Extending Moore’s Law

The growing role of advanced semiconductor materials and techniques; melting in reverse.

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By Ann Steffora Mutschler
For Moore’s Law to perpetuate, the materials used in semiconductor manufacturing must do their part to allow the scaling of devices to occur. Some of the latest include a carbonless film deposition technology for 20nm transistors and smaller, a plastic memory device and a material compound of silicon, copper, nickel and iron that researchers believe could lower manufacturing costs.

The need to fill smaller and deeper structures in advanced chip designs creates a physical roadblock for existing deposition technologies, but this week Applied Materials believes it has broken through this barrier with a flowable chemical vapor deposition (FCVD) technology that it claims solves one of the most critical challenges in scaling Moore’s Law by isolating densely-packed features at the 20nm manufacturing node with a carbon-free dielectric film and fills gaps with aspect ratios of more than 30:1.

Spintronics allows more data storage in less space

Another recent technology development hails from researchers at Ohio State University, who have demonstrated the first plastic computer memory device that uses the spin of electrons to read and write data as an alternative to traditional microelectronics.

So-called “spintronics” could store more data in less space, process data faster, and consume less power, and while the device is still in the lab testing phase, the researchers successfully recorded data on it and retrieved the data by controlling the spins of the electrons with a magnetic field.

Arthur J. Epstein, distinguished university professor physics and chemistry and director of the Institute for Magnetic and Electronic Polymers at Ohio State, said the material is a hybrid of a semiconductor that is made from organic materials and a special magnetic polymer semiconductor. In this way, it is a bridge between today’s computers and the all-polymer, spintronic computers that he and his partners hope to enable in the future.

“Spintronics is often just seen as a way to get more information out of an electron, but really it’s about moving to the next generation of electronics. We could solve many of the problems facing computers today by using spintronics,” Epstein said in a statement.

Typical circuit boards use a lot of energy. Moving electrons through them creates heat, and it takes a lot of energy to cool them. Chipmakers are limited in how closely they can pack circuits together to avoid overheating. By flipping the spin of an electron, it requires less energy, and produces hardly any heat at all, he explained, which means spintronic devices could run on smaller batteries. And if they were made out of plastic they would also be light and flexible allowing portable electronics on spin platforms.

The magnetic polymer semiconductor in this study, vanadium tetracyanoethanide, is the first organic-based magnet that operates above room temperature. It was developed by Epstein and collaborator Joel S. Miller of the University of Utah.

In the prototype device, electrons pass into the polymer, and a magnetic field orients them as spin up or spin down. The electrons can then pass into the conventional magnetic layer, but only if the spin of electrons there are oriented in the same way. If they are not, the resistance is too high for the electrons to pass. So the researchers were able to read spin data from their device based on whether the resistance was high or low.

As a test, the researchers exposed the material to a magnetic field that varied in strength over time. To determine whether the material recorded the magnetic pattern and functioned as a good spin injector/detector, they measured the electric current passing through the two magnetic layers. This method is similar to the way computers read and write data to a magnetic hard drive today.

Results of lab tests showed the magnetic data was retrieved in its entirety, exactly as stored. Researchers believe the patented technology should transfer easily to industry. An added bonus is that the device was made at room temperature, and the process is very eco-friendly.

Melting silicon to remove impurities
Finally, to combat the high cost of manufacturing for some silicon devices, a team of researchers at MIT has found that some oddball materials melt in reverse, thereby allowing impurities to be isolated, The finding is important because tiny amounts of impurities can significantly reduce device performance.

Just as ice melts when the temperature increases, most semiconductor materials melt as well. But the few that do the reverse can help to isolate impurities. The MIT researchers discovered that when silicon is compounded with copper, nickel and iron, it melts as it get cooler. As it cools below 900 degrees Celsius, compared to silicon’s melting point of 1,414 degrees C, the much lower temperature makes it possible to observe the behavior of the material during melting—based on specialized X-ray fluorescence microprobe technology using a synchrotron particle accelerator as a source.

Impurities tend to migrate to the liquid portion, leaving regions of purer silicon behind, which could make it possible to produce some silicon-based devices, such as solar cells, using a less-pure, and therefore less-expensive, grade of silicon that would be purified during the manufacturing process.

It is expected that this research also could lead to new methods for making arrays of silicon nanowires — tiny tubes that are highly conductive to heat and electricity.