Energy Spectroscopy for Low-energy Photons Using Diamond Detector Combined with Micro-CMOS Preamplifier
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2024-01-25 |
| Journal | Sensors and Materials |
| Authors | Kengo Oda, Junichi H. Kaneko, Daisuke Matsunaga, Takanori Hanada, Tsukasa Mizukoshi |
| Institutions | Horiba (Japan), Hokkaido University |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: MPCVD Diamond for Soft X-ray Spectroscopy
Section titled âTechnical Documentation & Analysis: MPCVD Diamond for Soft X-ray SpectroscopyâExecutive Summary
Section titled âExecutive SummaryâThis research successfully demonstrates the potential of single-crystal CVD (SCD) diamond detectors for high-resolution, room-temperature soft X-ray spectroscopy, validating key material properties achievable through advanced MPCVD synthesis.
- High-Resolution Detection: Achieved an energy resolution of $(484 \pm 10) \text{ eV}$ FWHM for $5.9 \text{ keV}$ X-rays, comparable to cooled silicon drift detectors, but operating efficiently at room temperature.
- Material Validation: Confirmed that $300 \text{ ”m}$ thick, electronics-grade SCD provides excellent charge carrier transport properties essential for utilizing the entire crystal thickness as the sensitive layer.
- System Miniaturization: Successful integration of the SCD detector via wire bonding to a micro-CMOS charge-sensitive preamplifier (13 fF feedback capacitance) minimizes parasitic noise and enables compact system design.
- Ultra-Low Noise Operation: The intrinsic low leakage current of the SCD ($\sim 1 \text{ pA}$ at $-120 \text{ V}$) is critical for achieving a high signal-to-noise ratio (SNR) necessary for soft X-ray measurements.
- Excellent Linearity: The detector response demonstrated high linearity ($R^{2} = 0.9993$) across the measured energy range of $5.9 \text{ keV}$ to $59.5 \text{ keV}$.
- Future Scalability: The findings support the development of larger area and multi-channel SCD detectors, addressing the current limitation of charge collection efficiency in low-field regions.
Technical Specifications
Section titled âTechnical SpecificationsâThe following table summarizes the critical performance metrics and material parameters extracted from the research, highlighting the capabilities of high-purity SCD for radiation detection.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Detector Material | Single-Crystal CVD Diamond | N/A | Electronics-grade, $300 \text{ ”m}$ thickness |
| Optimal Energy Resolution ($\Delta E$) | $484 \pm 10$ | eV (FWHM) | Measured for $5.9 \text{ keV}$ 55Fe X-rays at $-230 \text{ V}$ |
| $\gamma$-ray Resolution ($\Delta E$) | $3.8 \pm 0.1$ | keV (FWHM) | Measured for $59.5 \text{ keV}$ 241Am $\gamma$-rays |
| Operating Temperature | Room Temperature ($\sim 25$) | °C | Eliminates need for Peltier or cryogenic cooling |
| Optimal Bias Voltage | $-230$ | V | Voltage yielding highest energy resolution |
| Leakage Current Density | $1 \times 10^{5}$ | pA/m2 | Measured at $-120 \text{ V}$ bias |
| Energy Linearity ($R^{2}$) | $0.9993$ | N/A | High linearity between $5.9 \text{ keV}$ and $59.5 \text{ keV}$ |
| Readout Electrode Diameter | $\Phi 97$ | ”m | Ti/Au contact for CMOS connection |
| Preamplifier Feedback Capacitance | 13 | fF | Micro-CMOS charge-sensitive preamplifier |
| Detector Dimensions | $3 \times 3 \times 300$ | mm x mm x ”m | Sample size used in the experiment |
Key Methodologies
Section titled âKey MethodologiesâThe successful fabrication and testing of the diamond soft X-ray detector relied on precise material selection, surface preparation, and micro-fabrication techniques.
- Material Selection: Use of high-quality, electronics-grade single-crystal CVD diamond (SCD) to ensure excellent charge carrier transport properties and low intrinsic defect density.
- Surface Preparation: Chemical cleaning and oxygen-termination of the SCD surface using hot mixed acid, dichromic acid, and hot aqua regia to achieve high surface insulation and suppress leakage current.
- Incident Electrode Fabrication: A $100 \text{ nm}$ thick Aluminum (Al) electrode was deposited on the incident surface via thermal evaporation, covering the $3 \text{ mm} \times 3 \text{ mm}$ area.
- Readout Electrode Fabrication: A $100 \text{ nm}$ thick Titanium/Gold (Ti/Au) micro-electrode ($\Phi 97 \text{ ”m}$) was patterned on the readout side using photolithography.
- CMOS Integration: A micro-CMOS charge-sensitive preamplifier was placed adjacent to the detector and connected to the Ti/Au readout electrode using gold wire ultrasonic bonding to minimize parasitic capacitance ($C_{T}$).
- Spectroscopy Setup: The detector assembly was housed in an aluminum enclosure for electromagnetic shielding. Measurements were performed in air at room temperature using 55Fe and 241Am sources, with signals processed by a shaping amplifier (optimal shaping time $0.5 \text{ ”s}$) and multichannel analyzer (MCA).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD is uniquely positioned to supply the high-purity MPCVD diamond materials and custom fabrication services required to replicate, scale, and advance this soft X-ray detector technology. Our capabilities directly address the material specifications and future development goals outlined in the research.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate the high-performance detector described, 6CCVD recommends the following materials:
- High Purity SCD (Detector Grade): Required for achieving the low leakage current ($\sim 1 \text{ pA}$) and high charge carrier mobility necessary for excellent energy resolution at room temperature. Our SCD material is available in thicknesses from $0.1 \text{ ”m}$ up to $500 \text{ ”m}$, matching the $300 \text{ ”m}$ thickness used in this study.
- Large Area SCD Substrates: For future development toward larger sensitive areas (e.g., $8 \text{ mm} \times 8 \text{ mm}$ or $10 \text{ mm} \times 10 \text{ mm}$) mentioned in the paper, 6CCVD provides high-quality SCD substrates suitable for subsequent epitaxial growth or direct use as detector elements.
Customization Potential
Section titled âCustomization PotentialâThe research highlights the need for precise dimensions and specialized electrode structures. 6CCVD offers comprehensive customization services to meet these requirements:
| Research Requirement | 6CCVD Capability | Technical Advantage |
|---|---|---|
| Custom Dimensions | Plates/wafers up to $125 \text{ mm}$ (PCD) and large SCD substrates. | Enables scaling to multi-channel arrays and larger sensitive areas for practical applications. |
| Precise Thickness | SCD and PCD available from $0.1 \text{ ”m}$ to $500 \text{ ”m}$. | Allows optimization of detector thickness for specific photon energy ranges (e.g., matching the $300 \text{ ”m}$ free path of $5.9 \text{ keV}$ photons). |
| Custom Metalization | In-house deposition of Au, Pt, Pd, Ti, W, Cu, and Al. | We can replicate the required Ti/Au micro-electrode ($\Phi 97 \text{ ”m}$) and the Al incident electrode, or develop complex multi-layer contacts (e.g., for guard rings to suppress leakage current). |
| Surface Quality | Polishing capability to achieve $R_{a} < 1 \text{ nm}$ (SCD). | Ensures the ultra-high insulation and low surface leakage current critical for high SNR soft X-ray detection. |
| Micro-Patterning | Advanced laser cutting and photolithography services. | Essential for fabricating the micro-readout electrodes and complex multi-channel structures needed to improve charge collection efficiency across the entire crystal volume. |
Engineering Support
Section titled âEngineering SupportâThe challenges noted in the paperâspecifically incomplete charge collection in low-field regions and the need for multi-channel readoutârequire deep material and device physics expertise. 6CCVDâs in-house PhD team specializes in optimizing diamond properties for radiation detection.
We can assist researchers and engineers with:
- Material Selection: Consulting on the optimal SCD grade and thickness for specific soft X-ray or $\gamma$-ray applications.
- Device Design: Support in designing electrode geometries (including guard rings) and metalization schemes to maximize charge collection efficiency and minimize leakage current, thereby improving energy resolution.
- Process Optimization: Guidance on surface termination and cleaning protocols to ensure the high insulation required for low-noise operation at room temperature.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
To measure soft X-ray energy spectra at room temperature using diamond, we connected a 300-ÎŒm-thick single-crystal CVD diamond radiation detector with excellent charge carrier transport properties to a micro-preamplifier fabricated using CMOS technology via Ί97 ÎŒm electrodes.We attempted to measure the photon energy spectrum from a few keV to 60 keV at room temperature by reducing the leakage current and the total input capacitance to the preamplifier.The energy resolution for 5.9 keV X-rays from 55 Fe was ÎE = (484 ± 10) eV (FWHM).