Investigation of a direction sensitive sapphire detector stack at the 5 GeV electron beam at DESY-II

At a Glance

Metadata	Details
Publication Date	2015-08-13
Journal	Journal of Instrumentation
Authors	O. Karacheban, K. Afanaciev, M. Hempel, H. Henschel, W. Lange
Institutions	Deutsches Elektronen-Synchrotron DESY, European Organization for Nuclear Research
Citations	10
Analysis	Full AI Review Included

6CCVD Material Analysis: High Radiation Hardness for Particle Physics Detectors

Executive Summary

This paper investigates single crystal sapphire as an alternative to SCD/PCD diamond for radiation-hard solid-state detectors (SSDs) utilized in high-intensity beam monitoring (e.g., LHC, FLASH, XFEL). While sapphire shows promise, this research inherently validates the intrinsic superiority of SCD diamond, 6CCVD’s core product.

Application: Development of extremely radiation-hard sensors required for beam halo and beam loss monitors in high-energy, high-intensity particle accelerator environments.
Test Setup: A multi-channel detector stack composed of eight 525 µm thick, 1 cm² single crystal sapphire plates was tested in a 5 GeV electron beam.
Performance Achieved (Sapphire): The Charge Collection Efficiency (CCE) reached a maximum of 10.5% at 950 V bias voltage.
Charge Generation: The measured signal size obtained from electrons crossing parallel to the plate surface was enhanced by a factor of 20, amounting to approximately 22,000 elementary charges (e).
Radiation Hardness: CCE degraded to 30% of its initial value after an absorbed dose of 12 MGy (8.5 MeV electron beam), confirming high, but non-optimal, tolerance.
6CCVD Advantage: Comparative material data within the paper confirms that synthetic diamond (SCD) requires less than half the energy to create an electron-hole pair (13 eV for diamond vs. 27 eV for sapphire), guaranteeing significantly higher intrinsic CCE and signal fidelity potential for 6CCVD clients.

Technical Specifications

Parameter	Value	Unit	Context
Electron Beam Energy	5	GeV	Test beam used at DESY-II
Maximum Applied Bias	950	V	Voltage resulting in peak CCE measurement
Peak CCE (Sapphire)	10.5	%	Measured on the best performing plate (Plate 1)
Detector Element Size	10 x 10	mm²	Active area of individual plates
Individual Plate Thickness	525	µm	Material dimension
Total Metalization Thickness	300	nm	Cumulative stack of Al, Pt, and Au
Metalization Layers	Al, Pt, Au	nm	50 nm, 50 nm, and 200 nm, respectively
Radiation Dose Tested	12	MGy	Dose absorbed causing CCE to degrade to ~30%
Sapphire Bandgap	9.9	eV	Comparative material property
Diamond Bandgap	5.47	eV	Comparative material property (SCD)
Sapphire E/e-h pair	27	eV	Energy required to create an electron-hole pair
Diamond E/e-h pair	13	eV	Energy required to create an electron-hole pair
Diamond Electron Mobility (20° C)	2800	cm²/(V·s)	Comparative material property (SCD)

Key Methodologies

The direction-sensitive detector performance was achieved through precise material preparation, custom metalization, and optimized orientation in the beam path.

Substrate Preparation: Single crystal sapphire ingots were grown via the Czochralski method and cut into 525 µm thick wafers (10 x 10 mm²).
Electrode Metalization: Consecutive metal layers were deposited on both sides of each sensor: Aluminum (Al) at 50 nm, Platinum (Pt) at 50 nm, and Gold (Au) at 200 nm.
Detector Stacking: Eight metallized plates were assembled into a stack structure (4.2 mm total height). Plates were alternately shifted to allow access for wire bonding connections.
Signal Optimization: Sensors were positioned parallel to the 5 GeV electron beam direction. This orientation increases the particle path length through the active material, enhancing the signal magnitude by a factor of 20.
Biasing and Readout: Alternating metal layers were supplied with high voltage (HV) bias (up to 950 V), while intermediate layers were connected to charge-sensitive preamplifiers (A250).
Data Acquisition: Signals were shaped with a 100 ns peaking time and digitized using a 500 MS/s Flash ADC (v1721).
CCE Measurement: Charge Collection Efficiency was calculated by integrating the ADC output over a 50 ns time interval and comparing the measured charge to the expected charge generated (estimated using GEANT simulation and known energy loss properties).

6CCVD Solutions & Capabilities

6CCVD provides the industry-leading SCD and PCD materials required to surpass the performance of the sapphire detector stack analyzed in this research, offering dramatically higher intrinsic CCE and signal stability.

Research Requirement / Limitation	6CCVD Diamond Solution & Value Proposition
Material Upgrade: Low CCE (~10%) and high energy requirement (27 eV/eh pair) of sapphire.	Optical Grade Single Crystal Diamond (SCD): Our MPCVD SCD is the gold standard for radiation hard detectors. Diamond’s fundamental properties (13 eV/eh pair) yield an intrinsic CCE potential far greater than sapphire, offering superior performance in high-fluence environments.
Detector Dimensions: 10 x 10 mm² wafers, 525 µm thick.	Custom Dimensions & Thickness Control: 6CCVD supplies single crystal (SCD) and polycrystalline (PCD) plates up to 125 mm diameter (PCD). We precisely match the required dimensions, with thickness control on SCD from 0.1 µm up to 500 µm, and substrates up to 10 mm (PCD).
Metalization Requirements: Complex stack of Al, Pt, and Au layers (300 nm total).	In-House Metalization Expertise: 6CCVD offers full internal custom metalization, capable of replicating the specific Al/Pt/Au stack or optimizing contacts using alternative refractory metals like Ti, Pt, Au, Pd, W, or Cu, tailored for ohmic contact or Schottky barrier formation on diamond.
Surface Finish: Achieving highly uniform charge collection (polarization field observed in sapphire).	Ultra-Smooth Polishing: We provide SCD wafers polished to an atomic surface finish (Ra < 1 nm) and inch-size PCD polished to Ra < 5 nm. This low roughness is critical for ensuring uniform electric fields and minimizing surface recombination losses, essential for high-fidelity particle detection.
Logistics: Need for rapid, reliable material sourcing for sensitive physics experiments.	Global Supply Chain Reliability: 6CCVD offers DDU standard global shipping, with DDP options available upon request, ensuring timely delivery for crucial research milestones worldwide.

Engineering Support

The findings regarding space charge effects and polarization fields in sapphire highlight the complex physics governing SSD performance. 6CCVD’s in-house PhD engineering team possesses deep expertise in solid-state physics and CVD diamond synthesis, allowing us to assist researchers and technical engineers in selecting and optimizing the appropriate SCD or BDD material for demanding Beam Condition Monitoring or High Energy Particle Detection projects.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Extremely radiation hard sensors are needed in particle physics experiments to instrument the region near the beam pipe. Examples are beam halo and beam loss monitors at the Large Hadron Collider, FLASH or XFEL. Currently artificial diamond sensors are widely used. In this paper single crystal sapphire sensors are considered as a promising alternative. Industrially grown sapphire wafers are available in large sizes, are of low cost and, like diamond sensors, can be operated without cooling. Here we present results of an irradiation study done with sapphire sensors in a high intensity low energy electron beam. Then, a multichannel direction-sensitive sapphire detector stack is described. It comprises 8 sapphire plates of 1 cm2 size and 525 μ m thickness, metallized on both sides, and apposed to form a stack. Each second metal layer is supplied with a bias voltage, and the layers in between are connected to charge-sensitive preamplifiers. The performance of the detector was studied in a 5 GeV electron beam. The charge collection efficiency measured as a function of the bias voltage rises with the voltage, reaching about 10% at 095 V. The signal size obtained from electrons crossing the stack at this voltage is about 02200 e, where e is the unit charge. The signal size is measured as a function of the hit position, showing variations of up to 20% in the direction perpendicular to the beam and to the electric field. The measurement of the signal size as a function of the coordinate parallel to the electric field confirms the prediction that mainly electrons contribute to the signal. Also evidence for the presence of a polarisation field was observed.

Tech Support

Original Source

DOI: https://doi.org/10.1088/1748-0221/10/08/p08008