Two-dimensional detector arrays for gamma spectroscopy

We have developed a pixel detector hybrid called DANA-2 (Detector Array for Nuclear Applications). DANA-2 consists of a two-dimensional, monolithic Cadmium Zinc Telluride (CZT) detector array flip-chip bonded directly to a readout IC designed for high energy resolution. Both the detector and the IC have 16 × 16 pixels with a pitch of 0.5 mm × 0.5 mm; the detector thickness is 3 mm. Each readout channel features a low-noise, charge-sensitive input amplifier with continuous-reset feedback and two selectable energy ranges; a gain amplifier with a five-bit gain adjustment and eight-bit offset DAC; a shaper with eight selectable shaping times ranging from 0.5 μs to 4 μs; a peak detector; and a trigger comparator. The data readout is controlled by a programmable token logic, which affords the user a high degree of flexibility in the selection of nearest-neighbor channels to be read out to account for charge sharing between pixels. To process the signals from the detector cathode, one of the readout channels, which is normally connected to a corner pixel, can instead be connected to the cathode through a dedicated I/O pad. The different characteristics of these cathode signals are accommodated through user configuration options for the signal polarity and input FET size. Other features of DANA-2 include the ability to disable the trigger on any channel and thus turn off “hot” pixels, and several test features such as an AC-coupled test signal input and the option to operate any peak detector in follower mode and connect it to the analog output to continuously monitor the shaper signal. We present below details of the DANA-2 design and first results from its performance characterization.