Web Date: October 1, 2013
Proteins Help Researchers Build A Memory Device
In recent years, researchers have explored using proteins as scaffolding to build electronics at the nanoscale. Compared to current fabrication techniques, using proteins to arrange nanoparticles onto surfaces could enable the design of smaller memory devices and more complex, multilayer electronics. Now, researchers in Japan and Taiwan have demonstrated the first working flash memory device made using this biological approach (Langmuir 2013, DOI: 10.1021/la402742f).
Flash memory is found in devices such as camera memory cards and USB flash drives that rely on fast access to data. Improving the speed and storage capacity of the devices requires reducing the size of the memory cells that store bits of information, so engineers can fit more in a given volume. Using nanoparticles as those memory nodes is one way to achieve those goals. But traditional fabrication techniques, such as physical and chemical vapor deposition, require large, expensive machines and offer limited control over the size, shape, position, and density of nanoparticles.
Atsushi Miura, a chemist at the National Chiao Tung University, in Taiwan, and his colleagues think the biological scaffolding approach offers some advantages over the traditional approaches. The biological method is inexpensive, and because the protein scaffolds can self-assemble, the technique opens the possibility of precisely manipulating molecular design inside electronics with little effort from the engineers, Miura says. It also provides a way to deposit multiple layers of nanoparticles with more precision than traditional techniques can.
The researchers, including Ken-Ichi Sano of Nippon Institute of Technology, in Japan, wanted to show that they could use a biological approach to make devices of the same quality as those made with traditional fabrication methods. They started with a hollow, cage-shaped protein called ferritin. The cage, which is 7 to 8 nm in diameter, can house a range of inorganic nanoparticles. The researchers genetically engineered ferritin with peptides on its surface that have the ability to bind to silicon oxide.
To make the nanoparticles, the team mixed iron ions in a solution with ferritin. The ions flowed through channels in the ferritin cage and collected inside. Through redox chemistry within the cage, iron oxide forms. Then the researchers deposited the nanoparticle-smuggling molecules onto a silicon oxide layer on a silicon substrate. The peptides on the ferritin surface helped the proteins bind to the surface. Next, the researchers added another layer of silicon oxide on top. They then repeated the process, building multiple layers of iron-oxide-loaded ferritin molecules. After they added the desired number of layers, they treated the structure with ultraviolet light and ozone to remove the protein and leave behind the nanoparticles, which serve as the device’s memory cells. Finally, the researchers added electrodes to complete the device.
According to Miura, their multilayer flash memory device had twice the memory capacity of a conventionally made single-layer device, reflecting the increased amount of charge it can store. Their device was also stable over time, Miura says: The devices continued working even after 10,000 operations in which the cells were written to and subsequently erased.
Rajesh R. Naik, a materials scientist at the U.S. Air Force Research Laboratory, says that biomedical researchers have used protein cages like ferritin for years in medical diagnostics or to deliver drugs. Now the proteins have found their way into electronics fabrication. The novelty of this group’s work, he says, is in showing that the proteins can yield functional electronics.
Because the protein cages can also transport nanoparticles useful for solar cell applications, including zinc selenide and zinc sulfur, Sano and his team want to build solar cells with the proteins.
- Chemical & Engineering News
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