Near-Field-Coupled Bondless BAW Oscillators in WCSP Package with 46fs Jitter

This paper presents a 2.5 GHz bulk acoustic wave (BAW) resonator-based oscillator in a wafer chip scale package (WCSP). Electro-Magnetic coupling is used to eliminate rigid galvanic connections between the BAW die and the CMOS oscillator die. The BAW die is attached to the latter with soft die attach, which eliminates stress coupling between the two, resulting in excellent aging performance for the oscillator. The CMOS oscillator circuit is significantly simplified owing to the inductor, which reduces power consumption, enhances oscillator stability, and lowers the phase noise. The presented oscillator achieves best-in-class 46 fs jitter in a sub-1mm
³
WCSP package with less than 15 ppm aging over 10years.