Characterisation of strip silicon detectors for the ATLAS Phase-II Upgrade with a micro-focused X-ray beam

At a Glance

Metadata	Details
Publication Date	2016-07-01
Journal	White Rose Research Online (University of Leeds, The University of Sheffield, University of York)
Authors	L. Poley, A. Blue, R. L. Bates, I. Bloch, Sergio Cañas Díez
Institutions	Institute of Particle and Nuclear Studies, Deutsches Elektronen-Synchrotron DESY
Citations	3
Analysis	Full AI Review Included

6CCVD Technical Documentation: Detector Characterization for ATLAS Phase-II Upgrade

Executive Summary

This analysis focuses on the characterization of silicon microstrip detector prototypes developed for the ATLAS Inner Tracker (ITk) Phase-II Upgrade at the High Luminosity LHC (HL-LHC). The extreme radiation environment (targeting fluences over 1.0 * 10¹⁶ 1 MeV neq/cm²) necessitates materials with superior radiation hardness and thermal properties, making MPCVD diamond a critical component for future iterations of high-performance tracking.

Application Focus: Characterization of 320 µm thick silicon strip sensor modules (ATLAS12 Barrel and End-cap) using a micro-focused 15 keV X-ray beam for the ATLAS HL-LHC ITk.
Radiation Challenge: The HL-LHC mandates survival rates up to 3000 fb^-1, corresponding to radiation fluences that severely degrade standard silicon performance. MPCVD diamond offers intrinsic radiation hardness and stable electronic performance in these regimes.
Key Geometric Finding: High-resolution X-ray scans revealed that the effective detection width of the strip sensors is dictated by local sensor geometry (specifically the p-stop diffusion layers and wire bond pads), rather than the nominal strip pitch.
Thermal Management Criticality: The predecessor ASIC (ABCN-25) runs at ~20 W/module. The next-generation ABC130 chip significantly reduces power (~3 W/module), but effective heat dissipation remains mandatory, pointing toward diamond heat spreaders and substrates.
6CCVD Value Proposition: 6CCVD specializes in custom single-crystal (SCD) and polycrystalline (PCD) diamond suitable for high-flux particle detection and thermal management (heat sinks), providing the foundation necessary to meet the demanding operational environment of the HL-LHC.

Technical Specifications

Parameter	Value	Unit	Context
Target Luminosity ($\mathcal{L}$)	6 * 10³⁴	cm^-2s^-1	HL-LHC design goal (2025)
Total Radiation Fluence	> 1.0 * 10¹⁶	1 MeV neq/cm²	Required survival over 10 years (3000 fb^-1)
Silicon Thickness (DUTs)	320	µm	Stereo (Barrel) and Radial (End-cap) sensors
End-cap Strip Pitch	93 to 106	µm	Wedge-shaped strip design
Barrel Strip Pitch	74.5	µm	Nominal strip pitch
Micro-focused X-ray Energy	15	keV	Photon energy used for characterization
X-ray Beam Size (FWHM)	2.6 x 1.3	µm²	Beam profile (x and y directions)
End-cap Bias Voltage (ABCN-25)	120	V	Reverse bias (over-depleted V_depletion ≈ 50 V)
Barrel Bias Voltage (ABC130)	300	V	Reverse bias (full depletion)
ABCN-25 Power Density	~20	W/module	Fabricated in 250 nm CMOS process
ABC130 Power Density (Est.)	~3	W/module	Fabricated in 130 nm CMOS process
Electron-Hole Pair Creation Energy (Si)	3.6	eV	Used to calculate charge equivalence
Charge Equivalent (15 keV photon)	0.67	fC	Corresponding to ~4200 electrons
ABC130 Readout Clock Rate	80	MHz	Achieved data readout rate

Key Methodologies

The detector prototypes were characterized using micro-focused X-ray beam scans at the Diamond Synchrotron Light Source (B16 beamline). The methodology focused on spatial resolution and threshold performance across the strips.

X-ray Source Configuration:
- A water-cooled fixed-exit double crystal monochromator provided monochromatic beam (4 - 20 keV).
- A compound refractive lens (CRL) produced the 15 keV micro-focused beam.
Beam Profiling:
- Beam size was determined by transmission scans across a 200 µm gold wire.
- Resulting beam profile (FWHM) was 2.6 µm (x) and 1.3 µm (y).
Device Mounting and Operation:
- ABCN-25 (End-cap): Operated at 120 V bias. Cooled to 10 °C on an aluminum-plated jig due to high power consumption (~300 mW/ASIC).
- ABC130 (Barrel Mini): Operated at 300 V bias. Not actively cooled due to expected low power output.
Data Acquisition and Triggering (DAQ):
- Utilized a Digilent ATLYS readout board with a Xilinx Spartan 6 LX45 FPGA.
- Machine trigger (2 MHz) was reduced to 1 kHz for acquisition control.
Scan Protocol:
- Highly automated 3D stage movement controlled via custom Python scripts.
- Threshold Scans: Performed across 3 sensor strips (190 µm or 210 µm scan length) at various thresholds (80 mV to 444 mV range).
- Spatial Resolution: Step sizes were 5 µm (ABC130) and 10 µm (ABCN-25).
Critical Investigation Points: Scans focused specifically on the influence of the p-stop regions (implanted between n-doped strips to prevent short-circuits post-irradiation) and the wire bond pad geometry on charge collection efficiency.

6CCVD Solutions & Capabilities: Enabling the Next Generation of Particle Detectors

The extreme radiation environment and demanding thermal requirements of the ATLAS ITk Phase-II Upgrade (fluences > 10¹⁶ neq/cm²) highlight the inherent limitations of silicon detectors. MPCVD diamond, with its unmatched thermal conductivity and negligible radiation damage response, offers a high-performance alternative for next-generation tracking sensors, beam monitors, and thermal management solutions.

Applicable Materials

To replicate or extend this research using diamond detectors or thermal spreaders, 6CCVD recommends the following specialized materials:

6CCVD Material	Characteristic	Application Relevance (HL-LHC ITk)
Electronic Grade PCD	Highly uniform, large-area wafers up to 125mm.	Ideal for large-area tracking sensors, mimicking or surpassing the performance of the ATLAS silicon strips in radiation harsh environments.
High Purity SCD	Low intrinsic defects, highest charge collection efficiency.	Suitable for high-precision beam monitoring or reference sensors where the highest spatial and charge resolution is required, benefiting from intrinsic resistance to radiation damage.
Boron-Doped Diamond (BDD)	Customizable conductivity for electrodes or grounding.	Can be integrated as highly stable, conductive p-stop or ohmic layers within the microstrip structure, offering superior performance compared to diffusion implants in silicon.
Thermal Grade SCD/PCD	High thermal conductivity (> 1800 W/mK)	Essential for acting as passive heat sinks or substrates for high-power ASICs (like the ABCN-25) or high-density electronics to manage heat and maintain operating temperature.

Customization Potential

The experimental results emphasize the importance of sensor micro-geometry (strip pitch, bond pads, p-stops) on effective detection width. 6CCVD provides comprehensive manufacturing services essential for translating these complex designs onto diamond:

Custom Dimensions and Thickness: We can provide both PCD and SCD wafers/plates in thicknesses matching or exceeding those tested (320 µm) for optimal charge collection depth, up to 500 µm for both SCD and PCD.
Precision Polishing: Our internal capability ensures surfaces prepared for micro-patterning. SCD surfaces achieve Ra < 1 nm and inch-size PCD achieves Ra < 5 nm, crucial for high-quality metalization adhesion and patterning precision.
Advanced Metalization and Patterning: The paper utilized bi-metal readout layers and aluminum bond pads. 6CCVD offers in-house deposition and lift-off patterning of custom metal stacks, including Au, Pt, Pd, Ti, W, and Cu. This is vital for creating the precise microstrip electrodes, bond pads, and conductive structures necessary for interfacing with 130 nm CMOS ASICs (like ABC130).
Laser Cutting Services: For replicating specific geometric features or creating the miniaturized module sizes tested (like the 1x1 cm² mini sensor), 6CCVD provides precision laser cutting and scribing services.

Engineering Support

Our in-house team of PhD material scientists and technical engineers deeply understands the requirements for detectors used in High Energy Physics (HEP) tracking and beam monitoring. We specialize in designing custom diamond solutions (SCD, PCD, and BDD) that address radiation hardness challenges and thermal load management.

We provide dedicated support for:

Material selection optimization (e.g., balancing PCD area versus SCD resolution).
FEA consultation for thermal management using diamond heat spreaders.
Design and implementation of custom metalized contact structures and electrode geometry for new microstrip or pixel detector architectures.

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

View Original Abstract

The planned HL-LHC (High Luminosity LHC) in 2025 is being designed to maximise\nthe physics potential through a sizable increase in the luminosity up to 6 · 1034 cm−2\ns\n−1\n. A\nconsequence of this increased luminosity is the expected radiation damage at 3000 fb−1\nafter ten\nyears of operation, requiring the tracking detectors to withstand fluences to over 1 · 1016 1 MeV\nneq/cm2\n. In order to cope with the consequent increased readout rates, a complete re-design of the\ncurrent ATLAS Inner Detector (ID) is being developed as the Inner Tracker (ITk). Two proposed detectors for the ATLAS strip tracker region of the ITk were characterized at\nthe Diamond Light Source with a 3 µm FWHM 15 keV micro focused X-ray beam. The devices\nunder test were a 320 µm thick silicon stereo (Barrel) ATLAS12 strip mini sensor wire bonded\nto a 130 nm CMOS binary readout chip (ABC130) and a 320 µm thick full size radial (end-cap)\nstrip sensor - utilizing bi-metal readout layers - wire bonded to 250 nm CMOS binary readout chips\n(ABCN-25).\nA resolution better than the inter strip pitch of the 74.5 µm strips was achieved for both detectors.\nThe effect of the p-stop diffusion layers between strips was investigated in detail for the wire bond\npad regions.\nInter strip charge collection measurements indicate that the effective width of the strip on the\nsilicon sensors is determined by p-stop regions between the strips rather than the strip pitch.\n

Tech Support

Original Source

DOI: None