Circularly connected second-mode mechanical resonator chip for oscillator application

Abstract

We have developed a novel circularly connected mechanical resonator with rotational symmetry. Its unit resonator design is based on a second-mode free-free beam resonator, suspended by four 1.2 μm narrow support beams. The resonator achieves high quality factors (>10,000) and higher transmissions (>−20 dB) simultaneously in 50 Ω measurement. The frequency range experimentally obtained was from 26 MHz to 195 MHz. The mechanical resonators are completely encapsulated into the cavity. The cavity is vacuumed in aluminum sputtering process and hermetically sealed by aluminum plugs. After the in-line encapsulation, it is possible to handle the proposed resonators as conventional IC chips. In addition, all of the fabrication steps were processed in the conventional CMOS technology. The characteristics of a 45 MHz oscillator were evaluated by using a test circuit board with our 45 MHz resonator chip. The phase noise performance at a 10 Hz offset from the carrier frequency was −40 dBc/Hz and a noise floor was observed at −150 dBc/Hz, demonstrating applicability for practical clock generator circuits.