Ferroelectric random access memory (FRAM)
A ferroelectric random access memory (FRAM) is a nonvolatile semiconductor memory device capable of operation without the need for refresh as in a dynamic random access memory (DRAM) device. A ferroelectric random access memory uses a ferroelectric capacitor as a storage element of each memory cell. Each ferroelectric memory cell stores a logic state based upon electric polarization of its ferroelectric capacitor. Ferroelectric random access memory (FRAM) devices are "nonvolatile" memory devices because they preserve data stored therein even in the absence of a power supply signal. The nonvolatile nature of a ferroelectric memory cell is a direct consequence of using a ferroelectric material as the dielectric of the cell's capacitor. A ferroelectric material has a ferroelectricity. The ferroelectricity is a physical property in which if an external voltage is applied to electric dipoles arranged in the ferroelectric material, a spontaneous polarization of the electric dipoles is generated. The FRAMs using the ferroelectric material are largely classified into two types; a first type which operates by detecting a change in a charge amount stored in a ferroelectric capacitor, and a second type which operates by detecting a change in resistance of a semiconductor due to spontaneous polarization of the ferroelectric material. In the FRAM, a memory cell is composed of a ferroelectric capacitor and an access transistor and stores logical data `1` or `0` depending on an electrical polarization state of the ferroelectric capacitor. When a voltage is applied across the ferroelectric capacitor, a ferroelectric material is polarized according to the direction of an electric field. An FRAM has the advantage of remembering storage information even when there is a power loss, operates at a high-speed and at reduced power consumption reduction. An FRAM can be used as main memory in various electronic equipment having file storage and search functions, such as portable computers, cellular phones and game machines, or as a recording medium for voice or images.
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