R. Bowen

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

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.

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

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 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.

A Low Noise Chipset for Passive Millimeter Wave Imaging

Technology for passive millimeter wave imaging has been maturing over the last 4-5 years. One key piece of technology that will allow for large scale production is a low cost front-end receiver. We have developed a two chip solution that addresses this need at W-band. A four stage InP LNA with a pre-matched Sb-heterostructure diode provides a low noise equivalent temperature difference (NETD). Our fabricated chipset provides sensitivities of 10,000 mV/muW over a 22 GHz noise equivalent bandwidth and an NETD of 0.8 K. To our knowledge, this is the best performance to date of a two chip solution for a passive millimeter wave radiometer.

Sb-Heterostructure Low Noise W-Band Detector Diode Sensitivity Measurements

Sb-heterostructure diodes have become the detector of choice for W-band millimeter wave imaging cameras. Here we demonstrate lower impedance versions that optimize noise equivalent power (NEP). The goal is to decrease the gain required of the RF pre-amplifier, ideally to zero. Measured W-band sensitivities for three diodes are 3500, 5500, and 6000 V/W. Their zero bias differential resistance values imply Johnson noise limited NEPs of 0.98, 0.83, and 0.79 pW/Hzfrac12, respectively, much less than obtained from conventional Schottky diodes. A wideband transition from a horn antenna to the 6000 V/W detector has produced an integrated bandwidth of 30 GHz with implied temperature sensitivity (NEDeltaT) close to 10degK

A wideband radiometer module for an unamplified direct detection scalable W-band imaging array

A W-band unamplified direct detection radiometer module is described that provides a wideband response and is scalable to large arrays. The radiometer design is intended to provide sufficient sensitivity for millimeter wave imaging applications with a goal of 2K noise equivalent temperature difference (NETD) at a 30 Hz frame rate. This effort leverages previously reported device scaling to increase sensitivity. We present a radiometer module designed for 60 GHz RF bandwidth that utilizes HRLs antimonide-based backward tunnel diode. An impedance matching circuit with on- and off-chip elements, as well as ridged waveguide, provides a wideband match to the detectors. Modules were designed with two different microwave substrates: 125 micron thick quartz and 100 micron thick alumina. flip-chip bonding of the detectors is amenable to automated pick-and-place for high volume manufacturing. The modular nature of the array approach allows large arrays to be manufactured in a straightforward manner. We present the design approach along with both electromagnetic simulations and measured performance of the modules. This work was supported by phase II of DARPAs MIATA program.

Unamplified direct detection sensor for passive millimeter wave imaging

We have demonstrated a high efficiency package for zero bias Sb-based backward tunnel diodes developed for passive millimeter wave imaging. Flip-chip mounting of detector MMICs onto quartz substrates permit placement of the detector directly within the WR-10 waveguide feeds for diagonal horn antennas. This arrangement minimizes the losses between the detectors and antennas while providing an impedance match over a majority of W band. A 2x2 array of radiometers was fabricated, assembled, and measured using coherent measurement techniques. The resulting noise equivalent temperature difference, calculated assuming a 30 Hz frame rate is 10 degrees K.

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

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.

Sb-heterostructure diode detector W-band NEP and NEDT optimization

Sb-heterostructure diodes have become the detector of choice for W-band millimeter wave imaging cameras now being commercialized or in prototype development. Here we optimize the diode impedance to yield a minimum noise equivalent power (NEP). The goal is to decrease the gain required of the front-end LNA. Measured W-band sensitivities for two diodes are 3500 and 5500V/W. Their zero bias differential resistance values imply Johnson noise limited NEPs of 0.98 and 0.83pW/Hz1/2, respectively, much less than obtained from conventional biased Schottky diodes. A MMIC version of the diode detector has been simulated with an integrated bandwidth of ~ 30 GHz at W-band. The simulated temperature sensitivity (NEΔT) with an HRL W-band LNA on the front end is <1°K.