Very large area 20cm × 20cm flat panel phototubes using ALD microchannel plates

Novel borosilicate microcapillary array MCPs have been employed build large area (20 cm × 20 cm) flat panel phototube detectors. Design of the 20 cm sealed tube assembly comprises of a borosilicate entrance window, a proximity focused bialkali photocathode, a pair of MCPs, and a strip-line readout anode. Micro-capillary arrays have been processed to function as microchannel plates (MCPs) using atomic layer deposition (ALD) to produce the conductive and secondary emissive layers. Using borosilicate micro-capillary substrates has advantages over traditional MCPs, including the ability to be produced in large robust formats (20cm), low intrinsic background (<;0.06 events cm
^-2
sec
^-1
), high open area ratios (up to 85%), and stable gain during >7 C cm
^-2
charge extraction after preconditioning (vacuum bake and burn-in). The gain, pulse height distribution, imaging performance are equivalent, or better than conventional MCPs. The flat panel design employs a brazed ceramic walled enclosure with a hot indium seal and a transfer photocathode. We have achieved >20% quantum efficiency and good gain uniformity over the 20cm field of view, spatial resolution of <;1 cm and obtained event timing accuracy of close to 100ps FWHM.