Off-state Drain Breakdown Voltage Research Articles

Ti3 C2 Tx MXene van der Waals gate contact for GaN high electron mobility transistors.

Gate controllability is a key factor that determines the performance of GaN high electron mobility transistors (HEMTs). However, at traditional metal-GaN interface, direct chemical interaction between metal and GaN can result in fixed charges and traps, which can significantly deteriorate the gate controllability. In this study, Ti3 C2 Tx MXene films were integrated into GaN HEMTs as the gate contact, wherein van der Waals heterojunctions were formed between MXene films and GaN without direct chemical bonding. The GaN HEMTs with enhanced gate controllability exhibited an extremely low off-state current (IOFF ) of 10-7 mA/mm, a record high ION /IOFF current ratio of ∼1013 (which is six orders of magnitude higher than conventional Ni/Au contact), a high off-state drain breakdown voltage of 1085V, and a near-ideal subthreshold swing of 61mV/dec. This work shows the great potential of MXene films as gate electrodes in wide-bandgap semiconductor devices. This article is protected by copyright. All rights reserved.

Use of Bilayer Gate Insulator in GaN-on-Si Vertical Trench MOSFETs: Impact on Performance and Reliability.

We propose to use a bilayer insulator (2.5 nm Al2O3 + 35 nm SiO2) as an alternative to a conventional uni-layer Al2O3 (35 nm), for improving the performance and the reliability of GaN-on-Si semi vertical trench MOSFETs. This analysis has been performed on a test vehicle structure for module development, which has a limited OFF-state performance. We demonstrate that devices with the bilayer dielectric present superior reliability characteristics than those with the uni-layer, including: (i) gate leakage two-orders of magnitude lower; (ii) 11 V higher off-state drain breakdown voltage; and (iii) 18 V higher gate-source breakdown voltage. From Weibull slope extractions, the uni-layer shows an extrinsic failure, while the bilayer presents a wear-out mechanism. Extended reliability tests investigate the degradation process, and hot-spots are identified through electroluminescence microscopy. TCAD simulations, in good agreement with measurements, reflect electric field distribution near breakdown for gate and drain stresses, demonstrating a higher electric field during positive gate stress. Furthermore, DC capability of the bilayer and unilayer insulators are found to be comparable for same bias points. Finally, comparison of trapping processes through double pulsed and Vth transient methods confirms that the Vth shifts are similar, despite the additional interface present in the bilayer devices.

A Novel Backside Gate Structure to Improve Device Performance

A novel structure with backside gate was proposed in this study. The effect of backside gate to the device performance including DC performance and breakdown voltage was investigated. When the back-side gate was biased at -25V, the leakage current could be suppressed to one order lower. As a result, the subthreshold swing (SS) could be improved from 240 to 137 mV/dec. Most important of all, the off-state drain breakdown voltage could be increased by 40%. If the back-side gate is connected to the front-side gate, which could be viewed as a back-side gate field plate structure, the off-state drain breakdown voltage could be improved by 7%

Effect of proton irradiation on thermal resistance and breakdown voltage of InAlN/GaN high electron mobility transistors

InAlN/GaN high electron mobility transistors were irradiated from the front side with 340 keV protons to a dose of 5 × 1013 cm−2. Raman thermography showed that the irradiated devices had higher channel temperatures than unirradiated control devices, but only by ∼10% under typical biasing conditions. Accordingly, the irradiated devices have higher thermal resistance (400 °C/W) compared to reference devices (350 °C/W), based on the slope of the power versus channel temperature line. However, increases of 42% in off-state drain breakdown voltage (VBR) and of >92% in critical voltage (Vcri) were observed for the proton irradiated HEMT. This is ascribed to the reduction of the peak electric field at the gate edges by ∼50% through the introduction of negative trap charges created from vacancies generated by the proton irradiation.

Characteristics of gate leakage current and breakdown voltage of AlGaN/GaN high electron mobility transistors after postprocess annealing

The effects of postprocess annealing on the gate leakage current and breakdown voltage characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) was investigated. The fabricated AlGaN/GaN HEMTs were postannealed at 250, 300, 350, 400, or 450 °C under a nitrogen (N2) atmosphere by using rapid thermal annealing, and both direct current (dc) and pulsed measurements were performed to characterize the changes in device performance. The reverse gate leakage current (IG) at VG = −10 V was reduced by one order of magnitude and the off-state drain breakdown voltage (Voff) increased by over three-fold after postprocess annealing at 450 °C. The reverse gate leakage current was found to be independent of gate-to-drain potential after annealing. The gate pulse measurements revealed the activation of deep traps during the postannealing at elevated temperatures.

Enhancement of AlGaN/GaN High Electron Mobility Transistor Off-State Drain Breakdown Voltage via Backside Proton Irradiation

Proton irradiations from the backside of the AlGaN/GaN high electron mobility transistors (HEMTs) were employed to enhance its off-state drain breakdown voltage. Via holes were fabricated directly under the active area of the HEMTs by etching through the Si substrate for the backside irradiations. The steep drop at the end of proton energy loss profile allows radiation-induced defects to be placed at precise locations within the AlGaN/GaN HEMT structure. Neither degradation of drain current nor enhancement of off-state drain voltage breakdown voltage was observed for the HEMTs irradiated with the proton energy of 225 or 275 keV, for which the defects were put in the GaN buffer. HEMTs with defects placed in the two dimensional electron gas (2DEG) channel region and the AlGaN barrier, using 330 or 340 keV irradiations, not only showed degradations on drain current and extrinsic transconductance but also demonstrated improvements of the off-state drain breakdown voltage.

Enhancement of AlGaN/GaN high electron mobility transistors off-state drain breakdown voltage via backside proton irradiation

Proton irradiation from the backside of the samples were employed to enhance off-state drain breakdown voltage of AlGaN/GaN high electron mobility transistors (HEMTs) grown on Si substrates. Via holes were fabricated directly under the active area of the HEMTs by etching through the Si substrate for subsequent backside proton irradiation. By taking the advantage of the steep drop at the end of proton energy loss profile, the defects created by the proton irradiation from the backside of the sample could be precisely placed at specific locations inside the AlGaN/GaN HEMT structure. There were no degradation of drain current nor enhancement of off-state drain voltage breakdown voltage observed for the irradiated AlGaN/GaN HEMTs with the proton energy of 225 or 275 keV, for which the defects created by the proton irradiations were intentionally placed in the GaN buffer. HEMTs with defects placed in the two dimensional electron gas (2DEG) channel region and AlGaN barrier using 330 or 340 keV protons not only showed degradation of both drain current and extrinsic transconductance but also exhibited improvement of the off-state drain breakdown voltage. The Florida Object Oriented Device and Process Simulator Technology Computer Aided Design finite-element simulations were performed to confirm the hypothesis of a virtual gate formed around the 2DEG region to reduce the peak electric field around the gate edges and increase the off-state drain breakdown voltage.

Study on the effects of proton irradiation on the dc characteristics of AlGaN/GaN high electron mobility transistors with source field plate

The effects of proton irradiation dose on the dc characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) with source field plates were studied. The HEMTs were irradiated with various protons doses ranging from 5 × 1012 to 5 × 1015 cm−2 at a fixed energy of 5 MeV. HEMTs irradiated with proton dose below 5 × 1013 cm−2 showed less than 2% degradation of either saturation drain current (IDSS) or transconductance (gm). Significant changes of these parameters were observed for the devices irradiated with doses above 5 × 1013 cm−2. HEMTs irradiated with the highest proton dose of 5 × 1015 cm−2 showed a reduction of IDSS and gm of 86% and 64.7%, and a positive Vth shift of 0.84 V, respectively. Despite the significant IDSS and gm reductions, the off-state drain breakdown voltage (VBR) was improved more than five times at this particular irradiation condition. The significant improvement of off-state drain breakdown voltage was attributed to the formation of a virtual gate at drain side of gate edge, which was the result of the generation of defect centers at AlGaN/GaN interface.

Effect of proton irradiation on AlGaN/GaN high electron mobility transistor off-state drain breakdown voltage

The effect of proton irradiation on the off-state drain breakdown voltage of AlGaN/GaN high electron mobility transistors (HEMTs) grown on Si substrates was studied by irradiating protons from the backside of the samples through via holes fabricated directly under the active area of the HEMTs. There was no degradation of drain current nor enhancement of off-state drain voltage breakdown voltage observed for HEMTs irradiated with 275 keV protons, for which the defects created by the proton irradiation were intentionally placed in the GaN buffer. HEMTs with defects positioned in the 2 dimensional electron gas channel region and AlGaN barrier using 330 keV protons not only showed degradation of both drain current and extrinsic transconductance but also exhibited an improvement of the off-state drain breakdown voltage. Finite-element simulations showed the enhancement of the latter were due to a reduction in electric field strength at the gate edges by introduction of charged defects.

Enhanced Device Performance of AlGaN/GaN High Electron Mobility Transistors with Thermal Oxidation Treatment

We systematically investigated the effect of the thermal oxidation treatment on the performance of AlGaN/GaN high electron mobility transistors (HEMTs). The HEMTs with thermal oxidation treatment exhibit four orders of magnitude reduction in gate leakage current, 80% reduction of trap density, and more than two times improvement of off-state drain breakdown voltage, compared with those shown by HEMTs without thermal oxidation treatment. The simplicity in the thermal oxidation treatment process, coupled with the drastic improvement in device performance render the thermal oxidation treatment highly promising for GaN-based microwave power amplifier applications in communication and radar systems.

Enhanced Device Performance of AlGaN/GaN High Electron Mobility Transistors with Thermal Oxidation Treatment

We systematically investigated the effect of the thermal oxidation treatment on the performance of AlGaN/GaN high electron mobility transistors (HEMTs). The HEMTs with thermal oxidation treatment exhibit four orders of magnitude reduction in gate leakage current, 80% reduction of trap density, and more than two times improvement of off-state drain breakdown voltage, compared with those shown by HEMTs without thermal oxidation treatment. The simplicity in the thermal oxidation treatment process, coupled with the drastic improvement in device performance render the thermal oxidation treatment highly promising for GaN-based microwave power amplifier applications in communication and radar systems.

Gate length scaling for Al/sub 0.2/Ga/sub 0.8/N/GaN HJFETs: two-dimensional full band Monte Carlo simulation including polarization effect

Two-dimensional self-consistent full band Monte Carlo (FBMC) simulator was developed for electron transport in wurtzite phase AlGaN/GaN heterojunction (HJ) FET. Recessed gate Al/sub 0.2/Ga/sub 0.8/N/GaN HJFET structures with an undoped cap layer were simulated, where the spontaneous and piezoelectric polarization effects were taken into account. The polarization effect was shown to not only increase the current density, but also improve the carrier confinement, and hence improve the transconductance. An off-state drain breakdown voltage (BV/sub ds/) of 300 V and a maximum linear output power (P/sub max/) of 46 W/mm were predicted for a 0.9-/spl mu/m gate device. For a 0.1-/spl mu/m gate device, 60 V BV/sub ds/, 20 W/mm P/sub max/, and 160 GHz current-gain cutoff frequency were predicted. Although there is considerable uncertainty due to lack of information on the band structure, scattering rates, and surface conditions, the present results indicate a wide margin for improvements over current performance of AlGaN/GaN HJFETs in the future. To our knowledge, this is the first report on the FBMC simulation for AlGaN/GaN HJFETs.