Jongchan Kang

>70% Power-Added-Efficiency Dual-Gate, Cascode GaN HEMTs Without Harmonic Tuning

We report the state-of-the-art performance of deep-submicrometer gate length dual-gate GaN HEMTs and cascode GaN HEMTs with 10× reduced gate-to-drain feedback capacitance compared with single-gate GaN HEMTs. With 150-nm gate length field-plated gate structures, these GaN HEMTs demonstrated improvement of small-signal gain by 10 dB, compared with single-gate GaN HEMTs. Large-signal load-pull measurements showed peak power-added-efficiency (PAE) of 71%-74% without harmonic tuning at 10 GHz, up to a measured continuous-wave output power level of 2.3-2.5 W. The 74% PAE is very close to a theoretical maximum PAE of 78.5% without harmonic tuning. Compared with single-gate GaN HEMTs, both the dual-gate and cascode GaN HEMTs offer~10% improvement in peak PAE at the output power of 2.3-2.5 W.

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.

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.

Microwave and millimeter-wave flexible electronics

A novel method to fabricate substrate-less flexible and printable electronics for microwave and millimeter-wave applications is presented. InGaAs MHEMT technology is utilized in this work to demonstrate feasibility of the flexible electronics with bulk limited performance at microwave frequencies for the first time. The fabrication process and measurement results are discussed in detail.

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.

Broadband (100MHz -1GHz), High Power Active Circulator Architecture

We report very wideband 100 MHz to 1 GHz active circulator with high power operation up to 30 dBm for the first time. In order to achieve broadband high power circulation and isolation, a new architecture is developed using low-loss RF choke concept and it is implemented on alumina substrate with mounted GaN HEMT devices along with other SMTs. The performed test shows minimum 15 to 20 dB isolation up to 30 dBm and 15 dB directivity up to 26 dBm across the band with 2.5~5 dB insertion loss for 15 dB of minimum directivity.