Piezoelectric Transducers and Inertial Sensors using Piezoelectric Transducers

Abstract

Transducers comprising a frame structure made of piezoelectric material convert energy, through piezoelectric effect, between electrostatic energy associated with voltage differential between the electrodes sandwiching the frame structure and mechanical energy associated with deformation of the frame structure. Inertial sensors such as gyroscopes and accelerators, including inertial sensors comprising ring resonators, utilize said transducers both to generate oscillations of their resonators and to sense the changes in such oscillations produced, in the sensors' frame of reference, by Coriolis forces appearing due to the movement of the sensors.

Description

TECHNICAL FIELD[0001]The present invention relates generally to inertial sensors, and more particularly to microelectromechanical inertial sensors for measuring a rotational motion, such as ring gyroscopes.BACKGROUND ART[0002]It is known in the prior art to use inertial motion sensors to track the position, orientation, and velocity (linear or angular) of objects in the inertial reference frame, without the need for external references. Inertial motion sensors generally include gyroscopes, accelerators, and other motion-sensing devices. Gyroscopes are well-known and used for measuring or maintaining orientation based on the principles of conservation of angular momentum. Vibrating structure gyroscopes, due to their simplicity and low cost, gained popularity since 1980s over conventional, rotating gyroscopes. The physical principle of a vibrating structure gyroscope is very intelligible: a vibrating object tends to keep vibrating in the same plane as its support is rotated. In engine...

AI Technical Summary

Benefits of technology

[0010]Embodiments of a piezoelectric transducer of this invention permit transferring energy, through piezoelectric effect, between electrostatic energy associated with voltage differential between the top and bottom electrodes of the transducer and mechanical energy associated with deformation of frames of the transducer. In one embodiment, the transducer of the invention comprises a structure made of piezoelectric material that includes a set of substantially flat elongated concentric frames connected by bridges disposed symmetrically about a plane of symmetry of the structure. Such bridges allow the frames to deform in a reference plane which is substantially parallel to top and bottom surfaces of the frames. A set of at least two top electrodes is disposed on the top surfaces of the frames. A set of at least two corresponding bottom electrodes is disposed on the bottom surface of the frames opposite to the first set. Both the top and the bottom set of electrodes are disposed on at least two frames along a path that is symmetric about the plane of symmetry of the structure and crosses some of the bridges. Some of these electrodes may be used to apply a voltage differential between the top and bottom surfaces of the piezoelectric transducer, while some of the electrodes may be configured to sense the changes in motion of the frames of the transducer based on a voltage differential associated with such changes. In some embodiments, the deformation of the frames may be reciprocating, and may be characterized by amplitude that is higher in central portions of the frames than in peripheral portions of the frames.

Problems solved by technology

As would be appreciated by one skilled in the art, currently employed micromachining processes are not particularly compatible with widely used standard CMOS processes such as reactive-ion etch (RIE) or electron-beam milling.

Such incompatibility lengthens and complicates fabrication cycles and increases the cost of the resulting MEMS-based devices.

The air-gaps of MEMS structures are clearly susceptible to contamination with microparticles (during both the manufacturing process and operation) that may permanently incapacitate inertial sensors devices.

Moreover, an electrostatically driven mass or ring in such devices is susceptible to anomalies in charge distribution across a set of driving and sensing electrodes.

In vibrating gyroscopes, the non-uniform charge distribution can contribute to an offset drift and reduce the accuracy and precision of these devices or even nullify their performance.

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