The current status of ferroelectric random-access memory (FeRAM) technology is reviewed in this article. Presented first is the status of conventional FeRAM, in which the memory cells are composed of ferroelectric capacitors to store the data and cell-selection transistors to access the selected capacitors. Discussed next are recent developments in the field. Pb(Zrx, Ti1–x)O3 (PZT) and SrBi2Ta2O9 (SBT) films are being used to produce 0.13 mμ and 0.18 μm FeRAM cells, respectively, with a stacked capacitor configuration; these cells are easily embedded into logic circuits. A new class of FeRAM called 6T4C—containing static RAM (SRAM) cells composed of six transistors (6T) and four ferroelectric capacitors (4C)—has been commercially produced. This type of FeRAM features a nondestructive readout operation, unlimited read/write cycling, and a fast access time of less than 10 ns. Lastly, the status of field-effect-transistor (FET)-type FeRAM is reviewed, emphasizing that the data retention time of a ferroelectric-gate FET has been improved to more than a month in recent studies.
