By Phil LoPiccolo, Editor-in-Chief
Researchers investigating the intersection of biology and electronics will share their latest findings at the 52nd annual International Electron Devices Meeting (IEDM), Dec. 11-13 in San Francisco. Several of the presentations exploring this new frontier, from a total of than 225 papers from corporate, university, and government labs worldwide, will examine the innovative use of biologically directed self-assembly and patterning techniques to enhance nanodevice fabrication.
One novel technique, described in a paper from Matsushita in Japan, proposes fabricating nanoelectronic devices using self-assembling protein molecules. This approach takes advantage of several traits of proteins that make them ideal tools for forming precise nanostructures — they can self-assemble into complex and orderly arrangements, sequester inorganic materials useful in device manufacturing, and can be selectively removed from substrates while leaving the inorganic materials in place.
Specifically, the researchers employed apoferritin, a cage-shaped protein that permits ions to pass through its outer shell and “biomineralize” in its core, to synthesize such materials as ferrihydrite, chromium hydroxide, indium oxide, and other compounds (see figure below). After a layer of ferrihydrite-carrying apoferritin is placed directly on a silicon substrate, it self-assembles into a hexagonally close-packed array. When the protein is eliminated by heat or a UV/ozone treatment, an array of high-density nodes remains to form a floating nanogate memory. Matsushita claims that this new “bio nano process” opens up new pathways to bottom-up nano-structure fabrication.
Another paper, from CEA Saclay in France, describes a different biologically directed self-assembly approach, in this case to address the challenge of precisely arranging carbon nanotubes (CNT) onto integrated circuits. The technique makes use of DNA templates to pattern areas in a substrate to which the CNTs suspended in a solvent are selectively attracted. The researchers developed an e-beam lithography process to form patterned monolayers of a silane compound onto a SiO2 substrate. The method reportedly yields highly selective deposition of single- or multiwalled CNTs onto the substrate. FET devices built with the nanotubes demonstrated high-frequency (8GHz) performance and the ability to perform frequency mixing at rates up to 40GHz. The devices can be controlled electronically as well as optically, when coated with an optically active polymer, the researchers note, adding that the device could be used as a new type of multilevel memory.
Several other presentations will also look at bio-assisted techniques. For example, a paper out of Duke U. describes recent progress the university has made on several bio-nanotech fronts, including using DNA tiles as building blocks to study self-assembly nanofabrication, fabricating highly conductive metallic nanowires templated on DNA molecules, and building DNA-based nanotubes and nanoarrays. In addition, a paper from IBM researchers describes a biochemically driven polymer self-assembly method for patterning sublithographic features and ICs. Target applications include patterning nanocrystal floating gates for flash memories, defining dense FET channel arrays, and roughening capacitor surfaces to increase area and improve the efficiency of shallow-trench array devices.
IEDM presenters describing research in DNA-driven self-assembly contend that the technique holds enormous prospects for manufacturers of future generations of semiconductor devices. One advocate of this vision is Thom LaBean, of Duke U.’s computer science and chemistry department, and author of an IEDM paper on self-assembling DNA nanostructures and DNA-based nanofabrication.
“DNA is well known as the predominant chemical for duplication and storage of genetic information,” LaBean explains. “Properly designed synthetic DNA can be used as programmable building blocks that, via specific hybridization of complementary sequences, will reliably self-organize to form desired structures and superstructures.”
Such engineered nanostructures are suitable for use as templates and scaffolds for imposing specific patterns on various other materials, including metal and semiconductor nanoparticles, carbon nanotubes, and biomolecules, notes LaBean. And given the diverse mechanical, chemical, catalytic, and electronic properties of these specifically patterned heteromaterials, DNA is rapidly becoming a vital engineering material for the bottom-up nanofabrication of micron-scale objects with nanometer-scale feature resolution. — P.L.
Next week WaferNEWS will review more IEDM paper proposals that show how fabricated devices made by these biological processes are poised to return the favor, by advancing biological and medical research.