Ovenized and thermally tunable aluminum nitride microresonators

Frequency tuning of aluminum nitride (AlN) microresonators has been demonstrated via localized heating (ovenization) of the resonator. Specifically, piezoelectrically driven 625 MHz microresonators were heated by embedded joule heaters in vacuum. A temperature increase of 135°C was achieved with only 2.8 mW of power consumption. This increase corresponds to ~4500ppm of frequency shift. To minimize heat loss, the devices were suspended from the substrate by high thermal isolation beam type supports. The beams exhibit very high thermal resistance, not only due to their high length to cross-sectional area ratio, but also because they are made of thin-film deposited polycrystalline aluminum nitride. Thin AlN films have been shown to have thermal conductivities that are much lower than that measured in bulk materials. The availability of a power efficient frequency tuning method in aluminum nitride microresonators enables low power ovenization of AlN MEMS-based timing devices and tunable filtering for communication systems.