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 Etching Microstructures with Lasers
25.10.2016 | Fraunhofer-Institut für Lasertechnik ILT

nachricht Applying electron beams to 3-D objects
23.09.2016 | Fraunhofer-Institut für Organische Elektronik, Elektronenstrahl- und Plasmatechnik FEP

All articles from Process Engineering >>>

The most recent press releases about innovation >>>

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

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

Im Focus: How to inflate a hardened concrete shell with a weight of 80 t

At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).

Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...

Im Focus: Bacterial Pac Man molecule snaps at sugar

Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.

The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

Nothing will happen without batteries making it happen!

05.01.2017 | Event News

 
Latest News

Water - as the underlying driver of the Earth’s carbon cycle

17.01.2017 | Earth Sciences

Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

17.01.2017 | Materials Sciences

Smart homes will “LISTEN” to your voice

17.01.2017 | Architecture and Construction

VideoLinks
B2B-VideoLinks
More VideoLinks >>>