Scientists build 'magnetic semiconductors' one atom at a timeJuly 28, 2006Princeton, N.J. - In a stride that could hasten the development of computer chips that both calculate and store data, a team of Princeton scientists has turned semiconductors into magnets by the precise placement of metal atoms within a material from which chips are made. The effort marks the first time that scientists have achieved this degree of control over the atomic-level structure of a semiconductor, a goal that has eluded researchers for many years. The team used this unique capability to make a semiconductor magnetic, one atom at a time. Team leader Ali Yazdani said that manipulating semiconductors could eventually revolutionize computers by exploiting not just the flow of electrons but also their quantum property, called spin, for computation. "Using the tip of a scanning tunneling microscope, we can take out a single atom from the base material and replace it with a single metal that gives the semiconductor its magnetic properties," said Yazdani, a Princeton professor of physics. "The ability to tailor semiconductors on the atomic scale is the holy grail of electronics, and this method may be the approach that is needed." The team, which also includes scientists from the University of Illinois at Urbana-Champaign and the University of Iowa as well as Princeton, will publish their results as the cover article of the July 27 issue of the scientific journal, Nature. By incorporating manganese atoms into the gallium arsenide semiconductor, the team has created an atomic-scale laboratory that can reveal what researchers have sought for decades: the precise interactions among atoms and electrons in chip material. The team used their new technique to find the optimal arrangements for manganese atoms that can enhance the magnetic properties of gallium arsenide. Implementation of their findings within the chip manufacturing process could result in a major advance in the use of both the magnetic "spin" as well as electric charge for computation. "Chips might take on many new capabilities once such 'spintronic' technology is perfected," Yazdani said. "One thing we might be able to do is make chips that can both manipulate data and store it as well, which right now generally requires two separate parts of a computer working together." Computers use two different kinds of technology to calculate results and store data. While semiconductor chips - often based on silicon or more advanced materials such as gallium arsenide - do the calculating, data storage has generally been accomplished with magnetic materials within floppy disks or reels of tape. Combining these functions into a single device could reduce the size and energy requirements of computer hardware, a perennial goal of the industry. Although gallium arsenide "doped" with manganese has been a promising candidate material for such dual-function chips for a decade, working with the material has proven frustrating for a number of reasons. One difficulty is that researchers have not been able to engineer the material with optimal magnetic properties. "Up until now, we have not had a way to control how the manganese sits in the gallium arsenide substrate," Yazdani said. "We could not specify, for example, how large the bits of manganese would be, or how far apart they would be located. And because we couldn't study how changing these variables affected the semiconductor's performance, it was hard to know what its ideal specifications should be. For the most part, we had to just crystallize the material - with the dopant arranged more or less randomly - and hope." Dale Kitchen, a reasearcher in Yazdani's lab and first author of the Nature paper, hit upon a solution while working with a high-tech tool used to explore complex materials called a scanning tunneling microscope, which operates very differently than a desktop optical microscope. The device has a finely-pointed electrical probe that passes over a surface in order to detect variations with a weak electric field. The team, however, found that the charged tip could also be used to eject a single gallium atom from the surface, replacing it with one of manganese that was waiting nearby. "The important thing technically was that we could incorporate the manganese into the underlying crystal lattice," Yazdani said. "If you want to study how the semiconductor functions, it would not have been enough merely to deposit the manganese on the surface. They needed to become a single integrated material." Using their new technique, the team was able to find the precise arrangements of manganese atoms that exhibited magnetic properties, the important factor in developing spin-based electronics. The experimental data agreed with theoretical work that had been performed by Michael Flatté and his group at the University of Iowa, which had anticipated the atomic arrangement that optimized magnetism in the experiments. Yazdani cautioned that his team's technique would not translate immediately into new chip technology but would benefit fundamental research by providing a testbed for exploring magnetism in other semiconductors. "We can now ask questions about these magnetic atoms and get answers," he said. "How does it affect the semiconductors' performance when you change their orientation, for example, or their distance from one another? Answers to these questions may allow us to link the electric current and magnetic spin within these new semiconductors, and that's a goal the field has been seeking for many years." Princeton University |
|||||||||||||||||||||
| Related Semiconductor Current Events and Semiconductor News Articles Empa scientists synthesize graphene-like material Two-dimensional carbon layers, so-called graphenes, are regarded as a possible substitute for silicon in the semiconductor industry. MIT: Better way to harness waste heat New MIT research points the way to a technology that might make it possible to harvest much of the wasted heat produced by everything from computer processor chips to car engines to electric powerplants, and turn it into usable electricity. New study confirms exotic electric properties of graphene First, it was the soccer-ball-shaped molecules dubbed buckyballs. Then it was the cylindrically shaped nanotubes. Now, the hottest new material in physics and nanotechnology is graphene: a remarkably flat molecule made of carbon atoms arranged in hexagonal rings much like molecular chicken wire. Small nanoparticles bring big improvement to medical imaging If you're watching the complex processes in a living cell, it is easy to miss something important-especially if you are watching changes that take a long time to unfold and require high-spatial-resolution imaging. JQI researchers create entangled photons from quantum dots To exploit the quantum world to the fullest, a key commodity is entanglement-the spooky, distance-defying link that can form between objects such as atoms even when they are completely shielded from one another. Working together to design robust silicon chips Designers of high-speed silicon chips have often had to compromise on performance levels for their integrated circuit designs because of physical weaknesses appearing during design verification or even in production. Understanding mechanical properties of silicon nanowires paves way for nanodevices Silicon nanowires are attracting significant attention from the electronics industry due to the drive for ever-smaller electronic devices, from cell phones to computers. Caltech scientists develop DNA origami nanoscale breadboards for carbon nanotube circuits In work that someday may lead to the development of novel types of nanoscale electronic devices, an interdisciplinary team of researchers at the California Institute of Technology (Caltech) has combined DNA's talent for self-assembly with the remarkable electronic properties of carbon nanotubes, thereby suggesting a solution to the long-standing problem of organizing carbon nanotubes into nanoscale electronic circuits. New 'finFET' promising for smaller transistors, more powerful chips Purdue University researchers are making progress in developing a new type of transistor that uses a finlike structure instead of the conventional flat design, possibly enabling engineers to create faster and more compact circuits and computer chips. Technology May Cool The Laptop Does your laptop sometimes get so hot that it can almost be used to fry eggs? More Semiconductor Current Events and Semiconductor News Articles |
|||||||||||||||||||||
|
|||||||||||||||||||||
|
|||||||||||||||||||||