Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

New way to make nanoscale circuits is discovered

24.08.2004


An electron microscope image of a junction between bulk strontium titanate (left) and oxygen-deficient strontium titanate (right). Each bright-orange blob is a cluster of "oxygen vacancies" -- areas of missing atoms. The larger red dots are the strontium atoms and the smaller ones are the titanium atoms. Cornell Center for Materials Research


Time is fast running out for the semiconductor industry as transistors become ever smaller and their insulating layers of silicon dioxide, already only atoms in thickness, reach maximum shrinkage. In addition, the thinner the silicon layer becomes, the greater the amount of chemical dopants that must be used to maintain electrical contact. And the limit here also is close to being reached.

But a Cornell University researcher has caused an information industry buzz with the discovery that it is possible to precisely control the electronic properties of a complex oxide material -- a possible replacement for silicon insulators -- at the atomic level. And this can be done without chemicals. Instead, the dopant is precisely nothing.

In a paper in a recent issue of Nature (Aug. 5, 2004), David Muller, associate professor of applied and engineering physics at Cornell, and his collaborator, Harold Hwang of the University of Tokyo, report that by removing oxygen atoms from layers in thin films of the oxide strontium titanate, they can precisely control the conducting ability of the material by creating empty spaces, or vacancies, that act as electron-donating dopants. And they have used a scanning transmission electron microscope (STEM) to tell exactly where the missing atoms are in the material.



Across the semiconductor industry, such complex oxides are being sought as a replacement for silicon. The roadblock is that all the oxides tested easily lose a few oxygen atoms, making them leaky and defective when exposed to electric fields, typically stronger than those inside a lightning bolt.

"The important parts of the work are actually being able to see vacancies buried inside the material," says Muller. "From a materials analysis point of view, that’s very important. The reason is that missing atoms can change the properties of a material very dramatically." He adds, "We have been able to show that we can stop on a dime in controlling where you put these vacancies."

In an accompanying commentary to the Nature article called "The value of seeing nothing," Jochen Mannhart of the University of Augsburg, Germany, and Darrell G. Schlom of Pennsylvania State University, observe that the research by Muller and his colleagues "greatly broadens the options available for manipulating the electronic properties of oxides" at the nanometer scale. A nanometer is the width of three silicon atoms.

Strontium titanate is a titanium-containing material, known commercially as Lustigem, that was once popular as a diamond substitute. It is the simplest of the complex oxides and the one that can be made in the largest quantities. "The big problem with doing any work with oxides is that they form vacancies very easily," says Muller. "And generally this was viewed as a bad thing because the vacancies acted as dopants that couldn’t be controlled."

In his Tokyo laboratory, Hwang used a popular research technique called pulsed laser ablation, in which thin films of oxide materials are deposited layer by layer in a vacuum chamber. The atoms were deposited on the material in dribbles; in fact one laser blast deposited only 1/20th of a layer of the material. In this way layers of the material were built up, some only one atom thick. When Hwang decided to deposit a layer without atoms -- with vacancies -- he reduced the oxygen pressure inside the vacuum chamber. When atoms were laid down, says Muller, the process happened at great speed so that the atoms were "frozen into place" and thus lacked the energy to break their bonds and move into the next layer.

At Cornell, Muller used the STEM to identify exactly where each vacancy -- that is, the absence of one atom -- was in the layers within the strontium titanate. The emptiness itself was invisible, but the clusters of atoms around the vacancy caused a telltale excess scattering of electrons.

"This is the first step in making devices from strontium titanate," says Muller. "The question we now have to answer is, what happens if you pass huge currents through these materials?" Generally, though, he says, the ability to detect vacancies at the single-atom level is going to be very important for "debugging" these new semiconductor materials "because the problem is that vacancies at such low concentrations don’t show up in many of the traditional physical characterization methods."

Does this research mean that a new era of manipulating the electronic properties of oxides for semiconductors at the nano scale is close at hand? "I think we can do it now much better than we could before," says Muller. "We can tell what’s happening to every atom in the system, whereas before you knew on average if things worked out or if they didn’t. Now you can go out and identify the culprits at fault."

Muller and Hwang began their research at Bell Laboratories, Lucent Technologies. Their continuing research at Cornell was supported by the National Science Foundation-funded Cornell Center for Materials Research (CCMR). Their other collaborators on the Nature paper were John Grazul, co-manager of the Electron and Optical Microscopy Facility at CCMR; Naoyuki Nakagawa of the University of Tokyo; and Akira Ohtomo of Tohoku University, Japan.

David Brand | EurekAlert!
Further information:
http://www.cornell.edu

More articles from Process Engineering:

nachricht Design treatment of advanced metals producing better sculpting
08.03.2019 | Purdue University

nachricht Laser Processes for Multi-Functional Composites
18.02.2019 | Fraunhofer-Institut für Lasertechnik ILT

All articles from Process Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Magnetic micro-boats

Nano- and microtechnology are promising candidates not only for medical applications such as drug delivery but also for the creation of little robots or flexible integrated sensors. Scientists from the Max Planck Institute for Polymer Research (MPI-P) have created magnetic microparticles, with a newly developed method, that could pave the way for building micro-motors or guiding drugs in the human body to a target, like a tumor. The preparation of such structures as well as their remote-control can be regulated using magnetic fields and therefore can find application in an array of domains.

The magnetic properties of a material control how this material responds to the presence of a magnetic field. Iron oxide is the main component of rust but also...

Im Focus: Self-healing coating made of corn starch makes small scratches disappear through heat

Due to the special arrangement of its molecules, a new coating made of corn starch is able to repair small scratches by itself through heat: The cross-linking via ring-shaped molecules makes the material mobile, so that it compensates for the scratches and these disappear again.

Superficial micro-scratches on the car body or on other high-gloss surfaces are harmless, but annoying. Especially in the luxury segment such surfaces are...

Im Focus: Stellar cartography

The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in Arizona released its first image of the surface magnetic field of another star. In a paper in the European journal Astronomy & Astrophysics, the PEPSI team presents a Zeeman- Doppler-Image of the surface of the magnetically active star II Pegasi.

A special technique allows astronomers to resolve the surfaces of faraway stars. Those are otherwise only seen as point sources, even in the largest telescopes...

Im Focus: Heading towards a tsunami of light

Researchers at Chalmers University of Technology and the University of Gothenburg, Sweden, have proposed a way to create a completely new source of radiation. Ultra-intense light pulses consist of the motion of a single wave and can be described as a tsunami of light. The strong wave can be used to study interactions between matter and light in a unique way. Their research is now published in the scientific journal Physical Review Letters.

"This source of radiation lets us look at reality through a new angle - it is like twisting a mirror and discovering something completely different," says...

Im Focus: Revealing the secret of the vacuum for the first time

New research group at the University of Jena combines theory and experiment to demonstrate for the first time certain physical processes in a quantum vacuum

For most people, a vacuum is an empty space. Quantum physics, on the other hand, assumes that even in this lowest-energy state, particles and antiparticles...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

International Modelica Conference with 330 visitors from 21 countries at OTH Regensburg

11.03.2019 | Event News

Selection Completed: 580 Young Scientists from 88 Countries at the Lindau Nobel Laureate Meeting

01.03.2019 | Event News

LightMAT 2019 – 3rd International Conference on Light Materials – Science and Technology

28.02.2019 | Event News

 
Latest News

To proliferate or not to proliferate

21.03.2019 | Life Sciences

Magnetic micro-boats

21.03.2019 | Physics and Astronomy

Motorless pumps and self-regulating valves made from ultrathin film

21.03.2019 | HANNOVER MESSE

VideoLinks
Science & Research
Overview of more VideoLinks >>>