EAGER: Exploration of Magneto-Electric Hexaferrite Thin film Devices

摘要：目前使用的ME块状六角铁氧体材料所需的直流电压在100V至2000V的范围内，以观察任何显著的ME效应。这些所需的高电压条件对于基于cmos的器件来说是不切实际的，而不是低功耗和更小尺寸的要求。基于薄膜的器件预计将消耗非常低的功率，并且很容易与现有的CMOS器件集成。为了使现代无线通信系统、移相器、滤波器、传感器和/或医疗仪器具有更好的性能，迫切需要具有高结晶度和磁电效应的单相ME六角铁氧体薄膜。最近，PI已经在蓝宝石衬底上以最小的缺陷制备并表征了单相的ME六元铁氧体薄膜。初步表征结果表明，在不牺牲体相磁化强度变化的前提下，制作厚度约为100 nm的低电压(1V)ME六角铁氧体器件是可行的。为了实现这一点，建议(I)设计、制造和表征具有平面内和平面外几何形状的各种电容薄膜器件，(Ii)从根本上研究衬底(导电缓冲层)对薄膜生长机制的影响，(Iii)研究薄膜厚度对器件性能的影响，(Iv)探索低温(与CMOS兼容)生长ME六元铁氧体薄膜的方法；(V)从根本上系统地研究在这些薄膜中实现100%磁化变化的途径。智力上的优点：拟议的研究成果是在导电缓冲层上制备可以很容易地集成到CMOS中的六角铁氧体薄膜，从而形成低功率工作电压可调的磁性器件。探索了用于表征这些薄膜中的ME效应的两种器件配置，这将构成各种基于ME的器件的基础。这项研究将从根本上理解导电缓冲剂对薄膜六角铁氧体生长和由此产生的磁特性的影响。通过改进导电缓冲层与生长的ME晶体之间的晶格常数匹配，有望获得单晶ME薄膜，从而增强ME的线性耦合。该项目的研究成果将为实现单晶ME铁氧体薄膜提供一条途径，使其电压感生磁化强度显着提高(~30-50%)，具有广泛的应用前景。此外，通过这项工作获得的基本认识将为六元铁氧体薄膜控制生长过程奠定基础。更广泛的影响：拟议的研究如果成功，将在磁/CMOS应用中实现新型磁电设备和接口方面的重大突破，如平面电感、蜂窝电话中的双工器、单芯片锁相环频率变送器、GPS(全球定位系统)和DCS(数字蜂窝系统)移动通信、商业机载平台的负载CBS(空腔支持系统)天线。建议的研究成果将被纳入PI的研究生和本科课程“磁性微电子学”，该课程涉及用于无线通信的IC电路。PI将在东北大学每年两次举办的为期一天的“建造桥梁”活动中介绍ME概念，在该活动中，新英格兰地区的高中生通过简单的演示接触到正在进行的高级研究。我们还将在波士顿科学博物馆赞助的外展活动“Nanoday”计划中介绍建议研究的结果。

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.