基于多铁异质结的高频磁电微波器件研究

Aiming to resolve the current challenge of realizing prototype devices in multiferroic applications, we proposed to create novel epitaxial multiferroic heterostructures and deliver energy-efficient tunable microwave filters, which satisfy all the structural and performance requirements of being a high frequency and wide band signal processing system. The proposed novel heterostructures and devices will be investigated from different aspects, including the system integration between the magnetoelectric (ME) interaction and the filter design, the new mechanism behind the combination of both systems, and the novel platform for device operation and performance evaluation. As a crucial technique in this proposal, we use novel epitaxial refractory transition metal nitride (TMN) as the top electrode for the ME components and the conductive ground plane for the filters. The epitaxial growth of ferrite/TMN/ferroelectric heterostructures, which enables a strong mechanical coupling at interface, will be comprehensively studied. The ME coupling in the system will be experimentally and theoretically explored. In addition, the microwave performance as a function of magnetoelectric properties will be investigated and utilized to optimize the device design and fabrication. Given the strong interface mechanical coupling due to the epitaxial growth, as well as the anisotropic ME coupling in the heterostructure, voltage or electric impulse induced non-volatile control of the ferromagnetic resonance and the cut-off frequency in ME filters will be realized with the significant enhancment in the frequency tunable range, while the filter's sensitivity and magnetic loss remain the same. The successful development of the next generation of high-performance, frequency-agile microwave electronics in a lightweight, energy efficient format shows great prospects for the military related applications and significantly contributes to the National Security.

针对当前多铁研究领域亟待解决的器件应用转化问题，结合项目申请人的前期工作基础，选择可用于军事领域的高频微波信号处理器作为研究对象，从器件参数要求和结构设计出发，构建复合多铁性磁电异质结及滤波器原型器件,探索多铁材料与高频微波器件的系统整合方法、理论模型和测试平台,研究器件中氧化物/金属/氧化物外延异质结的生长机制及其强磁电耦合的内在机理，并建立相应数学预测模型。利用仿真计算，研究异质结磁电特性对滤波性能参数的影响，并用于指导和优化器件的结构设计和开发。在保证器件功能最大化的基础上，充分利用其外延生长所致牢固的界面机械耦合与异质结中强磁电耦合及其各向异性，实现电场（或脉冲电压）非易失性原位调控铁磁共振及滤波频率，进一步增大其频率调制范围，并保持小的共振线宽和灵敏度。成功地设计并开发新一代低功耗、微型化、低噪声、超快响应的新型高频磁电微波器件具有重要的国防安全意义。

本项目研究具有强磁电耦合效应的“铁磁/铁电”外延多铁异质结和可低电压（<5 V）调控的“离子液体（凝胶）/铁磁薄膜”异质结的可控制备方法，深入探索其强磁电耦合效应的物理机制和理论模型，围绕新型多铁异质结研究磁电存储器件和磁电微波器件原型，建立材料与器件的系统整合方法。取得以下重要进展：在La0.7Sr0.3MnO3/PMN-PT外延多铁异质结中实现了电场调控自旋波激发on/off状态的可逆切换，提出自旋—晶格耦合调控自旋波的理论模型。通过电场调控Ni0.5Zn0.5Fe2O4/PMN-PT外延多铁异质结的双磁子散射效应实现对铁磁共振线宽的大范围调控，该机制的调控效果远超过传统应变调控机制（最大可达24倍）。设计制备了Ni0.5Zn0.5Fe2O4/BaTiO3三维复合多铁性薄膜，在临界温度附近可实现高达1866 Oe的铁磁共振场偏移，这在微热驱动的微波器件和自旋电子器件等方面存在极大的器件化应用价值。分别在“铁磁/铁电”层合多铁异质结和“离子液体/铁磁薄膜”异质结中通过电压调控人工反铁磁结构的RKKY效应，实现了电压控制铁磁—反铁磁耦合的可逆转变，克服了传统方法难以调控反铁磁材料磁矩的难题，为开发基于反铁磁材料的自旋电子器件提供了新思路。通过离子液体低电压调控“YIG/Pt”和“YIG/Cu/Pt”异质结的磁近邻效应，实现4.5 V调控铁磁共振场漂移分别高达690 Oe和1400 Oe，较传统磁电耦合方法提高一个数量级，为研发低电压调控的可调微波滤波器奠定基础。建立了基于铁磁共振原理研究离子液体原位调控异质结磁性能的定量表征方法，实现了低电压调控垂直磁各向异性和自旋重取向相变，获得破纪录的378 Oe/V的磁电耦合系数，对开发低电压操纵的磁电存储器件具有重要意义。实现了室温下的电场调控垂直磁易轴翻转，伴随最大高达1100 Oe铁磁共振场的变化，发现了应变调控界面自旋-轨道效应的物理机制，其磁电耦合强度是传统机制的十倍。以多铁性磁电复合材料为磁芯设计制备了电压脉冲非易失性调控的可调电感，非易失性调谐率高达250%，为进一步开发电场可调滤波器等新型信号处理器件奠定基础。

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