| Posted: Oct 19, 2010 |
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New nanotechnology techniques integrate electron gas-producing oxides with silicon
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(Nanowerk News) In cold weather, many children can't resist breathing onto a window and writing in the condensation. Now imagine the window as an electronic device platform, the condensation as a special conductive gas, and the letters as lines of nanowires. A team led by University of Wisconsin-Madison Materials Science and Engineering Professor Chang-Beom Eom has demonstrated methods to harness essentially this concept for broad applications in nanoelectronic devices, such as next-generation memory or tiny transistors. The discoveries were published Oct. 19 by the journal Nature Communications.
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Eom's team has developed techniques to produce structures based on electronic oxides that can be integrated on a silicon substrate—the most common electronic device platform.
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"The structures we have developed, as well as other oxide-based electronic devices, are likely to be very important in nanoelectronic applications, when integrated with silicon," Eom says.
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The term "oxide" refers to a compound with oxygen as a fundamental element. Oxides include millions of compounds, each with unique properties that could be valuable in electronics and nanoelectronics.
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Usually, oxide materials cannot be grown on silicon because oxides and silicon have different, incompatible crystal structures. Eom's technique combines single-crystal expitaxy, postannealing and etching to create a process that permits the oxide structure to reside on silicon—a significant accomplishment that solves a very complex challenge.
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The new process allows the team to form a structure that puts three-atom-thick layers of lanthanum-aluminum-oxide in contact with strontium-titanium-oxide and then put the entire structure on top of a silicon substrate.
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These two oxides are important because an "electron gas" forms at the interface of their layers, and a scanning probe microscope can make this gas layer conductive. The tip of the microscope is dragged along the surface with nanometer-scale accuracy, leaving behind a pattern of electrons that make the one-nanometer-thick gas layer. Using the tip, Eom's team can "draw" lines of these electrons and form conducting nanowires. The researchers also can "erase" those lines to take away conductivity in a region of the gas.
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In order to integrate the oxides on silicon, the crystals must have a low level of defects, and researchers must have atomic control of the interface. More specifically, the top layer of strontium-titanium-oxide has to be totally pure and match up with a totally pure layer of lanthanum-oxide at the bottom of the lanthanum-aluminum-oxide; otherwise, the gas layer won't form between the oxide layers. Finally, the entire structure has been tuned to be compatible with the underlying silicon.
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