A tunable microwave monolithic integrated circuit includes a dielectric material with a variable dielectric constant. A superconducting material with a negative dielectric constant is provided which is arranged in relation to the dielectric material in such a way that at least one interface is formed between the superconducting material and the dielectric material. The dielectric material is a low loss non-linear bulk material. Phase velocity tuning of microwaves is provided through controlling the propagation of surface plasma waves of the microwaves along the interface(s).