Development of the MYTHEN III microstrip detector

The MYTHEN detector is a single photon counting microstrip detector with 50 μm pitch developed for powder diffraction experiments at the Swiss Light Source. After more than ten years of operation of MYTHEN II, a new readout chip MYTHEN III was designed in 110 nm UMC technology to upgrade the current detector and to improve all aspects, specifically noise performance, count rate capability, threshold dispersion and frame rate. Each readout channel of the MYTHEN III chip features a dual polarity front end consisting of a charge sensitive amplifier and a shaper with variable gain and shaping time, as well as three comparators and gateable 24-bit counters. The internal counting logic allows for different modes of operation: energy-windowing, charge sharing suppression, count rate improvement and pump-probe with multiple time slots. The first two prototypes have been characterised in the lab and at the synchrotron. The noise is reduced to 175 electrons and the untrimmed threshold dispersion was measured as 476 eV. Thanks to the three thresholds in the chip, we can detect pile-up of the analog signal in the shaper at high photon flux and thereby reach a count rate of 25 MHz. Based on these results, a full scale chip with 128 channels has been produced. The architectures of the chips, characterisation results of the final chip and module design of the new detector will be presented.