Electrical performance improvement using nano-oxide thin films deposited via atomic layer deposition on microchannel plates

摘要

Microchannel plate (MCP) is two dimensional arrays of microscopic channel electron multipliers. In this study, oxide thin films such as zinc oxide doped with aluminum oxide (AZO) as conductive layer and aluminum oxide (Al_2O_3) as secondary electron emission (SEE) layer were prepared in the pores of MCP via thermal atomic layer deposition (ALD). The bulk resistance of MCP in the suitable range (about 40～100 MΩ) was obtained by adjusting the percentage of zinc oxide (ZnO) cycles and the nano-oxide thin film thickness. As the tested voltage increased a behavior of negative temperature coefficient of the film was observed. After 5 days of continuous loading with 800 V bias, the resistance nearly doubled and stabilized. For the conduction mechanisms, the I-V curve obeys the ohmic law at low voltage region and the trap-controlled space-charge-limited conduction mechanisms as the applied voltage continue to increase. High gain performance (24000 @ 800 V) can be obtained by depositing only aluminum oxide film on traditional reduced lead glass microchannel plate. Meanwhile after the deposition of aluminum oxide film, the dark current density of the microchannel plate would increase to 1.8 picoampere in 15 minutes at DC 1000 V. Because of blocking effect the dark current density will drop to 0.03 picoampere in 50 minutes by depositing zinc oxide film with thickness of 4 nm before the SEE layer, and the resistance of MCP will reduce when the thickness of zinc oxide exceeds 4 nm.