Photoacoustic Detection of Terahertz Radiation for Chemical Sensing and Imaging Applications

The main research objective is the development of photoacoustic sensor capable of detecting weak terahertz (THz) electromagnetic radiation. The feasibility of THz remote sensing is seen in the utilization of Microelectromechanical systems (MEMS) cantilever-based sensor. The overall sensing functionality of the detector in development is based on the photoacoustic spectroscopy and direct piezoelectric effect phenomena, as a result of which significant part of investigation has been conducted in the areas of terahertz electromagnetic radiation and its detection. The main focus of this research work was the detector analytical and Finite Element Method (FEM) simulation modeling, involving necessary material properties investigations and adequate selections which were, beside the sensors\u27 geometry considerations, heavily engaged in the device modeling. Five different MEMS detector configurations have been analyzed and modeled as potential THz photoacoustic sensing options: Three configurations of rectangular shape, single piezoelectric layer cantilever-based sensors, Circular membrane sensing configuration and Square membrane sensing configuration. Some level of disagreement was discovered between the analytical and FEM simulated results, which has been analyzed and possible reasons were established. The obtained results indicated that the Square membrane has demonstrated the ability to respond effectively to any radiation level from the entire THz photoacoustic range exhibiting high sensitivity and thus was selected as the best terahertz photoacoustic sensing solution

A MEMS Photoacoustic Detector of Terahertz Radiation for Chemical Sensing

A piezoelectric Microelectromechanical system (MEMS) cantilever pressure sensor was designed, modeled, fabricated, and tested for sensing the photoacoustic response of gases to terahertz (THz) radiation. The sensing layers were comprised of three thin films; a lead zirconate titanate (PZT) piezoelectric layer sandwiched between two metal contact layers. The sensor materials were deposited on the silicon device layer of a silicon-on-insulator (SOI) wafer, which formed the physical structure of the cantilever. To release the cantilever, a hole was etched through the backside of the wafer and the buried oxide was removed with hydrofluoric acid. Devices were then tested in a custom made THz vacuum test chamber. Cantilever deflection was observed with a laser interferometer in the test chamber and preliminary data indicates the signals were caused by the photoacoustic effect. Future device data will also include the piezoelectric voltage signal analysis