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Thin-Film Multiferroic Heterostructures for Frequency-Agile RF Electronics


OBJECTIVE: The goal of the research is to demonstrate the feasibility of using thin-film multiferroic heterostructures as magneto-electric tunable RF isolators at frequencies above 10 GHz. DESCRIPTION: Magnetic-field tunable ferrite devices are currently used as resonators, filters, phase-shifters, circulators, isolators. Unfortunately, the tuning response times limit their use at higher frequencies, and the material losses and device noise characteristics are becoming unacceptable. Further, they are incompatible with RF semiconductor IC technology and have relatively high power requirements. Multiferroic materials have the potential to greatly improve on these properties and provide a viable solution for electrically tuned ferromagnetic RF resonance devices. The additional design space gained from exploiting either magnetically-modulated piezo-electric fields or electrically-modulated piezomagnetic fields could greatly expand the range of tuning in integrated microwave circuitry, resulting in RF systems that are much lighter, smaller, reliable and more affordable than current devices and systems. Single-phase multiferroics exhibit intrinsic magnetoelectric effects that are too small for RF device applications at frequencies of interest for military systems. However multilayered multiferroic hetero-structures can be engineered to simultaneously possess a net magnetic moment and an electric polarization that can then interact through a strain-induced coupling of the constituent lattice polarization field and magnetic domain ordering. Layered structures with large magnetoelectric effect have been demonstrated on a limited basis, e.g. bilayers with ferrites as the piezomagnetic phase and BST or PZT as the paraelectric phase.1) In particular, hexagonal ferrites (BaM) are also available and are magnetically self-biasing, which can allow for the design of enhanced ME effects and devices for operation at higher frequencies without the need for heavy and expensive magnets.2) PHASE I: Proposers should demonstrate a viable thin-film deposition technology for multiferroic heterostructures and then investigate the magneto-electric properties of the heterostructures in order to evaluate the feasibility of developing a magneto-electrically tunable RF isolator. The research should seek to develop a systematic understanding of the physics and high frequency behavior of the hybrid modes that arise in multiferroic heterostructures, and demonstrate the feasibility of establishing electronic control of the magnetic response of these hetero-ferroic film composites with minimal associated losses and noise. PHASE II: The small business should implement the processing innovations identified in Phase 1. Based on these studies the program should develop a methodology for achieving high speed tuning with the widest magneto-electric frequency range at the lowest applied electric field. This phase should include the production and testing of prototype devices. Phase 2 effort should optimize the materials and processing parameters for production of energy efficient, tunable RF isolators capable of operating at frequencies above 10 GHz and across the full military temperature range of -20 C to +125 C. PHASE III DUAL USE APPLICATIONS: Magnetic-field tunable ferrite devices are currently used in resonators, filters, phase shifters, circulators. Unfortunately, tuning response times are limited and the devices display rather large loss and noise characteristics. The present program will seek to introduce a new multiferroic technology that will provide improved microwave devices with superior tunability and overall performance standards. REFERENCES: 1) R.V. Petrov, A.S. Tatarenko, G. Srinivasan and J.V. Mantese,"Antenna Miniaturization with Ferrite-Ferroelectric Composites", Microwave and Optical Technology Lttrs, 50, 12 (December 2008), p. 3354-7 2) A.B. Ustinov and G.Srinivasan,"Subterahertz excitations and magnetoelectric effects in hexaferrite-piezoelectric bilayers", APL, 93, 142503 (2008).
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