• optomechanics
• microbolometers
• thz detection

The non-ionizing nature of THz rays can be exploited for imaging purposes,
with applications, among others, in security, medical diagnostics and quality control. Consequently, extensive research efforts have focused on creating fast, room-temperature, and miniaturized detectors that can serve as the core component in configurations like focal plane array (FPA) imaging systems. In particular, microbolometers based on MEMS resonators (thermomechanical bolometers) have demonstrated high sensitivity, compactness and rapid response time. These devices detect radiation by measuring the thermal shift in the resonant frequency of the microresonator when exposed to light-induced heating. Among the proposed geometric configurations, the trampoline shape represents a
good trade-off between a large device area and high thermal resistance of the links connecting it to the thermal sink. In particular, silicon nitride (Si3N4) trampoline TBs have shown low mechanical dissipation, making them suitable for infrared and sub-THz detection.
My thesis work is based on improving the state-of-the-art trampoline TBs for next-generation devices which could be implemented in FPA configurations. The first improvement was the implementation of a compact electrical read-out method, based on electromagnetic induction. A gold wire electrode is patterned along the border of the trampoline membrane. Its movement in a static magnetic field results in variations in the concatenated magnetic flux and, consequently, the generation of a detectable electromotive potential.
The second objective of my thesis was the introduction of smart absorbers, namely coating layers
capable of enhancing thermomechanical detection without impacting on the mechanical quality of the resonator. Weightless and stiff ultra-thin materials are the perfect candidates to this end. We considered various materials, including chromium-gold (Cr/Au) thin metallic layers, amorphous carbon based films, specifically pyrolytic carbon (PyC) and pyrolyzed photoresist film (PPF), and multi-layer graphene (MLG). As a preliminary characterization, we assessed the optical properties of the coatings across a broad frequency range employing FTIR spectroscopy for the infrared range (12-234 THz), and time-domain spectroscopy for the THz region (0.5–3 THz). Afterwards, we deposited each coating onto different trampoline membranes to evaluate their performance as TBs, employing our new all-electrical read-out. We used a near-infrared and a 140 GHz source. These two experiments illustrated the broadband operation of our devices and showcased their use in opposite configurations, employing a radiation source with spot size much smaller or much larger than the trampoline size, respectively. The addition of an absorbing coatings effectively enhanced detection performances, quantified by larger responsivities.