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PPPL physicists win Edison Award for X-ray imaging invention

Three scientists from the U.S. Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL) have won an Edison Patent Award from the Research and Development Council of New Jersey for their invention of an imaging apparatus that could be used to produce the next generation of integrated circuits. 

Physicists Manfred Bitter, Kenneth Hill, and Philip Efthimion are among 14 teams to win the 2017 Edison Patent Awards who will be honored at a Nov. 2 ceremony at the Liberty Science Center in Jersey City, New Jersey.  It is the second consecutive year PPPL’ers have received the award. Last year, Charles Gentile, George Ascione and Adam Cohen received an Edison Award for their invention of an on-demand method to create a widely-used isotope used in medical imaging devices. 

This year’s winners created an X-ray imaging apparatus that can be used for extreme ultraviolet light (EUV) lithography. “We are very grateful to have been selected for this award,” Bitter said. “It’s nice to come up with a new idea, if it is useful to somebody.” 

The three scientists recently went to the library at the inventor’s home and laboratory at the Thomas Edison National Historic Park in West Orange, New Jersey, to film a short video segment on their research that will soon be available on the Research & Development Council of New Jersey website. “It’s humbling and gratifying to do work that we enjoy and to do work that we hope will eventually help mankind and society,” Hill said. 

Efthimion, head of the Plasma Science & Technology Department, agreed with that sentiment. “It’s quite humbling to be mentioned in the same breath as Thomas Edison,” he said  

Efthimion said the technique of using extreme ultraviolet (EUV) lithography to make computer chips will be “revolutionary.” This technique is considered the next generation of computer chip manufacturing because the EUV light, called soft X-rays, are just 10 to 15 nanometers long. The current technology uses ultraviolet light, which is 200 nanometers long. That means “you should be able to place 100 times more components, like transistors, in the same area” of tiny computer chips, Efthimion explained. The linear distance between components is also 10 times shorter, he said, which means the speed of the chip could be 10 times faster.

EUV lithography uses reflectors to diffract EUV light off a mask that has an image of the information that will be imprinted on the chip. The EUV beam demagnifies the image to the size of the chip and imprints it onto the chip. But current EUV lithography technology, which is still being developed, can only do this by scanning a tiny piece of the image onto the chip at once. This is because only a small area of the reflector focuses the EUV beam to preserve the image – a fact known as the Bragg condition. 

The inventors’ device uses a multi-layered structure to reflect the EUV beams to produce a wider beam of light. This fulfills the Bragg condition on every point of the reflector and captures all the information on the mask and imprints it onto the computer chip without the need for scanning. Funding the invention was a Laboratory Directed Research and Development (LDRD) grant through the DOE.

Decades of experience

Bitter and Hill have decades of experience with manipulating X-rays in X-ray crystal spectrometers, which measure the temperature and other parameters of the plasma in fusion experiments. The two were the lead inventors on a 2012 patented invention that uses matched pairs of spherically-bent mirrors to eliminate astigmatic imaging errors in X-ray and EUV images  

Bitter and Hill began building such devices in the 1970s for the Princeton Large Torus (PLT). They built similar devices, as well as other diagnostics, for the Tokamak Fusion Test Reactor (TFTR) and the National Spherical Torus Experiment (NSTX) at PPPL. 

The most recent spectrometer is used to diagnose high-energy density plasmas, which are only a tenth of a millimeter wide. The spectra of the X-ray radiation emitted from these plasmas provides information on the temperature of the ions and other key data. A version of the device was recently used on laser-produced plasmas at the Omega EP Laser Facility at the University of Rochester in New York and was recently installed on the National Ignition Facility at the Lawrence Livermore National Laboratory in Livermore, California. 

Bitter and Hill spectrometers are also being used worldwide on doughnut-shaped tokamaks and twisty stellarators; the latter include the Large Helical Device in Japan and the Wendelstein 7-X stellarator in Germany. The two physicists are also working with a team of scientists at PPPL on the design of crystal spectrometers for ITER, the international fusion experiment being built in Cadarache, France. “These two gentlemen are renowned experts in X-ray technology and they’ve made many contributions to plasma technology,” Efthimion said. 

Bitter and Hill received PPPL’s Kaul Prize for Excellence in Plasma Physics Research and Technology Development in 2012. All three inventors have been at the Laboratory for nearly four decades. 

Bitter is a Princeton, New Jersey, resident who retired from PPPL in 2012 but continues to come into work three or four days a week. He received his undergraduate degree and Ph.D. from the Universities of Munich and Aachen. He was a staff member of the European Space Research Institute in Frascati, Italy, from 1969 to 1973 and a visiting scientist at the Centre de Recherches en Physique des Plasmas in Lausanne, Switzerland from 1973 to 1977 before joining PPPL in 1977. He was named a fellow of the American Physical Society in 1987 and received the Alexander von Humboldt Physics Prize in 1996, which allowed him to do research at the Forschungszentrum Jülich in Germany for one year. 

Hill, who lives in Plainsboro, New Jersey, is the author of more than 300 publications. He received a Ph.D. in atomic physics from the University of North Carolina at Chapel Hill in 1974. Before joining PPPL in 1978, he worked in ion-atom collision physics at the U.S. Naval Research Laboratory and in spectroscopic plasma diagnostics at the Oak Ridge National Laboratory. He has collaborated with research institutes around the world and is a member of the American Physical Society. 

Efthimion, who lives in Bedminster, New Jersey, joined PPPL after receiving his bachelor’s degree from Columbia University in 1970 and his Ph.D. from Columbia in 1977. He first worked on the Princeton Large Torus making measurements to support Bitter’s experiments in X-ray spectroscopy. He led a group of scientists on TFTR and has been head of the Plasma Science & Technology Department at PPPL since 2001. Efthimion is a fellow of the American Physical Society. 

Hill said he and Bitter complement each other. “Manfred is excellent at spatial visualization, at seeing special geometries and understanding how particular geometries can be useful for our X-ray work,” Hill said. “I am better at taking that analysis and using computer programs to visualize it and apply it to real situations. 

Efthimion is also a prolific inventor who has a total of six patents, including two others in the field of spectroscopy. He has encouraged his two colleagues to branch out into other areas in which their X-ray technology would be useful. 

Efthimion said he has been pairing early career scientists with Hill and Bitter so that the veteran scientists can pass along their knowledge. Hill has been at the Laboratory for 39 years and Bitter for 40 years. Bitter says he enjoys working with the young physicists. “We work together to tackle new subjects,” he said. 

Bitter and Hill say they hope their technology will someday be put to good use. “It is relevant and it’s a good idea,” Hill said. “It’s an idea that potentially may be used for some other aspect of lithography.” 

PPPL, on Princeton University's Forrestal Campus in Plainsboro, N.J., is devoted to creating new knowledge about the physics of plasmas — ultra-hot, charged gases — and to developing practical solutions for the creation of fusion energy. The Laboratory is managed by the University for the U.S. Department of Energy’s Office of Science, which is the largest single supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.


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