KITE: High frame rate, high count rate pixelated electron counting ASIC for 4D STEM applications featuring high-Z sensor

Abstract

KITE is a novel mixed-mode CMOS electron counting ASIC developed for the readout of pixelated semiconductor radiation detectors targeted to 4D STEM applications. The chip features a pixel pitch of 100 μm arranged in a 192 × 192 matrix and can be bump-bonded to both Si and high-Z sensor materials. The design of an extremely fast front-end electronics and the use of the instant retrigger mechanism allow for a non-paralyzable counting mode up to above 108 cts/s/pix, which corresponds to a 300 keV electron beam current of 14 pA/pix. The massive parallel readout in combination with two on-chip data compression techniques – 2 × 2 pixel digital binning and floating-point counter encoding – allows for frame rates higher than 100 kfps (this work), in principle extendable to almost 500 kfps with improved readout boards. We successfully characterized a first detector prototype featuring a 1500 μm-thick CdZnTe sensor with fluorescence X-rays from elemental targets and with 200 keV and 300 keV electrons in terms of energy response, threshold trimming accuracy, single event multiplicity distribution, spatial uniformity and temporal stability, count rate capability and imaging performances (MTF and DQE). Custom Monte Carlo simulations complemented when possible the experimental data for cross-validation purposes, generally with a very good matching. Finally, a proof-of-concept 4D STEM acquisition is presented and discussed.