As it is well known, semiconductor based non-volatile storage devices have left their central area, computers, in recent years and entered the world of consumer electronics. Especially qualities like low power and space consumption, silence and low marginal costs make them very attractive.
Applications like digital cameras or MP3 players are already entering the market and it seems to be only a question of time until they will have marginalized their precursors. Consequently the market for non-volatile memories is constantly growing and it is very unlikely that this will change soon.
This development got a significant boost of popularity with the introduction of Flash memory, which allows to program an arbitrary single cell and to electrically erase a large number of cells en block. This enhances their flexibility compared to electrically programmable read-only memories (EPROMs), which are electrically programmable as well, but demand an ultraviolet exposure to be erased. The electrically erasable and programmable read-only memories (EEPROMs) are programmable and erasable by single byte, but they demand more chip space compared to Flash technology, which makes them more expensive and limits their scope to special applications only [PBOZ97].
Still Flash memories have some not so highly appreciated properties. Compared to the supply voltage, their write and erase operations demand a significantly higher voltage, which leads to an increased complexity of the on-chip circuits and also to a rather high power consumption. Considering that non-volatile memories are especially attractive as storage device for mobile electronic components and that power consumption and compact circuit design are the main issues in this area, the search for alternative designs becomes reasonable.
The most attractive approach in this context is the introduction of ferroelectric materials. From 127 papers on non-volatile memory reported by the INSPEC data base between January 1999 and July 2000, 53 are on ferroelectrics.
Similar to ferromagnetics, ferroelectrics show a nonlinear dependence on the applied field and a remanent field component, just not in terms of magnetization but in terms of polarization. This leads to some very interesting effects compared to standard type non-volatile memory. First, as the information is stored inside the material, these memory cells are expected to be superior in terms of time stability without refresh. Data retention rates of more than ten years are expected [Maz00]. Another advantage is that designs are possible that use the on chip supply voltage for read and write operations.