Jeong-Sun Moon

Gate-recessed AlGaN-GaN HEMTs for high-performance millimeter-wave applications

We report deep-submicrometer gate-recessed and field-plated AlGaN-GaN HEMTs and their state-of-the-art continuous wave (CW) power performance measured at 30 GHz. The AlGaN-GaN HEMTs exhibit a CW power density of 5.7 W/mm with a power-added efficiency (PAE) of 45% and drain-efficiency of 58% at V/sub ds/=20 V. At V/sub ds/=28 V, the output power density is measured as high as 6.9 W/mm with both PAE and output power increasing with input power level. Compared to conventional T-gated AlGaN-GaN HEMTs, the output power density and PAE of gate-recessed AlGaN-GaN HFETs are improved greatly, along with the excellent pulsed IVs. We attribute the improvement to both a field-plating effect and a vertical separation of the gate plane from surface states.

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.

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.

Graphene FETs for Zero-Bias Linear Resistive FET Mixers

In this letter, we present the first graphene FET operation for zero-bias resistive FET mixers, utilizing modulation of graphene channel resistance rather than ambipolar mixer operations, up to 20 GHz. The graphene FETs with a gate length of 0.25 μm have an extrinsic cutoff frequency fT of 40 GHz and a maximum oscillation frequency fMAX of 37 GHz. At 2 GHz, the graphene FETs show a conversion loss of 14 dB with gate-pumped resistive FET mixing, with at least > 10-dB improvement over reported graphene mixers. The input third-order intercept points (IIP3s) of 27 dBm are demonstrated at a local oscillator (LO) power of 2.6 dBm. The excellent linearity demonstrated by graphene FETs at low LO power offers the potential for high-quality linear mixers.

Graphene FET-Based Zero-Bias RF to Millimeter-Wave Detection

We report direct radio-frequency (RF) and millimeter-wave detection of epitaxial graphene field-effect transistors (FETs) up to 110 GHz with no dc biases applied, leveraging the nonlinearity of the channel resistance. A linear dynamic range of >; 40 dB was measured, providing at least 20-dB greater linear dynamic range compared to conventional CMOS detectors at transistor level. The measured noise power of the graphene FETs was ~7.5 × 10-18 V2/Hz at zero bias and without 1/f noise. At a 50-Ω load, measured detection responsivity was 71 V/W at 2 GHz to 33 V/W at 110 GHz. The noise-equivalent power at 110 GHz was estimated to be ~80 pW/Hz0.5. For the first time, we demonstrated graphene FETs as zero-bias ultrawideband direct RF detectors with comparable or better performance than state-of-the-art FET-based detectors without dc biases applied.

Development toward high-power sub-1-ohm DC-67 GHz RF switches using phase change materials for reconfigurable RF front-end

We report GeTe-based phase change material RF switches with on-state resistance of 0.07 ohm*mm and off-state capacitance of 20 fF/mm. The RF switch figure-of-merit, Ron*Coff is comparable to RF MEMS ohmic switches. The PCM RF shunt and series switches were fabricated for the first time in a lateral FET configuration to reduce parasitics, different from the vertical via switches. In a shunt switch configuration, isolation of 30 dB was achieved up to 67 GHz with return loss of 15 dB. RF power handling was tested with ~10 W for series and 3 W for shunt configurations. Harmonic powers were suppressed more than 100 dBc at fundamental power of 1 W, for future tunable and reconfigurable RF technology.

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.

Wideband linear distributed GaN HEMT MMIC power amplifier with a record OIP3/Pdc

We report on multi-octave (100 MHz - 8 GHz) GaN HEMT nonuniform distributed amplifier (NDPA) with and without linearization in a MMIC architecture for the first time. The NDPAs were fabricated with 0.14-μm field-plate AlGaN/GaN HEMT technology with fT of 58 GHz and breakdown voltage of 90 - 100 V. The NDPAs were built with six sections in a nonuniform distributed amplifier approach. The small signal gain was ~10 dB over the band with saturated CW output power of 33 - 37 dBm at Vdd = 20 V. The PAE was >35% - 30% up to 6 GHz. The linear NDPAs consist of main and gm3 cells, and show a small signal gain of 6 - 9 dB due to input RF signal routing. The Psat was ~35 dBm at Vdd = 20 V. Based on two-tone testing, the linear NDPA shows improved OIP3 of >50 dBm, compared to OIP3 of 42 dBm of the NDPA without linearization. The resulting OIP3/Pdc is 16:1, which is the highest reported amongst GaN-based distributed amplifiers.

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.

Graphene-on-SiC and graphene-on-Si transistors and RF applications

The unique ambipolar nature of graphene FETs can benefit various RF circuit applications, such as frequency multipliers, mixers and high-speed radiometers. The future success of the RF circuit applications depends on vertical and lateral scaling of graphene MOSFETs to minimize parasitics and improve gate modulation efficiency in the channel. We present recent progress in epitaxial graphene (n, p)-MOSFETs on both SiC and Si substrates for graphene-on-SiC and graphene-on-Si technologies on 75 mm wafers. The epitaxial graphene MOSFETs are fabricated with simultaneous world-record performance in key device parameters: excellent I–V saturation behaviors, peak field-effect mobility of 9000 cm2/Vs for electron and 3000 cm2/Vs for hole, and peak transconductance of 770 mS/mm.