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Aluminum Nitride-Based Monolithic Microwave Integrated Circuits




OBJECTIVE: To develop aluminum nitride-based platform for monolithic microwave integrated circuits for extreme radio frequency and high-power operation.


DESCRIPTION: The next generation of devices and systems for electronic microwave applications need to offer high frequencies, high power, compactness, high-performance, and high temperature operation. Several materials platforms such as silicon carbide (SiC), gallium arsenide (GaAs), silicon (Si), and aluminum nitride (AlN) are competing for market share in this emerging high frequency applications. Among them however, AlN stands out as an exceptional material for next-generation monolithic microwave integrated circuits (MMICs), offering a multitude of advantages that are paramount for advanced electronic systems. These include its ultrawide and direct bandgap (6.2 eV), large critical electric field (15 MV/cm) and high thermal conductivity (340 W/mK) allowing for efficient heat dissipation, critical in maintaining high power operation and reliability of high-frequency circuits. Current research and development focus is being placed on gallium nitride (GaN) and aluminum gallium nitride (AlGaN) high electron mobility transistors (HEMTs) for operations requiring both high-power and high frequency. This has led to demonstration of the state-of-the-art GaN HEMTs with output power of up to 8.84 W/mm at up to 94 GHz. However, the GaN HEMTs were fabricated on SiC substrates. AlN's compatibility with GaN and AlGaN HEMTs facilitates seamless integration, avoiding the lattice mismatch issues encountered in SiC substrates. This would enable the development of compact, high-frequency devices with superior operational capabilities. Additionally, current availability of insulating AlN of high substrate quality and large enough size ensures precise and reliable MMIC fabrication, and unwanted electrical interactions, thus, enhancing signal integrity at high frequencies. However, despite these advantages, research and development of AlN-based MMICs are still in their infancy and more effort is needed to fully harness its capabilities. The utilization of high-purity semi-insulating AlN as a substrate for MMICs requires precise knowledge of materials properties of AlN at millimeter-wave frequencies (such as electrical permittivities) to accurately predict the propagation delay and attenuation of waves along the transmission lines.


The goal of this topic is to leverage recent achievements in AlN and AlGaN and create commercializable AlN-based MMICs which outperforms current state-of-the-art GaN MMICs for higher power/frequency applications. The needed work includes fundamental research and development to establish materials properties and fabrication routes for AlN-based devices. This would require design and fabrication of resonators for microwave or RF circuits, which could be accomplished via closed-loops, circular waveguides, or transmission lines to allow for resonance at specific microwave frequencies. The developed resonators would be used to extract fundamental materials properties such as permittivity and loss tangent. Subsequently, a route towards integration of the developed resonators with typical electronic components need to be pursued, focusing on the proposer’s defined application. The anticipated product is a fully integrated microwave circuit presented as a prototype.


PHASE I: In phase I, the awardee will describe a few important Army-relevant applications for AlN-based MMICs and select the particular application they wish to address. Using this application as a testbed, AlN-based microwave/mmWave resonators should be designed and fabricated. The fabricated resonators should be used to extract the substrate’s frequency-dependent material properties up to W-Band (i.e., 1 to 75 GHz). This information should then be used to design, fabricate, and test transmission lines with return loss < 10 dB and insertion loss < 0.6 dB/mm up to 75 GHz. At the end of Phase I, the feasibility of AlN-based MMICs should be assessed. With the growing demand for high frequency and high power MMICs for military and civilian applications, mmWave MMICs based on AlN projects strong commercialization potential.


PHASE II: During Phase II, the awardee will design, fabricate, and characterize the AlN-based resonators to obtain frequency-dependent material parameters up to 170 GHz. The performer must demonstrate a process for substrate thinning to a thickness of 100 µm or smaller. In addition, through substrate vias (TSV) should be demonstrated with a diameter less than 100 µm. This will result in the design, fabrication and characterization of low-loss waveguides and waveguide transitions with demonstrations in the W- and D-bands. The peak return loss and average insertion loss should be <18 dB and <0.5 dB/mm, respectively, up to 170 GHz. Then, in order to demonstrate the feasibility of AlN-based MMICs, the awardee will integrate the waveguides with an electronic element aligned with the proposed application, such as an amplifier, mixer, oscillator, or switch. At the end of Phase II, the awardee should demonstrate that the developed systems address limitations of current systems for the chosen application. In addition, the awardee should thoroughly investigate the commercial transition potential of AlN-based MMICs. Given their potential to advance high-frequency electronics significantly, the awardee is encouraged to explore this avenue, potentially positioning themselves as a key player in industries such as telecommunications, aerospace, and defense, where advanced electronic solutions are in high demand.


PHASE III DUAL USE APPLICATIONS: During Phase III approach, the work from Phase II should be continued. Here the focus should be on the development of a truly integrated MMIC. The awardee should undertake reliability testing/qualification, produce a process design kit. Moreover, the potential to transfer the technology to military systems (e.g., radar, electronic warfare, communication), as well as civilian applications should be explored. The awardee should work with Army primes and industry partners to commercialize the technology via a trusted foundry for technology availability to the defense and military markets.



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KEYWORDS: Aluminum Nitride, MMICs, Ultra-Wide Bandgap, High Frequency, Microwave, mmWAve

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