Implementation of avalanche photo diodes in (BI) CMOS processes

Abstract

A radiation detector (46) includes a semiconductor layer(s) (12) formed on a substrate (14) and a scintillator (30) formed on the semiconductor layer(s) (12). The semiconductor layer(s) (12) includes an n-doped region (16) disposed adjacent to the substrate (14), and a p-doped region (18) disposed adjacent to the n-doped region (16). A trench (20) is formed within the semiconductor layer(s) (12) and around the p-doped region (18) and is filled with a material (22) that reduces pn junction curvature at the edges of the pn junction, which reduces breakdown at the edges. The scintillator (30) is disposed over and optically coupled to the p-doped regions (18). The radiation detector (46) further includes at least one conductive electrode (24) that electrically contacts the n-doped region.

Description

technical field [0001] The present invention relates to medical imaging technology. It finds particular application to photodiodes such as avalanche photodiodes used in medical imaging systems and / or other applications. Background technique [0002] In positron emission tomography (PET), two simultaneously generated 511 keV gamma photons are detected by means of a scintillation crystal. Scintillation crystals detect gamma photons and convert some of their energy into light quanta with energies in the blue part of the electromagnetic spectrum. These photons are then detected by one or more photodetectors, typically photomultipliers. The number of detected photons indicates the actual energy of the gammas, which may be below 511 keV due to dispersion in the patient's body. The timing of the gamma strike is defined by the rising edge of the photodetector signal. Typically, for coincidence logic, temporal resolution in the nanosecond range is sufficient to detect simultaneou...

AI Technical Summary

Problems solved by technology

Photomultipliers have several disadvantages as vacuum devices: they are bulky, require high voltages, and do not work well in strong magnetic fields

Furthermore, although all required processing steps are usually available in standard CMOS or BiCMOS processes, their application to form the required guard ring structures is often hampered by design rules, and many such diode designs have to use Tricks to implement a guard ring with a given unchanged CMOS or BiCMOS process

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