Operating Temperature Optimization of CCD 236 X-Ray Fluorescence Detector

Abstract

Scientific Charge Coupled Device, CCD 236, designed to be used in Chandrayan II mission as high sensitive large area X-ray Fluorescence detector. CCD refers to an array of closely spaced MOS capacitors formed on a continuous oxide layer grown on a semi conductor substrate. The operation of a CCD is based on, the photo generation of charges within the pixels, charge collection, charge transfer and integration, when photons incident on its surface. Charge transfer efficiency (CTE) and bulk dark current are important parameters that determine the performance of a CCD. Both of them are expected to be affected by temperature variation. Hence an optimum temperature for the desired performance is to be determined. The resolution of CCD for 5.9 KeV Mn K and 6.4 KeV Mn K_β lines were studied over a temperature range of -15 to -30 degree Celsius. The clock frequency was varied over a frequency range of 90-130 KHz at clock bias of 7 .0 volts. It is found that, the resolution of the device increases considerably as the temperature is decreased in the above temperature range. Under the given condition the optimum temperature range is found to be -20 to -30 at desired clock frequency of 100 KHz.