We investigate the use of laterally-coupled High Overtone Bulk Acoustic Resonators (HBAR) based on AlN thin films sputtered on silicon and sapphire substrates in order to target an operation frequency between 2 and 5 GHz. Being tightly coupled, they generate an extremely narrow bandwidth, assimilated to a single resonance whose unloaded quality factors reach respectively 3,300 and 2,000 at 2.5 and 4.4 GHz on silicon substrates and 25,000 at both frequencies on sapphire substrates. The later lead to Q.f factors close to 1.1 10 14 Hz, reaching after twenty years the record established by Kline and Lakin [1]. More interestingly, for filters fabricated on Sapphire substrates, quality factors do not scale with frequency, indicating that viscoelastic losses in Sapphire are not yet the most limiting factor. Indeed, we demonstrate that a compromise needs to be drawn between insertion loss and quality factor in such structures.

This paper reports on the fabrication and characterization of piezoelectric micro-harvesters vibrating at 200Hz for acceleration lower than 0.25g (1g=9.81ms−2). A CMOS compatible process involving Aluminum Nitride (AlN) thin films was developed on Silicon On Insulator (SOI) substrate. A typical device exhibits a volume of 2.8mm3, harvests 0.62μW at 214Hz and 0.25g as input acceleration. The harvested power reaches the same level under vacuum but at only 0.15g. This result confirms that using a packaging under vacuum for piezoelectric energy harvesters is very interesting in order to improve the efficiency for a given acceleration. Finally, it turns out that our devices exhibit the highest Mitcheson figure of merit in the 0–1kHz range, namely 12.2%.

For its outstanding piezoelectric coefficients, thin-film sol-gel Pb(Zr0.52,Ti0.48)O3 (PZT) has been widely studied over the past few decades. In particular, the impact of Zr/Ti ratio control on e31,eff coefficient has been investigated at low fields. Yet, when it comes to actuation, PZT films are used with electric fields higher than the coercive field. In this paper, the influence of Zr/Ti gradient reduction on e31,eff coefficient is investigated in actuating conditions, ie under high fields.

In this paper, we present the fabrication of micro cantilevers and the extraction of the transverse piezoelectric coefficient d31. Micro cantilevers were fabricated on SOI wafers by surface micromachining processes. By controlling the crystallization conditions, 2 μm-thick (100) and (111) highly oriented PZT films were obtained. Piezoelectric properties were compared according to two crystalline orientations. A model was adapted to extract d31 from deflection measurements. The interest of this d31 extraction is that the piezoelectric coefficient is performed in actual conditions of actuation.

Valving is essential to microflow circuits and networks in microsystem technology. Many different types of valves have been designed and fabricated. Membranes of sacrificial material have already been designed for one-shot valving. However, the new design proposed here, based on sacrificial micro-membranes with embedded electrodes, has the advantages of being efficient, easily controllable and requiring very low energy levels. We have shown that a 100 mu m x 100 mu m x 500 nm Si3N4 membrane with a platinum electrode can be actuated to break up with an energy input of only 6 mu J, during an actuation time of 200 mu s. At rest, in the absence of actuation, such membranes can withstand a pressure of 1 bar. The goal of the development of such membranes is to hydrodynamically connect, one by one, a series of initially isolated micro-chambers implemented in a silicon chip.