Figure 2.

(a) Internal quality factor in single-photon regime of resonators grouped by fabrication technological features into groups. Group 1a—RIE Al, without substrate etching; group 1b—wet etching Al, without substrate etching; group 2a—wet etching Al, DRIE Bosch substrate; group 2b—wet etching Al, isotropic substrate etching; group 2c—wet etching Al, isotropic substrate etching, additional ultrasonic microcutting (crosses indicate the average value of Qi_LP for each resonator, whereas the error bars indicate the standard deviations and mean value). SEM images of the cross section of the resonators: (b) group 2a, (c) group 2b, (d) group 2c. (e) Intracavity photon number dependence of the internal quality factor of resonators with wet etching Al and isotropic etching of substrate with airbridges over feedline (blue lines), with airbridges over feedline and resonators (yellow lines), without airbridges (red lines, the bars show a typical error in determining the Qi) in 4—5 GHz range and outside this range (violet line) on average photon population in resonator. Lines were added for better visibility. (f) SEM image of the feedline section with bridges; (g) SEM image of the feedline and resonator section with bridges; (h) SEM image of a single bridge on resonator with etching of the substrate in the gap.