Development of low noise, back-side illuminated silicon photodiode arrays

We have developed low noise, high quantum efficiency photodiode arrays for use with positron-emission tomography (PET). A fabrication process developed for high-energy physics detectors was modified to allow for back-side illumination. A back-side contact consisting of a thin (10 nm) n⁺ polysilicon layer covered by an indium tin oxide (ITO) antireflection coating (57 nm) results in >70% quantum efficiency over the wavelength range of 400-1000 nm. The photodiodes are operated fully depleted (300 μm thick) resulting in a measured capacitance of 3.2 pF and typical leakage currents of 20-50 pA for a 3 mm square element. At room temperature the noise measured at a shaping time of 4 μs is 140 e^- rms. When coupled to a CsI(TI) scintillator and excited with 141 keV gamma rays, the energy resolution is 12% fwhm