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arXiv 0911.4536cond-mat.supr-concond-mat.mtrl-sci
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10 GHz铌共面波导谐振腔的膜厚特性

Film-thickness dependence of 10 GHz Nb coplanar-waveguide resonators

Kunihiro Inomata, Tsuyoshi Yamamoto, Michio Watanabe, Kazuaki Matsuba, Jaw-Shen Tsai

摘要:

我们研究了谐振频率为10-11 GHz的Nb λ/2共面波导(CPW)谐振器。谐振器具有不同的膜厚度,t=0.05、0.1、0.2和0.3 μ m。在低温T=0.02-5 K时,测量了散射矩阵元S_21,它是从一个端口到另一个端口的透射系数。在基础温度T=0.02-0.03 K时,谐振器过耦合到输入/输出微波线,并且加载的品质因数在10^3的量级。与电路模拟器的预测相比,谐振频率具有相当大的膜厚依赖性,电路模拟器仅考虑L_g来计算CPW的电感,其中L_g是由CPW几何形状确定的通常的磁电感。通过拟合理论S_21与频率的关系曲线,我们确定了每个膜厚的CPW的相速度,精度优于0.1%。大的膜厚依赖性必须是由于CPW中心导体的动态电感L_k。我们还测量了S_(21)在T=4-5 K范围内随温度的变化,并证实了L_k的厚度和温度依赖性与理论预测是一致的。

英文摘要:

We have studied Nb lambda/2 coplanar-waveguide (CPW) resonators whose resonant frequencies are 10-11 GHz. The resonators have different film thicknesses, t=0.05, 0.1, 0.2, and 0.3 um. We measured at low temperatures, T=0.02-5 K, one of the scattering-matrix element, S_21, which is the transmission coefficient from one port to the other. At the base temperatures, T=0.02-0.03 K, the resonators are overcoupled to the input/output microwave lines, and the loaded quality factors are on the order of 10^3. The resonant frequency has a considerably larger film-thickness dependence compared to the predictions by circuit simulators which calculate the inductance of CPW taking into account L_g only, where L_g is the usual magnetic inductance determined by the CPW geometry. By fitting a theoretical S_21 vs. frequency curve to the experimental data, we determined for each film thickness, the phase velocity of the CPW with an accuracy better than 0.1%. The large film-thickness dependence must be due to the kinetic inductance L_k of the CPW center conductor. We also measured S_21 as a function of temperature up to T=4-5 K, and confirmed that both thickness and temperature dependence are consistent with the theoretical prediction for L_k.

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