EAGER: Exploration of Magneto-Electric Hexaferrite Thin film Devices

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Summary: DC voltages required for currently used ME bulk hexaferrite materials are in the range of 100V to 2000V for observing any significant ME effects. These required high voltage conditions imposed are impractical for CMOS based devices in lieu of low power consumption and smaller size requirements. Thin film-based devices are expected to consume very low power and are easy to integrate with existing CMOS devices. To enable better performing highly versatile modern wireless communication systems, phase shifters, filters, sensors and/or medical instrumentation, there is dire need for single phase ME hexaferrite thin films with high crystallinity and magnetoelectric effects. Recently, PI has fabricated and characterized single-phase thin ME hexaferrite films on sapphire substrates with minimal defects. Preliminary characterization results indicated the feasiblility to fabricate a low voltage (1V) operational ME hexaferrite device with thickness ~100nm without sacrificing the percentage of magnetization changes that are present in their bulk counterparts. To achieve this it is proposed (i) to design, fabricate and characterize various capacitive thin film devices with in plane and out plane geometry, (ii) to fundamentally study the effect of substrates (conductive buffer layer) on the growth mechanism of the thin films, (iii) to study the effect of the film thickness on the performance of the devices, (iv) to explore methods for low temperature (CMOS compatible) growth of thin ME hexaferrite magnetic films and (v) to fundamentally study systematically pathways for achieving 100% magnetization changes in these films.Intellectual Merit:The proposed research outcome is to fabricate thin hexaferrite films on conductive buffer layers that can be readily incorporated into CMOS resulting in low power operation voltage tunable magnetic devices. Two device configurations for characterizing the ME effect in these thin films are explored which will form the basis for various ME-based devices. The proposed research will result in a fundamental understanding of the impact of conductive buffer on the growth and resultant magnetic characteristics of thin film hexaferrites. Through improved lattice constant matching between the conductive buffer layer and the grown ME crystal it is expected to achieve a single crystal ME thin film resulting in an enhanced ME linear coupling. The outcome of this project will provide a pathway for realizing single crystal ME hexaferrite thin films leading to a significant increase (~30-50%) voltage induced magnetization changes which have extensive applications. Furthermore the fundamental understanding gained through this proposed work will lay the foundation for a hexaferrite thin film controlled growth process. Broader Impact:The proposed research, if successful, can result in significant breakthrough in the realization of novel magneto electric devices and interfaces in the Magnetic/CMOS applications such as planar inductors, duplexers in cellular phones, single chip phase-locked-loop frequency trans-receivers, GPS (global positioning system) and DCS (digital cellular system) mobile communication, loaded CBS (cavity-backed system) antennas for commercial airborne platforms. The outcome of proposed research will be incorporated into PI's graduate and undergraduate course on "Magnetic Microelectronics' which entails IC circuits for wireless communications. The PI's will introduce ME concept in daylong event on "Building Bridges" held by NEU twice a year in which high school students in the New England area are exposed to ongoing advanced research through simple demonstrations. We will also introduce the outcome of the proposed research in the outreach activity "Nanodays" program sponsored by the Museum of Science, Boston.