June 10, 2013
Tohoku University
NEC Corporation

Spintronics-based logic LSI for text search by Tohoku University andNEC reduces power consumption to 1% or less of conventionalsystems- Superior power efficiency of spintronics-based logic integrated circuit
technology confirmed. -Tohoku University and NEC Corporation (NEC; TSE 6701) have developed aprototype chip for text search systems using spintronics-based logic integrated
circuit technology (Note 1). Early testing of the new prototype chip has
demonstrated that the power consumption required for text search has been
reduced to only 1 % or less when compared to conventional systems.

Text search processing currently requires a great amount of power to transfer
data between the DRAM and CPU within a server. Yet, using just alogic-in-memory structure (Note 2) to eliminate the data transfer processsimply increases standby power. The latest spintronics-based logic integrated
circuit for text search that Tohoku University and NEC’s joint research teamdeveloped takes on a logic-in-memory structure but is nonvolatile, and thus
requires no standby power. By setting up a structure that supplies power only
to necessary circuit blocks for the text search processing, the circuit can run
search with a minimal amount of power. This allows a significant reduction in
power consumption for text search processing.

With the recent advent of cloud computing and big data usage, the use andscale of computer systems continues to expand, which poses a challenge forthe reduction of power consumption.

-1-

Tohoku University and NEC address this issue by developing zero standby
power and other optimal methods for saving power in computer systems
through

theapplicationof

spintronics-based

logic

integrated

circuittechnology.

Features of the recently developed logic integrated circuit for text search
include the following:

1. Development and use of multi-functional CAM cells
The team developed and used new multi-functional CAM cells (Note2Note 3)

for text-search logic LSI.

In a text search, the computer looks into character strings of index data
in DRAM, where all the index data is loaded from a hard-disk inadvance, to find ones that match a search text. CAM-based searchsystems can complete the search for a large amount of index data
through a single operation, which eliminates power consumption fordata transfer between the DRAM and CPU that is conducted in aconventional text search system, and enables high-speed search
processing. However CAM-based systems need to run a search
operation with all index data on the CAM chips, regardless of thelength of the index text data.

When searching for short lengths of text within a large amount of index
data, the newly developed multi-functional CAM is able to avoid
searching for long index texts. This is accomplished by setting up
combinations (patterns) of input signals that represent long texts. Thisenables circuits to detect when a long text is input, and to avoid any
further unnecessary operations. The circuit also sets up patterns that-2-avoid searching for (will not run CAM cells for) empty spaces within
index data that has no characters. These two patterns allow circuits to
cut power consumption by reducing the processing required for a text
search.

Logic integrated circuits that use this multi-functional CAM cell for
text search will only run circuits that are necessary. This, incombination with its nonvolatile characteristics, reduces standby powerand significantly reduces overall power consumption.

2. 1Mb prototype chip fabrication and demonstration
The prototype chip has been fabricated and demonstrated using a 90 nm
CMOS circuit (Note 4) and a perpendicular MTJ (Note 5) device. It canstore character strings up to 1 Mb in volume, which stores 4,000 index
words of up to 32 letters. The prototype chip conducted search
operations consuming just 25.7 mW of power with almost zero standby
power.

This reduced power consumption to 1% or less of conventional search
processing methods using DRAM and CPU. In the future, gigabit-level
spintronics-based logic LSIs for text search systems are expected tohelp enable the commercialization of these technologies.

Tohoku University and NEC present their latest findings on June 13 at the2013

SymposiumonVLSI

Circuits,

aninternational

meeting

semiconductor circuit technology held in Kyoto from June 11-14.

Part of these findings were obtained through the Cabinet Office’s Funding
Program for World-Leading Innovative R&D on Science and Technology-3-on

(Subject Title: “Research and Development into Energy Efficient Spintronics
Logic Integrated Circuits”; directed by Professor Hideo Ohno of Tohoku
University) (Note 6).

Note 1:

Spintronics-based logic integrated circuit technology uses intrinsic characteristics ofelectrons – negative charge and minute spin (Note 1b) magnetics – to reverse the magnet’s
N/S poles according to the direction of electric current in order to memorize calculation
results. The technology allows all circuits on the logic integrated circuit to be nonvolatile.
Since nonvolatile circuits are effective in achieving less power consumption in ICT
equipment and systems, Tohoku University and NEC have applied this spintronics
technology to develop prototypes including an all-purpose integrated circuit (TCAM, Note1c) and an image processor, and run verification tests on these prototypes (Note 1d).

Note 1b: “Spin” is one of the properties of electrons (an elementary particle with negative electriccharge) that makes them behave like tiny magnets.
Note 1c: TCAM (ternary content-addressable memory) refers to a ternary state of stored data with a
two-bit memory circuit within the cell in order to give it a masking feature to achieve
flexible searching.
Note 1d: http://jpn.nec.com/press/201302/20130219_02.html
Note 2: Logic-in-memory is an architecture that locates memory and logic circuits near poles toshorten wiring distance and thereby cut delays in data transfer and use minimum power. It isalso called logic-embedded memory.
Note 3: CAM (content-addressable memory) is the collective name for search-use hardware that can
detect matches between search data and an extensive amount of stored data.
Note 4: CMOS circuit: A circuit structured by combining transistors of N and P channel types
Note 5: MTJ: magnetic tunnel junctionNote 6: The Funding Program for World-Leading Innovative R&D on Science and Technology is anational project with the goal of improving Japan’s international competitiveness byselecting core researchers in cutting-edge technologies and then pursuing research anddevelopment centered on these core researchers.

Press Contact:Tohoku University
Center for Spintronics Integrated Systems
Yutaka Kadowaki+81-22-217-6116
yut-kado@riec.tohoku.ac.jp-4-NEC Corporation
Corporate Communications Division
Joseph Jasper+81-3-3798-6511
j-jasper@ax.jp.nec.com