IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 41, NO. 4, APRIL 2013 661 Plasma Science and Technology in the Limit of the Small: Microcavity Plasmas and Emerging Applications J. G. Eden, Fellow, IEEE , S.-J. Park, Senior Member, IEEE, J. H. Cho, Member, IEEE, M. H. Kim, Student Member, IEEE, T. J. Houlahan, Jr., Student Member, IEEE, B. Li, E. S. Kim, T. L. Kim, S. K. Lee, K. S. Kim, J. K. Yoon, S. H. Sung, P. Sun, Student Member, IEEE, C. M. Herring, and C. J. Wagner Abstract—Over approximately the past decade, a subfield of plasma science has arisen that is redefining frontiers in the physics of low temperature plasma and its applications. Con- cerned with the confinement of weakly ionized, nonequilibrium plasma to cavities having mesoscopic dimensions, the emerging area of microcavity plasmas has advanced rapidly in surpassing several milestones, primarily with respect to electron density and cavity geometries, and is establishing new avenues of research. To date, peak electron densities above 10 17 cm -3 , cavity dimensions as small as 3 μm, microchannel aspect ratios (length: width) of 10 3 :1, plasma packets propagating at velocities up to 20 km s -1 , and coupling between e - -h + and e - -ion plasmas have all been Manuscript received December 1, 2012; revised March 7, 2013; accepted March 8, 2013. Date of current version April 6, 2013. This work was supported in part by the U.S. Air Force Office of Scientific Research, the National Science Foundation, the Department of Energy, and the Defense Advanced Research Projects Agency under Grant FA9550-10-1-0456, Grant CBET 08-53739, Grant DE-SC0008333, and Contract FA8650-12-C-7209. J. G. Eden, S.-J. Park, J. H. Cho, M. H. Kim, T. J. Houlahan, and P. Sun are with the Department of Electrical and Computer Engineering, Laboratory for Optical Physics and Engineering, University of Illinois, Urbana, IL 61801 USA (e-mail: jgeden@illinois.edu; sjinpark@uiuc.edu; jhchonf@illinois.edu; mhkim2@illinois.edu; thoulah2@illinois.edu; peter.pergsum@gmail.com). B. Li was with the Department of Electrical and Computer Engineering, University of Illinois, Urbana, IL 61801 USA, and is now with Intel, Boise, ID, 83716 USA. E. S. Kim was with the Department of Electrical and Computer Engineering, University of Illinois, Urbana, IL 61801 USA, and is now with LSIS, Anyang, Korea. T. L. Kim was with the Department of Electrical and Computer Engineering, University of Illinois, Urbana, IL 61801 USA, and is now with Micron Technology, Boise, ID 83707 USA. S. K. Lee was with the Department of Electrical and Computer Engineering, University of Illinois, Urbana, IL 61801 USA, and is now with Goldman Sachs, Singapore. K. S. Kim was with the Department of Electrical and Computer Engineering, University of Illinois, Urbana, IL 61801 USA, and is now with Samsung Electro-Mechanics, Suwon, Korea. J. K. Yoon was with the Department of Electrical and Computer Engi- neering, University of Illinois, Urbana, IL 61801 USA, and is now with LG Display, Paju, Korea. S. H. Sung was with the Department of Electrical and Computer Engineer- ing, University of Illinois, Urbana, IL 61801 USA, and is now with Intel, Portland, OR 97205 USA. C. M. Herring was with the Department of Electrical and Computer Engineering, University of Illinois, Urbana, IL 61801 USA, and is now with Eden Park Illumination, Champaign, IL 61821 USA. C. J. Wagner was with the Department of Electrical and Computer Engineer- ing, University of Illinois, Urbana, IL 61801 USA, and is now with Philips, Baldwin Park, CA 91706 USA. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TPS.2013.2253132 observed, but every indication is that these results are only a foretaste of the future. This review describes several recent device geometries and provides a synopsis of the physics. Promising applications of this technology in chemical processing, lighting, water disinfection, and medicine are also discussed briefly. Index Terms— Microcavity plasma, microplasma. I. I NTRODUCTION I N THE fields of electronics, photonics, and materials science (to name a few), miniaturizing devices, material structures, and entire systems to the micro or nano-spatial scales has yielded enormous technological benefits but has also given birth to entirely new avenues of scientific inquiry. Structures and processes as diverse as quantum wires and wells, Purcell’s effect, surface-enhanced Raman scattering, and atomic force microscopy owe their origin to the spatial local- ization of electric fields or materials and the charge carriers they bear. A similar revolution is now underway in plasma science, which has traditionally been concerned with media of comparatively large volume. Although at a much earlier stage, the emerging discipline of microchannel and microcavity plasmas is continually yielding phenomena and novel devices that have no counterparts in the macroscopic plasma domain. Recent examples include photonic crystal arrays of microplas- mas serving as microwave filters [1], plasma propagation in microchannels (mediated by charge on the channel wall) [2], [3], and transistors based on coupling between e - -h + and e - - ion plasmas [4]. In its decadal survey of physics and its assessment of the status of plasma physics, in particular, the National Academy of Sciences (U.S.) recognized the potential of microplasmas. A report written by the Physics 2010 panel of the National Research Council stated that [5] “[microplasma] devices open up a range of scientific and technological opportunities” and that “…fundamental physical phenomena associated with this new class of plasmas are important areas for future research.” From a broad perspective, one might claim (correctly) that microplasmas have been studied for decades and are known to exist in a variety of forms. One example is the streamer associ- ated with a corona discharge or conventional atmospheric pres- sure plasmas, such as those that generate ozone. Fig. 1 presents an example of a class of microplasmas that has become 0093-3813/$31.00 © 2013 IEEE