Technology News
05/01/2001
Bell Labs plastic superconductor
Lucent Technologies Bell Labs, Murray Hill, NJ, has created the world's first plastic material in which resistance to the flow of electricity vanishes below a certain temperature, making it a superconductor. Researchers believe that this inexpensive material could be widely used in future applications, such as quantum computing and superconducting electronics.
The work of Bell Lab researchers Ananth Dodabalapur, Zhenan Bao, Christian Kloc, and others was recently published in the magazine Nature.
"[This work] emphasizes that interdisciplinary work, involving both synthetic chemistry and condensed-matter physics, will advance the frontiers of both fields," wrote Denis Jérome at the Universitß Paris-Sud, Orsay, France, and Klaus Bechgaard at Risø National Laboratory, Denmark, in a commentary in Nature.
Added Prof. Olle Inganas of Linkoping University in Sweden, an authority in the field of organic materials: "This is stunning and truly beautiful work, and opens new vistas for coming studies."
The Bell Labs breakthrough was made possible by a multidisciplinary team of researchers whose backgrounds range from experimental low-temperature physics to materials science and organic chemistry.
Others involved with this work included Hendrik Schon and Bertram Batlogg. A collaborator from the University of Konstanz in Germany, Ortwin Schenker, also participated in the research. In addition to Bell Labs, Batlogg is affiliated with the solid-state physics laboratory at ETH Honggerberg in Switzerland.
The challenge in creating a plastic superconductor was overcoming the inherent structural randomness of a polymer — similar to strands of cooked spaghetti — that prevents the electronic interactions necessary for superconductivity. The Bell Labs scientists were able to overcome this by making a solution containing the plastic polythiophene.
They then deposited thin films of the solution onto an underlying layer so that the polymer molecules stacked up against one another like uncooked spaghetti. Instead of adding chemical impurities to change the material's electrical properties, as is often done, the researchers used a novel technique in which they removed electrons from the polythiophene.
The temperature below which polythiophene became superconducting was -455°F. Although this is extremely cold, these scientists are optimistic that they can raise the temperature in the future by altering the molecular structure of the polymer.
Polythiophene, which can be a conductor at room temperature and which has been used previously in making optoelectronic components and smart pixels, may be the first of many superconducting plastics.
"With the method we used, many organic materials may potentially be made superconducting now," said Bao of Bell Labs. There, scientists plan to study the inter-relationships among semiconducting, superconducting, and molecular electronics with materials such as polythiophene in the coming months.
New "nanobelts" hailed for more promising nanodevices
Research at the Georgia Institute of Technology has created a new type of nanometer-scale structure — dubbed nanobelts — that could be the basis for inexpensive ultra-small sensors, flat panel display (FPD) components, and other electronic nanodevices. This is the work of Zhong
Lin Wang (Fig. 1), professor of materials science and engineering and director of the university's Center for Nanoscience and Nanotechnology.
Wang says, "Current research in one-dimensional systems has largely been dominated by carbon nanotubes [see for example, "Y-junction carbon nanotubes behave like electronic devices at room temperature," Solid State Technology, January 2001, p. 32]. We are exploring other one-dimensional systems that may have important applications for nanoscale functional and smart materials. Our nanobelts are the next step in developing structures that may be useful in wider applications."
Wang and his group members, Zhengwei Pan and Zurong Dai, have produced nanobelts from oxides of zinc, tin, indium, cadmium, and gallium. These materials were chosen because they are transparent semiconducting oxides that are the basis for many functional and smart devices being developed today. But Wang believes other semiconducting oxides may also be used to make the unique structures.
 Figure 1. Zhong L. Wang with an oxide powder sample and high-temperature furnace in background. (Photo by Gary Meek, Georgia Tech Research Corp.) |
According to Wang, production of nanobelts is simple and should scale-up easily for high-volume production at industrial quantities. At Georgia Tech, the group places commercially available metal oxide powders in the center of an alumina tube. This tube is heated in an argon or nitrogen atmosphere to just below the melting point of the particular powder (~1100-1400°C). The powder evaporates and then forms a crystalline nanobelt as it returns to solid phase on an alumina plate in a cooler part of the furnace. No purification is needed. This process requires control of temperature, pressure, and processing times, but the growth of the nanobelts does not appear sensitive to temperature fluctuations or variations in the processing time.
Finished nanobelts appear as clumps that resemble a wad of cotton; under a microscope they appear like shredded paper (Fig. 2a). Despite their origin in normally brittle oxide compounds, the nanobelts are flexible and can be bent 180° without breaking (Fig. 2b). Typical widths are 30-300nm, thicknesses 10-15nm. Some have been produced in lengths of up to a few millimeters, though most are tens to hundreds of microns long.
"The crystallographic structure varies a great deal from one oxide to another, but they all have a common characteristic as part of a family of materials that have ribbon-like structures with a narrow rectangular cross-section," Wang explained. "In comparison to the cylindrical symmetric nanowires and nanotubes reported in the literature, these are really a distinctive group of materials."
Although nanobelts may not have the high structural strength of cylindrical carbon nanotubes, they make up for this characteristic with a uniformity that could make them useful in electronics and optoelectronics. Processes for producing carbon nanotubes still cannot be controlled well enough to provide large volumes of high purity, defect-free structures with uniform properties. Nanobelts, however, can be produced with structural control, allowing large quantities to be made in pure form and mostly defect-free.
"Defects in any nanostructures strongly affect their electronic and mechanical properties and possibly cause heating when electrical current passes through them. This creates problems if you want to integrate them into smaller and smaller devices at a high density," Wang noted. "More importantly, defects can destroy quantum-mechanical transport properties in nanowire-like structures, resulting in the failure of quantum devices fabricated using them."
Nanowires made of silicon and other materials have also generated interest, but these structures oxidize and require complex cleaning steps and handling in controlled environments. As oxides, however, nanobelts do not have to be cleaned or handled in special environments and their surfaces are atomically sharp and clean.
Based on known properties of the oxide nanobelts, Wang outlines for Solid State Technology at least three significant applications:
- Zinc oxide and tin oxide nanobelts could be the basis for ultra-small sensors because the conductivity of these materials changes dramatically when gas or liquid molecules attach to their surfaces.
- Tin-doped indium oxide nanobelts provide high electrical conductivity and are optically transparent, making them candidates for use in FPDs.
- Because of their response to infrared emissions, nanobelts of fluoride-doped tin oxide could find application in smart windows able to adjust their light transmission and heat preservation.
 Figure 2. a) Micrograph showing a "clump" of semiconducting zinc-oxide nanobelts and b) a TEM of an individual nanobelt. |
"This is a vitally important area of nanotechnology," says Wang. "If we are successful at these applications, it may lead to major technological advances in nano-size sensors and functional devices with low power consumption and high sensitivity."
The Georgia Tech researchers have done preliminary studies of nanobelt properties, though they would still like to learn more about the optical, electrical, and surface characteristics.
Wang expects that nanobelt technology will spawn a new area of nanoscience research.
"I believe this area will expand very rapidly. Just like carbon nanotubes, these nanobelts provide a new nanomaterials system that allows people to study nanoscale physics and device fabrication using smart and function oxide materials," he said. "Anybody can make these, and there is a lot to measure. There is certainly enough to be discovered to occupy researchers for several years."
IBM, MOSIS get SiGe with it
As demand continues for wireless product chips, IBM is opening access to its SiGe wafer production technology.
To assist emerging companies and universities worldwide in developing innovative SiGe chip designs using IBM's processes, Big Blue reached out to MOSIS, a 20-year-old high-tech cooperative based in Marina del Rey, CA.
The agreement will allow small companies and schools to develop SiGe chips and then combine their semiconductor designs into single runs at IBM's Burlington, VT, facility. Under the SiGe Multi-Project Wafer (MPW) initiative, customers share development and manufacturing expenses by submitting the chip designs, often prototypes, for consolidation and manufacture on a single wafer. MOSIS will contract directly with customers to integrate multiple chip designs onto a single mask set and arrange for MPW production through IBM.
 IBM's SiGe wafers |
"We created the SiGe MPW initiative to extend the reach of our advanced semiconductor technology to a community of talented chip designers who normally would not have an opportunity to work with IBM," said Kenneth Torino, director of wireless products for IBM. "By helping more companies and universities achieve easier access to the technology for prototype design, we intend to establish a solid base of current and future customers experienced with IBM's SiGe technology."
The benefits obviously flow both ways. Wes Hansford, deputy director of MOSIS, added, "IBM is creating a unique opportunity for chip designers by offering easier access to its advanced silicon germanium chip technology. This program will enable MOSIS customers to develop chips for high-performance, high-frequency applications such as wireless handsets."
IBM is also working with Cadence Design Systems of San Jose, CA, to provide cost-effective design services, design kit installation support, and a design software package to help facilitate the process for participants in the SiGe MPW program.
Teddy O'Connell, senior manager of wireless strategy and technical marketing at IBM, told SST that the evolution of wireless electronic devices will drive an increase in demand for SiGe chips, because of the properties the semiconductors possess.
"As we start to move forward in the wireless industry, things are starting to change. We're moving from purely voice communications to voice and data communications," said O'Connell. "You're going to need circuitry architectures that are very different. [As] RF subsystems change, you will need a much higher degree of linearity."
The wireless shift will also require semiconductors that use less power, to allow portable devices longer running time on DC power, said O'Connell. The chips will also have to perform well at higher frequencies, like the 2 GHz range, because the bandwidth at the current wireless frequency spectrum is already getting congested.
"All of these things are bringing about a need for a new technology," said O'Connell. "SiGe shines in all these attributes."
The benefit of working with a partner like MOSIS, said O'Connell, is the development of tomorrow's customer base.
"This allows us to get SiGe out there to everybody. We believe it's going to be the dominant technology," said O'Connell. "If MOSIS was not there, I think there would be fewer people able to take advantage of this technology who would probably end up using another technology which would not be optimal for their application."
Tech Briefs
Daikin Industries and Asahi Glass each say they are ready to start sampling highly transparent fluoropolymers for making 157nm photoresists. Selete reports Asahi's fluoropolymer has an "absorption coefficient of 1.5-1.0mm or less for 157nm light, resistance to dry etching comparable to that of ArF materials, and is soluble in standard developer solution." These properties make it a potential candidate for a platform for positive resist for exposure with fluoride dimmer laser sources. Daikin says its fluoropolymer base is more than 60% transparent.
Schlumberger has introduced a probe system based on the picosecond imaging circuit analyzer (PICA) technology that it licensed from IBM over a year ago. The PICA technology, which images light emitted as electrical signals travel around semiconductors devices, can be used to gather timing data and identify faults in ICs. This allows non-invasive de-bug of new devices in flip chip format, and Schlumberger is targeting such leading edge technologies as 0.13µm and SOI processes.
One fundamental difference between Schlumberger's new probe system and other such technologies is that it images something occurring on the device, rather than using a beam that interacts with the device, to gather information about a specific location on the device. This differentiates it from other probing or analysis techniques, allowing a bigger picture of the device behavior. The PICA process on Schlumberger's tool can also run unattended, with the output being stored electronically. This capability makes the results more accessible to engineers at different locations, who might be either working on the same project or addressing separate issues.