Panasonic and imec present
at the International Electron Devices Meeting in San Francisco an innovative
SiGe (silicon germanium) thin film packaged SOI-based MEMS resonator featuring
an industry-record Q factor combined with a low bias voltage.
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. This groundbreaking resonator paves the way towards miniaturization
and low power consumption of timing devices used in a variety of applications
such as consumer electronics and automotive electronics.
MEMS resonators offer enhanced miniaturization over conventional resonators
such as quartz crystals and piezoelectric ceramics. However, state-of-the art
MEMS resonators suffer from a low Q factor and a high bias voltage. Panasonic
and imec developed a novel packaged MEMS resonator achieving the highest Q factor
reported in the industry until now (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 due to viscous and squeeze film
damping, imec and Panasonic vacuum encapsulated the resonator in a hermetically
sealed environment. This thin-film encapsulation of the MEMS with a 4mm thick
SiGe film is realized with a monolithic fabrication process with the MEMS.
The narrow 130nm gap between the beam and drive and sense electrodes enables
a low bias voltage (1.8Vdc) and thus eliminates a charge pump in the oscillator
circuit. Moreover, using sacrificial layer etching through a microcrystalline
silicon germanium layer minimizes 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.
The packaged MEMS resonator was realized as part of imec’s CMORE service
which offers heterogeneous integration services to the industry. Imec builds
on its expertise in many research areas to tune and extend CMOS processes with
new processing steps to make novel CMOS micro- and nanodevices, adding functions
other than logic and memory to the chips. Possible applications of such MEMS
devices are smart sensors, actuators, power scavengers, resonators, biochips,
micro-implantable appliances, or solar cells. Imec’s CMORE services range
from development-on-demand, over prototyping, to low-volume production.
Posted December 7th, 2010