Structure and Device Characteristics of SrBi 2 Ta 2 O 9 -Based Nonvolatile Random-Access Memories

Recently there has been a paradigm shift in nonvolatile computer memories from silicon-technology-based EEPROMs (electrically erasable, programmable read-only memories) to devices in which the stored information is coded into + and − polarizations in thin-film ferroelectric capacitors. Such devices have read and erase/rewrite speeds of the order of 1–35 ns, many orders of magnitude faster than the erase/rewrite speeds of the best EEPROMs (Table I). However, fundamental questions concerning their lifetimes had delayed full commercialization. Because ferroelectrics normally have extremely large dielectric constants, their use as nonswitching capacitors in dynamic random-access memories (DRAMs) is also rapidly evolving. The majority of studies to date have emphasized lead zirconate titanate (PZT)-based capacitors for nonvolatile ferroelectric random-access memories (NVFRAMs) and barium strontium titanate-based capacitor DRAMs (see Table II).