Dustin Le

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.

Heterogeneous wafer-scale integration of 250nm, 300GHz InP DHBTs with a 130nm RF-CMOS technology

The performance advantages of InP based devices over silicon devices are well known, but the ability to fabricate complex, high transistor count ICs is limited both by the relative immaturity of the material system and a limited commercial market. Silicon based devices have made significant advances in device performance, but have not yet matched compound semiconductor device performance. A large commercial market, however, has allowed the silicon system to mature and produce billion transistor count ICs in high volume. It would be advantageous to combine the merits of both of these technologies in order to enable a new class of high performance ICs. This work demonstrates the wafer scale integration of an advanced 250 nm, 300 GHz fT/fMAX InP DHBT technology with IBMs 130 nm RF-CMOS technology (CMRF8SF). Such integration allows the rapid adoption of more advanced CMOS and InP DHBT technology generations.

A 4GHz 4th-Order Passive LC Bandpass Delta-Sigma Modulator with IF at 1.4GHz

A 4th-order bandpass DeltaSigma modulator utilizes a novel passive LC continuous-time DeltaSigma architecture to achieve the high IF (pass band) frequency (1.4GHz). A 3-bit quantizer is used to improve wideband performance. A novel architecture of noise-shaped quantizer is used to noise shape the DAC mismatch without introducing extra loop delay. Eight 2nd-order LC modulators are used for noise shaping with minimal transistor count and power consumption. Implemented with 5195 InP HBT transistors, this modulator achieved 76dB SNR and 90dB dynamic range in 1 MHz bandwidth at 1.4GHz with a 4GHz sample rate

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.

Ultrahigh-speed photonic analog-to-digital conversion technologies

This paper summarizes our recent work on high-speed photonic analog-to-digital conversion (A/D) technologies, where picosecond pulses generated by a 10 GHz mode-locked laser source were used to accomplish low-jitter photonic sampling. In addition, we describe our progress in the generation of 40 GHz wavelength-coded pulses for time-interleaved A/D, and the demonstration of photonic bandpass (at 1.6 GHz) Δ-∑ quantizers clocked at 10 GHz.

Graphene and Lateral Heterostructure for THz Imaging

We report millimeter-wave and sub-terahertz detection using graphene FETs up to 220 GHz at zero-bias to reduce 1/f noise. Detection leveraged the nonlinearity of the channel resistance through resistive field-effect transistor mixing for high-dynamic range. At a 50-Ω load, measured detection responsivity was 70 V/W at 2 GHz to 33 V/W at 110 GHz. The measured noise power of the graphene FETs was ~7.5 ×10-18 V2/Hz at zero-bias. Noise equivalent power at 110 GHz was estimated to be ~80 pW/Hz0.5. A linear dynamic range of > 40 dB was measured, providing 15-20 dB greater linear dynamic range compared to conventional CMOS detectors at the transistor level. The emerging graphene heterostructure diodes offer the RC limited cutoff frequency (fc) of 2.9 THz with the noise equivalent power of ~ 8 pW/Hz0.5 at 200 GHz due to its small junction-capacitance and diode nonlinearity.

Zero-bias THz detection using graphene transistors

We report zero-bias millimeter-wave and sub-THz detection using graphene FETs up to 220 GHz and graphene heterostructure diodes with reduced 1/f noise in direct detection. This detection leveraged the nonlinearity of the channel resistance through resistive field-effect transistor mixing. At a 50 ohm load, measured device responsivity was 70 V/W at 2 GHz to 33 V/W at 110 GHz. The measured noise power of the graphene FETs was ~7.5 × 10-18 V2/Hz at zero-bias. The NEP at 110 GHz was estimated to be ~80 pW/Hz0.5. A linear dynamic range of >40 dB was measured, providing 15 - 20 dB greater linear dynamic range compared to conventional CMOS detectors at the transistor level.

11 THz figure-of-merit phase-change RF switches for reconfigurable wireless front-ends

We report on GeTe-based, phase-change RF switches in a series configuration with an embedded micro-heater for thermal switching. With heater parasitics reduced, these GeTe RF switches show on-state resistance of 0.12 ohm*mm and off-state capacitance of 0.12 pF/mm. The RF switch figure-of-merit is estimated to be 11 THz, which is about 15 times better than state-of-the-art silicon-on-insulator switches. With 50-μm-wide GeTe switches, RF insertion loss was 0.25 dB and isolation was 24 dB at 20 GHz. Harmonic powers were suppressed >90 dBc at 35 dBm, meeting wireless requirements. The GeTe switches were characterized under W-CDMA signals without spectral regrowth up to 25 dBm.

100 MHz–8 GHz linear distributed GaN MMIC power amplifier with improved power-added efficiency

We report on a multi-octave (100 MHz–8 GHz), linear nonuniform distributed amplifier (NDPA) in a MMIC architecture using scaled 120-nm short-gate-length GaN HEMTs. The linear NDPAs were built with six sections in a nonuniform distributed amplifier approach, where each cell consists of main and gm3 cells. The small signal gain was >10 dB over the band, with saturated CW output power of ∼35 dBm at Vdd = 17 V. The PAE improved by 7%–10% within the band compared to the previous NDPA with 150-nm gate-length GaN FETs. Based on two-tone testing, the linear NDPA showed improved OIP3 of ∼50 dBm, compared to OIP3 of 42 dBm for the NDPA without linearization. Under QPSK LTEwaveform, the ACPR1improved by ∼10 dBc at average output power of 23 dBm, without digital pre-distortion.