blasts make cheap memory
Technology Research News
In today's factories, memory chips are
made by shining lasers through patterned masks onto silicon wafers that
sport light-sensitive coatings, and then using chemicals to etch away
the exposed areas. This produces tiny cells that store the electrical
charges that represent digital bits.
Researchers from the National Institute of Advanced Industrial Science
and Technology (AIST) in Japan have found a simpler way to make these
memory chip cells.
They were able to dispense with the usual masks and chemicals and instead
zap layers of material with a laser. "Simplicity is the important advantage
in our technology," said Jooho Kim, a principal research scientist at
The researchers haven't yet made entire memory chips, but their process
to make individual memory cells is the first step toward manufacturing
memory in a considerably simpler and potentially cheaper way than those
used in today's factories. The cost of making memory using the technique
could be as low as 10 percent of the cost of today's technology, said
The new laser process could also be used to make semiconductor components
like solar cells and the photodiodes used in light sensors, according
To make the memory cells, the researchers sandwiched a 20-nanometer mix
of terbium, iron and cobalt metals between 50- and 100-nanometer layers
of mixed zinc sulfide and silicon dioxide insulators. A nanometer is one
millionth of a millimeter.
They fired a laser at the materials to heat small sections to temperatures
between 300 and 510 degrees Celsius. The heat melted the layers, causing
sulfur and oxygen from the insulating materials to mix with the metals.
This changed the electrical properties of the metals.
Depending on how much they heated the materials, the researchers were
able to turn sections into semiconductors, which allow less electric current
through than metals, or insulators, which block current entirely. Semiconductors
are useful for controlling the flow of electricity; electronic devices
generally consist of combinations of metals, semiconductors and insulators.
The researchers have formed 50-nanometer semiconductor and insulator dots
in the layers this way, according to Kim. The dots could be used to make
the cells in dynamic random access memory (DRAM) commonly used in today's
computers or flash memory chips used in devices like digital cameras,
The presence of a charge in a dot would represent a 1 and the absence
a 0. The dots could be changed from 0 to 1 by a specific type of electric
field, said Kim. When an electric current running through a metal or semiconductor
encounters a magnetic field oriented perpendicularly to the current, the
current and magnetic field spawn an electric field running through the
junction of the two like an arrow passing through the middle of an 'X'.
When the current and magnetic field intersect over a dot, the electric
field enters the dot, making it a 1, said Kim.
The researchers plan to read the bits by reversing the direction of the
electric current in order to detect the stored charge, Kim said. They
would erase bits to turn a 1 into a 0 by applying a decreasing, alternating
current, which drains the stored charge, he said.
The smaller the dots, the more information a memory chip can hold. It
is possible to make dots as small as 5 nanometers by using electron beams
rather than lasers to heat the chips, said Kim. This is because electrons
have much smaller wavelengths than visible or ultraviolet light; magnetic
fields can be used to focus beams of electrons to about one nanometer
or the length of 10 carbon atoms.
Using 5-nanometer dots, it would be possible to make memory chips that
contain 250 billion bits per square inch, according to Kim. This is 50
times more than today's RAM chips, which contain as many as 10 billion
bits per square inch, and 1,000 times more than today's flash memory chips,
which contain 250 million bits per square inch, he said.
Using regular lasers, the method could produce memory devices that hold
25 gigabits per square inch, or about a quarter the data today's memory
chips hold and 10 times more than today's flash memory, said Kim.
The limits of laser light could be a problem, however. The ultraviolet
lithography used to make today's memory chips is higher resolution than
the researchers' laser reaction process, said Franz Himpsel, a physics
professor at the University of Wisconsin. Because the AIST method depends
on a laser, "its wavelength puts a limit on the... resolution," he said.
Using electron beam lithography to increase the resolution may be impractical,
he added. Current electron beam lithography equipment is costly and is
not widely used in commercial chipmaking.
The laser reaction process could be used in practical applications in
two to five years, according to Kim.
Kim's research colleagues were Hiro Akinaga, Nobufumi Atoda and Junji
Tominaga of the National Institute of Advanced Industrial Science and
Technology in Japan. They published the research in the April 15, 2002
issue of the journal Applied Physics Letters. The research was funded
by the National Institute of Advanced Industrial Science and Technology
in Japan and Samsung Electronics Co., Ltd.
Timeline: 2-5 years
Funding: Government, Corporate
TRN Categories: Integrated Circuits; Data Storage Technology
Story Type: News
Related Elements: Technical paper, "Nanoelectronic Devices
with Reactively Fabricated Semiconductor," Applied physics Letters, April
Chip juggles droplets
reading into writing
Radio ID locks lost laptops
gets the picture
Laser blasts make memory
Research News Roundup
Research Watch blog
View from the High Ground Q&A
How It Works
News | Blog
Buy an ad link