Impact of the variability of microfabrication process parameters on CMUTs performance

As CMUT technology moves towards the industrial phase, the robustness of the fabrication process becomes a key aspect to produce reliable and well-performing devices. CMUT arrays typically show a variability of the electromechanical and acoustic behavior among the transducer elements, which is mainly ascribed to tolerances of process-related parameters. This paper investigates the impact of process-related parameters variability on the performance of CMUT arrays, by proposing a local sensitivity analysis technique performed according to a Design of Experiments (DoE) approach based on Vertex Analysis. The sensitivity analysis is performed by simulating a Reverse-Fabricated CMUT using Finite Element Modeling (FEM), and computing the CMUT electromechanical parameters by varying the thicknesses of the front membrane layer, of the top and bottom passivation layers and of the sacrificial layer within a 10% tolerance range around the nominal set of values. The sensitivity analysis results are then compared to the variability observed in the data obtained characterizing a 256-element Reverse-Fabricated CMUT linear array for medical imaging.