Noise spectrum analysis of superconducting kinetic inductance detectors

As a newly developed pair-breaking superconducting detector, microwave kinetic inductance detectors aresimple to integrate in the frequency domain and have already been used in astronomical detection and arrayimaging at the (sub)millimeter and optical wavelengths. For these applications, the dark noise level of kineticinductance detector is one of the key performance indicators. Herein a noise power spectrum analysis method isintroduced in detail, which can accurately and effectively analyze the noise spectrum of kinetic inductancedetector in a wide frequency range. This method can well balance the noise spectrum resolution and varianceperformance, by taking the noise data at the resonance frequency with two sampling rates and setting theappropriate frequency resolutions for different frequency bands. This method is used to characterize andcompare the noise of aluminum (Al) kinetic inductance detectors made from two different micromachiningprocesses. We deposite a 25-nm-thick aluminum film on high-resistivity silicon substrate for one device, whileplace one silicon nitride (SiNx) film on the top and one on the bottom of the aluminum film for another device.It is found that the frequency noise of the device with two silicon nitride films is about 25% to 50% of the barealuminum device. Using this double silicon nitride film fabrication technique, we further fabricate a few groupsof lumped-element aluminum kinetic inductance detectors with various inductor and interdigitated capacitordesigns. We investigate the noise properties of these devices at different microwave driven power and bathtemperatures, and the experimental results show typical two-level system noise behaviors. Our work provides astandard method to characterize the noise power spectrum of kinetic inductor detector, and also paves the wayto developing low-noise aluminum kinetic inductance detectors for terahertz imaging, photon-counting andenergy-resolving applications