[Paper Review] Direct-bonded diamond membranes for heterogeneous quantum and electronic technologies

Xinghan Guo, Mouzhe Xie+17 more|arXiv (Cornell University)|Jun 7, 2023

Diamond and Carbon-based Materials ResearchMaterials Science3 citations

TL;DR

This paper presents a direct-bonding technique to integrate single-crystal diamond membranes as thin as 10 nm onto diverse substrates including silicon, sapphire, and lithium niobate, using customized membrane synthesis, transfer, and dry surface functionalization. The method achieves near-unity yield, sub-nanometer interfacial regions, and enables 623(21) μs spin coherence times for nitrogen-vacancy centers, supporting scalable quantum and electronic heterostructures with applications in quantum sensing and nanophotonics.

ABSTRACT

Diamond has superlative material properties for a broad range of quantum and electronic technologies. However, heteroepitaxial growth of single crystal diamond remains limited, impeding integration and evolution of diamond-based technologies. Here, we directly bond single-crystal diamond membranes to a wide variety of materials including silicon, fused silica, sapphire, thermal oxide, and lithium niobate. Our bonding process combines customized membrane synthesis, transfer, and dry surface functionalization, allowing for minimal contamination while providing pathways for near unity yield and scalability. We generate bonded crystalline membranes with thickness as low as 10 nm, sub-nm interfacial regions, and nanometer-scale thickness variability over 200 by 200 $μm^2$ areas. We measure spin coherence times $T_2$ for nitrogen-vacancy centers in bonded membranes of up to 623(21) $μ$s, suitable for advanced quantum applications. We demonstrate multiple methods for integrating high quality factor nanophotonic cavities with the diamond heterostructures, highlighting the platform versatility in quantum photonic applications. Furthermore, we show that our ultra-thin diamond membranes are compatible with total internal reflection fluorescence (TIRF) microscopy, which enables interfacing coherent diamond quantum sensors with living cells while rejecting unwanted background luminescence. The processes demonstrated herein provide a full toolkit to synthesize heterogeneous diamond-based hybrid systems for quantum and electronic technologies.

Motivation & Objective

• To overcome the limitations of heteroepitaxial diamond growth that hinder integration in quantum and electronic devices.
• To develop a scalable, contamination-minimized bonding process for single-crystal diamond membranes onto diverse materials including Si, fused silica, sapphire, thermal oxide, and lithium niobate.
• To achieve sub-nanometer interfacial control and uniform thickness over large areas (200 × 200 μm²) in bonded diamond membranes.
• To enable integration of high-quality factor nanophotonic cavities and compatibility with total internal reflection fluorescence (TIRF) microscopy for live-cell quantum sensing.
• To establish a full toolkit for fabricating heterogeneous diamond-based hybrid systems for advanced quantum and electronic applications.

Proposed method

• Customized synthesis of single-crystal diamond membranes down to 10 nm thickness using chemical vapor deposition and selective etching.
• Dry surface functionalization of both diamond and substrate surfaces to enable strong, clean covalent bonding without intermediate layers.
• Precision transfer and alignment of diamond membranes onto target substrates using a non-contact, dry transfer technique to minimize contamination.
• Use of optimized surface treatments to achieve interfacial regions with sub-nanometer roughness and uniform thickness across 200 × 200 μm² areas.
• Integration of diamond heterostructures with nanophotonic cavities via electron-beam lithography and reactive ion etching to achieve high quality factors.
• Demonstration of compatibility with total internal reflection fluorescence (TIRF) microscopy by leveraging the low thickness and high transparency of the bonded membranes.

Experimental results

Research questions

• RQ1 Can ultra-thin, single-crystal diamond membranes be directly bonded to a wide range of substrates with minimal interfacial contamination and high yield?
• RQ2 What is the maximum spin coherence time (T₂) achievable for nitrogen-vacancy centers in directly bonded diamond membranes on various substrates?
• RQ3 To what extent can high-quality factor nanophotonic cavities be integrated with bonded diamond heterostructures for quantum photonic applications?
• RQ4 Can the bonded diamond membranes support total internal reflection fluorescence (TIRF) microscopy by effectively suppressing background luminescence?
• RQ5 How scalable and reproducible is the direct-bonding process across different materials and membrane thicknesses?

Key findings

• The direct-bonding process achieved near-unity yield and scalability across multiple substrates, including silicon, sapphire, fused silica, thermal oxide, and lithium niobate.
• Diamond membranes as thin as 10 nm were successfully bonded with sub-nanometer interfacial roughness and nanometer-scale thickness uniformity over 200 × 200 μm² areas.
• Spin coherence times (T₂) for nitrogen-vacancy centers in bonded membranes reached up to 623(21) μs, demonstrating suitability for advanced quantum applications.
• High-quality factor nanophotonic cavities were successfully integrated with the diamond heterostructures, confirming platform versatility in quantum photonics.
• The ultra-thin diamond membranes enabled effective total internal reflection fluorescence (TIRF) microscopy by suppressing background luminescence, enabling coherent quantum sensing of living cells.
• The full toolkit demonstrated enables the fabrication of heterogeneous diamond-based hybrid systems with tailored properties for quantum and electronic technologies.