Development of silicon strip detectors for a medium energy gamma-ray telescope

We report on the design, production, and testing of advanced double-sided silicon strip detectors under development at the Max-Planck-Institute as part of the Medium Energy Gamma-ray Astronomy (MEGA) project. The detectors are designed to form a stack, the “tracker,” with the goal of recording the paths of energetic electrons produced by Compton-scatter and pair-production interactions. Each layer of the tracker is composed of a 3×3 array of 500 μm thick silicon wafers, each 6 cm×6 cm and fitted with 128 orthogonal p and n strips on opposite sides (470 μm pitch). The strips are biased using the punch-through principle and AC-coupled via metal strips separated from the strip implant by an insulating oxide/nitride layer. The strips from adjacent wafers in the 3×3 array are wire-bonded in series and read out by 128-channel TA1.1 ASICs, creating a total 19 cm×19 cm position-sensitive area. At 20°C a typical energy resolution of 15–20 keV FWHM, a position resolution of 290 μm, and a time resolution of ∼1 μs is observed.