Fabrication and signal readout of the Si-based delay-line radiation detector

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 validated a structurally simple time-based measurement scheme, in which a delay-line electrode structure is used to isolate the position of charge collection [1]. If the transmission-line electrode structure is properly designed, then the time difference between the pulses at the readout ends can be used to measure the position at which the charge was collected. Furthermore, if the timing uncertainty is significantly less than the transit time along a single strip in that design, then the position can be isolated to one strip of the pattern or better. In this paper, we describe the fabrication techniques used to overcome the two greatest limitations of the previous 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 laminated and/or thicker electrodes and the use of low-loss dielectrics as a part of asymmetric strip line design. To accomplish low leakage designs, we describe the fabrication of both delay-line PIN devices as well as detectors with metal-semiconductor junctions. Finally, we discuss the trade-offs when employing current-sensing for semiconductor-based radiation detectors and demonstrate the means by which the current profiles are translated into maps at which the charge is initially deposited.