Pixel detectors for particle physics and imaging applications

doi:10.1016/S0168-9002(03)01905-3

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment

Volume 512, Issues 1–2, 11 October 2003, Pages 277-288

https://doi.org/10.1016/S0168-9002(03)01905-3 Get rights and content

Abstract

Semiconductor pixel detectors offer features for the detection of radiation which are interesting for particle physics detectors as well as for imaging e.g., in biomedical applications (radiography, autoradiography, protein crystallography) or in X-ray astronomy. At the present time hybrid pixel detectors are technologically mastered to a large extent and large-scale particle detectors are being built. Although the physical requirements are often quite different, imaging applications are emerging and interesting prototype results are available. Monolithic detectors, however, offer interesting features for both fields in future applications. The state of development of hybrid and monolithic pixel detectors, excluding CCDs, and their different suitability for particle detection and imaging, is reviewed.

Introduction

The requirements on semiconductor pixel detectors for charge particle detectors in high energy physics compared to those from imaging can be very different. In particle physics experiments individual charged particles, usually triggered by other subdetectors, have to be identified with high demands on spatial resolution and timing. In imaging applications the image is obtained by the un-triggered accumulation (integrating or counting) of the quanta of the impinging radiation, often also with high demands (e.g., $≳1 MHz$ per pixel in certain radiography or CT applications). Si pixel detectors for high energy charge particle detection can assume typical signal charges collected at an electrode in the order of 5000–10,000 electrons even taking into account charge sharing between cells and detector deterioration after irradiation to doses as high as $60 Mrad$ . In tritium autoradiography, on the contrary, or in X-ray astronomy the amount of charge to be collected with high efficiency can be much below 1000e. The spatial resolution is governed by the attainable pixel granularity from a few to about $10 μm$ at best, obtained with pixel dimensions in the order of 50– $100 μm$ . The requirements from radiology (mammography) are similar, while some applications in autoradiography require sub-μm resolutions, not attainable with present day pixel detectors. For applications with lower demands on the spatial resolution $(O (10 μm))$ but with demands on real time and time resolved data acquisition, semiconductor pixel detectors are however attractive.

Thin detector assemblies are mandatory for the vertex detectors at collider experiments, in particular for the planned linear e⁺e⁻ collider. While silicon is almost a perfect material for particle physics detectors, allowing the shaping of electric fields by tailored impurity doping, the need of high photon absorption efficiency in radiological applications requires the study and use of semiconductor materials with high atomic charge, such as GaAs or CdTe. For such materials the charge collection properties are much less understood and mechanical issues in particular those related to hybrid pixels are abundant, most notably regarding the hybridization of detectors when they are not available in wafer scale sizes. Last but not least the cost-performance ratio is an important factor to consider if an imaging application should be commercially interesting.

Section snippets

Hybrid pixel detectors for particle physics

In the “hybrid pixel technique” sensor and FE-chips are separate parts of the detector module connected by the small conducting bumps applied by using the bumping and flip-chip technology. All of the LHC-collider-detectors [1], [2], [3] ALICE, ATLAS, and CMS, LHCb for the RICH system [4], as well as some fixed target experiments (NA60 [5] at CERN and BTeV [6] at Fermilab) employ the hybrid pixel technique to build large-scale (∼m²) pixel detectors. Pixel area sizes are either rectangular

Radiology

There is a vast amount of radiology detection and imaging techniques. The discussion in this paper will be limited to an application which possibly opens new directions in radiology due to fully digital imaging, i.e., pixel detectors with individual X-ray photon counting in every pixel cell. This approach offers many features which are very attractive for X-ray imaging: excellent linearity and an infinite dynamic range (at least in principle), optimal exposure times and a good image contrast

Monolithic pixel detectors

Monolithic pixel detectors, in which amplifying and logic circuitry as well as the radiation detecting sensor are made from one piece of silicon, have been the dream of semiconductor detector physicists. The first monolithic pixel detector, successfully operated in a particle beam was made by Snoeys and collaborators [27] as early as in 1992. They used a high purity, high resistivity p-type bulk pin-diode in which the junction has been created by an n-type diffusion layer. On one side, an array

Summary

Driven by the demands for high spatial resolution, high rate particle detection in high energy physics, semiconductor pixel detectors have also started to become exploited for imaging applications. Hybrid pixel detectors, in which sensor and electronic chip are separate entities, connected via bump bonding techniques represent today's state of the art for both, particle detection and imaging applications. Monolithic detectors, in the form of CMOS sensors, are already used for imaging in CMOS

Acknowledgements

I would like to thank Woitek Dulinski for an honest discussion of the features and technicalities of the MIMOSA Active Pixel concept.

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^☆: Work supported by the German Ministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF) under contract No. 05HA8PD1, by the Ministerium für Wissenschaft und Forschung des Landes Nordrhein-Westfalen under contract No. IV A5-106 011 98. and by the Deutsche Forschungsgemeinschaft DFG.

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Pixel detectors for particle physics and imaging applications☆

Abstract

Introduction

Section snippets

Hybrid pixel detectors for particle physics

Radiology

Monolithic pixel detectors

Summary

Acknowledgements

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The CMS pixel detector

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The pixel hybrid photon detectors for the LHCb-RICH project

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