N23A-T028   TITLE: Broadband, High Power, Low Loss N-polar GaN Radio Frequency (RF) Switches

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): 5G; Microelectronics; Networked C3

OBJECTIVE: Maximize radio frequency (RF) Switch performance in Nitrogen-polar (N-polar) Gallium Nitride (GaN) based on a high electron mobility transistor (HEMT) epitaxial layer structure capable of 4 W/mm power density.

DESCRIPTION: RF switches are used in virtually all wireless systems. Losses or distortion in front-end switches directly impacts final system performance metrics. Traditional solid state RF switch performance is limited by the underlying switch transistor or diode device�s figures of merit including switch cutoff frequency, linear and saturation current density, and breakdown voltage. New switch device technologies including MEMS and phase change materials have shown higher performance but have drawbacks including lacking the switch cycle endurance needed for many applications, the difficulty of integration that adds losses which can negate some of their performance advantages, and for MEMs a greater vibration/shock susceptibility.

N-polar GaN has recently shown record solid-state transistor switch performance metrics including a 1.7 THz switch cutoff frequency, and a straightforward path exists for monolithic integration of N-polar GaN power amplifiers (PAs) which are expected to also show record performance. Integration of an RF switch, power amplifier, and low noise amplifier (LNA) will enable low cost transceiver technology for applications addressing microwave to mm-wave systems. Recent results reported for N-polar GaN HEMT on Sapphire point to a very low-cost manufacturing for an integrated RF switch with a PA, and complete transceivers.

Switch circuit application examples and metrics that can be pursued in this STTR topic:

Ultra-broadband medium power low-loss switch: DC-100 GHz SPDT switch with > 2W 1dB compression point, > 10W off-state power handling, < 2 dB loss, 20 dB isolation

Low-loss, high linearity, Ka-band antenna tuning switch: 26.5-40 GHz SP4T switch with 50 dBm IP3

High-power S-Ku band switch: 2-18 GHz SPDT switch with > 10W P1dB

Alternate switch applications offered by proposers will be considered.

PHASE I: Fabricate, characterize, and model switch device cells needed for the range of designs. Design and simulate switch circuits, using an epitaxy which supports power devices with 4W/mm and 25% power-added efficiency (PAE) at W-band. Characterize the switch device cell for loss, isolation, linearity, and power handling. Report on switch circuit design and simulation including loss, isolation, linearity and harmonic performance, and power handling for different applications.

PHASE II: Refine models and fabricate switch circuits. Characterize switch circuits against the metrics and fabricate optimized designs based on specific applications proposed for Phase II. Implement fabrication process variations to correlate process parameters on field-effect transistor (FET) performance in a fab process flow suitable for integration with N-polar GaN PAs.

PHASE III DUAL USE APPLICATIONS: Demonstrate an integrated RF switch with PA in N-polar GaN, and alternatively a complete transceiver including RF switch, PA, and LNA relevant to the metrics in the above Description and the Phase I goals.

Dual use applications are expected to include commercial SATCOM, terrestrial backhaul communications for 6G and higher, Wi-Fi 6, and next generation wireless networks.

REFERENCES:

1.       Romanczyk, Brian et al, "Evaluation of linearity at 30 GHz for N-polar GaN deep recess transistors with 10.3 W/mm of output power and 47.4% PAE", Applied Physics Letters, vol.119, no.7, pp.072105, 2021

2.       Romanczyk, Brian et al., "Demonstration of Constant 8 W/mm Power Density at 10, 30, and 94 GHz in State-of-the-Art Millimeter-Wave N-Polar GaN MISHEMTs," in IEEE Transactions on Electron Devices, vol. 65, no. 1, pp. 45-50, Jan. 2018, doi: 10.1109/TED.2017.2770087

3.       Romanczyk, B. et al. "mm-Wave N-polar GaN MISHEMT with a self-aligned recessed gate exhibiting record 4.2 W/mm at 94 GHz on Sapphire."2016 74th Annual Device Research Conference (DRC), Jun. 2016, vol. 2016,pp. 1�2. doi: 10.1109/DRC.2016.7548464

 

KEYWORDS: GaN; Gallium Nitride; High Electron Mobility Transistor; HEMT; Nitrogen Polar; RF Switch

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