Planar inertial sensor, in particular for portable devices having a stand-by function

#1. Field of the Invention

#The present invention relates to a planar inertial sensor, in particular for portable devices having a stand-by function, of micro-electro-mechanical-system (MEMS) type.

#In particular, the subject matter of the present invention is an inertial sensor for detecting movement that is able to generate a capacitive variation signal, as a function of an input acceleration having any direction parallel to the plane of the sensor.

#For a better understanding of the present invention, some preferred embodiments thereof are now described, purely by way of non-limiting example, with reference to the attached drawings, wherein:

#FIG. 1 shows a schematic plan view of the inertial sensor according to a first embodiment of the invention, in the resting condition;

#FIG. 2 is a view similar to the previous one after displacement from the resting condition;

#The present sensor, according to various embodiments of the invention, may be advantageously used as an inertial switch, for example for re-activating, from stand-by, portable electronic apparatus, such as palm-top computers, cellphones, pocket video-games or calculators. These devices in fact are able to switch off, or set in stand-by, some of their components or some of their functions when they are not used, so as to reduce the consumption of electric power. Thus, the problem exists of re-activating the full functionality as soon as the device exits the resting condition. To this end, acceleration is detected, and an exit-from-stand-by command is issued when this acceleration is higher than a given threshold.

#FIG. 1 illustrates schematically a first embodiment of an inertial sensor 1 according to the present invention. The inertial sensor 1 comprises a mobile central moving element (referred to hereinafter as rotor 2) and a fixed element (referred to hereinafter as stator 3), which surrounds the rotor 2. In a way not shown, the rotor 2 is suspended above a substrate of semiconductor material and is anchored thereto so as to be able to translate, with respect to the stator 3, in any direction of the plane of the rotor 2. Preferably, the rotor 2 is supported by a central anchor formed by a pin projecting from the substrate. Alternatively, the rotor 2 can be connected to the fixed structure (but electrically isolated from the stator 3) through springs (not shown), which are coplanar to the rotor 2 and to the stator 3 and enable movement thereof in the plane.

#The rotor 2 and the stator 3 form the two plates of a capacitor, the capacitance whereof depends upon the distance between them and is thus variable according to the displacement of the rotor 2 with respect to the stator 3.