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Achieving Ultrahigh Recording Density by Use of Multi-Stable Vortex States in Ferroelectric Nanostructures
About
Technology # 04-29 (related to technology 09-18 ) Use of Nanodots of Ferroelectric Material to Store Information (FerroElectric Memory) This is a new invention that will revolutionize the data-storage capability of ferroelectric random accessed memory (FRAM) by a dramatic and unprecedented increase up to a record high of 80 Terabits/inch2, which is five orders of magnitude large than those currently available. The approach is to use our newly-discovered multiple degenerate states formed by ordered toroid moment in low-dimensional nano-scale ferroelectric structures, for instance, at low temperature, ferroelectric nanodisks of lead zirconium titanate (PZT) exhibit two robust bi-stable states with clockwise or counterclockwise concentric vortex rings, and these states with opposite toroid moments can be used as the logic states to store "O" and "1'7 in memory devices. This approach is drastically different from---and more superior to----the conventional approach where macroscopic polarization is used. In fact, macroscopic polarization does not exist in the nanodisks and thus can not be utilized for the purpose of memory devices. The minimum size (i.e., the diameter) of the nanodisks that display bi-stable toroid moment in PZT is discovered to be 2.8nm, demonstrating that the ultimate storage density of our invented new approach will be 80 Terabits/inch2.This far exceeds the current storage capability of IGbits/inch2 using magnetic recording.
Key Benefits
Simulations by the scientists resulted in a method of changing the spin state of the vortex, allowing the possibility of writing a "1" or a "0" on each specific nanostructure such as a nanodot. The ability to change the spin state of the nanodot is based on the application of inhomogenous electric fields. Static electric charges can be placed near the nanodot, and when they are switched or moved, the spin of the nanodot changes. Nanodots can then be used as memory cells, and because of the very small size of the nanodots, the density of the memory elements can go up dramatically from the 1 billion bits per square inch now achieved with magnetic recording to 80 trillion bits per square inch, or about 4 orders of magnitude greater memory density.
Applications
The use of nanodots of ferroelectric material to store information is especially helped by the use of the vortex spin state to record the bits, because the vortex has a closed electric field that will not interact with neighboring nanodots, thus eliminating crosstalk between the memory elements. Crosstalk in conventional memory cell capacitors requires the use of passgate transistors to deal with the problem of cross talk. In addition to making memory elements for ultradense nonvolitile ferroelectric random access memory (NFERAM‚), the use of ferroelectricity in nanoscalestructures can be applied to piezoelectric sensors, efficient actuators, nanoscale dielectric capacitors for energy storage, and nanoscale ultrasounds for medical use.