N251-072 TITLE: Lithium Niobate Fabrication and Processing

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Microelectronics;Quantum Science;Space Technology

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 innovative solutions for the fabrication, production, and processing of optical quality lithium niobate substrates.

DESCRIPTION: Lithium niobate (LiNbO3 or LN) is a versatile optical material used in a range of active optical components such as acousto-optic and electro-optic modulators, Pockels cells, and non-linear optics [Ref 1]. It supports optical wavelengths spanning the visible through infrared bands favored for telecom applications. It is an excellent substrate for optical waveguides either in bulk form or in the form of thin film lithium niobate (TFLN) on insulators. TFLN provides a versatile platform for the development of photonic integrated circuits (PICs), providing a path to the miniaturization and integration of complex optical systems into packages of lower size, weight, and power (SWaP). LN is a critical material used in many high precision inertial sensors for DoD applications, which includes an integrated optical component (IOC) that is typically a y-branch LN crystal waveguide. It also plays a key role in various active components that support cold atom based quantum inertial sensors, such as electro-optic phase and frequency shifters.

LN substrates exist in a variety of grades. Though somewhat loosely defined, optical grade represents the highest quality grade, best suited for use in optical waveguides and modulators. This is characterized by its highly uniform composition, typically achieved by tightly controlled crystal growth conditions, and lack of impurities and defects. For the purposes of this SBIR topic, the following goal specifications for optical quality are defined:

• Composition uniformity: +/- 0.01 mol% Li2O

• Curie temperature uniformity: +/- 1 °C

• Refractive index / birefringence uniformity: +/- 1e-4

• Impurities: < 1 ppm (each transition metal)

Over time, the U.S. supplier base for optical quality LN substrates has declined to the extent that nearly all single crystal LN must now be obtained from foreign sources [Ref 2]. The Navy has an interest in developing a robust supply chain for LN source material that can support the U.S. photonics industry. This SBIR topic seeks innovative approaches for LN fabrication processes for the growth of LN single crystals through wafer processing.

PHASE I: Perform an initial study to assess the feasibility of the proposed production methods and the expected material specifications. Optimize for any crystal composition (such as congruent, stoichiometric, doped) and provide an assessment of the targeted uniformity and purity of the material (neglecting any proposed dopants) and the expected optical quality. Propose methods of testing substrates to be developed in Phase II for defect concentration and other relevant measures of optical quality.

The Phase I Option, if exercised, will include the initial process specifications and capabilities description to build prototype wafers in Phase II.

PHASE II: Grow and process LN wafers with the following target specifications:

• Orientation: x-cut or z-cut (+/- 0.5 degrees)

• Minimum wafer diameter: 150 mm

• Wafer thickness: 1 mm (nominal)

• Wafer flatness: 15 microns (total thickness variation)

Characterize both the surface quality of substrates and the concentration of material defects according to methods defined in Phase I. Deliver five (5) wafer substrates to the Navy at the conclusion of Phase II.

PHASE III DUAL USE APPLICATIONS: Continue development in collaboration with the Navy and potential industry transition partners. Refine the wafer substrates to the requirements for LN substrates relevant for Navy applications. Define specific crystal specifications.

This work will result in a more robust supply chain for components and quantum inertial sensors. This work will have relevance for commercial dual use applications for telecommunications components, Light Detection and Ranging (LIDAR), and quantum information processing.

REFERENCES:

1. Andreas Boes et al. "Lithium niobate photonics: Unlocking the electromagnetic spectrum." Science, Vol 379, Issue 6627, 2023. DOI: 10.1126/science.abj4396

2. "National Strategy on Microelectronics Research A Report by the Subcommittee on Microelectroncs Leadership Committee on Homeland and National Security of the National Science and Technology Council." March 2024. https://www.whitehouse.gov/wp-content/uploads/2024/03/National-Strategy-on-Microelectronics-Research-March-2024.pdf

KEYWORDS: Lithium niobate; thin-film lithium niobate; wafer processing; optical modulation; non-linear optics; photonic integrated circuits

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