Electrical and spectroscopic characterization of 7-cell Si-drift detectors

Abstract

Ten detector modules based on monolithic 7-cell Si-drift detectors with integrated junction field effect transistors (JFETs) are currently under production. The modules’ hexagonal shape with a wrench size of 16 mm allows very small distances to the samples and a compact multi-module arrangement. The sensors have active areas of ∼ 50 mm 2 and a thickness of 450 μ m . A proper spectroscopy operation of all modules was obtained by five common supply voltages and a 6th voltage which must be individually adopted. Detector capacitances varied from 83 to 145 fF, where statistical spreading caused by device mismatch amounts to 0.4%. On-chip scattering of the JFET's transconductance and source potential in a source-follower configuration are around 1%. Their spreading caused by process variations and device mismatch remain below 8%. Typical spectral resolution and non-linearity is about 300 eV and below 1% between 4.5 and 18 keV, respectively. After irradiation with a total dose of ∼ 2 Mrad the resolution decreases by ∼ 40 % . By shielding the cell borders and JFETs from direct irradiation with usage of a Zr mask, a spectral peak-to-valley ratio of ∼ 1000 was achieved.