Future Memory Technology and Ferroelectric Memory as an Ultimate Memory Solution

Abstract

Silicon industries have notched up notable achievements of computer-related technology over the past two decades, leading to rapid progression in information technology (IT). As a result of such a great improvement in IT applications, it is now not unusual to find mobile applications such as personal digital assistants, mobile phones with digital cameras, smart phones, smart pads able to access the Internet and hand-held personal computers. These mobile applications currently require an array of single-functioned conventional memories as they are not sufficient individually in functionality, but must combine their separate functions. For example, dynamic random access memory (DRAM) is capable of processing massive amounts of data speedily (e.g., main memory in personal computers and servers). DRAM is highly scalable (several gigabit are commonly accessible), but requires lots of power consumption even in stand-by mode (~10-3 Ampere) because of the necessity of refreshing cycles in its operation. By contrast, static random access memory (SRAM) saves power1 because its stand-by current is a few micro-Amperes. The demerit of SRAM is not readily to make it high density. This is due to the fact that its unit memory element consists of four complementary metal-oxide-semiconductor (CMOS) transistors along with two conventional transistors. SRAM’s cost-benefit ratio is too high because the 6 components need much more area per unit bit memory. Data retention of both DRAM and SRAM is volatile in bit-storing nature when power goes off. In contrast to these two memories, flash memory is non-volatile. However, operation voltage during either write or erase on flash memory is too high to use the raw voltage-level of power input, Vcc (the term of Vcc comes from collector to collector voltage in a bipolar transistor). Thus during the write or erase operation, internal dummy operation (so called “charge pump”) are used to pump up the input power Vcc to 5 times more than Vcc level; this is crucial in flash memory devices due to imbalance of read and write energy. The reason why the memory needs to boost the write/erase voltage up to such a high level is that hot carriers, e.g., high energy electrons, are forced to be injected through tunnel oxide to a floating gate of the transistor structure. As a result, there are two kinds of performance restrictions for use of IT applications. Writing speed of flash memory is not fast enough of an order of several milliseconds. That