<title>Electron trapping for mass-data-storage memory</title>

Abstract

A new approach to rewritable optical data storage is under development which has the potential for satisfying all of the key requirements for a dynamic on-line data storage system including removability, high data density, high speed and long cycle life. The storage media consists of alkaline earth crystals doped with rare-earth elements. Thin crystalline films of these media deposited on disk substrates can store information in the form of trapped electrons. The information is written, read, and erased entirely by optical signals in this purely electronic process. Electrons are raised to a higher energy state by the absorption of visible light photons, filling available trap sites. An electron in the elevated energy state can be released from its trap site by imputing sufficient energy to the electron to permit it to escape from the well. When this occurs, the electron falls back to its ground state and emits a corresponding photon, indicating the existence of a binary ''1'' at the storage location site. The basic advantages of the ET media arise from the physical process which is purely photoelectronic. Read and write data transfer rates are very high because the process in the ET media is electronic rather than thermal in nature. The writing sensitivity of ET is approximately 100 times better than other optical media. This implies that the data recording rate can be made 10 times higher while using only 1/10 of the optical power of other systems. In addition, thermal cycling performance degradation is not a factor in contrast to the heat induced changes wrought by the write/erase laser beam in other optical storage media.