We survey developed techniques in MEMS/NEMS and silicon foundaries used to form vacuum micromachined photodetectors, with gain from dynodes or nanomachined microchannel plates, and to form high quantum efficiency photocathodes because of geometric field or topological areal enhancements. Examples and properties of recent and proposed devices will be shown. Prospects for novel materials such as GaAs MCP and diamond SE dynodes are discussed. Some allied applications of micromachining in all solid state detectors such as APD or integration with readout electronics will be presented. Benefits for high energy physics include fully channelized no-cross-talk pixels, high gain-bandwidths, thickness to the beam of a few mm, tileablility/low dead area, low areal mass, and high magnetic field operation. Because the technologies are amenable to standard wafer fab practice, lower costs may result. Potential applications in selected HEP experiments will be surveyed, varying between very large photodetectors for astroparticle physics, and fiber array detectors.