Sub-mm four-side butt-able plug-in multi-energy photon-counting semiconductor x-ray detectors for security screening

We have fabricated direct conversion cadmium telluride (CdTe) and cadmium zinc telluride (CZT) semiconductor multi-energy x-ray detectors using custom application specific integrated circuits (ASICs). The detectors use a modular four-side butt-able geometry and can be tiled in two dimensions covering a large field of view (FoV). The CdTe and/or CZT semiconductor sensors have sub-millimeter pixel dimensions with a 0.68 mm pitch perpendicular to the scanning direction for high spatial resolution. The semiconductor sensors are guard ring free and detectors have been fabricated in a range of thicknesses for high detective quantum efficiency (DQE) within the different dynamic ranges required for different security screening applications. The mixed signal ASICs have four thresholds per pixel for up to four contiguous energy windows across a dynamic range from 25 keV to $160 \mathrm{keV}, 180 \mathrm{keV}$, and 220 keV from sensors that are $2.5 \mathrm{~mm}, 2.5 \mathrm{~mm}$, and 3 mm thick respectively. The ASICs and operate at a fast peaking time for high output count rates of up to 20 million counts per second per square millimeter ($\mathrm{Mcps} / \mathrm{mm}^{2}$). We have also integrated field programmable gate arrays (FPGAs), in addition to the ASICs, within the active area of the sensors. Using advanced interconnects, the vertically integrated sensors, ASICs, and FPGAs, produces a detector module with 100% active area that contains digital data processing capabilities which are normally performed in either a back-plane readout or computer. Multiple four-side butt-able detector modules, each with $3.5 \mathrm{~cm}^{2} ~\mathrm{FoV}$, have been tiled in one dimension in lengths of up to 17.5 cm suitable for demonstration use in stationary and rotating computed tomography (CT) security screening systems. We will report the output count rate capability, dynamic range, and the spatial and energy resolution, as well as the uniformity and stability under conditions for carry-on and checked baggage inspection screening lanes at airports.