Ferro RAM (FRAM) or Ferro Electric RAM (FeRAM) is the counterpart to Magneto-resistiveRAM( MRAM), it retains its stored data even when disconnected from the supply voltage. FRAMs use ferroelectric materials, unlike MRAMs which use ferromagnetic materials. Ferroelectric materials exhibit a spontaneous electrical polarization that can be changed by electric fields. This polarization effect is used to store digital states.
FRAMs use lead zirconate titanate(BZT) as the ferroelectric material, which forms the dielectric of the capacitor in which the logic states are stored. The hysteresis of the material is similar in its voltage-charge curve, to that of ferromagnetic materials. Since lead zirconate titanate does not contain iron, it is insensitive to magnetic fields.
The structure of FRAMs consists of a field-effect transistor( FET) and a capacitor with ferroelectric dielectric for charge storage. This structure is that of a 1T1C memory cell and corresponds to that of Dynamic RAMs( DRAM). The principle of FRAMs is based on the fact that in ferroelectric materials, when an electric field is applied, the crystalline structure of the material polarizes and this polarization is maintained even after the electric field is turned off. The digital information is stored in the polarization direction. The switching and erasing process is triggered by changing the polarization in a ferroelectric layer. It is extremely energy-saving.
The write and read times of FRAMs are in the two- and three- digit nanosecond range, the number of write-read cycles is up to `10^15` and they do not require a special erase voltage.
FRAMs are characterized by low power consumption and are particularly suitable for use in mobile devices, mobile electronic equipment and automotive technology. A further development of FeRAMs are the Ferroelectric Transistor Random Access Memories( FeTRAM), which are also non-volatile and are characterized by a short access time and very low power consumption.