N151-046 TITLE: Low-Cost Gallium Nitride (GaN) on Diamond Semiconductors for Microwave Power Amplifiers

TECHNOLOGY AREAS: Sensors, Electronics, Battlespace

ACQUISITION PROGRAM: PEO IWS 2, Above Water Sensors

OBJECTIVE: Develop a production process for GaN on diamond semiconductor wafers suitable for radio frequency integrated circuit (RFIC) fabrication to reduce cost and enhance performance.

DESCRIPTION: The purpose of this effort is to identify and develop an innovative GaN on diamond manufacturing process that serves to make high quality, RFIC-grade wafers available at competitive prices. The superior performance of GaN on diamond has been validated by testing representative circuits under laboratory conditions. Since the semiconductor itself is retained, circuit and processing design changes need not start from scratch, reducing risk. There are few (if any) technical arguments against adoption of GaN on diamond as a next-generation semiconductor for RFICs. However, GaN on diamond development has been restrained due to simply the availability of GaN on diamond wafers, the accompanying high cost, and the limited manufacturing base that is built on highly proprietary processes and has limited capacity. Industry has no current incentive to attack the cost of producing low cost GaN on diamond semiconductors due to the limited number of producers of the more expensive GaN on silicon.

Most future Navy sensors operating in the frequency bands L through X will be based on transmit/receive modules (TRMs) employed in large numbers, typically in phased array apertures (Ref. 1). In some future systems, particularly in radar, TRMs deployed on a single ship will number in the thousands, representing the predominant cost of the system. Within the TRM itself, the radio frequency (RF) power amplifiers are typically the single greatest component cost. Furthermore, the power amplifiers drive other considerations, such as the amount and means of cooling supplied to the TRM. Heat spreaders, heat pipes, special materials, and integrated cooling of the TRM package, attributable to the power amplifier, account for considerable cost associated with TRM design and manufacturing. Even modest changes to the power amplifier design have a cascading effect on total system cost.

The current state-of-the-art in power RF technology is the Gallium Nitride (GaN) semiconductor on a Silicon Carbide (SiC) substrate (Refs. 2, 3). When introduced, GaN technology represented a leap forward in performance due to the fundamental electronic properties of the material. Millions of dollars were invested to mature the basic manufacturing processes required to exploit the GaN technology for efficient, reliable, and affordable power amplifier designs. Today incremental advances in GaN on SiC manufacturing and design continue, however, the basic performance and cost of the technology has largely stabilized.

The next evolution of GaN technology for RF power amplifiers is GaN on diamond substrate (Ref. 4). That is, not a change to the semiconductor itself, but an improvement to the substrate, which is fundamental to the mechanical and thermal performance of the semiconductor. Diamond offers a significant increase in thermal conductivity over that of SiC, allowing circuit elements to be spaced more closely on the chip while dissipating heat more effectively to maintain operation at safe temperatures. Consequently, more Radio Frequency Integrated Circuits (RFICs) can potentially be obtained from a GaN on diamond wafer than from a corresponding GaN on SiC wafer (assuming equivalent yields). This has the potential for far ranging impacts, not just in cost, but in unprecedented performance as well. The enhanced thermal characteristics of GaN on diamond make it especially attractive for millimeter-wave RFIC designs where circuit elements are closely spaced.

The value of the process will be evaluated by comparison with the existing GaN on SiC state-of-the-art, both in technical parameters (wafer flatness, defect incidence, and others) and in cost. Product quality, process consistency and cost are paramount considerations.

PHASE I: The company will define and develop a concept for the production of GaN on diamond semiconductor wafers suitable for RFIC fabrication that meet the requirements stated in the topic description. The company will demonstrate the feasibility of their concept in meeting Navy needs and will establish that the concept can be feasibly produced. Scaled process testing, analysis and/or modeling will establish feasibility.

PHASE II: Based on the results of Phase I and the Phase II contract statement of work, the company will develop a prototype process for evaluation. The prototype process will be evaluated to determine its capability to meet Navy requirements for production of GaN on diamond semiconductor wafers suitable for RFIC fabrication. The GaN on diamond process will be demonstrated through prototype evaluation and/or modeling. Evaluation results will be used to refine the developed process prototype into a fully functional and operational production process that meets Navy requirements. The company will prepare a Phase III development plan to transition the technology for commercial use to supply Navy needs.

PHASE III: The company will be expected to produce GaN on diamond semiconductor wafers. The company will develop and fully document the production process of GaN on diamond semiconductor wafers suitable for RFIC fabrication according to the Phase III development plan. The production process will be evaluated to determine its effectiveness in full rate production of the wafers. This may require the small business to license other manufacturers for the actual production.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The US domestic RF semiconductor business supplies commercial as well as military markets, and advances in semiconductor and RFIC technology, though first implemented in military systems, eventually transition to commercial product lines. Since this topic seeks to develop a process for semiconductor material, and not a specific military application, the potential for commercial application is unfettered. The potential commercial market is essentially unlimited, should the technology prove cost competitive.

REFERENCES:
1. Kopp, Bruce A., Borkowski, Michael, and Jerinic, George. "Transmit/Receive Modules." IEEE Trans. Microwave Theory and Techniques 50 March 2002: pp. 827-834.

2. Katz, Allen, and Franco, Marco. "GaN Comes of Age." IEEE Microwave Magazine 11 (Supplement) Dec. 2010: pp. S24-S34.

3. Campbell, Charles F., et al. "GaN Takes the Lead." IEEE Microwave Magazine 13 Sept./Oct. 2012: pp. 44-53.

4. Felbinger, Jonathan G., et al. "Comparison of GaN HEMTs on Diamond and SiC Substrates." IEEE Electron Devices Letters 28 Nov. 2007: pp. 948-950.

KEYWORDS: Gallium Nitride; Silicon Carbide; diamond substrate; GaN on diamond; transmit/receive modules; Radio Frequency Integrated Circuits

** TOPIC AUTHOR (TPOC) **

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