Still 0 and 1? Check this out: Memory leads the way to better computing

April 12, 2015

Correspondence: H.-S. Philip Wong & Sayeef Salahuddin

H.-S. Philip Wong - Department of Electrical Engineering and the Stanford SystemX Alliance, Stanford University, Stanford, California 94305, USA

Sayeef Salahuddin - Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, California 94720, USA

Nature Nanotechnology 10, 191–194 (2015) doi:10.1038/nnano.2015.29

More about Authors:
http://web.stanford.edu/~hspwong/
https://www.eecs.berkeley.edu/Faculty/Homepages/salahuddin.html

Introduction
Current memory devices store information in the charge state of a capacitor; the presence or absence of charges represents logic 1's or 0's. Several technologies are emerging to build memory devices in which other mechanisms are used for information storage. They may allow the monolithic integration of memories and computation units in three-dimensional chips for future computing systems1. Among those promising candidates are spin-transfer-torque magnetic random access memory (STT-MRAM) devices, which store information in the magnetization of a nanoscale magnet. Other candidates that are approaching commercialization include phase change memory (PCM), metal oxide resistive random access memory (RRAM) and conductive bridge random access memory (CBRAM).

Today's computing systems use a hierarchy of volatile and non-volatile data storage devices to achieve an optimal trade-off between cost and performance2. The portion of the memory that is the closest to the processor core is accessed frequently, and therefore it requires the fastest operation speed possible; it is also the most expensive memory because of the large chip area required. Other levels in the memory hierarchy are optimized for storage capacity and speed (Fig. 1). The main memory is often located in a separate chip because it is fabricated with a different technology from that of the microprocessor.

For over 30 years, static random access memory (SRAM)3 and dynamic random access memory (DRAM)3 have been the workhorses of this memory hierarchy4. Both SRAM and DRAM are volatile memories — that is, they lose the stored information once the power is cut off. For non-volatile data storage, magnetic hard disk drives (HDDs) have been in use for over five decades5, 6, 7. Since the advent of portable electronic devices such as music players and mobile phones, however, solid-state non-volatile memory known as Flash memory8 has been introduced into the information storage hierarchy between the DRAM and the HDD. Flash has become the dominant data storage device for mobile electronics; increasingly, even enterprise-scale computing systems and cloud data storage systems are using Flash to complement the storage capabilities of HDD.

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