João Mouro

International Iberian Nanotechnology Laboratory

Microcantilevers are increasingly being used to create sensitive sensors for rheology and mass sensing at the micro- and nano-scale. When operating in viscous liquids, the low quality factor of such resonant structures, translating to poor signal-to-noise ratio, is often manipulated by exploiting feedback strategies. However, the presence of feedba...

Emerging applications such as the Internet-of-Things and more-electric aircraft require electronics with integrated data storage that can operate in extreme temperatures with high energy efficiency. As transistor leakage current increases with temperature, nanoelectromechanical relays have emerged as a promising alternative. However, a reliable and...

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 ar...

We investigate the response of a digitally controlled and parametrically pumped microcantilever used for sensing in a Phase-Locked Loop (PLL). We develop an analytical model for its dynamical response and obtain an explicit dependence on the rheological parameters of the surrounding viscous medium. Linearization of this model allows to find improve...

Sensors based on self-excitation of microcantilevers have been proposed as effective devices for the measurement of rheological properties of the fluid where they are immersed. However, embedding microcantilevers in a feedback loop causes complex phenomena that need to be investigated. Specifically, a variable delay in the loop originates jumps in...

This work describes a new platform for sensing mass or rheological properties of gases with unprecedented responsivity and limits of detection. The system consists of a microcantilever working in a Phase-Locked Loop with an imposed phase between its excitation and deflection signals. The optically detected cantilever deflection is demodulated again...

This work presents a feedback closed-loop platform to be used for viscosity or viscoelasticity sensing of Newtonian or non-Newtonian fluids. The system consists of a photothermally excited microcantilever working in a digital Phase-Locked Loop, in which the phase between the excitation signal to the cantilever and the reference demodulating signals...

A self-oscillating microcantilever in a feedback loop comprised of a gain, a saturator, and an adjustable phase-shifter is used to measure the viscosity of Newtonian fluids. Shifting the signal of the loop with the adjustable phase-shifter causes sudden jumps in the oscillation frequency of the cantilever. The exact position of these jumps depends...

The emergence of augmented reality, robotics and point-of-care biosensors has pushed forward the frontiers of compliant sensors with mechanical resilience and capability of being arbitrarily shaped upon demand. Here, we report exchange-biased spin valve structures directly fabricated on 25μm thick commercial polymeric substrates. Linear electrical...

Surface adhesion forces play a critical role in the operation of NEM relays, but characterization data for micro/nanoscale contact areas of relevant materials are scarce. A novel technique to estimate the adhesion force between two contacting surfaces is presented. This method uses the hysteresis in the pull-in/-out voltages measured experimentally...

A versatile mass-sensing platform based on the nonlinear dynamical response of a microcantilever embedded in a self-excitation feedback loop is proposed. It is experimentally shown that the delay imposed in the feedback loop by an adjustable phase-shifter can be used to finely tune this system to work in three different modalities, according to the...

A viscosity sensor based on the nonlinear behaviour of a microcantilever embedded in a self-excitation loop with an adjustable phase-shifter is proposed. The self-sustained oscillation frequencies of the cantilever are experimentally and theoretically investigated as functions of the fluid viscosity and of the imposed phase shift of the signal alon...

The integration of microelectromechanical devices (MEMS) with its driving integrated circuits is fundamental to expanding the applications of both technologies. This integration puts important demands on the MEMS processing and their electromechanical performance. This work presents the electrical characterization of flexural microresonators made o...

Hydrogenated amorphous silicon thin-film flexural resonators with sub-micron actuation gaps are fabricated by surface micromachining on glass substrates. Experimentally, the resonators are electrostatically actuated and their motion is optically detected. Three different configurations for the electrostatic excitation force are used to study the dy...

Thin-film MEMS resonators fabricated at low temperatures can be processed on CMOS ICs, forming high-sensitivity transducers within complete sensing systems. A key focus for the MEMS devices is increasing the resonant frequency, enabling, among other benefits, operation at atmospheric pressure. However, at increased frequencies, parasitics associate...

Flexural and in-plane vibrating thin-film resonators fabricated on glass substrates using low temperature surface micromachining and hydrogenated silicon structural layers with sub-micron gaps are demonstrated. Using hydrogenated silicon thin-films with distinct types of mechanical stress as the resonator structural layer allows controlling the qua...

Thin-film silicon allows the fabrication of MEMS at low processing temperatures, including on large-area, low-cost, and flexible substrates. For MEMS applications, the main film properties to consider are the deposition rate, electrical conductivity, and mechanical stress. In this paper, n(+)-doped hydrogenated amorphous/nanocrystalline silicon thi...

Thin-film MEMS bridges as micro-resonators have proven attractive for various sensing applications (acceleration, mass, chemical, pressure, etc.) by using frequency shift as a basis for sensing [1]. Low-temperature processing of amorphous-silicon (a-Si:H) enables low-cost fabrication of high-Q MEMS bridges having excellent compatibility with CMOS p...

Thin-film silicon allows the fabrication of MEMS devices at low processing temperatures, compatible with monolithic integration in advanced electronic circuits, on large-area, low-cost, and flexible substrates. The most relevant thin-film properties for applications as MEMS structural layers are the deposition rate, electrical conductivity, and mec...