TOKYO----Feb. 16, 2007--In addressing the need for
next-generation high-density on-chip non-volatile memory technology,
Hitachi, Ltd. and Renesas Technology Corp. today announced the
development of a 512-kbyte (4-Mbit equivalent) phase change memory
module operating at a 1.5-V power supply voltage, which achieves
416-kbyte/sec high-speed write and read speeds with a 20-nanosecond(1)
access time. Using the previously developed "low-power phase change
memory cells" with a 100-uA (micro(2)-ampere) write current, the two
companies developed a peripheral circuit technology to enable the
high-speed write and read operations.
Hitachi and Renesas Technology presented these results at the
International Solid-State Circuits Conference (ISSCC) held in San
Francisco, U.S.A from February 11, 2007.
In recent years, microcontrollers have become core components in
various kinds of control and information devices ranging from
industrial equipment to in-vehicle systems, home electronics, and
mobile phones. As products become more sophisticated and versatile,
the amount of information handled by these microcontrollers has been
rapidly increasing. Therefore, these microcontrollers require higher
levels of performance and density in on-chip nonvolatile memory for
storing data and programs. At the same time, phase change memory is
becoming a promising candidate for next-generation on-chip nonvolatile
memory due to its high endurance of write cycles, simple structure,
and ease of fabrication.
Phase change memory is a type of nonvolatile memory that exploits
two-phase changes in electrical resistance of a film caused by Joule
heat, which is generated by a current -- an amorphous state(3) (high
resistance) and a crystalline state (low resistance). Using these
differences in electrical resistance as "1" and "0" information, it
performs storage and readout operations. Hitachi and Renesas
Technology have previously developed a low-power-operation phase
change memory that can be written with a 1.5-V power supply voltage
and 100-uA current using tantalum pentoxide for the interfacial layer.
As the write voltage can be lowered compared with conventional on-chip
nonvolatile memory, this memory offers advantages such as eliminating
a need for a power supply circuit that generates a high voltage within
a chip, helping to reduce the module size, and achieving a high level
of density. However, because the readout current is small, it is
critical to have a memory array circuit technology that enables
high-speed operation despite its small current.
Features of the newly developed circuit technology are as follows.
(1) Write circuit technology enabling high-speed writing with a small
1) Data write scheme with two-step current control
High-speed writing is achieved by controlling the current
flowing through the phase change film during writing in two
steps, first at 100 uA and then at less than 100 uA, and
generating Joule heat efficiently.
2) Serial write scheme
Normally, memory writing is performed simultaneously for
multiple bits that need to be written. As the current
necessary for writing is (cell write current x number of
bits simultaneously written), the peak current during
writing operation is large when many bits are written. A
serial write scheme has now been developed whereby bits are
written serially one at a time, and the peak current is
suppressed by allowing only one bit to be written.
(2) High-speed read circuit supporting minute read current
Despite its advantage in realizing write operations with a small
current, an earlier problem with phase change memory developed
by Hitachi and Renesas Technology was its slow reading time,
caused by the small readout current. Now, to solve this problem,
a read circuit has been developed in which a two-stage sense
amplifier (amplification circuit) is used, and a signal is
amplified gradually, optimizing the operating voltage of each
sense amplifier. Compared with the use of a single-stage sense
amplifier, amplification can be performed in a shorter time, and
a faster read time can be achieved while suppressing the sense
amplifier current consumption to 280 uA.
(3) Circuit technology enabling measurement of minute currents on the
order of nano-amperes
In order to test the quality of fabricated memory cells, it is
important to accurately measure the readout current value before
a signal is read. However, in normal operation, a minute readout
current on the order of nano-amperes is obscured by a current
leakage generated in the memory circuit, and it has been
difficult to measure accurately. Thus, a new circuit technology
has been developed that reduces current leakages to a minimum
level by optimizing the memory circuit voltage, making it
possible for the minute readout current of a memory cell to be
measured with a high degree of accuracy. Feeding back
measurement results to the manufacturing process makes it
possible to contribute to improvements in memory cell quality.
An experimental 512-kbyte memory module was fabricated using a
130-nm CMOS process, employing the newly developed circuit technology
for cells writable at 100 uA. Test results confirmed the possibility
of 416-kbyte/sec write operations and 20-nanosecond read operations,
and high-speed operation was achieved while maintaining the
performance of low-power-operation phase change memory cells.
This technology is expected to promote the implementation of
next-generation highly-integrated on-chip nonvolatile memory, and to
support significant advances in the development of future
microcontrollers for embedded systems.
About Hitachi, Ltd.
Hitachi, Ltd., (NYSE:HIT)(TOKYO:6501), headquartered in Tokyo,
Japan, is a leading global electronics company with approximately
356,000 employees worldwide. Fiscal 2005 (ended March 31, 2006)
consolidated sales totaled 9,464 billion yen ($80.9 billion). The
company offers a wide range of systems, products and services in
market sectors including information systems, electronic devices,
power and industrial systems, consumer products, materials and
financial services. For more information on Hitachi, please visit the
company's website at http://www.hitachi.com.
About Renesas Technology Corp.
Renesas Technology Corp. is one of the world's leading
semiconductor system solutions providers for mobile, automotive and
PC/AV (Audio Visual) markets and the world's No.1 supplier of
microcontrollers. It is also a leading provider of LCD Driver ICs,
Smart Card microcontrollers, RF-ICs, High Power Amplifiers, Mixed
Signal ICs, System-on-Chip (SoC), System-in-Package (SiP) and more.
Established in 2003 as a joint venture between Hitachi, Ltd.
(TOKYO:6501)(NYSE:HIT) and Mitsubishi Electric Corporation
(TOKYO:6503), Renesas Technology achieved consolidated revenue of 906
billion JPY in FY2005 (end of March 2006). Renesas Technology is based
in Tokyo, Japan and has a global network of manufacturing, design and
sales operations in around 20 countries with about 26,200 employees
worldwide. For further information, please visit
*Product names, company names, or brands mentioned are the
property of their respective owners.
(1) Nano: One billionth
(2) Micro: One millionth
(3) Amorphous state: A state in which atoms, molecules, and so
forth making up a solid do not have a regular structure like that of a
crystal. Also referred to as a noncrystalline state.
CONTACT: Renesas Technology Corp. (Japan)
Yoshinobu Sato, +81-3-6250-5554
Renesas Technology America, Inc. (US)
Akiko Ishiyama, +1-408-382-7407