Capacitively coupled pickup in MCP-based photodetectors using a conductive metallic anode

Abstract

We have designed and tested a robust 20 × 20 cm 2 thin metal film internal anode capacitively coupled to an external array of signal pads or micro-strips for use in fast microchannel plate photodetectors. The internal anode, in this case a 10nm-thick NiCr film deposited on a 96% pure Al 2 O 3 3mm-thick ceramic plate and connected to HV ground, provides the return path for the electron cascade charge. The multi-channel pickup array consists of a printed-circuit card or glass plate with metal signal pickups on one side and the signal ground plane on the other. The pickup can be put in close proximity to the bottom outer surface of the sealed photodetector, with no electrical connections through the photodetector hermetic vacuum package other than a single ground connection to the internal anode. Two pickup patterns were tested using a small commercial MCP-PMT as the signal source: 1) parallel 50Ω 25-cm-long micro-strips with an analog bandwidth of 1.5 GHz, and 2) a 20 × 20 cm 2 array of 2-dimensional square 'pads' with sides of 1.27 cm or 2.54 cm. The rise-time of the fast input pulse is maintained for both pickup patterns. For the pad pattern, we observe 80% of the directly coupled amplitude. For the strip pattern we measure 34% of the directly coupled amplitude on the central strip of a broadened signal. The physical decoupling of the photodetector from the pickup pattern allows easy customization for different applications while maintaining high analog bandwidth.

Development of Large-Area MCP-PMT photo-detectors for a Precision Time-of-Flight System at the Fermilab Test Beam Facility

“…Capacitively-coupled MCP-PMT anodes have been implemented using resistive thick films or semi-conductors [78,79,80,81,82,83,84], and MCP-PMTs with resistive capacitivelycoupled anodes are commercially available [80,85]. During this thesis work, it was demonstrated that a thin-metal layer made of NiCr can also transmit the high-frequency components of MCP-PMT pulses to an external array of electrodes, provided that the resistance is greater than about 1 kΩ per square [58].…”

“…At the same time, the bottom interior surface of the tile is coated by evaporation. The first step is evaporation of 10 nm of NiCr on the anode for capacitively coupling to exterior signal boards[58]. A second set of evaporation masks are used to deposit a metallic border overlapping the NiCr anode and connected to a copper pin, providing a charge drainage path to ground.…”

High resolution MCP-PMT Readout Using Transmission Lines

“…In order to limit the number of the electronics channels but keep high time resolution, we develop a read-out scheme using transmission lines as presented in this publication. This read-out scheme is inspired by the approach developed in [19][20][21][22], but has substantial differences in the way we plan to use it. In references [19][20][21][22] the PMT is coupled to high yield scintillation crystal (LYSO, LSO), thus a large number of optical photons induce signals on all lines.…”

“…This read-out scheme is inspired by the approach developed in [19][20][21][22], but has substantial differences in the way we plan to use it. In references [19][20][21][22] the PMT is coupled to high yield scintillation crystal (LYSO, LSO), thus a large number of optical photons induce signals on all lines. In such configuration, it is not possible to distinguish signals from individual photons, but rather reconstruct the mean position of the induced signals along and across lines.…”

Performance of Large Area Picosecond Photo-Detectors (LAPPDTM)

“…Second generation LAPPDs are also currently under active development by Incom Inc., with our university collaborators [8]. Most notable is a next generation design that incorporates an anode capacitively coupled through a thin metal film deposited onto the inside bottom of the detector, to an application specific printed circuit board, positioned beneath the detector tile, outside of the vacuum package.…”