Optimizing the SNR from a radiation detector with delay-line position-sensing electrodes

In order to image the radiation field, instruments measure the position of interaction of the incident quanta, a task typically accomplished by partitioning the detector or its readout. We previously performed a fundamental investigation of the electrode design and pulse shape analysis routines required to optimize the detectorʹs position resolution, when limited by both temporal and carrier uncertainties. If the transmission-line electrode structure is balanced at the frequencies of interest, then the time difference between the pulses at the readout end of a serpentine delay-line electrode structure can be used to measure the position at which the charge was collected. In this paper, we describe the fabrication techniques used to overcome the two greatest limitations of the early detectors, namely, high leakage currents and high propagation losses. In the following, we describe, through both models and measurements, the means by which: (a) one can achieve impedance matching by conversion of the electrode into a 50 Ω asymmetric strip line and (b) one can minimize the propagation losses by the use of thick high-conductivity electrodes and the use of low-loss dielectrics (BaSrTiO3 and BaTiO3), as a part of an asymmetric strip line design. In order to accomplish low leakage designs, we describe the fabrication of delay-line PIN devices with metal field plates (MFPs) and multiple floating guard rings.