High-Count-Rate, High Resolution Single Photon Detector
Megapixel-class imaging systems with single-photon sensitivity, high time resolution (sub-ns), and the capabilities to detect and process photons at high rates (above 108 detected photons per second) are highly desirable for a number of DOE, homeland security, national defense, and nuclear medicine applications. The event timing resolution largely depends on the specific application, but can range from as little as milliseconds for astronomical applications, to nanoseconds for remote sensing, and to as little as 100 ps for biological fluorescence and synchrotron instruments. One of the major drawbacks of existing photon counting systems is their limited counting rate and spatial resolution capabilities. There are currently only a few commercially available single photon detectors which can simultaneously provide time resolution with nanosecond precision and imaging with more than 100x100 pixels for a quasi-continuous photon flow. Photon counting systems with reduced photon arrival ambiguity, event timing better than 1 nanosecond, and spatial resolution on the scale of a single micron are very much needed. A solid-state ROIC optimized for integration with cross-strip (XS) photon counting sensors will be developed, which combines best features of the traditional XS readout techniques and solid-state readout techniques to increase the photon count rate and photon time resolution of XS photon detectors. The proposed complementary metal oxide semiconductor (CMOS) ROIC is comprised of an array of digital microcell elements. In each sub-pixel, a comparator will sense the MCPs electron cloud and then the amplified and buffered signals from sub-pixel will be placed onto transmission lines, aligned along different coordinate axes. On each bus, the signals from all the sub-pixels connected to that bus are aggregated as current. In this way, a super-pixel is defined as those sub-pixels that are sensed by a unique pair of busses. At the end of each bus, the current signals are conditioned by resistive transimpedance amplifier (RTIA) and pulse processing. The column pulse detection circuits are capable of sub-nanosecond timing, approximately 10x better than existing XS detector capabilities. The sensor will be designed, among other applications, for incorporation into a vacuum-sealed image tube detector with an image intensifier photocathode, an MCP (microchannel plate), and a hermetic body envelope. The circuits of the hybrid XS pixelated anode (HXPA) will be designed and simulated in Phase I. Working with the DOE representatives, detector developers, and end-users, the HXPAs microcell size, the number of sub-segments in each pixel, and the orientation and layout of buses for the three axes will be determined. After completing the baseline architecture design, we will optimize the microcells amplifier, comparator, and current source circuits, and then the column-end RTIA and CFD circuits. Using circuit simulation tools, including those that extract bus capacitance and resistance values, we will simulate the HXPA detectors signal-to-noise (STN) and temporal response as a function of various intensity and spot-sized electron clouds arriving at different rates. We will complete the design process once we can meet the target specifications including photon count rate (global and local), time resolution, and spatial resolution.
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