Transferring the gallium nitride sensors to metallic foils and flexible polymers doubles their sensitivity to nitrogen dioxide gas, and boosts response time by a factor of six. The simple production steps, based on metal organic vapor phase epitaxy (MOVPE), could also lower the cost of producing the sensors and other optoelectronic devices.
Sensors produced with the new process can detect ammonia at parts-per-billion levels and differentiate between nitrogen-containing gases. The gas sensor fabrication technique was reported November 9 in the journal Scientific Reports.
“Mechanically, we just peel the devices off the substrate, like peeling the layers of an onion,” explained Abdallah Ougazzaden, director of Georgia Tech Lorraine in Metz, France and a professor in Georgia Tech’s School of Electrical and Computer Engineering (ECE). “We can put the layer on another support that could be flexible, metallic or plastic. This technique really opens up a lot of opportunity for new functionality, new devices – and commercializing them.”
The researchers begin the process by growing monolayers of boron nitride on two-inch sapphire wafers using an MOVPE process at approximately 1,300 degrees Celsius. The boron nitride surface coating is only a few nanometers thick, and produces crystalline structures that have strong planar surface connections, but weak vertical connections.
Aluminum gallium nitride (AlGaN/GaN) devices are then grown atop the monolayers at a temperature of about 1,100 degrees Celsius, also using an MOVPE process. Because of the boron nitride crystalline properties, the devices are attached to the substrate only by weak Van der Waals forces, which can be overcome mechanically. The devices can be transferred to other substrates without inducing cracks or other defects. The sapphire wafers can be reused for additional device growth.
“This approach for engineering GaN-based sensors is a key step in the pathway towards economically viable, flexible sensors with improved performances that could be integrated into wearable applications,” the authors wrote in their paper.
So far, the researchers have transferred the sensors to copper foil, aluminum foil and polymeric materials. In operation, the devices can differentiate between nitrogen oxide, nitrogen dioxide, and ammonia. Because the devices are approximately 100 by 100 microns, sensors for multiple gases can be produced on a single integrated device.
“Not only can we differentiate between these gases, but because the sensor is very small, we can detect them all at the same time with an array of sensors,” said Ougazzaden, who expects that the devices could be modified to also detect ozone, carbon dioxide and other gases.
The gallium nitride sensors could have a wide range of applications from industry to vehicle engines – and for wearable sensing devices. The devices are attractive because of their advantageous materials properties, which include high thermal and chemical stability.
“The devices are small and flexible, which will allow us to put them onto many different types of support,” said Ougazzaden, who also directs the International Joint Research Lab at Georgia Tech CNRS.
To assess the effects of transferring the devices to a different substrate, the researchers measured device performance on the original sapphire wafer and compared that to performance on the new metallic and polymer substrates. They were surprised to see a doubling of the sensor sensitivity and a six-fold increase in response time, changes beyond what could be expected by a simple thermal change in the devices.
“Not only can we have flexibility in the substrate, but we can also improve the performance of the devices just by moving them to a different support with appropriate properties,” he said. “Properties of the substrate alone makes the different in the performance.”
In future work, the researchers hope to boost the quality of the devices and demonstrate other sensing applications. “One of the challenges ahead is to improve the quality of the materials so we can extend this to other applications that are very sensitive to the substrates, such as high-performance electronics.”
The Georgia Tech researchers have previously used a similar technique to produce light-emitting diodes and ultraviolet detectors that were transferred to different substrates, and they believe the process could also be used to produce high-power electronics. For those applications, transferring the devices from sapphire to substrates with better thermal conductivity could provide a significant advantage in device operation.
Ougazzaden and his research team have been working on boron-based semiconductors since 2005. Their work has attracted visits from several industrial companies interested in exploring the technology, he said.
“I am very excited and lucky to work on such hot topic and top-notch technology at GT-Lorraine,” said Taha Ayari, a Ph.D. student in the Georgia Tech School of ECE and the paper’s first author.
In addition to Ougazzaden, the research team includes Georgia Tech Ph.D. students Taha Ayari, Matthew Jordan, Xin Li and Saiful Alam; Chris Bishop and Youssef ElGmili, researchers at Institut Lafayette; Suresh Sundaram, a researcher at Georgia Tech Lorraine; Gilles Patriarche, a researcher at the Centre de Nanosciences et de Nanotechnologies (C2N) at CNRS; Paul Voss, an associate professor in the Georgia Tech School of ECE; and Jean Paul Salvestrini, a professor at Georgia Tech Lorraine and adjunct professor in the Georgia Tech School of ECE.
The research was supported by ANR (Agence Nationale de Recherche), the National Agency of Research in France through the “GANEX” Project.
CITATION: Taha Ayari, et al., “Gas sensors boosted by two-dimensional h-BN enabled transfer on thin substrate foils: towards wearable and portable applications,” (Scientific Reports, 2017). http://dx.doi.org/10.1038/s41598-017-15065-6
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]]>The Consulate General of France in Atlanta has announced that Berger has been awarded the Chevalier dans L'Ordre des Palmes Académiques for her “exceptional dedication and significant accomplishments in the field of science and education,” says Rami Abi Akl, French attaché for science and technology in Atlanta.
The Palmes Académiques is presented to French citizens and non-citizens who have made significant contributions to French education, science, and culture. The first Palmes Académiques was presented by Napoleon in 1808.
Berger’s “pioneering work in physics, particularly on graphene, has not only advanced scientific knowledge, but also served as an inspiration to others in her field,” Abi Akl says.
In addition to her research and classes at Georgia Tech, Berger is Director of Research at the French National Center for Scientific Research (CNRS), which has been home to 12 Nobel Prize and 10 Fields Medal winners. Berger’s affiliation is with the CNRS International Research Lab, with its main campus at Georgia Tech-Europe in Metz, France, and an affiliated lab at Georgia Tech’s Atlanta campus.
Approximately 50 colleagues from both countries have conducted collaborative research at both Georgia Tech campuses, thanks to Berger’s efforts.
“Her selection for this honor also reflects her remarkable impact on both the American and French scientific communities,” Abi Akl says. “Her collaborative efforts and contributions to scientific research have fostered strong ties between France and the United States, strengthening the bonds of scientific diplomacy.”
“A very big thank you to the French General Consulate in Atlanta for submitting my name for this distinctive honor,” Berger recently shared. “Among other funding agencies and foundations, I am particularly grateful to the French Embassy for their partnership grants that funded travel and helped collaboration between almost 60 faculty members, postdoctoral scholars, and students.”
“I also want to thank Georgia Tech and the School of Physics for their full support,” she added. “All that travel and dedicated lab work wouldn’t have happened without the love and support at home from my husband and our three sons.”
Berger was born in Paris, France, and received her Ph.D. from the Université Grenoble Alpes. She joined Georgia Tech in 2001, and she quickly established herself as a noted researcher of the electronic properties of graphene, a material with a flat, two-dimensional structure that is touted as a potential successor to silicon in computer processors.
Berger and School of Physics Regents’ Professor Walter de Heer are working on graphene discoveries that could lead to smaller, more energy-efficient processing that is expected to usher in a new era of quantum and high performance computing.
Walter de Heer welcomed Berger into his lab when she arrived at Georgia Tech, she says. “I want to thank him for being an incredible team leader in this adventure, for his continuous support, his insights, dedication and passion for science.”
Berger co-authored the first article demonstrating the two-dimensional properties of graphene and a possible electronics platform for the material. Berger, de Heer, and School of Physics Professor Phillip First also co-authored the first patent for graphene electronics in 2003.
She is the co-author of more than 200 publications in international journals. From 2014 to 2019, she was among the top one percent most cited researchers in physics.
Berger says she was given the letter by the General Consul of Atlanta announcing her award during an event at the Embassy. “I was so surprised by the nomination that I was fumbling trying to find my words. This was a great — and a bit embarrassing — moment at the same time.”
One of her good friends, Bill Moon, is a fellow Palmes Académiques winner for promoting French language instruction at private and public schools in Atlanta and Decatur. “He founded the International Community School in Clarkston, Georgia, a public charter elementary school serving the needs of U.S. and refugee families now living in DeKalb County, and he continues to be active in the service of communities,” Berger says. “To be awarded the same medal as Bill is an incredible honor.”
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Kippelen, the current vice provost for International Initiatives and the Steven A. Denning Chair for Global Engagement, received the award in a ceremony at the Residence of France in Atlanta on November 6, 2023.
The President of the French Republic had previously conferred the honor upon this year’s civilian recipients on June 2, 2023. The National Order of Merit is the second national Order of France after the Legion of Honor. Its purpose is to, “reward ‘distinguished merit’ and encourage the lifeblood of the country.”
“On behalf of the Georgia Tech community, I extend my heartfelt congratulations to Bernard, a true science diplomat, who has made extraordinary contributions to research and to strengthening ties between the United States and France” said Georgia Tech President Ángel Cabrera. “Georgia Tech is indebted to him for all he has done and continues to do to enhance our reach, reputation, and impact on the global stage."
During the award ceremony, John McIntyre, the founding executive director of the Georgia Tech Center for International Business Education and Research (CIBER), bestowed the medal upon Kippelen. President Cabrera and Anne-Laure Desjonquères, the consul general at Consulate of France in Atlanta, were joined by Kippelen's family, friends, and colleagues at the ceremony.
“Professor Kippelen has been instrumental in fostering collaborations and partnerships and facilitating researcher and student mobility between France and the Southeast,” said Desjonquères. “The French consulate is profoundly grateful to Bernard Kippelen for his invaluable support to our annual series of events France-Atlanta, as well as to our exchange and mobility programs.”
Kippelen joins Yves Berthelot (vice provost for International Initiatives, retd.), Marta H. Garcia (associate vice president for Development), and Steve McLaughlin (provost and executive vice president for Academic Affairs) as fellow Georgia Tech recipients of the Knight of the French National Order of Merit distinction.
In 2003, Bernard joined the Georgia Tech faculty and served as director of the Center for Organic Photonics and Electronics (COPE) from 2011-2019. He is a co-founder and co-president of the Institut Lafayette, an innovation platform located at Georgia Tech-Europe in Metz, France.
While at Georgia Tech, he has worked with the Office for Science and Technology (OST) of the Embassy of France to support the Technology Venture Accelerator (NETVA) program established to develop technological partnerships in the United States for young and innovative French startups.
Kippelen was raised in Soultz, Alsace, France, and is a U.S. and French citizen. He studied at the University Louis Pasteur in Strasbourg, France (Ph.D. 1990) and was a member of the Centre National de la Recherche Scientifique (CNRS). Before joining Georgia Tech, he was on the faculty of the Optical Sciences Center at the University of Arizona.
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Top photo caption:
Bernard Kippelen receiving the Knight of the French National Order of Merit on Nov. 6, 2023 at the Residence of France in Atlanta. In the photo are (L-R): Yves Berthelot, Beth Cabrera, Ángel Cabrera, Virginie Kippelen, Bernard Kippelen, Steve McLaughlin, Marta H. Garcia, John McIntyre, and Anne-Laure Desjonquères.