Robert Grabar

92–96 GHz GaN power amplifiers

We report the test results of a family of 92-96 GHz GaN power amplifiers (PA) with increasing gate peripheries (150 µm to 1200 µm). The 1200 µm, 3-stage PA produces 2.138 W output power (Pout) with an associated PAE of 19% at 93.5 GHz (VD=14V). The amplifier offers Pout over 1.5W with associated PAE over 17.8% in the 92–96 GHz bandwidth. The measured data show that the maximum Pout scales linearly with increasing gate periphery at an almost constant PAE around 20%. This demonstrates the high efficiency of on-chip power combining and enables W-band high power single chip solid state power amplifiers.

W-band power performance of AlGaN/GaN DHFETs with regrown n+ GaN ohmic contacts by MBE

We report our second-generation mm-wave GaN double-heterostructure FET (DHFET) device technology which uses MBE regrowth of n+ ohmic regions to reduce parasitic resistance, and an improved T-gate process which demonstrated reduced current-collapse. These devices were utilized in a MMIC with a 600 µm wide output stage which achieved 1024 mW of output power (1.7 W/mm) and PAE of 19.1% at 95 GHz at a bias of 14V. This combination of power and PAE represents a substantial improvement over competing technologies, such as InP HEMTs, as well as our own previous reports of GaN MMIC amplifiers in this frequency range.

GaN Technology for E, W and G-Band Applications

Highly scaled GaN T-gate technology offers devices with high ft/fMAX, and low minimum noise figure while still maintaining high breakdown voltage and high linearity typical for GaN technology. In this paper we report an E-band GaN power amplifier (PA) with output power (Pout) of 1.3 W at power added efficiency (PAE) of 27% and a 65-110 GHz ultra-wideband low noise amplifier (LNA). We also report the first G-band GaN amplifier capable of producing output power density of 296mW/mm at 180 GHz. All these components were realized with a 40 nm T-gate process (ft= 200 GHz, fMAX= 400 GHz, Vbrk > 40V) which can enable the next generation of transmitter and receiver components that meet or exceed performance reported by competing device technologies while maintaining > 5x higher breakdown voltage, higher linearity, dynamic range and RF survivability.

Monolithic Integration of Enhancement- and Depletion-Mode AlN/GaN/AlGaN DHFETs by Selective MBE Regrowth

We have achieved the monolithic integration of two Ill-nitride device structures through the use of etching and re growth by molecular beam epitaxy (MBE). Using this regrowth technique, we integrated enhancement-mode (E-mode) and depletion-mode (D-mode) AIN/GaN/AlGaN double-heterojunction field-effect transistors (DHFETs) on a single SiC substrate, wherein the E-mode devices had a 2-nm-thick AlN barrier layer and the D-mode devices had a 3.5-nm-thick AlN barrier layer. The direct-current and radio-frequency (RF) performance of the resulting DHFETs was equivalent to devices fabricated using our baseline process with a normal MBE growth. D-mode devices with a gate length of 150 nm had a threshold voltage Vth of -0.10 V, a peak transconductance gm value of 640 mS/mm, and current gain and power-gain cutoff frequencies fT and fmax of 82 and 210 GHz, respectively. E-mode devices on the same wafer with the same dimensions had a Vth value of +0.24 V, a peak gm value of 525 mS/mm, and fT and fmax values of 50 and 150 GHz, respectively. The application of this regrowth technique is not, in any way, limited to the integration of E- and D-mode devices, and this method greatly expands the design possibilities of RF and power switching circuits in the nitride material system.

>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.

High-Speed, Enhancement-Mode GaN Power Switch With Regrown

We report a novel GaN heterojunction field-effect transistor device that incorporates vertically scaled epilayers, a nanoscale gate with integrated staircase-shaped field plates, and regrown ohmic contacts. This device technology has an unprecedented combination of high breakdown (176 V), low ON-resistance (1.2 Ωmm), enhancement-mode operation (VTH=+0.35 V), and excellent high-frequency performance (fT/fmax=50/120 GHz), which enables new applications as a high-frequency power switch or a microwave power amplifier. The gate design manages the electric field at the drain edge of the gate, which mitigates dynamic ON-resistance degradation.

{\rm n}+

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 Ohmic Contacts and Staircase Field Plates

We report an X-band class-E GaN power amplifier with built-in electroformed heat sink. Our novel approach for packaging, cooling and interconnecting allows “known good die” GaN MMICs to be combined with other components (Si, SiGe, passives etc) and enable GaN based RF front-ends. The presented amplifier offers continuous wave (CW) output power (Pout) of 34 dBm (power density of 3.2W/mm) with associated power added efficiency (PAE) of 72% and drain efficiency (DE) of 82% when biased at 15V. At 21V the PA offers CW Pout of 36.4 dBm (power density of 5.5W/mm) and associated PAE of 57%. Compared to identical PAs mounted on Cu-W heat sinks with silver epoxy and AuSn eutectic solder this corresponds to a 2x and 1.5x improvement in Pout respectively.

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

We report a new wafer-level, low-cost, scalable RF front-end packaging approach that enables heterogeneous integration of GaN integrated circuits (IC) with other ICs (Si, SiGe, InP, GaAs etc) and RF passives in a 3D package that includes RF/DC interconnects and thermal management. This is achieved by forming a composite substrate utilizing double-side polished alumina wafers with embedded electroformed heat spreaders and through substrate vias. We call this composite substrate Integrated Thermal Array Plate (ITAP). Compared to conventionally mounted GaN power amplifier (PA) using AuSn and silver epoxy the ITAP pckaged X-band PA demonstrated 1.42x and 2x improvement in output power respectively (36.4 dBm, with 57% associated power added efficiency). By using a junction temperature (Tj) evaluation circuit we demonstrated that the ITAP reduces the Tj by 40° when the dissipated power is 2W/mm or increases the power handling by 1.45x when the Tj is held at 150°C. Using the same approach we are also reporting wafer-level packaged GaN power switches as well as thermal cycling and thermal shock test data that show no performance degradation.

X band highly efficient GaN power amplifier utilizing built-in electroformed heat sinks for advanced thermal management

We report the first W-band GaN receiver components using a next generation, highly scaled GaN device technology. This technology (40nm, fT= 220 GHz, fmax= 400 GHz, Vbrk > 40V) enables receiver components that meet or exceed performance reported by competing device technologies while maintaining > 5x higher breakdown voltage, higher linearity, dynamic range and RF survivability. This paper includes results for a 4 and a 5 stage low noise amplifier (LNA) (gain over 5 dB/stage at 110 GHz), a single-pole single-throw (SPST) and a single-pole double-throw (SPDT) switch with loss of 0.9 dB and 1.3 dB respectively and a reflective type phase shifter