Data underlying the publication: Hydrogenated Amorphous Silicon Carbide: A Low-Loss Deposited Dielectric for Microwave to Submillimeter-Wave Superconducting Circuits

Low-loss deposited dielectrics will benefit superconducting devices such as integrated superconducting spectrometers, superconducting qubits and kinetic inductance parametric amplifiers. Compared with planar structures, multi-layer structures such as microstrips are more compact and eliminate radiation loss at high frequencies. Multi-layer structures are most easily fabricated with deposited dielectrics, which typically exhibit higher dielectric loss than crystalline dielectrics. We measured the sub-kelvin and low-power microwave and mm-submm wave dielectric loss of hydrogenated amorphous silicon carbide (a-SiC:H), using a superconducting chip with NbTiN/a-SiC:H/NbTiN microstrip resonators. We deposited the a-SiC:H by plasma-enhanced chemical vapor deposition at a substrate temperature of 400°C. The a-SiC:H has a mm-submm loss tangent ranging from 0.80±0.01×10^−4 to 1.43±0.04×10&−4 in the range of 270 to 385 GHz. The microwave loss tangent is 3.2±0.2×10^−5. These are the lowest low-power sub-kelvin loss tangents that have been reported for microstrip resonators at mm-submm and microwave frequencies. We observe that the loss tangent increases with frequency. The a-SiC:H films are free of blisters and have low stress: −20 MPa compressive at 200 nm thickness to 60 MPa tensile at 1000 nm thickness.

低损耗沉积电介质将助力集成超导光谱仪、超导量子比特（superconducting qubits）与动态电感参量放大器等超导器件的性能优化。相较于平面结构，微带线类多层结构不仅更为紧凑，还可消除高频段的辐射损耗。沉积电介质是制备多层结构最简便的选择，但其介电损耗通常高于晶体电介质。
我们采用搭载NbTiN/a-SiC:H/NbTiN微带谐振器的超导芯片，对氢化非晶碳化硅（hydrogenated amorphous silicon carbide）的亚开尔文、低功率微波及亚毫米波段介电损耗进行了测试。该a-SiC:H薄膜通过等离子体增强化学气相沉积法制备，制备过程中衬底温度控制为400℃。
该a-SiC:H在270至385 GHz频段内的亚毫米波段损耗正切值介于(0.80±0.01)×10⁻⁴至(1.43±0.04)×10⁻⁴之间，其微波频段损耗正切值为(3.2±0.2)×10⁻⁵。上述结果为目前已报道的、微带谐振器在亚毫米及微波频段下的最低低功率亚开尔文损耗正切值。我们观测到损耗正切值随频率升高而增大。
该a-SiC:H薄膜无气泡缺陷，且应力水平较低：厚度为200 nm时为-20 MPa的压应力，厚度为1000 nm时则为60 MPa的拉应力。