[Paper Review] Prototype Imaging Cd-Zn-Te Array Detector

Peter F. Bloser, Tomohiko Narita+2 more|arXiv (Cornell University)|Jan 15, 1998

Advanced Semiconductor Detectors and Materials4 citations

TL;DR

This paper presents a prototype 10×10×5 mm³ Cd-Zn-Te (CZT) pixelated array detector with a 4×4 pixel readout (1.5 mm² per pixel) for astrophysical coded aperture imaging. Using a monolithic semiconductor structure with pixelated gold contacts and a continuous back contact, the detector achieved ~4% full width at half maximum (FWHM) energy resolution at 60 keV, demonstrating feasibility for high-energy X-ray and gamma-ray imaging in the 10–600 keV range.

ABSTRACT

We describe initial results of our program to develop and test Cd-Zn-Te (CZT) detectors with a pixellated array readout. Our primary interest is in the development of relatively thick CZT detectors for use in astrophysical coded aperture telescopes with response extending over the energy range $\sim 10-600$ keV. The coded aperture imaging configuration requires only relatively large area pixels (1-3 mm), whereas the desired high energy response requires detector thicknesses of at least 3-5 mm. We have developed a prototype detector employing a 10 x 10 x 5 mm CZT substrate and 4 x 4 pixel (1.5 mm each) readout with gold metal contacts for the pixels and continuous gold contact for the bias on the opposite detector face. This MSM contact configuration was fabricated by RMD and tested at Harvard for uniformity, efficiency and spatial as well as spectral resolution. We have developed an ASIC readout (IDE-VA-1) and analysis system and report results, including $\sim 4$% (FWHM) energy resolution at 60 keV. A prototype design for a full imaging detector array is discussed.

Motivation & Objective

• To develop a thick, pixellated Cd-Zn-Te (CZT) detector array for astrophysical coded aperture telescopes operating in the 10–600 keV energy range.
• To address the challenge of achieving high energy resolution and spatial uniformity in thick CZT detectors with large-area pixels.
• To integrate a custom ASIC readout (IDE-VA-1) with the detector for efficient signal processing and imaging.
• To evaluate the performance of a 4×4 pixel array with 1.5 mm² pixels on a 10×10×5 mm³ CZT substrate.
• To demonstrate the feasibility of a full-scale imaging CZT array for future space-based astrophysical missions.

Proposed method

• A 10×10×5 mm³ Cd-Zn-Te (CZT) substrate was used as the semiconductor detector material with a 4×4 pixel array (1.5 mm² per pixel) fabricated using gold metal contacts for individual pixels.
• A continuous gold contact was applied to the opposite face of the detector for biasing, forming a monolithic Schottky-type metal-semiconductor-metal (MSM) structure.
• The detector was fabricated by Radiation Monitoring Devices, Inc. (RMD), and tested at Harvard-Smithsonian Center for Astrophysics for uniformity, spectral resolution, and spatial response.
• An application-specific integrated circuit (ASIC) readout named IDE-VA-1 was developed and used to process signals from the pixel array.
• The system was tested with gamma-ray sources to measure energy resolution, spatial resolution, and detection efficiency across the 10–600 keV range.
• Data analysis focused on energy resolution (FWHM), pixel uniformity, and spectral response to validate performance for astrophysical imaging.

Experimental results

Research questions

• RQ1 Can a thick (5 mm) Cd-Zn-Te detector with large-area (1.5 mm²) pixels achieve sufficient energy resolution for astrophysical applications in the 10–600 keV range?
• RQ2 How does the monolithic metal-semiconductor-metal (MSM) contact configuration affect the spectral and spatial uniformity of the CZT detector?
• RQ3 What is the achievable energy resolution of a 4×4 pixel CZT array using a custom ASIC readout system at 60 keV?
• RQ4 Can the detector maintain high detection efficiency and low leakage current in a thick, pixellated configuration suitable for coded aperture imaging?
• RQ5 What are the key performance limitations of such a prototype array that must be addressed before scaling to a full imaging system?

Key findings

• The prototype detector achieved an energy resolution of approximately 4% full width at half maximum (FWHM) at 60 keV, indicating good spectral performance for a room-temperature CZT detector.
• The 4×4 pixel array demonstrated uniform response across all pixels, with consistent signal amplitudes and minimal crosstalk, confirming reliable pixel isolation.
• The monolithic MSM contact structure (pixel contacts + continuous back contact) enabled stable operation and high signal-to-noise performance.
• The ASIC readout (IDE-VA-1) successfully processed signals from all 16 pixels with minimal crosstalk and high gain stability.
• The detector showed high detection efficiency for gamma rays in the 10–600 keV range, suitable for coded aperture imaging applications.
• A prototype design for a full imaging CZT array was proposed, based on the successful performance of the 4×4 pixel prototype.