Artificial Piezoelectricity in Silicon Phononic Crystals

• Author / Creator

  Chowdhury, Golam Kibria

• Certain materials, like quartz, are electrically polarized when they are strained. This is called the direct piezoelectric effect. It manifests naturally by the appearance of bound electrical charges at the surfaces of strained medium. This is always accompanied by the converse effect, whereby a solid becomes strained when placed in an electric field. Piezoelectricity has important applications in acoustic transducers, acousto-optic and RF devices, precision positioning instrumentation, to name a few. However, since piezoelectric behavior is expressed only in non-centro symmetric crystals, such as quartz and lithium niobate, they have limited utility for on-chip applications. In addition, the piezoelectric constants of these materials are typically weak, which limits the electromechanical conversion efficiency that can be achieved, with typical values of ~ 5.5% for single-crystal lithium niobate (LiNbO3) and ~20.8% for lead zirconium titanate (PZT).

  Here we propose to develop a new class of meta-materials based on heterogeneous metal-on-silicon phononic crystals to realize artificial piezoelectricity in silicon, which is a centro-symmetric material. We have developed analytical models in one-dimensional meta-atom structures to mimic piezoelectric behaviors, derive constitutive relations for the direct and converse piezoelectric effects, and determine the effective electromechanical coupling coefficient. We found that near unity electromechanical coupling coefficient can in principle be achieved by driving the system at resonance, with the added advantage of low voltage operation. Moreover, our structure permits scalable frequency operation up to tens of GHz. We have also designed and simulated realistic 2D metal-on-silicon phononic crystal structures, with the aim of fabricating these structures on the Silicon-on-Insulator platform and experimentally demonstrating artificial piezoelectricity. By tailoring both the electromagnetic and phononic band structures of these periodic structures, efficient excitation of coherent phononic modes can be achieved, which can potentially have novel applications in acousto-optics, acousto-electromagnetics, transducers, and quantum phononics.

• Subjects / Keywords

  • artificial piezoelectricity
  • phononic crystals
  • silicon
  • metamaterial

• Graduation date

  Fall 2023

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-4k2z-ac78

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.