System design of multi-layer (3-dimensional) integrated circuits

Research carried out on beam processing of semiconductors led to the concept of a three dimensional integrated circuit. It was shown that MOS devices could be made on both sides of a laser-recrystallized thin film of silicon, deposited on an insulating substrate (SOI) and also on vertically arranged, recrystallized silicon films separated by insulating layers of silicon dioxide and/or silicon nitride/oxide combinations. It follows from these observations that integrated circuits can be made by vertically interconnecting devices made on separate layers. Such circuits could lead to improved packing density, which would be important for memory applications; and possibly to increased circuit speed, which would be important for logic application.