Energy Spectroscopy for Low-energy Photons Using Diamond Detector Combined with Micro-CMOS Preamplifier
At a Glance
Section titled “At a Glance”| 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 |
Executive Summary
Section titled “Executive Summary”This study successfully demonstrated high-resolution soft X-ray energy spectroscopy using a single-crystal CVD diamond detector operating at room temperature, leveraging diamond’s ultra-low leakage current and excellent carrier transport properties.
- Core Achievement: Achieved an energy resolution of (484 ± 10) eV (FWHM) for 5.9 keV X-rays (55Fe source) at room temperature, a significant step toward achieving performance comparable to cooled silicon drift detectors.
- Detector Design: A 300 µm thick electronics-grade CVD diamond was coupled to a micro-CMOS charge-sensitive preamplifier featuring an extremely low feedback capacitance of 13 fF.
- Noise Reduction: High signal-to-noise ratio was achieved by minimizing total input capacitance (CT) and utilizing the diamond’s inherent low leakage current (measured at approximately 1 pA at -120 V).
- Energy Range and Linearity: The detector successfully measured photons across a wide range (5.9 keV to 59.5 keV), exhibiting high energy linearity with a decision count of R2 = 0.9993.
- Limitation Identified: Incomplete charge collection was observed due to the small Φ97 µm readout electrode, which limits the high electric field intensity to a small region near the contact.
- Future Direction: Development will focus on implementing a multi-channel readout method using multiple microelectrodes to ensure uniform charge collection across the entire crystal volume.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Detector Material | Single-crystal CVD Diamond | N/A | Electronics-grade (Element Six) |
| Detector Dimensions | 3 × 3 × 300 | mm | Thickness: 300 µm |
| Readout Electrode Diameter | Φ97 | µm | Ti/Au contact |
| Preamplifier Footprint | 0.5 × 0.5 | mm2 | CMOS technology (HORIBA Ltd.) |
| Preamplifier Feedback Capacitance | 13 | fF | Designed for minute signal amplification |
| Optimal Shaping Time (τs) | 0.5 | µs | Value providing highest energy resolution |
| Operating Temperature | ~25 | °C | Room temperature |
| Optimal Bias Voltage (5.9 keV) | -230 | V | Used for best resolution |
| Leakage Current (Ileak) | ~1 | pA | At -120 V bias, 25 °C |
| Energy Resolution (5.9 keV X-ray) | (484 ± 10) | eV (FWHM) | Measured using 55Fe source at -230 V |
| Energy Resolution (59.5 keV γ-ray) | 3.8 ± 0.1 | keV (FWHM) | Measured using 241Am source at -300 V |
| Energy Linearity (R2) | 0.9993 | N/A | Between 5.9 keV and 59.5 keV |
| Average E-H Pairing Energy (Diamond) | 13.1 | eV | Comparison: Si is 3.62 eV |
| Detector Capacitance (Calculated) | 120 | fF | Close to the allowable limit of the preamplifier |
| Charge Carrier μτ Product (Diamond) | 10-3 | cm2/V | Limits lateral charge collection |
| Preamplifier Rise Time (10-90%) | 20 | ns | For 5.9 keV X-rays |
Key Methodologies
Section titled “Key Methodologies”The detector fabrication and measurement setup were optimized to minimize noise and maximize charge collection efficiency for soft X-ray spectroscopy at room temperature.
- Diamond Preparation: Electronics-grade single-crystal CVD diamond (3 mm × 3 mm × 300 µm) was chemically cleaned and oxygen-terminated using hot mixed acid, dichromic acid, and hot aqua regia to ensure high surface insulation.
- Electrode Deposition:
- A large Al electrode (3 mm, 100 nm thick) was deposited on the incident surface by thermal evaporation.
- A small Ti/Au micro-electrode (Φ97 µm, 100 nm thick) was deposited on the readout side using photolithography.
- Preamplifier Integration: A micro-CMOS charge-sensitive preamplifier (13 fF feedback capacitance) was placed near the detector and connected directly to the Ti/Au readout electrode using gold wire ultrasonic bonding to minimize parasitic capacitance (CP).
- I-V Characterization: Leakage current was measured at room temperature (25 °C) under high vacuum, confirming a low value of approximately 1 pA at -120 V.
- Spectroscopy Setup: The detector was placed in an Al housing for electromagnetic shielding.
- Bias voltage (0 to -300 V) was applied to the incident Al electrode.
- Signals were processed using an ORTEC 672 shaping amplifier set to an optimal shaping time of 0.5 µs.
- Energy spectra were recorded using a multichannel analyzer (MCA).
- Simulation: A 2D electric field intensity simulation was performed using the finite element method (Elmer solver) to analyze charge collection dynamics within the 300 µm thick diamond structure.
Commercial Applications
Section titled “Commercial Applications”The development of a room-temperature, high-resolution diamond soft X-ray spectrometer addresses critical needs in fields where cooling mechanisms are impractical or restricted.
- X-ray Fluorescence (XRF) Analysis: Applicable in X-ray fluorescence analyzers, particularly for microscopes or portable devices that require soft X-ray energy spectra measurement in confined spaces without the need for Peltier cooling.
- Accelerators and Nuclear Fusion: Diamond’s high radiation resistance and high-temperature operation capability make it suitable for monitoring and diagnostics in harsh environments like nuclear reactors and fusion experiments.
- Medical and Biological Imaging: Near bioequivalence and fast response times support applications in medical diagnostics and radiation dosimetry.
- General Radiation Detection: Use as a robust, high-performance radiation detector for alpha particles, neutrons, and heavy charged particles, expanding beyond traditional silicon limitations.
- Space Applications: The ability to operate reliably at room temperature and its inherent radiation hardness make it ideal for space-based X-ray detection systems where cooling is complex and power is limited.
View Original Abstract
To measure soft X-ray energy spectra at room temperature using diamond, we connected a 300-μm-thick single-crystal CVD diamond radiation detector with excellent charge carrier transport properties to a micro-preamplifier fabricated using CMOS technology via Φ97 μm 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 ΔE = (484 ± 10) eV (FWHM).