Low-Damping Ferromagnetic Resonance in Electron-Beam Patterned, High-Q Vanadium Tetracyanoethylene Magnon Cavities

Integrating patterned, low-loss magnetic materials into microwave devices and circuits presents many challenges due to the specific conditions that are required to grow ferrite materials, driving the need for flip-chip and other indirect fabrication techniques. The low-loss (α=3.98 x 10^-5), room-temperature ferrimagnetic coordination compound vanadium tetracyanoethylene (V[TCNE]_x) is a promising new material for these applications that is potentially compatible with semiconductor processing. Here we present the deposition, patterning, and characterization of V[TCNE]_x thin films with lateral dimensions ranging from 1 micron to several millimeters. We employ electron-beam lithography and liftoff using an aluminum encapsulated PMMA/P(MMA-MAA) copolymer bilayer on sapphire. Growth occurs in an argon atmosphere at 30 mTorr and 50 °C. Films patterned via this method maintain low-loss characteristics down to 25 microns with only a factor of 2 increase down to 5 microns. A manifold of thickness and radial confined spin wave modes reveals the quality of the patterned films. This work establishes the versatility of V[TCNE]_x for applications requiring highly coherent magnetic excitations ranging from microwave communication to quantum information.