Sub-10 nm Precision Engineering of Solid-State Defects via Nanoscale Aperture Array Mask
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-02-08 |
| Journal | Nano Letters |
| Authors | Tae-Yeon Hwang, JungâHyun Lee, Seung-Woo Jeon, YongâSu Kim, YoungâWook Cho |
| Institutions | Korea University of Science and Technology, Korea Institute of Science and Technology |
| Citations | 9 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Precision NV Center Engineering
Section titled âTechnical Documentation & Analysis: Precision NV Center EngineeringâExecutive Summary
Section titled âExecutive SummaryâThis research demonstrates a breakthrough in the deterministic positioning of Nitrogen Vacancy (NV) centers in diamond, a critical step toward scalable solid-state quantum systems.
- Precision Achievement: Sub-10 nm precision engineering of NV centers using a novel Nanoscale Aperture Array (NAA) mask combined with Electron Beam Lithography (EBL).
- Record Mask Dimensions: Achieved the smallest reported single aperture mask opening area (28 nmÂČ) and the closest center-to-center width (~10 nm) for ion implantation.
- Material Foundation: Utilized high-purity Single Crystal Diamond (SCD) substrates ([N] < 5 ppb, [B] < 1 ppb) to minimize intrinsic defects.
- Qubit Confinement: Successfully confined clusters of up to three NV spins within a 30 nm diameter EBL hole spot, verified by g(2) and ODMR measurements.
- Strong Coupling Potential: The 10 nm separation distance is suitable for realizing strong spin-spin magnetic dipolar coupling on timescales shorter than the spin coherence time (T2,Hahn).
- Future MPCVD Requirement: The study identifies the need for subsequent diamond layer re-growth via Microwave Plasma Chemical Vapor Deposition (MPCVD) to eliminate surface defects and enhance the spin coherence time (T2,Hahn), a core 6CCVD capability.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Purity (Nitrogen) | < 5 | ppb | Substrate intrinsic concentration |
| Diamond Purity (Boron) | < 1 | ppb | Substrate intrinsic concentration |
| NAA Aperture Size (da) | 5.87 ± 0.82 | nm | Optimized mean aperture diameter |
| Aperture-to-Aperture Distance | 10.7 | nm | Center-to-center separation |
| NAA Aspect Ratio | 10 | N/A | Ratio of thickness to aperture size |
| NAA Thickness | 55 | nm | Al-Si thin film thickness |
| EBL Secondary Mask Diameter | ~30 | nm | Circular hole pattern used for confinement |
| Ion Implantation Species | 14N+ | N/A | Nitrogen ions |
| Ion Implantation Energy | 10 | keV | Used for all samples |
| Ion Implantation Dose | 4 x 1013 | /cmÂČ | Target dose |
| Projected Range (SRIM) | 30.1 | nm | Penetration depth of 10 keV ions |
| Longitudinal Straggle (SRIM) | 15.3 | nm | Depth variation |
| Smallest Mask Opening Area | 28 | nmÂČ | Achieved in this work (Table 1) |
| Achieved NV-NV Coupling Distance | ~10 | nm | Moderate coupling regime |
| Average Single NV T2,Hahn | 4.5 | ”s | Limited by shallow implantation/surface noise |
| Target T2,Hahn for Strong Coupling | ~20 | ”s | Required for 10 nm separation |
| High-Temperature Annealing 1 | 800 | °C | 8 hours (NV generation) |
| High-Temperature Annealing 2 | 1100 | °C | 2 hours (NV generation) |
| Surface Annealing | 450 | °C | 4 hours (O2 termination for T2,Hahn improvement) |
Key Methodologies
Section titled âKey MethodologiesâThe deterministic placement of NV centers relied on a multi-step nanofabrication process using high-purity SCD:
- Diamond Cleaning: Substrates were cleaned via tri-acid boiling (sulfuric, perchloric, nitric acid) for >1 hour at 170 °C.
- Al-Si Thin Film Deposition: A 55 nm thick, phase-separated eutectic Al-Si thin film was deposited directly onto the diamond surface using RF sputtering.
- Parameters: Ar working pressure 0.3 mTorr, substrate temperature 100 °C, RF power 150W, deposition rate 15.8 nm/min.
- NAA Formation: Selective etching of Al nanowires was performed by immersing the samples in 5% phosphoric acid overnight, leaving the NAAs layer composed of amorphous silicon oxide.
- Secondary Masking (EBL): A secondary EBL mask (ZEP520a, ~200 nm thick) with circular hole patterns (~30 nm diameter) was applied to isolate small clusters of NAAs.
- Nitrogen Ion Implantation: 14N+ ions were implanted at 10 keV energy and a dose of 4 x 1013/cmÂČ through the double-layered NAA/EBL mask.
- NV Generation Annealing: Samples were annealed sequentially at 800 °C (8h) and 1100 °C (2h).
- Surface Termination: An additional O2 annealing process was performed at 450 °C (4h) to induce oxygen termination for improved shallow NV spin coherence.
- Characterization: Optical (PL, g(2)) and spin (ODMR, Hahn-echo T2,Hahn) measurements were performed using a home-built confocal microscope at room temperature.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research highlights the critical need for ultra-high purity diamond and advanced surface engineering techniques, both of which are core competencies of 6CCVD. Our MPCVD capabilities are essential for replicating and extending this work toward truly scalable quantum systems.
Applicable Materials
Section titled âApplicable Materialsâ| Research Requirement | 6CCVD Solution | Material Specification |
|---|---|---|
| High-Purity Substrate | Optical Grade SCD | Ultra-low [N] (< 5 ppb) and [B] (< 1 ppb) for minimal background noise and long intrinsic coherence times. |
| Scalability & Uniformity | Large Format SCD Plates | Custom dimensions up to 125mm (PCD equivalent) and large SCD plates, enabling high-throughput fabrication of quantum nodes. |
| T2,Hahn Improvement | High-Quality SCD Overgrowth | MPCVD epitaxial re-growth (0.1 ”m to 500 ”m thickness) to bury shallow NV centers, eliminating surface-related noise and achieving target T2,Hahn (> 20 ”s). |
| Masking/Etching Compatibility | Custom Thickness Substrates | SCD substrates up to 10mm thick, polished to Ra < 1 nm, ensuring optimal surface quality for subsequent nanofabrication steps (sputtering, EBL, etching). |
Customization Potential
Section titled âCustomization PotentialâThe NAA-EBL double-layer mask technique requires precise control over thin film deposition and subsequent processing. 6CCVD offers comprehensive support for these advanced requirements:
- Custom Thickness Control: We provide SCD wafers with thickness control from 0.1 ”m to 500 ”m, allowing researchers to precisely tune the depth of the implanted NV layer relative to the surface noise, a key factor in T2,Hahn optimization.
- Integrated Metalization Services: While this paper focused on Al-Si masks, future quantum device architectures often require integrated microwave delivery structures (e.g., coplanar waveguides). 6CCVD offers in-house metalization capabilities including Au, Pt, Pd, Ti, W, and Cu deposition, crucial for delivering microwave signals for ODMR and spin manipulation.
- Advanced Polishing: The success of thin film deposition (like the 55 nm Al-Si layer) relies on an atomically smooth surface. 6CCVD guarantees SCD polishing to Ra < 1 nm, ensuring uniform mask adhesion and high-fidelity pattern transfer.
Engineering Support
Section titled âEngineering SupportâThe low average T2,Hahn (4.5 ”s) observed in this study is a common challenge for shallow NV implantation. The paper correctly identifies MPCVD diamond re-growth as the solution to eliminate surface defect noise and increase coherence time (p. 13).
6CCVDâs in-house PhD team specializes in optimizing MPCVD recipes for quantum applications. We can assist researchers in designing the optimal epitaxial overgrowth layer (thickness, purity, growth rate) required for similar Scalable Qubit System projects, ensuring the buried NV centers achieve the target coherence time of 20 ”s or greater necessary for strong dipolar coupling.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Engineering a strongly interacting uniform qubit cluster would be a major step toward realizing a scalable quantum system for quantum sensing and a node-based qubit register. For a solid-state system that uses a defect as a qubit, various methods to precisely position defects have been developed, yet the large-scale fabrication of qubits within the strong coupling regime at room temperature continues to be a challenge. In this work, we generate nitrogen vacancy (NV) color centers in diamond with sub-10 nm scale precision using a combination of nanoscale aperture arrays (NAAs) with a high aspect ratio of 10 and a secondary E-beam hole pattern used as an ion-blocking mask. We perform optical and spin measurements on a cluster of NV spins and statistically investigate the effect of the NAAs during an ion-implantation process. We discuss how this technique is effective for constructing a scalable system.