A Flip-Chip Assembled Millimeter-Wave Oscillator Stabilized with a Micromachined Cavity on a Thin-Film Substrate

A low-cost 47 GHz microwave integrated circuit (MIC) oscillator stabilized with a micromachined cavity is presented using a thin-film substrate with a flip-chip interconnection. A GaAs pseudomorphic high electron-mobility transistor (pHEMT) was flip-chip assembled on the thin-film substrate as an active device to generate negative resistance. A micromachined cavity, which is employed to stabilize a 47-GHz MIC oscillator as a series-feedback element, is fabricated using a low-cost silicon micromachining technique and flip-chip assembled on the thin-film substrate with integrated passives. The fabricated cavity shows an unloaded Q-factor of 671 with a resonant frequency of 46.91 GHz. The cavity oscillator developed shows an output power of about 11.5 dBm and a low phase noise of -95 dBc/Hz at 1 MHz offset with an oscillation frequency at 47.06 GHz, which is a 17-dB improvement over a free running MIC oscillator. This work demonstrates the great potential of a thin-film substrate with a flip-chip interconnection for a low-cost and high-performance mm-wave system-on-package (SOP) technology.