High Impedance Niobium Geometric Inductors

Planar spiral resonators made from superconducting Aluminum have recently been shown to achieve impedances that surpass the resistance quantum owing to their high geometric inductance. These geometric superinductors are an interesting new element in the quantum circuit toolbox with applications in noise protected qubits, quantum metrology and coupling to single spins. However, to integrate these devices with typical spin qubit architectures, they need to be magnetic-field compatible. Here we present fabrication and characterization of Niobium spiral resonators with high critical fields. We use a subtractive process where thin film Niobium is sputtered on Si wafers, patterns are written with ebeam lithography and etched with a reactive ion etch. We characterize the devices in a 1K setup and show quality factors in excess of Q>10⁴ for resonators with impedances exceeding 1 kΩ. We validate our model for the resonators by extracting the ratio of geometric/kinetic inductance from temperature sweep data and verify that indeed over 95% of the inductance is geometric. Finally, we will discuss the prospects of integrating these devices with quantum-dot devices for coupling between microwave photons and electron spins.