  We introduce a microwave circuit architecture for quantum signal processing
combining design principles borrowed from high-Q 3D resonators in the quantum
regime and from planar structures fabricated with standard lithography. The
resulting '2.5D' whispering-gallery mode resonators store 98% of their energy
in vacuum. We have measured internal quality factors above 3 million at the
single photon level and have used the device as a materials characterization
platform to place an upper bound on the surface resistance of thin film
aluminum of less than 250nOhms.
