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and processing, rf characterization (wired and wireless) of materials and devices, and additive manufacturing of microelectronic packaging. One specific example of a successful project is development of a ceramicbased ferroelectric ink. Many rf and microwave applications critically need to actively tune the frequency response of a system. One way to make a tunable device, such as a varactor (a tunable capacitor), is to use a material whose dielectric properties can be tuned by an applied electric field. Such ferroelectric materials often come in a ceramic form— a primary example is BaxSr1–xTiO3 (BST). Some microwave systems already have developed the high-temperature processing required to enable use of thick and thin films of BST. However, despite increasing demand for printed tunable rf systems that are flexible, conformal, or wearable, no practical solution had realized an all-printed, high-frequency varactor that could be printed on flexible plastic substrates (e.g., polyimide films or polyethylene naphthalate) without typical high-temperature processes. Therefore, we wanted a ferroelectric ink that would enable low-temperature printing and processing on plastic substrates using direct ink-writing methodologies. Because no such ferroelectric ink commercially existed, we developed our own formulation. We made a multiphase composite by suspending BST nanoparticles in thermoplastic cyclic olefin copolymer and dissolved that composite in a solvent with dispersant to achieve the ferroelectric ink. This work was done in partnership with U Mass Lowell professor Alkim Akyurtlu, whose expertise is in electromagnetic modeling and design. She is using this ink technology to build tunable frequency selective surfaces and printed phased array antennas. The composite ink benefits from processing flexibility of the polymer—a <200°C curing step suffices to solidify the material, thus bypassing sintering steps traditionally required for ferroelectric materials. To enable tunability in the composite, we optimized three intercorrelated parameters: BST Ba/Sr ratio; BST More parternships @ ceramics.org • Open access: Argonne opens doors to industry collaboration ceramics.org/open-access • DOE announces $40M to advance materials for renewable energy ceramics.org/clean-energy-materials • NSF-supported center parters with industry on materials research ceramics.org/nsf-partner-industry nanoparticle size; and BST loading fraction. In particular, we selected Ba/ Sr ratio of BST nanoparticles from a narrow window dependent on particle size of inclusions. Initial studies have demonstrated a tunability of 10% at 1 GHz. RURI has applied for a patent on this material. RURI researchers now are developing printed varactors and phase shifters from this material for systems such as phased array antennas and tunable frequency selective surfaces. About the expert Craig Armiento is codirector of RURI, director of the Printed Electronics Research Collaborative (PERC), director of the Center for Photonics, Electromagnetics, and Nanoelectronics (CPEN), and professor in the Department of Electrical and Computer Engineering at the University of Massachusetts Lowell. Contact Armiento at Craig_Armiento@uml.edu. n VERSION 4.1 PHASE EQUILIBRIA DIAGRAMS FOR CERAMIC SYSTEMS 778 NEW entries! 1,656 New Reduce research time and diagrams! avoid costly experimentation with ACerS-NIST criticallyevaluated phase diagrams for ceramic systems. ORDER NOW Single User License: $950 Multi User Licence: $1,625 ORDER TODAY ceramics.org/phase | 866-721-3322 | 240-646-7054 American Ceramic Society Bulletin, Vol. 95, No. 3 | www.ceramics.org 35


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