Deep depletion charge-coupled devices for X-ray and IR sensing applications

In this paper, we describe the fabrication of charge-coupled devices on high resistivity (10-20KΩ-cm) silicon substrates. This material was selected to provide exceptionally deep depletion layers (165µm-254µm deep) for sensing penetrating radiations such as x-rays in the 0.5 to 15KeV range and IR with wavelengths in the vicinity of 1.06. The deep depletion depth prevents recombination loss and allows for a thick device with a large active sensing volume. The high fields (>1000 V/cm) which run through the depletion layer channel charge to the surface, minimize MTF degradation and allow for a back-surface illumination of devices whose thickness is the depletion depth. We present calculations of device performance indicating near unity quantum efficiency for x-rays in the 0.5-15 KeV range. Calculations indicate that for a 254µm thick totally depleted device, diffusive spreading of electron-hole pairs over the entire thickness of the device will be <10µm. We also present data on a 80 element 10 mil thick line array fabricated (buried p-channel) on 15KΩ-cm silicon. We have imaged a slit in the back surface illumination mode using Mn Kα x-rays(penetration depth 28µm). The radiation fluence per frame time of the array was 10 Mn Kα x-ray photons per pixel.