planar distributed channel is realized by standard ion implantation, which is compatible with device isolation. • Simulation and experimental results support each other very well. AlGaN/GaN HEMTs with planar distributed channel were fabricated on a silicon substrate. With a standard ion implantation isolation process, the area between the ohmic contacts was divided into conductive and non-conductive regions. Compared to a conventional HEMT, simulations and experimental results indicate the decreased channel temperature and improved RF power performance in the distributed channel device, while there is no significant degradation in small signal characteristics. The fabricated multi-finger distributed channel devices with 0.65-mm gate periphery demonstrated a decrease in channel temperature from 186 °C to 162 °C, accompanied by a 15.6 % increase (from 3.2 W/mm to 3.7 W/mm) in output power density, and an 8 % increase (from 42.0 % to 50.0 %) in drain efficiency at 3.5 GHz. [ABSTRACT FROM AUTHOR]

In this paper, AlN films grown by magnetron sputtering method have been proposed as the gate insulator layer of AlGaN/GaN high electron mobility transistors (HEMTs) to decrease gate leakage current and suppress the interface trap. The effect of the temperature of substrate on the quality of AlN films have been investigated. By inserting the thin AlN film (35 nm) as a gate insulator layer, the on-state resistance of AlGaN/GaN HEMTs decrease from 11.1 Ω mm to 10.3 Ω mm @ V g = 0 V, the current collapse decreases from 16.6% to 3.2%, the gate leakage can be reduced from 1.2 Ă— 10âˆ'1A mmâˆ'1 to 4.4 Ă— 10âˆ'6A mmâˆ'1 @ V g = 2 V by five orders of magnitude, and the fast interface states disappear and the normal trap density decreases from 0.96â€"1.3 Ă— 1013 cmâˆ'2eVâˆ'1 to 1.3â€"3.4 Ă— 1012 cmâˆ'2 eVâˆ'1, proving that magnetron-sputtered AlN is an effective way to improve the performance of GaN HEMTs. [ABSTRACT FROM AUTHOR]

In this work, a high linearity AlGaN/GaN HEMT integrated dual threshold coupling (DT) technology and Schottky–Ohmic drain (SOD) were fabricated and analyzed. Since the architecture of DT synthesized planar- and recess-HEMT periodically along the gate width, SOD alleviated the peak electric field (E-field) around the gate region and the peak transconductance (Gm-max) of 248 mS/mm with the associated transconductance plateau of ∼4.0 V at Vds = 28 V was obtained, which is evidently flatter than that of HEMT without the SOD structure. Attributed to the improved Gm linearity at high E-field, the DT-SOD HEMT exhibits the predicted linearity figure of merit of 5–13 dB when biased at class AB operation, which is ∼10 dB higher than that of DT-HEMT. Moreover, the fabricated device yields a nearly constant fT/fmax of 47/118 GHz over a wide gate voltage, and load-pull measurements at 30 GHz reveal that these devices deliver output power density (Pout) of 7.8 W/mm with the associated 1-dB compression point (P1dB) of 28.5 dBm at Vds = 28 V. The experimental results indicate that the employment of DT technology and SOD structure is an attractive approach to enhance the linearity at high E-field for millimeter wave devices. [ABSTRACT FROM AUTHOR]

This work reports an AlN/GaN/InGaN high electron mobility transistor (HEMT) with a steep subthreshold swing (SS) of sub-60 mV/dec utilizing a coupling-channel architecture. The fabricated transistors show a negligible hysteresis, a SS of 39 mV/dec, a large gate voltage swing of >4.2 V, and achieving an excellent quality factor Q = gm/SS of 6.3 μS-dec/μm-mV. The negative differential resistance effect was found in the subthreshold region in the gate current–voltage (Ig–VGS) curve. The hot carrier transfer mechanism that occurred in the turn-on/pinch-off progress of the CC-HEMT under the dual-directional sweep, proved by the VDS- and Lg-dependent bi-directional transfer I–V characteristics, can be responsible for these excellent device performances. This work is believed to encourage further study of the AlN/GaN platform to power the future group III-nitrides CMOS technology. [ABSTRACT FROM AUTHOR]

In this work, ultrathin barrier (∼6 nm) AlGaN/GaN high-electron-mobility transistors (HEMTs) with in situ SiN gate dielectric and slant-field plate (SFP) T-gates were fabricated and analyzed. Since the proposed scheme of gate dielectric and SFP effectively suppresses the gate leakage and alleviates the peak electric field (E-field) around gate region, the maximum breakdown voltage (VBK) was improved to 92 V, which is 54 V higher than that of the conventional device. The fabricated ultrathin AlGaN/GaN HEMT with 60-nm SFP-T-gate exhibited the peak fT of 177 GHz and peak fmax of 393 GHz, yielding high figure-of-merits of fT · VBK = 16 THz V and fmax·VBK = 36 THz V. Moreover, load-pull measurements at 30 GHz reveal that these devices deliver output power density (Pout) of 4.6 W/mm at Vds = 20 V and high power-added efficiency up to 52.5% at Vds = 10 V. Essentially, the experimental results indicate that the employment of SFP and in situ SiN gate dielectric is an attractive approach to balance the breakdown and speed for millimeter wave devices. [ABSTRACT FROM AUTHOR]

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/cm2, 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. [ABSTRACT FROM AUTHOR]

In this work, high-performance millimeter-wave AlGaN/GaN structures for high-electron-mobility transistors (HEMTs) are presented using a Si-rich SiN passivation layer. The analysis of transient and x-ray photoelectron spectroscopy measurements revealed that the presence of the Si-rich SiN layer leads to a decrease in the deep-level surface traps by mitigating the formation of Ga–O bonds. This results in a suppressed current collapse from 11% to 5% as well as a decreased knee voltage (Vknee). The current gain cutoff frequency and the maximum oscillation frequency of the devices with the Si-rich SiN layer exhibit the values of 74 and 140 GHz, respectively. Moreover, load-pull measurements at 30 GHz show that the devices containing the Si-rich SiN deliver excellent output power density of 8.7 W/mm at Vds = 28 V and high power-added efficiency up to 48% at Vds = 10 V. The enhanced power performance of HEMTs using Si-rich SiN interlayer passivation is attributed to the reduced Vknee, the suppressed current collapse, and the improved drain current. [ABSTRACT FROM AUTHOR]

The combined effects of proton irradiation and forward gate-bias stress on the interface traps of AlGaN/GaN heterostructure have been studied in this article. It is found that the effect of proton irradiation and forward gate-bias on the shift of flat band voltage $V_{\mathrm {FB}}$ is independent. By utilizing the frequency-dependent conductance technique, it is found that the trap density $D_{\mathrm {T}}$ at metal/AlGaN interface decreases after proton irradiation and the $D_{\mathrm {T}}$ at most energy levels increases after the following forward gate-bias. The $D_{\mathrm {T}}$ at AlGaN/GaN interface increases after proton irradiation and then decreases after the following forward gate-bias. The energy level range of metal/AlGaN interface traps reduces significantly under the forward gate-bias for the irradiated devices, however, that of AlGaN/GaN interface traps decreases little. In summary, the combined effect of proton irradiation and forward gate-bias stress on the interface traps is more complex than that on the bulk traps in AlGaN layer. [ABSTRACT FROM AUTHOR]

This work investigates the intrinsic degradation mechanism of InGaN/GaN UVA (320–400 nm) light emitting diodes (LEDs) after swift heavy ion irradiation from the defect aspect using temperature-dependent low frequency noise measurement. The UVA LEDs were exposed to 1423 MeV Ta ions with a fluence of 108–1010 ions cm−2. The optical power decreases and the leakage current increases evidently after irradiation. The defect behaviors were characterized to analyze the degradation mechanism. It is indicated that the ∼0.2 eV energy level defect decreases, and the defect with an energy level of about 0.65 eV increases with the increasing fluence, resulting in device degradation. Combining the defect energy level and the decreased yellow luminescence in the photoluminescence spectrum, the possible defect transform process is the newly created N interstitial atoms fill in the intrinsic VGa and form NGa after irradiation. [ABSTRACT FROM AUTHOR]

A 1.5-μm polycrystalline diamond was deposited on the AlGaN/GaN heterojunction on SiC substrate with a 20-nm SiN dielectric layer. A (5.8 ± 0.1)% increase in 2DEG density after the diamond growth due to the increase in tensile strain of GaN layer was confirmed by micro-Raman measurements. Top-side integration of polycrystalline diamond heat spreader with AlGaN/GaN high electron mobility transistors was demonstrated. Using a dry/wet combined etching process for the removal of the diamond and SiN interlayer, the integration fabrication of diamond heat spreader and GaN HEMTs with low surface damage was achieved. After the diamond growth, Off-state drain current shows no degradation. Besides, both the drain current and peak transconductance of the GaN HEMTs were enhanced. Temperature reduction of 25 °C at power density of 20 W/mm was achieved by electro-thermal simulation using the thermal properties determined by TDTR measurements. [Display omitted] • Diamond was deposited on the AlGaN/GaN heterojunction with a 20-nm SiN layer. • A dry/wet combined etching was used for the removal of diamond and SiN interlayer. • No degradation of the off-state drain current was achieved after device fabrication. • Drain current and peak transconductance of the GaN HEMTs were enhanced. [ABSTRACT FROM AUTHOR]

• A large area AlGaN/GaN RTD grown by MOCVD is manufactured. • The device adopts air-bridge structure suitable for the terahertz (THz) band. • NDR characteristics of the RTD are observed under bipolar bias at room temperature. • The enhancement of the reverse NDR performance is theoretically investigated. • The reproducible NDR characteristics of the RTD are reported under bipolar bias. A large area AlGaN/GaN resonant tunneling diode (RTD) grown by metal–organic chemical vapor deposition (MOCVD) is manufactured. The device adopts air-bridge structure suitable for the terahertz (THz) band, and a commercially available high-frequency GaN technology is applied in the process of device fabrication. Negative differential resistance (NDR) characteristics of the device are observed under the bipolar bias voltage at room temperature, which exhibits clear anti-symmetry in the peak-to-valley current ratio (PVCR), peak voltage and peak current density. The work systematically investigates how the built-in electric field introduced by polarization effects modulates the resonant tunneling transport utilizing TCAD tool Silvaco-ATLAS, and analyzes the enhancement of the resonant tunneling under negative bias voltage of the RTD with low-aluminum content AlGaN as barriers. The AlGaN/GaN RTD with conventional double-barrier single (DBS) quantum well (QW) structure shows reproducible NDR characteristics under the bipolar bias voltage at room temperature, which facilitates the design and extensive study of complicated device structures. [ABSTRACT FROM AUTHOR]