Investigation of Microwave Crosstalk in Spiral-MKIDs Array

Microwave crosstalk between rewound-spiral resonators was estimated for the optimal design of a microwave kinetic inductance detectors (MKIDs) array. An electromagnetic simulator (sonnet EM) was used to calculate the frequency responses. First, we analyzed the microwave interactions by changing the geometrical distance, D
_rr
, between the centers of two resonators and the frequency interval, Δf, placed in the horizontal direction and the vertical direction. To analyze the microwave crosstalk, we changed the kinetic inductance, L
_k
, at one resonator, and we estimated the resonant frequencies. Our simulated results reveal that the microwave crosstalk was less than 0.22% placed on the horizontal and vertical directions with D
_rr
= 1000 μm and Δf = 9 MHz. We then used these elements to design a 25-element spiral-MKIDs array and fabricated it by using an NbN thin film deposited on an r-sapphire substrate. The crosstalk was estimated using a vector network analyzer and a signal generator for pumping to the single element. In the measured results, 25 resonant dips were clearly observed in the frequency range between 2.70 and 2.95 GHz at 3.45 K. Furthermore, we could estimate the crosstalk between the resonators and found it to be less than 10-4% in both horizontal and vertical patterns.