基于本征约瑟夫森结阵列的可调超导滤波器及非线性机制研究

Due to the low insertion loss, high selectivity, high sensitivity and small size, tunable superconducting filters have broad application prospects in many areas such as mobile communications, satellite communications, and military weapons.Tunable superconducting filter based on intrinsic Josephson junction arrays and its nonlinear characteristic would be studied in this project by using theoretical analysis, numerical simulation and experimentation. Phase-locking of intrinsic Josephson junction arrays is the key problem to realize tunable equivalent inductance and to correct the centre frequency, bandwidth and skirt characteristics of superconducting filter independently. We would give phase-locking regions of different parameters and develop 10-pole tunable filter with central frequency of 1.9GHz, bandwidth of 20MHz and tuning range of 20%. Symmetric distortions and asymmetric distortions are also investigated theoretically and experimentally. Furthermore we perform exploratory research on nonlinear mechanism in tunable superconducting filter. The project will also study nano-particle additions in superconducing films and introducing buffer layer to get multilayer films to generate the pinning centers and improve the flux pinning strength and critical current density. Finally,a noveltunable superconducting filter without distortions would be realized using this film with high power-handling ability.

超导可调滤波器凭借低损耗、高选择性、高灵敏度和小体积等优点在移动通信、卫星通信以及军事电子设备等领域应用前景。本项目将采用理论分析、数值仿真和实验相结合的方法，研究基于本征约瑟夫森结阵列的可调超导滤波器及其非线性机制。相位锁定特性是实现约瑟夫森结阵列等效电感可调的核心问题，而将可调电感嵌入耦合型超导滤波器就可以实现滤波器的中心频率、带宽和陡峭度独立可调节。本项目将研究中心频率1.9GHz，带宽20MHz，可调范围20%的10阶超导滤波器，并探索调谐过程中非线性失真产生的原因，给出抑制失真的参数范围。 项目还将研究提高滤波器功率承载能力的方法，利用纳米颗粒修饰衬底表面和直接引入纳米颗粒制备多层结构超导薄膜两种方法，诱导薄膜内部出现晶界缺陷，提高薄膜的磁通钉扎强度和临界电流密度，最终制备出高功率承载能力的可调超导滤波器。

作为超导电子技术的基础，约瑟夫森结具有一系列优异的性能，如：灵敏度高，噪声低，功耗小，响应速度快，工作频率极高等。因此约瑟夫森结及结型器件具有重要的研究和应用价值。本项目通过理论分析、数值仿真和实验的方法对约瑟夫森结阵列的相位锁定和稳定时间进行了较为系统的研究，同时基于本征结阵列研制出中心频率连续可调的超导滤波器，并成功抑制了非对称失真。项目主要内容和研究结果如下：.通过仿真给出了约瑟夫森结阵列的相位锁定参数空间和稳定时间与外加偏置的关系，同时制备出超长本征约瑟夫森结阵列，实测其最大等效电感为79.3nH。研究得到约瑟夫森等效电感的非线性特性，观察到两种失真现象：外加大交流信号时对称失真和外加小交流信号时非对称失真。在施加强度为十分之一的结临界电流时，找到抑制非对称失真的方法：纳米点植入超导薄膜。通过纳米点植入多层薄膜的方法提高磁通钉扎强度，制备出高临界电流密度的铊系超导薄膜。.探索出单晶衬底上金属及金属氧化物纳米颗粒的生长方法，将厚度在0.5μm范围内的超导薄膜临界电流密度在原有基础上提高了2倍，抑制了超导可调滤波器中的非对称失真。最后利用仿真加实验的手段研制出中心频率1.9GHz，带宽100MHz的切比雪夫滤波器。该超导滤波器中心频率在1.6GHz至2.2GHz范围内连续可调，可调范围达31.6%。在调节范围内保持带宽不变，插损从1dB增加到2.5dB。