Metal-oxide resistive-switching RAM technology

Article By:

Hou, Tuo-Hung Department of Electronics Engineering and Institute of Electronics, National Chiao Tung University, Taiwan, Province of China.

Last reviewed:2011

DOI:https://doi.org/10.1036/1097-8542.YB110172

The emergence of portable electronics, such as cell phones, MP3 players, digital cameras, and netbooks, over the past 20 years has led to skyrocketing demand for nonvolatile (retaining information after power is removed) flash memory because of its small cell size and low power consumption. However, the further scaling of flash memory beyond 15-nanometers (feature dimension) technology is highly problematic because of the fundamental limit of the cell structure. The unit cell of flash memory is very similar to the conventional metal-oxide-semiconductor field-effect transistor (MOSFET), except for the additional floating gate to store electric charges. It is unclear whether MOSFET technology can be scaled beyond the channel length of 15 nm, since the physical constraint of quantum-mechanical-tunneling current may dominate at such short channel lengths. Meanwhile, there has been very active research into alternative nonvolatile memories to replace flash. Among the most mature are ferroelectric random access memory (FRAM), magnetoresistive random access memory (MRAM), and phase-change random access memory (PCRAM). Although MOSFET technology is not necessary to store data in these technologies, adding it into the unit cells is inevitable in most cases to ensure the correct read and write operations in the memory array, where the disturbance from neighboring cells is a serious concern. Therefore, the scalability of these technologies beyond current flash memory is implausible. We will revisit this point later in the article. In addition, because their unit cells (made of a MOSFET plus a memory element) are larger than those of flash, the cost would be higher. As a result, they are unlikely to compete directly with flash memory in the mainstream market. Indeed, the current applications of FRAM, MRAM, and PCRAM are limited to niche areas, such as aerospace systems.

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