TECHNOLOGY AREAS: Sensors; Space Platforms; Information Systems; Air Platform; Battlespace OBJECTIVE: This topic seeks to develop alternative low-cost manufacturing processes for producing high quality thin film lithium niobate (TFLN) that do not rely on the prevailing "Smart-Cut" ion implantation technique. These processes should be scalable and versatile, able to produce a variety of film thicknesses, crystallographic orientations, and on multiple substrates at low cost with minimal NRE. Proposed technologies should have clear compatibility with existing TFLN use cases and show a path towards widespread commercial use, ideally by providing homogenous 3-4 inch wafers of TFLN on relevant substrates such as quartz, but other approaches suitable for volume device manufacturing will also be considered. In either case a demonstration RF or photonic device must be fabricated using the TFLN produced under this effort. Films on the order of 300nm to several microns thick should be producible with desired total thickness variation of less than 3 percent and a surface roughness of less than 1 nanometer. The overall goal is a manufacturing process capable of several hundred wafers or equivalent devices per year at a cost of less than $2000 per wafer or a greater than 25 percent cost reduction. Ideally these technologies would also be transferrable to other thin film electro-optic materials such as Barium titanate. DESCRIPTION: Thin Film Lithium Niobate (TFLN), which consists of a thin film (300nm+) of lithium niobate, traditionally on insulator, is a key electro-optic material for next generation sensor and communication systems needed by the U.S. Space Force, Air Force, and DoD at large. TFLN offers significant improvements over bulk lithium niobate in processing, size, weight, and performance as well as enabling new capabilities in photonics, ultra-wideband Radio Frequency, surface acoustic wave filters (SAW) and quantum sensing and computing. Currently the leading technology of choice for TFLN manufacturing is ion slicing, otherwise known as "Smart-Cut", which uses ion implantation to induce a cleavage plane at some depth determined by ion dose and energy in the bulk lithium niobate wafer. This wafer is then bonded to the handle substrate wafer, annealed, and exfoliated. This leaves the damaged ion implant layer as a thin film on the handle wafer, which can then be further annealed and polished using chemical mechanical polishing (CMP) to remove defects and improve uniformity. CMP can also be used exclusively to grind away most of the bulk wafer, but this process has not yet achieved the uniformity of Smart-Cut at the wafer scale. While the Smart-Cut process is capable of producing highly uniform films, it has high capital investment costs (or high service cost using 3rd parties) for the ion implantation step. It also suffers from high non-recurring engineering costs for different TFLN wafer compositions, as well as increased cost for thicker films due to the increased ion dose required. This effort should mature, adapt, or improve upon alternative existing or demonstrated thin film manufacturing technologies to produce high quality TFLN for use by researchers and in DoD and commercial systems with reduced cost and capacity to scale. Offerors should plan to demonstrate the technology at the chip or wafer scale and with enough iterations to extract meaningful statistical data on scalability, yield, and cost. Work plans are expected to build towards the objectives stated above through process development and use this data to map out the parameter space of the manufacturing technology. Aside from establishing viability, yield, and cost, a key component is to demonstrate the ability to quickly and cheaply adapt the technology to produce TFLN of varying thickness, crystal geometry, and/or substrate. Offerors are expected to work with researchers, device designers or manufacturers to ensure compatibility of their process and to produce a demonstration device using their material. For any proposals requiring heterogenous integration, that should be demonstrated under this effort. Preference will be given towards those technologies that can produce homogenous lithium niobate on insulator at the 3-4 inch wafer scale. Desired characterization includes surface roughness, total thickness variation, crystallinity, flatness, and film thickness. Bond strength should be tested at relevant operating temperatures. The final report should include a qualitative and quantitative cost and scaling analysis comparing the developed technology to the current technologies described above. PHASE I: Under a Phase I award the awardee shall provide a qualitative and quantitative study of the proposed solution along with experimental proof of their process. This includes justifying, insofar as possible, the scientific and technical merit and feasibility of ideas appearing to have commercial potential. At a minimum, the offeror must: (1) Demonstrate capability and competence with the proposed manufacturing process by providing initial results producing thin film lithium niobate or past work with a comparable material, in which case they shall also provide technical justification for applicability to lithium niobate and the topic objectives. (2) Provide a comparison with the existing processes described in the topic description in the context of the stated objectives. This must specifically include substantiated cost estimates for obtaining or producing the proposed wafer compositions using established techniques and estimated cost savings. (3) Define a complete, clear, realistic, and actionable plan with the proposed solution and the AF customer. Describe if/how the demonstration can be used by other DoD or Governmental customers. PHASE II: Under the Phase II effort, the awardee shall sufficiently develop a manufacturing process capable of producing thin film lithium niobate and characterize parameters including surface roughness, total thickness variation, crystallinity, flatness, and film thickness. Through sufficient statistical data the manufacturing process will be evaluated by establishing a baseline cost per wafer or cost savings per fabricated device, a cost-scaling estimate for volume manufacturing (to 1000s of wafers or 10000s of devices a year), and yield estimates. The offeror must demonstrate through fabrication the ability to modify the manufacturing process to produce multiple compositions of varying film thickness and/or substrate and document the non-recurring engineering (NRE) cost and process to do so. Finally, suitability for RF or photonics applications must be demonstrated through device fabrication and/or heterogenous integration. Temperature and mechanical stability of bonded material should be verified to relevant device operating conditions. At the end of the effort material shall be provided to Department of the Air Force for independent verification. Identification of manufacturing/production issues and or business model modifications required to further improve product or process relevance to improved sustainment costs and material availability should be documented. These Phase II awards are intended to provide a path to commercialization, not the final step for the proposed solution. PHASE III DUAL USE APPLICATIONS: The awardee may pursue commercialization of the thin film lithium niobate manufacturing process developed in Phase II for transitioning expanded mission capability to a broad range of potential government and civilian users and alternate mission applications. Direct access with end users and government customers will be provided with opportunities to receive Phase III awards for providing the government additional research & development, or direct procurement of products and services developed in coordination with the program. This work should meet Technology Readiness Level 5 and Manufacturing Readiness Level 4 before entry into a Phase III. For technologies requiring heterogenous integration, special tooling or skillsets, or other large capital investment, suitable partnerships should be identified (e.g. a foundry such as AIM Photonics). Phase III candidates should have a viable plan to scale to high volume (1000s of wafers or 10000s of devices) and plan to supply both the DoD and commercial markets. REFERENCES: 1. Karan Prabhakar, Ryan J. Patton, Ronald M. Reano; Stress reduction and wafer bow accommodation for the fabrication of thin film lithium niobate on oxidized silicon. J. Vac. Sci. Technol. B, Vol 39. (2021); 2. Chia-Cheng Wu, Ray-Hua Horng, Dong-Sing Wuu, Tsai-Ning Che, Shih-Shian Ho, Chia-Jen Ting and Hung-Yin Tsai; "Thinning Technology for Lithium Niobate Wafer by Surface Activated Bonding and Chemical Mechanical Polishing." Japanese Journal of Applied Physics, Vol 45, Page 3822. (2006); 3. Ryo Takigawa, Eiji Higurashi, Tadatomo Suga, Tetsuya Kawanishi; "Room-temperature transfer bonding of lithium niobate thin film on micromachined silicon substrate with Au microbumps."Sensors and Actuators A: Physical, Vol 264, Pages 274-281. (2017); 4. Payam Rabiei, Jichi Ma, Saeed Khan, Jeff Chiles, and Sasan Fathpour, "Heterogeneous lithium niobate photonics on silicon substrates," Opt. Express 21, 25573-25581 (2013); 5. Adcock, J.C., Ding, Y. Quantum prospects for hybrid thin-film lithium niobate on silicon photonics. Front. Optoelectron. 15, 7 (2022); 6. G. Poberaj, et al. "Ion-sliced lithium niobate thin films for active photonic devices" Opt. Mater., 31, pp. 1054-1058 (2009); KEYWORDS: thin-film; lithium niobate; lithium niobate on insulator; low cost; chemical mechanical polishing; wafer manufacturing; heterogeneous integration; wafer bonding; microwave photonics
