Such micro-loudspeakers were developed by the Fraunhofer Institutes for Digital Media Technology (IDMT) and Silicon Technology (ISIT). MEMS technology stands for microelectromechanical systems and combines classical semiconductor technology with miniature mechanics in the micrometer range. The ISIT scientists are thus heralding a paradigm shift: Loudspeakers can thus be made of silicon in the same way as computer chips. This allows high quantities to be produced at comparatively low prices.
Both Institutes have been working for three years on the joint research project “Smart Speaker – Smart MEMS speakers for mobile applications” on the development of energy-efficient and completely integrable chip-based loudspeakers. While Fraunhofer ISIT is responsible for the development and pilot production of piezoelectric microdrives and their integration into highly miniaturized intelligent microsystems, Fraunhofer IDMT deals with the intelligent signal control of miniature loudspeakers.
The breakthrough has now been achieved. The characteristics of the chip-based loudspeaker are impressive: With currently a area of 4×4 millimeters, the MEMS loudspeaker can be optimally integrated into headphones, hearables and hearing aids. They cover the entire frequency range from 20 Hz to 20 kHz as a one-way system – comparable HiFi loudspeakers typically consist of woofer, a midrange loudspeaker and a tweeter for the high frequencies. The tiny MEMS speakers achieve a sound pressure level of 110 dB for in-the-ear applications – this corresponds to the noise level of a jet aircraft at a distance of 100 meters.
Despite their miniature design, the MEMS loudspeakers impress with their high fidelity and low energy consumption, which is of particular relevance for battery-powered devices. Last but not least, the production with silicon technology enables cost-efficient chip production and assembly at a large scale.
MEMS loudspeakers use piezoelectric thin films as active elements that deform when electrical voltage is applied. This mechanical deflection displaces the surrounding air and thus generates sound waves. The use of silicon for the development of MEMS loudspeakers has proven its worth. Thanks to modern chip manufacturing technologies, the semiconductor material silicon can be processed in its smallest structures and is ideal for this electromechanical application. And it is also a very cost-effective material.
In the future, the transmission bandwidth is to be expanded to beyond 20 kHz by combining several miniature loudspeakers to form a multi-way system. “This puts us in a position to meet the high quality demands of the HD headphone market,” says Daniel Beer, project manager at the IDMT.
Semiconductor expert Bernhard Wagner of Fraunhofer ISIT sees important development opportunities for the manufacture of MEMS loudspeakers:”We want to use new piezoelectric materials that are more energy-efficient and IC-compatible in the future. This will further reduce power consumption and enable mass production of MEMS loudspeakers in all major semiconductor factories”.
The two Fraunhofer Institutes will present their achievements to the public for the first time at the annual conference of the German Society for Acoustics (DAGA) in Munich from March 19 to 22.