Diamond Membranes Enable Scalable Quantum Technologies and Enhanced Device Fabrication.

The pursuit of scalable quantum technologies necessitates advanced materials and fabrication techniques, particularly in the creation of diamond-based devices which utilise the unique quantum properties of colour centres, such as nitrogen-vacancy (NV) centres, to store and process information. Achieving both high precision and large-scale production of these structures remains a significant challenge. Researchers at the University of Basel and the École Polytechnique Fédérale de Lausanne (EPFL) address this issue with a novel approach to diamond nanostructuring, detailed in their paper, ‘Homogeneous Free-Standing Nanostructures from Bulk Diamond over Millimeter Scales for Quantum Technologies’. Andrea Corazza, Silvia Ruffieux, Yuchun Zhu, Claudio A. Jaramillo Concha, Yannik Fontana, Christophe Galland, Richard J. Warburton, and Patrick Maletinsky, demonstrate a refined photolithographic process capable of producing millimetre-scale, atomically smooth diamond membranes, down to 70 nanometres in thickness, suitable for fabricating large arrays of photonic nanostructures and enabling robust, scalable quantum devices. These membranes exhibit low surface roughness, measured at less than 200 picometres, and maintain a high degree of homogeneity, crucial for consistent device performance.

Recent advances in diamond microfabrication demonstrate a significant improvement in deep reactive ion etching (DRIE) techniques, yielding high-quality membranes suitable for both quantum and nanomechanical applications. The process addresses longstanding challenges associated with structuring diamond, traditionally hampered by surface damage and limitations in achieving both high aspect ratios and uniformity, by consistently producing atomically smooth surfaces with minimal defects. This enables the creation of millimetre-scale, thin diamond membranes, reaching thicknesses down to 70 nanometres, while maintaining exceptional structural integrity and opening new avenues for device innovation.

The DRIE process utilises a pulsed gas chemistry, strategically employing oxygen to form a passivating oxide layer, sulphur hexafluoride to etch the diamond, and argon as a sputtering gas to remove the oxide and expose fresh material. Performing the etching at a relatively low temperature, approximately 200°C, further minimises defect formation and preserves the crystalline structure of the diamond. This combination achieves high selectivity, enabling rapid etching of diamond without significant damage to other materials potentially present in the structure, and ensures the creation of robust and reliable microstructures. Selectivity refers to the process’s ability to etch the target material, in this case diamond, at a much faster rate than any surrounding materials.

Characterisation utilising atomic force microscopy (AFM) confirms the reduced surface roughness achieved with this new DRIE process, demonstrably improving upon traditional fabrication methods and establishing a new benchmark for diamond microfabrication. Scanning electron microscopy (SEM) visualises the etched structures, validating their geometry and confirming the successful creation of large fields of free-standing photonic nanostructures, which are crucial for hosting nitrogen-vacancy (NV) centres and building nanomechanical resonators. These structures exhibit exceptional homogeneity and structural integrity, paving the way for advanced device functionalities. Photonic nanostructures are microscopic arrangements designed to manipulate light, and nanomechanical resonators are tiny vibrating structures used to detect forces or measure mass.

The research team integrates a refined photolithography-based strategy with a micromanipulation station and binary markers to ensure precise control and characterisation throughout the fabrication process. Binary markers facilitate accurate platelet orientation during AFM measurements, providing precise topographical data, while the micromanipulation station enables pick-and-place transfer for heterogeneous integration, allowing for the creation of complex device architectures. This combination of techniques yields robust, contamination-free structures directly suitable for use in quantum sensing, communication technologies, and advanced nanomechanical devices. Heterogeneous integration refers to combining different materials or components into a single device.

The process offers enhanced scalability and compatibility with diverse integration strategies, enabling the creation of larger and more complex devices. Researchers demonstrate the ability to fabricate large fields of free-standing photonic nanostructures, validating the scalability and versatility of the DRIE process and opening possibilities for mass production. This scalability, combined with the compatibility with various integration techniques, positions this process as a key enabler for the development of next-generation quantum and nanomechanical devices.

These structures are essential components for advanced quantum sensing applications, particularly those leveraging nitrogen-vacancy (NV) centres in diamond, where surface defects negatively impact coherence times. The smooth, defect-free surfaces maximise NV centre performance, enhancing the sensitivity of quantum sensors and enabling the development of more accurate and reliable sensing devices. NV centres are point defects in the diamond lattice that exhibit quantum mechanical properties, making them useful for sensing magnetic fields, electric fields, and temperature. Coherence time refers to how long these quantum properties can be maintained.

Researchers continue to refine the DRIE process, exploring new materials and techniques to further improve the quality and performance of diamond microstructures. Future research will focus on developing even more precise and efficient etching methods, as well as exploring new applications for diamond microstructures in areas such as quantum computing, sensing, and energy storage. This ongoing research promises to unlock the full potential of diamond as a material for advanced technological applications.