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

Synchrotron radiation (SR) has become a widespread tool across a broad spectrum of forefront science. 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. In a number of cases, expensive beamlines are limited by the lack of suitable fast X-ray imaging systems. This project will develop a radiation-hard, sub-nsec, pixelated, thinned (10 µm), monolithic, Si avalanche photodiode (APD) array as an SR detector for time-resolved photon counting measurements of spatial intensity distributions. In Phase I, prototype back-illuminated APDs of varying thickness and pixel dimension were fabricated using silicon-on-insulator (SOI) silicon wafers engineered for high gain, low dark current, and low excess noise avalanche gain. Using the results of detailed modeling and simulation, the design of the APD array was optimized and used to procure SOI wafers, which were custom engineered with electrically activated dopants. A 100 x 100 mm2 pixel architecture (including low noise amplifier, two-level discriminator, and two user-enabled 16-bit counters) was designed. A fully functional prototype will be fabricated in Phase II. Commercial Applications and Other Benefits as described by the awardee: In addition to synchrotron X-ray science, highly-efficient, back-illuminated APD detectors should have a wide variety of applications in astronomy, fluorescence microscopy, electron microscopy, semiconductor test, soft X-ray spectroscopy, hybrid image intensifier tubes, DNA sequencing, laser radar (LADAR) assisted autonomous navigation, and cruise control.