Vertical Surface Phononic Mach-Zehnder Interferometer

Abstract

In this work, we propose and evaluate a novel non-planar design of a doublestage phononic crystal (PnC) consisting of a Si substrate, a bottom layer of ZnO, Si pillars and another ZnO layer on top of the pillars. The proposed double-stage PnC exhibits interesting properties such as routing of incoming elastic wave based on source polarization and frequency. In addition, the elastic energy profile of the surface coupled modes are distributed between surface layers including two ZnO layers and pillars dividing the incoming elastic wave between top and bottom ZnO layers. Therefore, the proposed doublestage PnC can be considered as a building block in the design of a super-sensitive structure. The top ZnO layer's conductivity is modulated based on acoustoelectric effect when exposed to an external excitation like UV light illumination and environmental gases such as hydrogen. The proposed super-sensitive device, benefits from higher coupling between local resonators and therefore, the higher phase change between two branches of the elastic Mach-Zehnder which leads to a sensitivity and transmission as high as 23 and -8 dB at 8.6 GHz. Moreover, the proposed elastic Mach-Zehnder has the advantage of avoiding the non-sensing parts such as bottom ZnO layer as the reference branch, pillars and substrate to be affected by the external excitation due to the vertical configuration.