Unlike wet coating processes, metal evaporated (ME) media are fabricated by physical deposition of vaporized cobalt or cobalt-nickel mix in a vacuum chamber. There is no synthetic binder to hold particles together; instead, they adhere directly to polyester tape substrate. An electron beam melts source metal, creating a continuous directional flow of cobalt atoms towards the tape. The zone of contact between the beam and the tape is blown with a controlled flow of oxygen, which helps formation of polycrystalline metal-oxide coating. A massive liquid-cooled rotating drum, which pulls the tape into the contact zone, protects it from overheating.
Metal evaporated coatings, along with barium ferrite, have the highest information density of all rerecordable media. The technology was introduced in 1978 by Panasonic, initially in the form of audio microcassettes, and matured through the 1980s. Metal evaporated media established itself in analogue (Hi8) and digital (Digital8, DV and MicroMV) videotape market, and data storage (Advanced Intelligent Tape, Linear Tape Open). The technology seemed promising for analogue audio recording; however, very thin metal evaporated layers were too fragile for consumer cassette decks, the coatings too thin for good MOL, and manufacturing costs were prohibitively high. Panasonic Type I, Type II and Type IV metal evaporated cassettes, introduced in 1984, were sold for only a few years in Japan alone, and remained unknown in the rest of the world.