M. Hu

Epitaxial-Graphene RF Field-Effect Transistors on Si-Face 6H-SiC Substrates

We report dc and the first-ever measured small-signal radio-frequency (RF) performance of epitaxial-graphene RF field-effect transistors (FETs), where the epitaxial-graphene layer is formed by graphitization of 2-in-diameter Si-face semi-insulating 6H-SiC (0001) substrates. The gate is processed with a metal gate on top of a high-k Al2 O3 gate dielectric deposited via an atomic-layer-deposition method. With a gate length (Lg) of 2 mum and an extrinsic transconductance of 148 mS/mm, the extrinsic current-gain cutoff frequency (fT) is measured as 4.4 GHz, yielding an extrinsic fT ldr Lg of 8.8 GHz middot mum. This is comparable to that of Si NMOS. With graphene FETs fabricated in a layout similar to those of Si n-MOSFETs, on-state current density increases dramatically to as high as 1.18 A/mm at Vds = 1 V and 3 A/mm at Vds = 5 V. The current drive level is the highest ever observed in any semiconductor FETs.

Top-Gated Epitaxial Graphene FETs on Si-Face SiC Wafers With a Peak Transconductance of 600 mS/mm

In this letter, we present state-of-the-art performance of top-gated graphene n-FETs and p-FETs fabricated with epitaxial graphene layers grown on Si-face 6H-SiC substrates on 50-mm wafers. The current-voltage characteristics of these devices show excellent saturation with on-state current densities (I_on) of 0.59 A/mm at V_ds = 1 V and 1.65 A/mm at V_ds = 3 V. I_on/I_off ratios of 12 and 19 were measured at V_ds = 1 and 0.5 V, respectively. A peak extrinsic g_m as high as 600 mS/mm was measured at V_ds = 3.05 V, with a gate length of 2.94 ¿m. The field-effect mobility versus effective electric field (E_eff) was measured for the first time in epitaxial graphene FETs, where record field-effect mobilities of 6000 cm²/V·s for electrons and 3200 cm²/V·s for holes were obtained at E_eff ~ 0.27 MV/cm .

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

W-Band GaN MMIC with 842 mW output power at 88 GHz

We report W-band GaN MMICs that produce 96% more power at a frequency of 88 GHz in continuous wave (CW) operation than the highest power reported in this frequency band for the best competing solid state technology[1], the InP HEMT. W-band power module containing a single three stage GaN MMIC chip with 600 µm wide output stage produced over 842 mW of output power in CW-mode, with associated PAE of 14.7% and associated power gain of 9.3 dB. This performance was measured at MMIC drain bias of 14 V.

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.

Wideband AlGaN/GaN HEMT MMIC low noise amplifier

A 3-18 GHz AlGaN/GaN high electron mobility transistor low noise amplifier on silicon carbide is reported. The measured gain (S/sub 21/) is 20 dB +/- 2.5 dB between 3-18 GHz. The minimum measured noise figure is 2.4 dB. To the authors knowledge, this is the highest gain reported over multiple octaves up to 18 GHz using GaN technology.

55% PAE and High Power Ka-Band GaN HEMTs With Linearized Transconductance via

We report small- and large-signal performances of 140-nm gatelength field-plated GaN HEMTs at Ka-band frequencies, in which the GaN HEMTs were fabricated with n+ source contact ledge. The parasitic channel resistance is reduced by ~ 50%, whereas the peak extrinsic transconductance is improved by 20% from 370 to 445 mS/mm. The GaN HEMTs with n+ source ledge exhibit improvement of maximum stable gain by at least 0.7 dB over reference devices without n+ ledge. At 30 GHz, CW output power density of 10 W/mm is measured with peak PAE of 40% and associated gain of 8.4 dB at Vds = 42 V. At Vds = 30 V, the output power density is measured as 7.3 W/mm with peak PAE of 50%, peak DE of 58%, and associated gain of 8.5 dB. The best PAE was measured as 55% at 5 W/mm at 30, 33, and 36 GHz, where the associated gains were 7.9, 7.6, and 8.2 dB, respectively.

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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.

GaN Source Contact Ledge

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

We report the development of Ka-band GaN MMIC power amplifiers in CPW and microstrip topologies. This is, to the best of our knowledge, the first demonstration of millimeter wave MMICs in GaN technology. The single stage CPW MMIC utilizes four 2/spl times/100 /spl mu/m wide GaN HFETs whilst four 4/spl times/60 /spl mu/m wide HFETs with individual through substrate source vias were used for the microstrip MMICs. The CPW amplifier has a gain peak of 8 dB at 33 GHz with 4 GHz bandwidth while the microstrip amplifier has a peak gain of 9 dB at 27 GHz and gain higher than 8 dB over the 2.45 GHz to 33 GHz frequency range. The saturated CW output power of the amplifiers measured into a 50 /spl Omega/ system at 33 GHz was, respectively, 1.6 W for the microstrip MMIC. The corresponding power density of 2.3 W per mm of gate periphery for the microstrip MMIC is by a factor of 4 higher than that of a typical GaAs pHEMT MMIC at this frequency. Microstrip MMIC performance was further improved through external output impedance matching, resulting in power levels of up to 2.8 W (27% associated PAE) and peak PAEs of up to 36.2% (1.2 W associated power).