CMOS Integration of MEMS Resonators

Technology #16174

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FIG 1. (a) Cross-section SEM of a CMOS-MEMS resonators showing PnC patterned in metal stack and FEOL resonant cavity, (b) details of resonant cavity showing drive and sense transducers, (c)  COMSOL simulation of the PnC unit cell showing bandgap 2.65 GHz - 6.32 GHz.FIG 2. 2D COMSOL simulation of PnC resonator with resonances at 2.81 GhZ (Q of 310) and 4.5 GHz (Q of 300).
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Inventors
Professor Dana Weinstein
Department of Electrical Engineering - Computer Science, MIT
External Link (www.eecs.mit.edu)
Wentao Wang
Department of Mechanical Engineering, MIT
Radhika Marathe
Department of Electrical Engineering - Computer Science, MIT
Bichoy Bahr
Department of Electrical Engineering - Computer Science, MIT
Managed By
Christopher Noble
MIT Technology Licensing Officer - Clean and Renewable Energy
Patent Protection

Photonic Crystals for CMOS Integration of MEMS Resonators

US Patent 9,232,289
Publications
Phononic crystals for acoustic confinement in CMOS-MEMS resonators
IEEE Frequency Control Symposium (FCS 2014), 1-4 (2014)
Theory and Design of Phononic Crystals for Unreleased CMOS-MEMS Resonant Body Transistors
Journal of Micro Electro Mechanical Systems , April 28, 2015, p. 1520 - 1533

Applications

MEMS resonators are widely used in applications such as communications, inertial sensing, and navigation.

Problem Addressed

Traditional MEMS resonators are freely suspended or released and operated under vacuum/air to ensure free boundary conditions for acoustic reflection. However, when a resonator is fully encapsulated and surrounded by solid material the lack of perfect acoustic reflections at the boundary as well as energy losses to the surrounding medium result in a much reduced quality factor as well as output signal. To maintain a high quality factor for unreleased resonators, Phononic crystals (PnCs) and Acoustic Bragg reflectors (ABRs) can be used as confinement structures and trap specific frequencies within the cavity.

Technology

Integration of MEMS resonators with CMOS to form a single chip allows operation at GHz-frequencies, while reducing size, weight, and power consumption of the overall system. This technology is a method for creating acoustic localization structures, such as PnCs and ABRs, to surround a MEMS resonator and form an acoustic cavity. PnCs are structures with periodic variations in space in their mechanical properties, which lead to the existence of frequency bandgaps. ABRs are composed of periodic layers which are usually two or more materials alternatively located in space. By applying ABRs on the side of unreleased resonator, it is possible to reestablish the desired free or fixed boundary condition. In CMOS technology, such material combinations are effectively created using metal layers, vias, and the dielectric used to electrically isolate neighboring metal layers which naturally surrounds the vias.

Advantages

  • Fully CMOS compatible, requires no packaging or post-processing
  • Increases quality factor
  • Reduces power consumption

Related Technologies

  • Unreleased MEMS Resonator Using Acoustics Bragg Reflector – 14571
  • Piezoelectric Resonant Body Transistor (PRBT) - 14912