High Count Rate, Pixelated APDs for Direct X-Ray Detection

Synchrotron radiation is used at DOE user facilities for materials science studies.  However, with advances in the brightness of synchrotron radiation sources, a wide gap has developed between the ability of these sources to deliver high photon fluxes and the ability of detectors to measure the resulting photon, electron, or ion signals. This project will use engineered SOI CMOS (silicon-on-insulator, complimentary metal oxide semiconductor) materials and commercial CMOS foundries to fabricate avalanche photo-diodes (APDs) with low noise, fast response, and high pixilation. The design will allow the APDs to be made at any of the small thicknesses (e.g., from 5µm to 650µm) required for energy resolution, and to be stacked to improve efficiencies. The back-illuminated fully-depleted APDs will be optimized for sub-nsec response and will increase instrument performance and avoid photon pile-up. In Phase I, prototype APDs of varying thickness and pixel dimension will be fabricated, their temporal and energy resolution will be measured, and reliability tests will be conducted. In Phase II, large area arrays, with approximately 50-micron dimension pixels, will be manufactured; their performance will be demonstrated; and candidate designs will be integrated with existing 2.5 GHz SOI-CMOS-readout integrated circuits. Also in Phase II, a fully-functional prototype APD array will be fabricated and demonstrated in the operational environment. Commercial Applications and Other Benefits as described by the awardee: Highly efficient, back-illuminated APD detectors should have a wide variety of applications, including astronomy, fluorescence microscopy, semiconductor testing, soft x-ray spectroscopy, DNA sequencing, and laser radar (LADAR) navigation (including automobile cruise control).