Principle Operation of 3-D Memory Device based on Piezoacousto Properties of Ferroelectric Films (2010)

At present, the main driving forces for rapidly growing the market of nonvolatile memory devices and nonvolatile memory technology are portable electronics. Technical innovations will continue to drive the increase of memory density and speed in the future. For traditional nonvolatile memory devices like NOR flash, scaling could stop even before the 32nm node, while scaling of mass storage devices like NAND flash, is going to be very difficult beyond the 20nm node, too. In recent years, more research efforts have been devoted to finding a new memory technology able to overcome performance and scalability limits of currently memory devices. However as lithographic scaling becomes more challenging. Novel architectures are needed to improve memory device performances in embedded as well as stand-alone memory applications. It is now generally recognized that 3-D integration and vertically stacking are possible alternatives to scaling. In order to realize stacked memory cells a novel physical principle operation of a memory element is needed. Many new ideas have been proposed to find out the solution of such problems. Recently, it were developed a rewriteable 3-D NAND flash memory chip called Bit Cost Memory (BiCS) in which it stacked memory arrays vertically However, there is a cross talk between neighbouring memory cells in the same plane and between vertical neighbours in adjacent planes, too. It is a new challenge in addition to scaling issues. The major limitation, however, is likely to be power dissipation where 3-D designs are not efficient at dissipating heat. More over 3-D architectures are required to overcome a tyranny of interconnects. From physical point of view, a memory device based on ferroelectric phenomena is more suitable for creating 3-D architectures of universal memory devices. Ferroelectric materials can be electrically polarized in certain direction. Then, the polarization is retained after the polarizing field is removed. Therefore, these materials have intrinsic memory. Ferroelectric random access memory (FeRAM) is widely considered as an ideal nonvolatile memory with high write speeds, low-power operation and high endurance FeRAM also have an added significant advantage, which is high radiation hardness. FeRAM are inherently radiation-hard making it very suitable for space applications. The FeRAM with lowest active power is a voltage-controlled device as www.intechopen.com Ferroelectrics 4 opposed to a magnetic, a phase change and a switchable resistor type of memory, which are current-controlled devices with high power consumption. In scaled memory device, currentdriven devices have not survived. There is needed a low resistance material for a nanoscale signal-line. In order to realize all good performance of ferroelectric memory devices and to simplify a problem of creating 3-D memory devices a novel physical principle of memory device operations are needed. The one of the advantages a physical principle of ferroelectric memory device operation is Acousto-Ferroelectric Memory Device (AFeRAM) has been published recently The new universal memory device is called Acousto-Ferroelectric RAM (AFeRAM) makes use of acoustic method of detecting the direction of the spontaneous polarization of the ferroelectric memory cells. The physical principle of AFeRAM device operations is based on a polarization dependent of an acoustic response from a ferroelectric memory cell under the action of applied electrical field pulse. In this chapter, it will be presents physical principle, 3-D architectures and operation modes of the new type of universal memory devices based on piezoacusto properties of ferroelectric materials.