Foundry-Enabled Patterning of Diamond Quantum Microchiplets for Scalable Quantum Photonics

TL;DR

This work tackles the scaling bottleneck in diamond quantum photonics by shifting pattern-definition from diamond to foundry-processed silicon masks that are transferred onto diamond via micro-transfer printing. The authors demonstrate wafer-scale patterning of diamond quantum microchiplets (QMCs) comprising photonic-crystal nanobeam cavities coupled to tin-vacancy emitters, achieving improved optical performance and compatibility with PIC/CMOS platforms. Key results include cavity resonances around 620–635 nm with Q factors up to ~5000, high chiplet yield, and a tunable spectral window of up to ~10 nm via gas adsorption to align cavities with emitter transitions, enabling Purcell-enhanced coupling. The study shows that chiplet-based, foundry-compatible fabrication offers a practical path toward large-scale, heterogeneous quantum photonic systems, with robust post-fabrication replacement and integration into existing semiconductor manufacturing infrastructure.

Abstract

Quantum technologies promise secure communication networks and powerful new forms of information processing, but building these systems at scale remains a major challenge. Diamond is an especially attractive material for quantum devices because it can host atomic-scale defects that emit single photons and store quantum information with exceptional stability. However, fabricating the optical structures needed to control light in diamond typically relies on slow, bespoke processes that are difficult to scale. In this work, we introduce a manufacturing approach that brings diamond quantum photonics closer to industrial production. Instead of sequentially defining each device by lithography written directly on diamond, we fabricate high-precision silicon masks using commercial semiconductor foundries and transfer them onto diamond via microtransfer printing. These masks define large arrays of nanoscale optical structures, shifting the most demanding pattern-definition steps away from the diamond substrate, improving uniformity, yield, and throughput. Using this method, we demonstrate hundreds of diamond "quantum microchiplets" with improved optical performance and controlled interaction with quantum emitters. The chiplet format allows defective devices to be replaced and enables integration with existing photonic and electronic circuits. Our results show that high-quality diamond quantum devices can be produced using scalable, foundry-compatible techniques. This approach provides a practical pathway toward large-scale quantum photonic systems and hybrid quantum-classical technologies built on established semiconductor manufacturing infrastructure.

Figures (5)

• Figure 1: Foundry-enabled diamond QMC fabrication workflow. a) Schematic of a diamond QMC, comprising nanophotonic waveguides and cavities patterned in single-crystal diamond using a transfer-printed silicon (Si) hard mask. Arrays of QMC chiplets are fabricated at the wafer scale. b) Wafer-scale heterogeneous integration of diamond QMCs onto CMOS substrates, enabling dense co-integration of diamond nanophotonics with electronic circuitry. c) Heterogeneous integration of diamond QMCs on photonic integrated circuits (PICs), illustrated with representative layouts and microscope/SEM images showing photonic routing and cavity arrays. d) Fabrication workflow: QMC and mask design, foundry mask fabrication, $\mu$-transfer printing of the Si hard mask onto diamond, and diamond etching to define QMCs. This work addresses the foundry-enabled silicon mask fabrication and diamond patterning steps highlighted here; heterogeneous integration with PIC and CMOS platforms is shown as an enabled capability.
• Figure 2: Schematic illustration of the fabrication process. a) Silicon hard masks patterned on commercial silicon-on-insulator (SOI) wafers using foundry lithography are released and transferred onto bulk diamond substrates via micro-transfer printing. The transferred mask defines arrays of nanobeam cavities and waveguides during subsequent oxygen plasma etching, followed by mask removal to yield suspended diamond nanophotonic structures. b) Optical micrographs of the fabrication process: (i) silicon mask prior to release, (ii) etched and suspended silicon membrane mask (shown in white-light illumination highlighting interference effects), (iii) mask stamped on diamond, and (iv) fabricated diamond QMCs. (c-e) Scanning electron microscope (SEM) images of the resulting diamond nanophotonic structures, highlighting waveguides and cavity regions patterned with high fidelity.
• Figure 3: Optical characterization and cavity measurements. a) Optical microscope image of fabricated nanostructures. b) Raster scan of a single chiplet showing summed confocal photoluminescence (PL) at each location. c) PL spectrum from the location marked by the blue dot in b). d) Cavity characterization for a single chiplet. i) Hyperspectral map of the region in the dashed box in b. Cavities are identified using a peak finding algorithm and colored according to their center frequency. ii) Example spectrum on (dark blue) and off (light blue) a cavity. iii) and iv) histograms showing distribution of center frequency and $Q$ for this chiplet. e) Cavity characterization across the entire mask for all 120 chiplets. i), ii),iii) histograms showing center frequency and $Q$ distribution, as well as fill fraction. iv) spatial maps of center frequency and $Q$ with standard deviations for each (<s>) shown in v).
• Figure 4: Representative gas tuning of cavity resonances and Purcell enhancement of coupled SnVs. a) Cavity reflection spectrum showing a Fano resonance near 625 nm. i) Overlaid reflection and PL spectra for the cavity in a). b) Reflection spectrum as a function of time as nitrogen gas is added to the chamber. c) PL spectra showing the 645nm SnV peak as a function of time as the cavity from b) is tuned into resonance using nitrogen deposition.
• Figure 5: Analysis of fabrication-induced variation. (a-c) SEM-based extraction of geometric parameters from fabricated nanobeam cavities. (d-e) Sensitivity of cavity resonance wavelength to geometric variations, obtained from FDTD simulations. (f-i) Comparison between experimentally measured wavelength distributions and the range of thickness variation required to account for the observed optical spread. (j-l) Independent thickness measurements obtained from tilted SEM images using geometric projection of the waveguide cross-section. Together, these analyses indicate that thickness variation is the dominant contributor to cavity wavelength inhomogeneity and that its magnitude is consistent with direct geometric measurements.