Cryogenic Integration for Quantum Computer Using Diamond Color Center Spin Qubits
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-05-01 |
| Authors | Toshiki Iwai, Kenichi Kawaguchi, T Miyatake, Tetsuro Ishiguro, Shoichi Miyahara |
| Institutions | Fujitsu (Japan), Delft University of Technology |
| Citations | 1 |
| Analysis | Full AI Review Included |
Cryogenic Integration for Quantum Computer Using Diamond Color Center Spin Qubits
Section titled âCryogenic Integration for Quantum Computer Using Diamond Color Center Spin QubitsâAnalysis of Iwai et al. (2023) for 6CCVD Engineering & Sales
This document analyzes the research on robust cryogenic integration techniques for diamond-based quantum processors, highlighting how 6CCVDâs specialized MPCVD diamond materials and custom fabrication services directly enable the scaling and reliability demonstrated in this work.
Executive Summary
Section titled âExecutive SummaryâThis research successfully validates a highly reliable cryogenic integration method essential for scaling diamond color center quantum computers.
- Core Achievement: Demonstrated stable electrical connections using gold (Au) stud bump flip-chip bonding between a test chip and an interposer down to 10 K.
- Application: Enables vertical integration of quantum photonic chips (diamond qubits) with electrical control circuits (interposers/antennae) for large-scale quantum processors.
- Reliability: The bonded structure exhibited exceptional mechanical robustness, achieving an average shear strength of 67.4 g per bump.
- Electrical Performance: Measured line resistance was extremely low (3.32-3.67 Ω) at the critical operating temperature of 10 K.
- Methodology Advantage: Gold stud bump bonding avoids contamination risks associated with traditional solder bumps, preserving the integrity of sensitive quantum photonic circuits.
- Scaling Potential: The successful integration of 15 x 15 mm2 test chips confirms the feasibility of scaling integration technology for systems targeting 102 qubits and larger.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the experimental results regarding the integrated structure and bonding process.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Minimum Operating Temperature | 10 | K | Confirmed stability of flip-chip connection (Test Chip to Interposer). |
| PCB Integration Temperature | 80 | K | Confirmed stability of packaged chip connection to PCB via wire bond. |
| Flip-Chip Bonding Temperature | 350 | °C | Thermocompression bonding head temperature. |
| Bonding Pressure | 50 | N | Applied force during thermocompression bonding. |
| Bonding Time | 90 | s | Duration of thermocompression bonding. |
| Line Resistance (Cryogenic) | 3.32 - 3.67 | Ω | Measured resistance of 16 lines at 10 K. |
| Line Resistance (Room Temp) | 8.71 - 9.54 | Ω | Measured resistance of 16 lines at 300 K. |
| Average Shear Strength | 67.4 | g/bump | Mechanical robustness of the Au stud bump bonds. |
| Test Chip Dimensions | 15 x 15 | mm2 | Area designed for allocating ~102 color center qubits. |
| Interposer Dimensions | 20 x 20 | mm2 | Used for electrical control and measurement lines. |
| Metallization Stack (Thickness) | 500 / 100 / 30 | nm | Au / Ni / Ti sputtered layers on the silicon substrate. |
| Stud Bump Height (Average) | 26.0 | ”m | Measured height after thermocompression bonding. |
Key Methodologies
Section titled âKey MethodologiesâThe integration process focused on creating a stable, low-resistance electrical interface compatible with cryogenic quantum operation.
- Substrate Preparation: Silicon (Si) substrates were diced into 15 x 15 mm2 (Test Chip) and 20 x 20 mm2 (Interposer) components.
- Metallization Deposition: A metal stack of Ti (30 nm) / Ni (100 nm) / Au (500 nm) was sputtered onto the silicon substrates using a two-layer lift-off process.
- Gold Stud Bump Fabrication: Gold stud bumps were fabricated on the Test Chip using a standard wire bonder.
- Flip-Chip Bonding: Thermocompression bonding was executed using a flip-chip bonder under controlled conditions (350 °C, 50 N, 90 s) to achieve reliable Au-Au bonding.
- Cryogenic Measurement (Chip/Interposer): Electrical resistance was measured between 10 K and 300 K in a vacuum environment using a mechanical cryogenic prober station.
- Packaged Integration: The flip-chip bonded structure was mounted onto a Printed Circuit Board (PCB) and connected via gold wire bonding for further testing at 80 K.
- Mechanical Analysis: Chip shear strength was tested at a speed of 50 ”m/s to quantify the mechanical reliability of the gold stud bumps.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe successful integration of diamond color center qubits relies fundamentally on high-quality diamond material and precise interface engineering. 6CCVD provides the necessary MPCVD diamond substrates and customization services to replicate and advance this critical cryogenic integration technology.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate or extend this research using actual quantum chips, the following 6CCVD materials are required:
- Optical Grade SCD (Single Crystal Diamond): Essential for hosting high-coherence spin qubits (e.g., NV- centers, SiV- centers). Our SCD features ultra-low impurity levels (< 1 ppb N) and minimal strain, maximizing qubit coherence time (T2).
- High-Purity SCD Substrates: Required for epitaxial growth or ion implantation to create shallow color centers necessary for efficient photonic coupling.
- BDD (Boron-Doped Diamond): For applications requiring integrated electrical components or highly conductive diamond layers (e.g., integrated microwave antennae or ground planes), 6CCVD offers custom BDD layers.
Customization Potential
Section titled âCustomization PotentialâThe integration scheme requires precise material dimensions and tailored electrical interfaces, capabilities where 6CCVD excels:
| Research Requirement | 6CCVD Customization Service | Technical Advantage |
|---|---|---|
| Large-Scale Substrates (Scaling beyond 15 x 15 mm2) | Custom Dimensions up to 125 mm (PCD) / Large Area SCD. We supply SCD plates up to 500 ”m thick and substrates up to 10 mm thick, meeting the demands of large-scale quantum processors. | Enables the fabrication of quantum chips containing 103 or more qubits on a single, high-quality diamond platform. |
| Custom Metallization Stacks (Ti/Ni/Au used for bonding) | Internal Metalization Capability (Au, Pt, Pd, Ti, W, Cu). We can deposit multi-layer stacks (e.g., Ti/Pt/Au) optimized for adhesion, diffusion barriers, and specific bonding techniques like the Au stud bump process demonstrated. | Guarantees robust, low-loss electrical contacts that maintain integrity during cryogenic cycling (10 K to 300 K). |
| Ultra-Low Surface Roughness (For Photonic Circuits) | SCD Polishing to Ra < 1 nm. Our proprietary polishing process achieves near-atomic flatness on the SCD surface. | Critical for minimizing optical scattering losses and enabling high-fidelity fabrication of integrated photonic components (waveguides, switches) directly on the diamond. |
| Precise Thickness Control (Qubit layer optimization) | SCD Thickness Control (0.1 ”m to 500 ”m). We offer precise control over the thickness of the active diamond layer. | Allows researchers to optimize the depth of the color centers and the geometry of the integrated photonic circuits for maximum efficiency. |
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house team of PhD material scientists and engineers specializes in diamond for quantum applications. We offer comprehensive support for projects requiring:
- Material Selection: Assistance in choosing the optimal SCD grade (e.g., low-strain, specific nitrogen concentration) to maximize qubit coherence and yield.
- Interface Design: Consultation on metal stack selection and geometry to ensure compatibility with advanced packaging techniques like the cryogenic Au stud bump flip-chip bonding demonstrated in this paper.
- Custom Fabrication: Support for laser cutting, dicing, and polishing services to meet the precise dimensional and surface quality requirements of complex quantum chips.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
<p>For quantum computing modules using diamond color centers, we propose an integrated structure of a quantum chip with photonic circuits and an interposer with electric circuits. The chip and interposer are connected via gold stud bumps using flip-chip bonding technology. For evaluating the proposed integrated structure, we bonded a test chip of 15 Ă 15 mm2, corresponding to the area that allows the allocation of color center qubits in the order of 102, with an interposer of 20 Ă 20 mm2, including test measurement lines. We confirm all connections of 16 lines with two bumps for each line at 10 K. The resistance of the lines with two bumps at 10 K is ~ 3.5O, These resistances are mainly attributed to the gold lines on the interposer, which is confirmed by simulations. The shear strength of the flip-chip bonded structure is 67 g/bump. It is larger than that of previous reports where the chips passed the standard temperature cycle test. Moreover, we integrate the flip-chip bonded structure with a printed circuit board (PCB). We confirm a connection between the connector terminal of the PCB and the test chip at 80 K. It is shown that the integrated structure using gold stud bumps has a potentially highly reliable connection at cryogenic temperature. These results will lead to realizing large-scale diamond spin quantum processors. </p>
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 2009 - Gold to gold thermosonic bonding Characterization of bonding parameters
- 2017 - Entanglement distillation between solid-state quantum network nodes [Crossref]