Scintillation light read-out by thin photodiodes in silicon wells

Several applications of X-ray and gamma ray imaging detectors, e.g. in medi cal diagnostics, require millimeter or sub-millimeter spatial resolution an d good energy resolution. In order to achieve such features we have propose d a new type of camera, which takes advantage of micromachining technology. It consists of an array of scintillator crystals encapsulated in silicon w ells with photodiodes at the bottom. Several parameters of the photodiode n eed to be optimised: uniformity and efficiency of the light detection, gain , electronic noise and breakdown voltage. In order to evaluate these parame ters we have processed 3 x 3 arrays of 1.8 mm(2), similar to 10 mu m thick photodiodes using (100) wafers etched in a KOH solution. Their optical resp onse at 675 nm wavelength is comparable to that of a 500 mu m thick silicon PIN diode. Their low light detection efficiency is compensated by internal amplification. Several scintillator materials have been positioned in the wells on top of the thin photodiodes, i.e. a 200 mu m thick film of structu red CsI(TI), single crystals of CsI(TI) and Lu2S3(Ce3+). First experiments of gamma-ray detection have been performed. (C) 2000 Elsevier Science B.V. All rights reserved.