Influences of internal stress in the dynamic behavior of integrated photonic ultrasound transducers

Integrated photonic ultrasound transducers (IPUTs) are compact, high-sensitivity devices that combine mechanical sensing with optical readout using integrated photonics. IPUTs are composed of optical waveguides placed on a mechanical resonator. In most cases, the mechanical resonator is a membrane, formed from thermally oxidized silicon dioxide layers—commonly used in photonic fabrication processes. The oxidation process induces significant internal compressive stress—typically between 200 and 400 MPa—upon cooling to room temperature. These stresses can strongly influence the membrane’s dynamic response. This study investigates how internal stress affects the resonance frequency and receive transfer function (RTF) of IPUTs. Finite element models incorporating residual stress are developed and validated against experimental data and prior literature. Parametric analysis shows that increasing compressive stress reduces the resonance frequency and increases the RTF, up to the critical buckling load. Beyond this point, post-buckling deformation leads to excitation of higher-order vibration modes, causing a sharp increase in resonance frequency and a corresponding drop in RTF. These nonlinear effects highlight the importance of incorporating internal stress effects into the early-stage design of IPUTs and similar membrane-based acoustic sensors to ensure optimal dynamic performance and system reliability, particularly in applications requiring precise frequency response and consistent sensitivity.