W.-S. Wong

GaN HFET for W-band Power Applications

In this paper we report high frequency GaN power device and measured power performance of the first W-band (75 GHz-110 GHz) MMIC fabricated in GaN material system. The first W-band GaN MMIC with 150 mum of output gate periphery produces 316 mW of continuous wave output power (power density =2.1 W/m) at a frequency of 80.5 GHz and has associated power gain of 17.5 dB. By comparison the reported state of the art for other solid state technologies in W-band is 427 mW measured in a pulsed mode on an InP HEMT MMIC with 1600 mum of output periphery (power density = 0.26 W/mm). The reported result demonstrates tremendous superiority of GaN device technology for power applications at frequencies greater than 75 GHz

GaN double heterojunction field effect transistor for microwave and millimeterwave power applications

We report development of a novel AlGaN/GaN/AlGaN double heterojunction field effect tansistor (DHFET) with improved device performance over the conventional single heterojunction GaN FET (SHFET). The GaN DHFETs with low Al content Al/sub 0.04/Ga/sub 0.96/N buffer layer exhibit three orders of magnitude lower subthreshold drain leakage current and almost three orders of magnitude higher buffer isolation than corresponding SHFET devices (600 M/spl Omega//sq. vs. 1 M/spl Omega//sq.). In GaN DHFETs with 0.15 /spl mu/m conventional T-gates we observed 30% improvement in saturated power density and 10% improvement in PAE at 10 GHz over a corresponding SHFET device.

GaN MMIC technology for microwave and millimeter-wave applications

In this paper we demonstrate the merits of GaN MMIC technology for high bandwidth millimeter-wave power applications and for microwave robust LNA receiver applications. We report the development of a broadband two-stage microstrip Ka-band GaN MMIC power amplifier, with 15dB of flat small signal gain over the 27.5GHz to 34.5GHz frequency range and 4W of saturated output power at 28GHz, with a power added efficiency of 23.8%. This is to the best of our knowledge the best combination of output power, bandwidth and efficiency reported for a GaN MMIC in Ka-band frequency range. We also report a robust two-stage wideband (0.5GHz-12GHz) GaN LNA MMIC, which can survive 4W of incident input RF power in CW mode without input power protective circuitry. The presented LNA MMIC has, to the best of our knowledge, the best combination of NF, bandwidth, survivability and low power consumption reported to date in GaN technology.

Microwave noise performance of AlGaN-GaN HEMTs with small DC power dissipation

We report low microwave noise performance of discrete AlGaN-GaN HEMTs at DC power dissipation comparable to that of GaAs-based low-noise FETs. At 1-V source-drain (SD) bias and DC power dissipation of 97 mW/mm, minimum noise figures (NF/sub min/) of 0.75 dB at 10 GHz and 1.5 dB at 20 GHz were achieved, respectively. A device breakdown voltage of 40 V was observed. Both the low microwave noise performance at small DC power level and high breakdown voltage was obtained with a shorter SD spacing of 1.5 /spl mu/m in 0.15-/spl mu/m gate length GaN HEMTs. By comparison, NF/sub min/ with 2 /spl mu/m SD spacing was 0.2 dB greater at 10 GHz.

GaN MMIC PAs for E-Band (71 GHz - 95 GHz) Radio

High data rate E-band (71 GHz- 76 GHz, 81 GHz - 86 GHz, 92 GHz - 95 GHz) communication systems will benefit from power amplifiers that are more than twice as powerful than commercially available GaAs pHEMT MMICs. We report development of three stage GaN MMIC power amplifiers for E-band radio applications that produce 500 mW of saturated output power in CW mode and have > 12 dB of associated power gain. The output power density from 300 mum output gate width GaN MMICs is seven times higher than the power density of commercially available GaAs pHEMT MMICs in this frequency range.

Robust Broadband (4 GHz - 16 GHz) GaN MMIC LNA

We report robust GaN MMIC LNA operating over 4 GHz-6 GHz frequency range. An FET biased in common-drain configuration is used on the second stage of the MMIC to obtain good input return loss at the optimum noise match over the entire frequency range. The measured noise figure of the MMIC is less than 2 dB over the 4.5 GHz to 16 GHz frequency range and NF has a minimum of 1.45 dB at a frequency of 6.5 GHz. The MMIC gain is more than 10 dB and the input return loss of the MMIC is less than -10 dB over the 4 GHz-15 GHz frequency range. Reported MMIC can survive 5.4 W of incident RF power without front end protection. To the authors knowledge this is the best combination of the noise figure, input return loss, RF survivability and broadband response reported to date in this frequency range using GaN technology. The noise figure of the reported GaN MMIC is 0.5 dB lower than the overall noise figure of an equivalent GaAs pHEMT module consisting of the state of the art LNA and a 5 Watt power limiter at the front end.

GaN HFETs with excellent low noise performance at low power levels through the use of thin AlGaN Schottky barrier layer

State-of-the-art noise performance of AlGaN/GaN HFETs in the 2-20 GHz frequency range for ultra low power operation of 10 mW (10 mA drain current and 1 V drain bias) is reported. A record low minimum noise figure (NF/sub min/) of 0.4 dB with 16 dB associated gain at 5 GHz was measured. The NF/sub min/ is below 0.8 dB across the 2-12 GHz frequency-band, with associated gains of better than 12.5 dB. This noise performance is achieved by using a vertically scaled device structure where the thickness of the AlGaN Schottky layer is reduced to 15 nm compared to the standard thickness of 30 nm previously used for our baseline devices. Indeed. NF/sub min/ of the scaled device is better than the baseline device across the 2-20 GHz band.

Q-Band GaN MMIC LNA Using a 0.15μm T-Gate Process

We report a robust Q-band GaN MMIC LNA operating in the 42-47GHz frequency range using a 0.15 mum T-gate process. The measured noise figure of the MMIC is less than 3.1 dB over the band of interest and the NF has a minimum of 2.9 dB at a frequency of 45.5 GHz. The MMIC gain is between 19 and 20 dB across the band and the input return loss of the MMIC is less than -10 dB. The measured OIP3 of the MMIC is 28 dBm at 45 GHz. The 3 stage MMIC is 2.5times1.3 mm2 and consumes less than 400 mW. To the authors knowledge this is the best combination of RF GaN performance at Q-band and the first reported GaN MMIC LNA in this frequency band.

GaN HFETs on SiC Substrates Grown by Nitrogen Plasma MBE

AlGaN/GaN heterojunction field effect transistors (HFETs) have recently demonstrated power-handling capabilities exceeding by almost an order of magnitude those of GaAs-pHEMTs. In addition, several groups have reported that low-noise performance of these high power devices almost matches that of the state of the art GaAs-pHEMTs, despite the relative immaturity of GaN HFET technology. A growing demand for GaN HFET parts that has been created by the recent promising performance of GaN HFETs led to the expansion of our research effort to include a small-scale production capability. Device results and run-to-run reproducibility data presented in this paper clearly demonstrate, that plasma assisted MBE is a viable tool for production of GaN HFETs on SiC wafers.