A 2.4 GHz VCO with an integrated acoustic solidly mounted resonator

A GaAs/AlGaAs HBT VCO designed for 2.36 GHz to 2.48 GHz was integrated with a solidly mounted resonator (SMR) (fo=2.347 GHz). The resonator consisted of a thin film of zinc oxide sputtered over an acoustic mirror. The SMR used in this VCO was fabricated separately on a silicon substrate and combined in package with the HBT oscillator, which was fabricated at a commercial foundry. ne two chips are compatible in that the SMR could potentially be integrated onto one GaAs HBT chip since the SMR can be grown regardless of substrate material. The prototype reported here shows the potential for stable, low phase noise single-chip VCOs. Another VCO of similar design was fabricated using an on-chip LC resonator. The SMR-based VCO showed a phase noise improvement of 24 dB at 10 kHz offset, and 8 dB improvement at 100 kHz. Moreover, the introduction of the SMR greatly reduced spurious signals and significantly reduced frequency drift compared to the LC oscillator.