Ferroelectric Memory Devices

Now that we entered the age of information technology, storage is one of the key issues. Upon scaling down and lowering the operating voltage, FLASH will no longer work. In this paper one of the alternatives is being reviewed; ferroelectric memory devices. Ferroelectrics show non-volatility and can operate at low voltage thresholds. Ferroelectricity shows a P-V hysteresis on which the two level logic scheme of a memory device can be based. PZT and BST are among the materials already in use as prototypes. Ferroelectricity is believed to be preserved down to several unit cells and this makes ferroelectric materials interesting for nanoscience. However at low thickness depolarizing fields and strain come into play. Ferroelectrics can be used as capacitors and field-effect-transistors. The FeRAM shows fast writing and low-power consumption. However the read-out is destructive which leads to high fatigue. FeFETRAM does not show this problem, but no materials have yet been found with retention times higher than a couple of days. Comparing these devices with other memory technologies, FeRAM and FeFETRAM are still lacking behind on capacity and high density arrays. However their writing speed is faster and they are low-power consuming. Economically speaking they can be very productive. In order for ferroelectric devices to become the storage technology of the future adequate knowledge, good design models and the ongoing search for materials with better properties is required. Frontpage picture: mapping of polarization on an atomic scale[1]. Spontaneous small-size nano-vortices were found to occur at ferroelectric hetero interfaces of BiFeO3 . Image comes from a sub-angstrom resolution transmission electron microscope[2].