A NEW DESIGN OF HIGH QUALITY FACTOR, LOW MOTIONAL RESISTANCE AND COMPACT MEMS OSCILLATOR FOR TIMING APPLICATIONS
-Reference oscillators are the heartbeat of digital electronic systems, providing the clock signal against which all other signals are synchronized. Up until now, oscillators have been based on quartz crystals, but silicon MEMS have opened the door for radical improvements.
-This invention consists of several MEMS designs that realize a combination of high quality factor (even in air) and low motional resistance. This reduces the cost and power consumption of MEMS-based oscillators, enhancing their commercial potential.
The growing interest for MEMS based oscillators
- Reference oscillators are used in timing circuits and electronics of all types requiring a clock. They are also indispensable for ensuring proper synchronization in modern wireless communication devices.
- Current technology relies on bulky crystal-based resonators that do not allow for easy on-chip integration with MEMS devices and electronic circuits.
- MEMS resonators are attracting interest as an alternative to crystal-based resonators due to their small size and potential for on-chip integration with other MEMS devices and electronic circuits. This is especially important for handheld and wearable electronic devices addressing high volume consumer orientated applications where weight, size, and cost are critical parameters.
- A key challenge in the design of MEMS resonators is to achieve a combination of high quality factor and low motional resistance.
New designs of MEMS resonator structures for high performance MEMS oscillators
- Researchers at École de Technologie Supérieure in Montreal have developed new designs and methods for fabricating MEMS resonator structures in order to produce high performance MEMS oscillators.
- One new design is based on a LAME mode resonator and is implemented through dual wafer SOI technology. The structures are implemented by patterning two wafers with different etched depths and wafer bonding them to create the released movable structures.
- One anchoring architecture incorporates a central anchoring support which is suitable for creating high performance bulk-mode gyroscopes.
- A transimpedance amplifier circuit (TIA) provides a feedback loop between the sensing and driving electrodes of the oscillator. The TIA is used to achieve low phase noise high performance MEMS-based oscillators.
- Other MEMS resonator designs based on piezoelectric resonators and single wafer technology have also been created by the research team in order to achieve a desirable combination of high quality factor and low motional resistance without requiring any DC voltage for operation.
Unparalleled combination of high quality factor, low motional resistance and SoC integration
- Fabricated devices were measured to operate at quality factors as high as ~42000 at atmospheric pressure and ~871000 in 100-mTorr vacuum. The resonators also exhibit a f.Q product of 1.56×1013 in vacuum, which is one of the highest reported in the literature. Accordingly, the devices are well-suited to a wide range of MEMS resonator applications such as timing, and can provide relatively high performance even in air, reducing the packaging costs.
- The novel circuit design was integrated with MEMS resonators to realize superior performance oscillators achieving very low power and high-performance phase noise (the measured phase noise in air and under vacuum is about -104 dBc/Hz and -116 dBc/Hz, respectively, at a 1-KHz offset, while the phase noise floor reaches -130 dBc/Hz). The short-term stability of the MEMS-based oscillator is ±0.38 ppm.
- Timing circuits
- Electronics of all types that require a clock for timing
- Consumer electronics
- Portable electronics
- Wireless circuits that require a reference clock for carrier generation
- Technology available for licensing
- US patent application US 16,182,902
École de Technologie Supérieure (ÉTS)
Professor in Electrical Engineering Department, ÉTS
Prof. Nabki received the B.Eng. degree in Electrical Engineering with Honors from McGill University in 2003, where he graduated with distinction. In 2009, he completed a Ph.D. degree in Electrical Engineering at McGill University in RFIC and MEMS. From 2008 to 2016 he was a Professor in microelectronics engineering at UQAM. He is now an Associate Professor in the Department of Electrical Engineering of the École de technologie supérieure (ETS), a constituent of the University of Quebec. Nabki’s research interests include microelectromechanical systems (MEMS) and RF/analog microelectronics, the integrating of MEMS devices with CMOS phase-locked loops, ultra-wideband transceivers, and MEMS interface circuits.