Superconducting Microstrip Losses at Microwave and Submillimeter Wavelengths

Abstract

We present a lab-on-chip experiment to accurately measure losses of superconducting microstrip lines at microwave and submillimeter wavelengths. The microstrips are fabricated from Nb-Ti-N, which is deposited using reactive magnetron sputtering, and amorphous silicon which is deposited using plasmaenhanced chemical vapor deposition (PECVD). Submillimeter wave losses are measured using on-chip Fabry-Perot resonators (FPRs) operating around 350 GHz. Microwave losses are measured using shunted half-wave resonators with an identical geometry and fabricated on the same chip. We measure a loss tangent of the amorphous silicon at single-photon energies of tan δ = 3.7 ± 0.5 × 10 −5 at approximately 6 GHz and tan δ = 2.1 ± 0.1 × 10 −4 at 350 GHz. These results represent very low losses for deposited dielectrics, but the submillimeter wave losses are significantly higher than the microwave losses, which cannot be understood using the standard two-level system loss model.

Terahertz Band-Pass Filters for Wideband Superconducting On-Chip Filter-Bank Spectrometers

“…The measured data for those filters well-within the quasioptical pass-band show a modest peak coupling efficiency of |S i1 (f i )| 2 ≈ −5.7 dB and a loaded quality factor of Q l ≈ 940, which is higher than the targeted spectral resolution of 500. Both these results may be explained from the moderate internal quality factor Q i ≈ 3300 (which is slightly lower than the dielectric Q i reported in [38]), and the high coupling quality factors Q c1 ≈ 2860 and Q c2 ≈ 2680 of the couplers surrounding the resonators. 17.…”

“…17. Simulated coupling quality factor variation as function of the microstrip metal thickness (t MS ) and the a-Si over-etch using the fabricated dimensions of the filters, the measured electrical properties of the superconductors and the dielectric loss reported in [38]. Instead Q des c is the design performance of the fully planar coupler using nominal dimensions and electrical properties on a lossless dielectric.…”

“…However, practical microstrip devices require deposited dielectrics, which incur more losses than crystalline substrates as reported in [36] for microwave frequencies. At THz frequencies data on dielectric loss is very sparse: a CPW on crystalline Sapphire shows a Q i in excess of 15000 [15], whereas microstrips fabricated from NbTiN and Plasma-Enhanced Chemical Vapor Deposition (PECVD) SiN report Q i ≈ 1400 at 200 GHz [37], and NbTiN microstrips on PECVD a-Si [30] show Q i ≈ 4750 at 350 GHz [38]. Despite the dielectric losses in deposited a-Si still being high for an ideal THz filter-bank, these are sufficient to design and build microstrip-based filters, thereby avoiding the moderelated issues of co-planar technology.…”

“…The fabrication route of this chip is similar to [38] and it is described in great detail in [43]. It starts with a 260 nm-thick NbTiN layer (T c = 15 K, ρ = 90.0 µΩ•cm) being deposited on top of a Si wafer using reactive sputtering of a NbTi target in a Nitrogen-Argon atmosphere [44].…”

Characterization of low-loss hydrogenated amorphous silicon films for superconducting resonators

“…The 1∕Q i is roughly equal to the dielectric loss tangent in the case of a superconducting microstrip filter. [11][12][13] An increase in Q i will enable a proportional increase in R at a particular filter transmission value. A mm-submm Q i of 1440 has been achieved with amorphous silicon nitride (SiN x ).…”