N221-085 TITLE: Integration Strategy for Complementary Metal Oxide Semiconductor-based Terahertz Spectroscopy Systems

OUSD (R&E) MODERNIZATION PRIORITY: Nuclear

TECHNOLOGY AREA(S): Sensors

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Develop prototypes that achieve low-loss coupling of sub-THz radiation (frequency range: 200-300 GHz) between a Complementary Metal Oxide Semiconductor (CMOS)-based structure and a compact, hermetically-sealed waveguide. The integration strategy must minimize size, weight, and power (SWaP) of the combined CMOS plus waveguide system; and must be robust to environmental instabilities such as ambient temperature changes.

DESCRIPTION: In the past decade there has been significant interest in and development of THz-based instruments for applications including imaging (e.g., non-ionizing medical diagnostics, security screening), molecular spectroscopy (chemical detection and precision timekeeping), extreme wideband communications, and radar [Ref 1]. Recently, advanced high-speed CMOS integrated circuit designs have led to transmitters (Tx) and receivers (Rx) in the THz regime with vastly reduced SWaP relative to competing technologies [Refs 2, 3]. In addition, THz waveguides have been miniaturized via microfabrication techniques [Ref 4]. When coupled to a millimeter-scale waveguide filled with a molecular gas, these CMOS-based Tx/Rx designs can form the basis of an extremely low-SWaP spectroscopy platform for use in DoD-relevant applications (e.g., a chip-scale clock [Ref 5]). This architecture also contains no electro-optic components, making it much more resilient to radiation effects that are known to degrade the performance of lasers, photodetectors, etc. As a result, CMOS-based THz spectroscopy systems are of great utility in DoD applications that require a combination of low-SWaP and radiation hardness.

Despite the recent CMOS design progress, significant additional development is needed to fully integrate a low-SWaP, low-cost, manufacturable spectroscopy instrument. Given the scalable advantages of CMOS-based manufacturing, this effort is anticipated to yield units that match the SWaP of modern miniaturized atomic systems (e.g. chip-scale atomic clock; ~100mW, 15 cm3) but at > 10X reduced cost (hundreds of dollars rather than thousands of dollars per unit) Some development considerations include:

1. The coupling efficiency between the CMOS Tx/Rx and the waveguide structure must be maximized without introducing stringent alignment requirements that introduce high assembly costs.
2. The waveguide containing the molecular sample must be designed to maximize its length while minimizing its volume and loss properties.
3. The mechanical coupling between the CMOS and waveguide must be robust enough to operate in a shock/vibe/temperature range environment consistent with DoD applications.

Design concepts must be communicated in sufficient detail that their approach can be adapted straightforwardly to any frequency in the specified range of 200-300 GHz. The performance targets in Table 1 must be achieved through the production of an integrated prototype. This does not require the waveguide to be sealed with a specific molecular species, it does require that the waveguide incorporates a hermetic seal.

Table 1: Performance targets

Parameter Value

CMOS-to-Waveguide coupling loss: < 3 dB per interface

Waveguide loss: < 0.5 dB/cm

Waveguide dimensions Goal: maximize length within a 1 cm3 volume constraint; minimum acceptable length = 3 cm

Integrated CMOS + waveguide volume: < 2 cm3

Temperature Sensitivity: < 3 dB change in end-to-end coupling over temperature range of -20� to +85�Celsius

PHASE I: Perform a design study that includes a trade space analysis and modeling of system performance with sufficient completeness and fidelity to demonstrate the feasibility to achieve the performance targets in Table 1. This includes a design of a CMOS device with sufficient test structures to demonstrate the required CMOS-to-waveguide coupling efficiency, the waveguide, and the details of how it will be fabricated, and the mechanical structure and assembly procedure for integration. The Phase I Option, if exercised, will include the initial design specifications and capabilities description to build a prototype solution in Phase II. A detailed test and evaluation plan is required in order to assess the hardware developed in Phase II.

PHASE II: Finalize designs of the CMOS-to-waveguide coupling strategy (CMOS device plus waveguide input/output), the waveguide structure, and the mechanical approach for integration. Produce and deliver five (5) integrated CMOS Tx/Rx structures plus waveguide prototypes and evaluate them against the performance targets in Table 1. A detailed test report must be delivered that clearly documents test procedures, performance vs. targets, hermetic seal leak rates, and a path forward to meet any targets not achieved. The prototypes should be delivered by the end of Phase II.

PHASE III DUAL USE APPLICATIONS: The prototypes developed in Phase II establish a path to integrating sensors based on THz spectroscopy. Further development must lead to fully miniaturized systems that robustly operate in shock and vibration environments relevant to Navy missions. In addition to the metrics demonstrated by the Phase II prototypes, this goal will require hermetically sealing a target gas species in the waveguide structure, incorporating all spectroscopic functionality (e.g., THz generation, transmission, reception, and signal processing) onto the CMOS chip, and generating derived sensor outputs. Support the Navy to ensure that the integration strategy can be included in future system development efforts that are targeted at specific applications. For example, a low-SWaP, low-cost, radiation-hardened clock based on a THz frequency reference would find wide usage in military, space and commercial applications that require a stable and precise timing source. Examples include navigation and communications in GPS-challenged environments, communication via satellite constellations, high-speed network synchronization, and undersea oil exploration via reflection seismology.

REFERENCES:

1. Pawar, A.Y.; Sonawane, D.D.; Erande, K.B. and Derle, D.V., "Terahertz technology and its applications," Drug Invention Today, Vol. 5, no. 2, pp. 157-163, 2013. https://doi.org/10.1016/j.dit.2013.03.009.
2. Lee, T. "Terahertz CMOS integrated circuits," 2014 IEEE International Symposium on Radio-Frequency Integration Technology, Hefei, China, 2014. https://doi.org/10.1109/RFIT.2014.6933268.
3. Fujishima, M. and Amakawa, S. "Design of Terahertz CMOS Integrated Circuits for High-Speed Wireless Communication", Institute of Engineering and Technology, 2019. https://doi.org/10.1049/PBCS035E.
4. Ermolov, V.; Lamminen, A.; Saarilahti, J.; Walchli, B.; Kantanen, M. and Pursula, P. "Micromachining integration platform for sub-terahertz and terahertz systems," International Journal of Microwave and Wireless Technologies, Vol. 10, no. 5-6, pp. 651-658, 2018. https://doi.org/10.1017/S175907871800048X.
5. Wang, C.; Yi, X.M.J.; Kim, M.; Wang, Z. and Han, R. "An on-chip fully electronic molecular clock based on sub-terahertz rotational spectroscopy," Nature Electronics, Vol. 1, no. 7, pp. 421-427, 2018. https://doi.org/10.1038/s41928-018-0102-4.

KEYWORDS: Terahertz; Transmitters; Receivers; Waveguides, Spectroscopy; CMOS; Radiation Hardness