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中国物理学会期刊

铌酸锂衬底超导非对称共面波导传输线设计与制备

Design and Fabrication of Superconducting Asymmetric Coplanar Waveguide Transmission Lines on Lithium Niobate Substrate

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  • 本文面向跨温区光电互联的低温电光调制器应用,设计并制备了一种高性能、可扩展的弯曲结构超导非对称共面波导传输线.传输线采用非对称共面波导结构,将中心电场强度提升了约90%;圆环弯曲结构实现了有限芯片面积内传输线长度有效拓展;集成介质桥结构显著改善了弯曲区域阻抗不连续的问题.设计了一种基于SU-8光刻胶的介质桥制备工艺流程,利用微纳加工技术在铌酸锂衬底上实现集成介质桥结构的超导传输线制备,并使用低温探针台对其低温下的高频传输特性进行测试.结果表明,所制备的弯曲传输线在4.2 K低温环境下展现出59 GHz的3 dB带宽,证明该结构能够有效满足长超导行波电极的制备需求.

    Cryogenic electro-optic modulators have promising applications in cryogenic optical interconnect for superconducting computing systems. Lithium niobate Mach-Zehnder modulators benefit from the large Pockels coefficient of lithium niobate and, when combined with superconducting traveling-wave electrodes, have the potential to achieve low half-wave voltage and high-speed data transmission. In this paper, a high-performance and scalable bent superconducting traveling-wave electrode is designed and fabricated with asymmetric coplanar waveguide (ACPW) transmission line. By introducing unequal ground gaps on the two sides of the signal line, the proposed ACPW structure concentrates the electric field toward the narrower-gap side, resulting in an approximate 90% enhancement of the central electric field intensity compared to conventional symmetric design, which is expected to improve modulation efficiency. Within a limited chip area, a circular bent transmission-line geometry is implemented. SU-8 photoresist dielectric bridges are employed to suppress discontinuities and parasitic mode conversion in the bent regions, improving high-frequency signal integrity significantly. The high-frequency performance of the fabricated ACPW is characterized at cryogenic temperature in a cryogenic probe station. Measurement results show that the dielectric bridges suppress parasitic resonances induced by impedance discontinuities in the bent regions effectively, improving the 3 dB electrical bandwidth from 9 GHz to 59 GHz at 4.2 K. The dielectric-bridge fabrication process demonstrated in this work is applicable to other superconducting device platform

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