Inkjet-printed thin film radio-frequency capacitors based on sol-gel derived alumina dielectric ink

Abstract

Abstract There has been significant interest in printing radio frequency passives, however the dissipation factor of printed dielectric materials has limited the quality factor achievable. Al 2 O 3 is one of the best and widely implemented dielectrics for RF passive electronics. The ability to spatially pattern high quality Al 2 O 3 thin films using, for example, inkjet printing would tremendously simplify the incumbent fabrication processes – significantly reducing cost and allowing for the development of large area electronics. To-date, particle based Al 2 O 3 inks have been explored as dielectrics, although several drawbacks including nozzle clogging and grain boundary formation in the films hinder progress. In this work, a particle free Al 2 O 3 ink is developed and demonstrated in RF capacitors. Fluid and jetting properties are explored, along with control of ink spreading and coffee ring suppression. The liquid ink is heated to 400 °C decomposing to smooth Al 2 O 3 films ~120 nm thick, with roughness of 450 pF/mm 2 , and quality factors of ~200. The devices have high break down voltages, >25 V, with extremely low leakage currents, −9 A/cm 2 at 1 MV/cm. The capacitors compare well with similar Al 2 O 3 devices fabricated by atomic layer deposition.