1.5-GHz CMOS voltage-controlled oscillator based on thickness-field-excited piezoelectric AlN contour-mode MEMS resonators

This paper reports on the first demonstration of a 1.5 GHz CMOS oscillator based on thickness-field-excited (TFE) piezoelectric AlN MEMS contour-mode resonators (CMRs). The measured phase noise is -85 dBc/Hz at 10 kHz offset frequency and -151 dBc/Hz at 1 MHz. This is the highest frequency MEMS oscillator ever reported using a laterally vibrating mechanical resonator. The high frequency operation has been enabled by optimizing the geometrical design and micro-fabrication process of TFE AlN CMRs, so that a low effective motional resistance around 50 Ω is achieved together with a high unloaded quality factor (Q_u) approaching 2500 and simultaneously high k_t² up to 1.96%. A tunable-supply oscillator design is proposed for fine frequency tuning (or trimming) over a narrow bandwidth. The circuit design enables a novel GHz voltage-controlled oscillator (VCO) without the use of any low-Q tunable component. The 1.5 GHz VCO exhibits a 1500 ppm tuning range by a DC voltage change of 2.5 V. This technique can be utilized for fine frequency trimming and temperature compensation applications.