In this work, we demonstrate a fully integrated three-axis Hall magnetic sensor by exploitingmicrofabrication technologies applied to a GaAs-based heterostructure. This allows us toobtain, by the same process, three mutually orthogonal sensors: an in-plane Hall sensor andtwo out-of-plane Hall sensors. The micromachined devices consist of a two-dimensionalelectron gas AlGaAs/InGaAs/GaAs multilayer which represents the sensing structure, grownon the top of an InGaAs/GaAs strained bilayer. After the release from the substrate, thestrained bilayer acts as a hinge for the multilayered structure allowing the out-of-planeself-positioning of devices. Both the in-plane and out-of-plane Hall sensors show a linearresponse versus the magnetic field with a sensitivity for current-biased devices higher than1000 V A-1 T-1, corresponding to an absolute sensitivity more than 0.05 V T-1 at 50 ?A.Moreover, Hall voltage measurements, as a function of the mechanical angle for both in-planeand out-of-plane sensors, demonstrate the potential of such a device for measurements of thethree vector components of a magnetic field.

Electroactive microelectromechanical device of the Artificial Hair Cell type, comprising a moving cilium structure including a substrate (11, 12; 42) and a cantilever (18; 48), partly or entirely in.piezoelectric material, subject to bending or deformation following the action of a force and/or an applied voltage (Vapp1), said cantilever (18; 48) comprising a multilayer (13, 14a, 14b, 16) inducing a stress-driven geometry in which a portion (19) of said cantilever (18; 48) lies outside of a plane defined by the substrate (11, 12; 42). According to the invention said cantilever (18; 48) is associated to a piezoresistive element, in particular of piezoresistive material (15) configured to measure the bending or deformation of said cantilever (18; 48).