New frontiers in sensing: combining classical optical techniques with innovative miniaturized devices

The rapid advancement of micro-electronics, micro-machining and micro-manufacturing in high-tech areas has created a strong demand for miniaturized electromechanical devices that offer fast response, low power consumption, high resolution, and immunity to electromagnetic interference. The miniaturization of opto-electronic devices has become crucial across scientific and industrial fields, enabling innovative solutions for optical sensing in a totally non-contact and non-invasive approach in healthcare, biotechnology, environmental monitoring, microfluidics, and beyond. The research activity carried out during my Ph.D. program in Microelectronics aims at significantly promoting scientific innovation and advancement in the field of miniaturized devices, including their testing and applications. The common thread connecting the various research activities that I performed can be found in the fundamental role played by principles of optics in the design and characterization of the investigated tiny devices and of the ultra-compact sensing systems exploiting them. I investigated, implemented and applied a compact, fiber-based interferometric setup to carry out the modal analysis of piezo-actuated silicon micro-plates, which are buckled due to the built-in stress induced by the MEMS thin-film fabrication technology. I gained insight on the fabrication and contributed to the characterization of piezo-actuated adaptive lenses, by incorporating a 50 μm-thick stiff glass membrane between two 100 μm-thick sheets of piezo-material to form a sandwich structure, which also includes a flexible silicone membrane that acts as fluid reservoir. I developed a straightforward method to measure the real part of the refractive index (RI) of transparent fluids by shining a light beam through a fluid filled cuvette with rectangular cross section and detecting the output spot with a CMOS camera. As a further innovation step, the configuration has been modified by exploiting the features of a piezo-actuated adaptive glass lens. Towards the development of a more compact and more sensitive RI measuring system, I investigated an optofluidic sensing configuration for contactless and remote detection of liquid samples that exploits a simple and intuitive principle of operation based on the measurement of the laser beam displacement with a position sensitive detector. I also contributed to a successful implementation of the same principle of optical detection with an innovative microfluidic device provided with integrated reflectors. My scientific and engineering journey throughout the Ph.D. program in Microelectronics has contributed to the advancement of miniaturized devices, optical sensing, and their applications.