Piezoelectric MEMS for Sensing, RF, and Power Management

3 credits · Graduate

Historically, piezoelectric materials (e.g., PZT and Quartz) have been the backbone of many electroacoustic technologies, spanning from sonar and phonographs to signal filters for TV/radio and gas igniters. Some of these technologies have been subjected to constant improvements and miniaturization throughout the decades, but their dependency of bulk piezoelectric materials to operate has impaired their integration with electronics. The adoption of microelectromechanical systems (MEMS) manufacturing methods together with the advent of sputtering-based piezoelectric materials (e.g., AlN) has transformed the field of piezoelectric sensors and resonators to the point that now all these technologies can be mass manufactured and packaged in small form-factor chips. In this course, you will learn the basics behind the design, fabrication, characterization, and packaging of piezoelectric MEMS, as well as their most successful commercial applications in the areas of sensing, RF, and power management. We will review the fundamentals of elasticity that will be recurrently used throughout the course. To determine the sensitivity of piezoelectric transducers, we will derive the Euler-Bernoulli and Sophie-German equations that respectively determine elasticity in flexural beams and plates, including the effect of residual film stress. Regarding dynamic analysis, we will dive into the mathematical tools needed to compute the effective mass and natural resonance frequency of vibrating rectangular slabs (e.g., Rayleigh's energy method) and uncover the main damping mechanisms that limit their Q factor. The piezoelectric effect will be the transduction mechanism of focus, so you will learn relevant material science concepts associated with it, such as piezoelectric stiffening and electromechanical coupling. As examples of piezoelectric MEMS sensors, this course will cover piezoelectric MEMS microphones, Quartz crystal microbalances (QCMs) and piezoelectric micromachined ultrasound transducers (PMUTs). In RF, the holy grail of piezoelectric MEMS is bulk acoustic wave (BAW) resonators with its different flavors: film bulk acoustic resonators (FBAR) and solidly mounted resonators (SMR). We will learn their linear and nonlinear modeling circuit techniques and how they can be arranged with electronics to form filters and oscillators. Finally, we will explore two emerging areas of development in power management using piezoelectric MEMS: piezoelectric energy harvesters and piezoelectric DC-DC converters, which are key to supply energy to low and high power systems, respectively. All this knowledge will be complemented with Finite Element Modeling (FEM) using COMSOL Multiphysics and put in practice in real MEMS technology applications