Unreleased MEMS Resonator Using Acoustics Bragg Reflector

Technology #14571

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 FIG. 1 illustrates a side cross-section view of an unreleased resonator according to an exemplary embodiment.  FIG. 2 illustrates a plan view of an unreleased resonator according to an exemplary embodiment.FIGS. 3 a-3 e illustrate frequency responses in unreleased resonators according to two different embodiments.FIG. 4 illustrates reflection and transmission of acoustic energy at a boundary between two media, according to one embodiment
Professor Dana Weinstein
Department of Electrical Engineering - Computer Science, MIT
External Link (www-mtl.mit.edu)
Wentao Wang
Department of Mechanical Engineering, MIT
Managed By
Christopher Noble
MIT Technology Licensing Officer - Clean and Renewable Energy
Patent Protection

Unreleased MEMS Resonator and Method of Forming Same

US Patent 9,041,492
Acoustic Bragg Reflectors for Q-Enhancement of Unreleased MEMS Resonators
IEEE Frequency Control Symposium (FCS 2011) , May 1-5, 2011
Phononic Crystals for Acoustic Confinement in CMOS-MEMS Resonators
IEEE Frequency Control Symposium (FCS 2014) , 1-4 (2014)


Monolithic integration of microelectromechanical (MEM) devices with complementary metal-oxide semiconductors (CMOS) is essential for successful implementation of high-frequency MEMS resonators. Applications for this technology include wireless communication, telecommunication, microprocessor technology, and transceiver circuitry.

Problem Addressed

Integrating released resonators with CMOS is difficult as these devices require a release step to freely suspend the moving structure. This requires costly complex encapsulation methods and restricts MEMS fabrication to back end of line (BEOL) processes. Current unreleased MEMS resonators suffer from low Q (quality) factor. The integration of MEMS resonators with CMOS to form a single chip solution allows operation at higher frequencies than the restricted devices that rely on a release step, while reducing size, weight, and power consumption. Film Bulk Acoustic Resonators (FBARs) and released resonators are widely used in comminication and other applications that involve MEMS. This technology will enable direct integration into front-end-of-line (FEOL) processing, making these devices an attractive choice for on-chip signal generation and processing.


This technology describes an unreleased MEMS resonator device that seamlessly integrates with CMOS technology. The device incorporates acoustic Bragg reflectors (ABRs) to localize acoustic energy.  ABRs are able to act as a one-dimensional photonic crystals to provide bandgaps for acoustic waves by inducing total reflection, and thus, limiting the subsequent reduction in quality factor (Q) caused by acoustic energy leakage. The ABR is composed of periodic layers comprising of two or more alternating materials in space. The ABR removes the need for free surfaces from release steps that are commonly used for perfect reflection, and thus, eliminates the obstacles of acoustic energy leakage and subsequent reduction in quality due to the solid boundary.


  • Operating at mm-wave frequency range
  • Fully CMOS compatible as a BEOL or FEOL
  • High Q factor
  • Small footprint
  • Lower power consumption
  • High yield, low cost