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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

CSTR: 32037.14.aps.75.20251601

Design and fabrication of superconducting asymmetric coplanar waveguide transmission lines on lithium niobate substrate

CSTR: 32037.14.aps.75.20251601
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  • 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. 同时设计了一种基于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 interconnects for superconducting computing systems. Because of lithium niobate’s high Pockels coefficient, lithium niobate Mach-Zehnder modulators can achieve low half-wave voltage and high-speed data transmission when combined with superconducting traveling-wave electrodes. In this paper, a high-performance and scalable bent superconducting traveling-wave electrode is designed and fabricated using an 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, yielding an approximately 90% enhancement in central electric field intensity compared with conventional symmetric designs, 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, significantly enhancing high-frequency signal integrity. The high-frequency performance of the fabricated ACPW is characterized at cryogenic temperatures using a cryogenic probe station. Measurement results demonstrate that the dielectric bridges effectively suppress parasitic resonances induced by impedance discontinuities in the bent regions, 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 platforms.

     

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