Resolution limits of silicon detectors and electronics for soft X-ray spectroscopy at non cryogenic temperatures

This paper deals with the limits of the resolution achievable in soft X-ray spectroscopy using silicon detectors of different dimensions (pad, pixel and drift detectors) operated at non-cryogenic temperatures. The role of the front-end electronics in achieving high resolution is examined with special care. It is found that in a common experimental setup the ultimate performance of the spectrometer is not limited by the thermal and shot white noises: the main contribution to the resolution performance arises from the non-white component of parallel noise due to the dielectric losses in the passive devices connected to the preamplifier input, especially when the detector leakage current is in the pA range. By using high quality feedback capacitors we have obtained significant improvements in the resolution performance. With a ceramic feedback capacitor and a commercial device as input transistor we have obtained at room temperature an Equivalent Noise Charge as low as 15 electrons rms (130 eV FWHM). We discuss the ultimate limits and the perspectives for room temperature operation of silicon soft X-ray detectors.