Aluminum nitride (AlN) has gained wide interest owing to its high values of elastic modulus, band gap, dielectric strength, resistivity, thermal conductivity and acoustic velocities, especially because it retains most of its properties and versatility in the thin-film form. This review focuses on applications where the CMOS integration of AlN MEMS has been effectively demonstrated. First, the fundamental concepts of piezoelectricity on polycrystalline $c$ -axis oriented thin-films are introduced and AlN is compared to other common piezoelectric materials, namely LiNbO ₃ , LiTaO ₃ , quartz, lead zirconate titanate (PZT), ZnO and GaN by thoroughly discussing the material properties, processing and technological implications. After presenting the possible MEMS-CMOS integration strategies, recent demonstrations of AlN-based devices are reviewed, namely energy harvesters, film bulk acoustic resonators (FBAR), contour mode resonators (CMR), gas sensors, imagers, microphones, transducers for chip-scale communication and calorimetric sensors. Finally, other recent applications/integration opportunities are outlined for AlN-based micro-mirrors, flexible sensors and transducers for liquid media and harsh environments. [2022-0006]

A microcantilever is a suspended micro-scale beam structure supported at one end which can bend and/or vibrate when subjected to a load. Microcantilevers are one of the most fundamental miniaturized devices used in microelectromechanical systems and are ubiquitous in sensing, imaging, time reference, and biological/biomedical applications. They are typically built using micro and nanofabrication techniques derived from the microelectronics industry and can involve microelectronics-related materials, polymeric materials, and biological materials. This work presents a comprehensive review of the rich dynamical response of a microcantilever and how it has been used for measuring the mass and rheological properties of Newtonian/non-Newtonian fluids in real time, in ever-decreasing space and time scales, and with unprecedented resolution.

Microelectromechanical sensors have extreme mass sensitivities, making them promising for mass sensing, gas sensing, and biosensing applications. Despite the numerous examples of MEMS/NEMS mass sensors in the literature, the characterization of the resonator or oscillator system is often incomplete. Resonant mass sensor studies should include phase noise (or Allan deviation), as the use of these metrics allows for the identification of the noise mechanisms, the optimization of the measurement and actuation parameters, the prediction of the limit of detection, and the comparison of different types of resonators or vibration modes. In this paper, we summarize the metrics we consider to be the most important in the characterization of dynamic mass sensors, and then apply them to low-cost, hydrogenated amorphous silicon (a-Si:H) thin-film MEMS cantilever resonators. The effects of the actuation voltage on the phase noise were studied. The mass sensitivities of these resonators were calibrated using patterned thin-films localized at the tip of the cantilevers as well as uniform ultra-thin films of SiO₂. The experimental mass sensitivities in vacuum ranged -98 Hz/pg to -4.6 kHz/pg. The limits of detection were calculated to be 100-833 fg in vacuum and 37-846 pg at atmospheric pressure. [2019-0006]

As an additive manufacturing process, material jetting techniques allow to selectively deposit droplets of materials in liquid or powder form through a small-diameter aperture, such as a nozzle of a print head. For the fabrication of printed electronics, a variety of inks and dispersions of functional materials can be deposited by drop-on-demand printing on rigid and flexible substrates. In this work, zero-dimensional multi-layer shell-structured fullerene material, also known as carbon nano-onion (CNO) or onion-like carbon, is printed on polyethylene terephthalate substrates using drop-on-demand inkjet printing. CNOs are produced using a low-cost flame synthesis technique and characterized by electron microscopy, Raman, x-ray photoelectron spectroscopy, and specific surface area and pore size measurements. The produced CNO material has an average diameter of ∼33 nm, pore diameter in the range ∼2–40 nm and a specific surface area of 160 m².g⁻¹. The CNO dispersions in ethanol have a reduced viscosity (∼1.2 mPa.s) and are compatible with commercial piezoelectric inkjet heads. The jetting parameters are optimized to avoid satellite drops and to obtain a reduced drop volume (52 pL), resulting in optimal resolution (220 μm) and line continuity. A multi-step process is implemented without inter-layer curing and a fine control over the CNO layer thickness is achieved (∼180 nm thick layer after 10 printing passes). The printed CNO structures show an electrical resistivity of ∼600 Ω.m, a high negative temperature coefficient of resistance (−4.35 × 10⁻² °C⁻¹) and a marked dependency on relative humidity (−1.29 × 10⁻² RH_% ⁻¹). The high sensitivity to temperature and humidity, combined to the large specific area of the CNOs, make this material and the corresponding ink a viable prospect for inkjet-printed technologies, such as environmental and gas sensors.

Label-free approaches to biomolecular detection in microfluidics avoid potential labeling interference, are suitable for the screening of analytes that are not easily tagged, and simplify assay development toward point-of-use applications. In this paper, multimodal label-free detection of biomolecules was performed in a microfluidic system: 1) optically, with an integrated hydrogenated amorphous silicon thin-film photodiode and 2) electrically, using integrated electrochemical impedance interdigitated microelectrodes. Bovine serum albumin, single-stranded DNA, and a mixture of human immunoglobulins G were selected as model biomolecules. The sensitivities of the biomolecular detection were first evaluated in a bare microfluidic channel. The lower limit of detection obtained, for each transducing technique, was 10 nM for the impedimetric detection of ssDNA and 80 nM for the optical detection of a mixture of antibodies. These sensitivities were considered fit-for-purpose when applied to microfluidic systems aimed at monitoring molecular adsorption to different immobilized ligands. To validate the proposed multimodal detection, the model biomolecules were detected in a microfluidic structure packed with ion exchange chromatography agarose microbeads and the target biomolecules were monitored in real time both at bead level and downstream of the packed beads. The application of these label-free sensors ranges from bioprocess optimization to molecular purification and potentially the development of rapid analytics, with the advantages of device compactness, cost effectiveness, high speed of analysis, and multiplexed signal acquisition.