Tuning of a superconducting microwave resonator at 77 K using an integrated micromachined silicon vertical actuator

A silicon micromachined actuator is used to tune a high temperature superconducting microwave resonator. The superconducting resonator is only 1.24 mm x 0.66 mm and demonstrates a Q of up to 1078 at 6.3 GHz and at 77 K. A tuning range of 12% is demonstrated with a maximum applied voltage of 40 V. The frequency of the resonator is controlled by the proximity of a silicon tuning probe. The room temperature resistivity of the silicon is measured to be 20 Omega cm; this value drops as the device is cooled, but remains the limiting factor in the quality factor of the device. This proof of principle experiment demonstrates the application of silicon micromachining for tuning of superconducting microwave circuits, which is achieved despite the difficulties presented by differing material properties and thermal constraints when cooling to 77 K.