Thin film packaged mems resonator has ‘industry record’ Q factor

The announcement was made at the International Electron Devices Meeting in San Francisco. The high Q factor was achieved by implementing a resonator that operates in a torsional vibration mode and by vacuum encapsulation of the resonator in a thin film package. According to the two organisations, the resonator paves the way towards miniaturisation and low power consumption of timing devices used in applications such as consumer and automotive electronics. Panasonic and imec say that the Q factor achieves 220,000 at a resonant frequency f=20MHz (f•Q product of 4.3X10¹²Hz)) and low bias voltage by combining different advanced mems technologies. The application of a torsional vibration mode enables low anchor losses and lower squeeze film damping compared to flexural mode resonators, resulting in a higher Q factor. Since the Q factor also depends on the ambient pressure and starts to decrease above a critical pressure, imec and Panasonic vacuum encapsulated the resonator in a hermetically sealed environment. The thin film encapsulation of the mems with a 4µm thick SiGe film was achieved with a monolithic fabrication process with the mems. The 130nm gap between the beam and drive and sense electrodes enables a low bias voltage (1.8Vdc) and eliminates a charge pump in the oscillator circuit. Using sacrificial layer etching through a microcrystalline silicon germanium layer minimises the chances of deposition of the sealing material inside the cavity and thus enables to position the etching holes right above the beam surface, leading to a smaller chip size.