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Successful Development of New Next-Generation
Non-Volatile Memory cell.
( December 24, 2003 )
Asahi Glass Co., Ltd.
Bio Devices Lab., Dept. of Bioengineering and Robotics,
Tohoku University
Asahi Glass Co., Ltd. (headquarters: Tokyo; President: Shinya
Ishizu) and research group led by Koyanagi, professor of Graduate
school of Engineering, Tohoku University, have succeeded in
development of a new non-volatile memory, named Metal
Nano Dot (MND) Memory (Fig.1,2). The MND memory is
applied the deposition technology of MND film based on the
synergy ceramic technologies possessed by Asahi Glass Co.
As is shown in Fig.3, the MND film is composed extremely high
dense metal nano dots embedded in insulating matrix. The MND
memory is expected to be substituted for existing flash Memory
in the near future.
While Asahi Glass Co. has leveraged the broad array of materials
and technologies it has cultivated over many years, encompassing
both inorganic and organic materials (such as glass, ceramics
and chemical products), it develops, manufactures and markets
semiconductor devices & materials. The new memory is an
application of the formation technology on the ultra fine
metallic structure embedded in insulator, which was derived
through research into synergy ceramics, a national project
in which Asahi Glass Co. has been involved.
Meanwhile, Professor Koyanagi has been engaged in design and
fabrication of sub-micron semiconductor devices, one of the
most famous researchers in the world. And his research group
has obtained excellent results.
Demand to a high density and high performance non-volatile
memory has rapidly grown as the market of mobile information
devices has expanded in recent years, therefore many kinds
of non-volatile memories have been proposed and investigated.
Flash memory is the most widely used of the non-volatile memories,
because of its high density, low manufacturing cost and stable
operation and so on. However, it is said that scaling-down
of the flash memory cell size has become more and more difficult
because the tunneling oxide thickness can not be scaled down
with the cell size due to keeping excellent charge retention
and endurance. In order to solve this problem, new types of
memory cells, such as silicon nano dots memory and MONOS memory,
have been proposed. However, these memories do not have sufficiently
high density of charge retention sites, therefore magnitude
and uniformity of memory window are not enough. Professor
Koyanagi paid attention to the MND film developed by Asahi
Glass Co. to apply to new non-volatile memory, the MND memory,
and has worked with Asahi Glass engineers on the trial devices.
The fabrication of the trial devices was carried out at Venture
Business Laboratory of Tohoku University.
The followings feature the MND Memory
| (1) |
In the conventional flash memory cell and
the silicon nano dots memory, floating gates retaining
charges are made of silicon. On the other hand, in the
MND Memory the MND film is used as charge retention layer,
and each metal nano dot in the MND film works as a floating
gate. The MND film consists of metal nano dots with diameter
of around 2 nanometers dispersing at high density in insulator
such as silicon dioxide (Fig. 3). Compared with the size
and the density of the silicon nano dots conventionally
studied, the size of the metal nano dots is about less
than half, and the density is higher than 10 times, about
2 x 1013/cm2.
These features enable to stabilize the memory operation
due to wide and uniform memory window and also deliver
on dramatic gains in long retention time and excellent
endurance even in highly advanced scaling down device
in future. |
| (2) |
Since the sputtering method is applied
to the MND film deposition, it can be formed readily and
at low cost. The metal nano dot is formed self-organically
in the insulating matrix, and the MND film grows with
phase separating of metal and insulator. Therefore, no
special treatment for formation of the metal nano dots,
such as heating after film formation, is required. As
characteristics of trial MND memory device with these
remarkable features was successfully evaluated, it was
highly attracted audiences' attention at the International
Electron Devices Meeting 2003 held in Washington D.C.
from December 8 to December 10. |
In the near future, Asahi Glass Co. intends to license the basic
technologies on the MND Memory to semiconductor manufacturers,
and hopes to increase the share in the existing flash memory
market (1 trillion yen) and magnetic storage media market such
as hard disk (2.6 trillion yen).
For questions and comments on the subject, please direct
your inquiries to:
Shinichi Kawakami, Director, Corporate Communications
Division, Asahi Glass Co., Ltd. |
(Person in charge: Y. Saito
Tel: 03-3218-5509 E-mail: info-pr@agc.co.jp) |
<Reference>
Fig. 1 Cross sectional SEM image of MND Memory cell. |
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Fig. 2 Cross sectional diagram of MND Memory cell |
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Fig. 3 Cross sectional TEM image of MND (Co/SiO2)
film |
<Terms>
1. Synergy ceramics
The name of synergy ceramics is derived from Research &
Development Program of Synergy Ceramics, the name of a project
started in 1994 under the Research & Development System
for Industrial Science and Technology, which was organized by
Agency of Industrial Science and Technology of the then Ministry
of International Trade and Industry (now the Ministry of Economy,
Trade and Industry). The term of "synergy" denotes
symbiosis and cooperative effects. The project aims to create
revolutionary ceramic materials that allow for highly advanced
symbiosis and the synergic effects of properties and functions
(that are regarded as difficult to maintain concurrently), under
the concept of "structural control at advanced dimensions,"
intended for controlling several structures of materials simultaneously.
2. Non-volatile memory
Non-volatile memory denotes semiconductor memory that retains
stored data even power supply stops. ROM (Read Only Memory)
is one of the non-volatile memories. In the narrow sense,
it refers to ROM that allows writing and erasure, or flash
memory.
3. Floating gate
Floating gate works as charge retention part in flash memory,
electrically floating due to embedded in insulator between
substrate and control gate.
4. Sputtering method
The sputtering method is that, ions are accelerated to hit
target in plasma, and the sputtered atoms of the target are
depositing on wafer.
5. International Electron Devices Meeting
Nicknamed the "World Cup of Semiconductor", the
International Electron Devices Meeting is one of the most
authoritative meeting on semiconductor in the world at which
leading-edge device development results from around the world
are carefully screened out and reported. It is held in December
annually in the United States.
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