A microchannel plate is a slab made from resistive material (most often glass) 0.5 to 2mm thick with a regular array of tiny tubes (microchannels) leading from one face to the other.  The microchannels are typically 5-20 micrometers in diameter, parallel to each other and enter the plate at a small angle to the surface (8-13° from normal).  Plates are often round disks, but can be cut to any shape from sizes 10mm up to 200mm.  They may also be curved.