This Small Business Innovation Research (SBIR) Phase II project will investigate a novel Micro-electro-mechanical systems (MEMS) microphone based on new design principles. By abandoning the design principles of traditional microphones (both MEMS and full-scale), a vastly superior acoustical design is being explored that has resulted in substantial improvements in fidelity and size reduction (15 dB signal to noise ration[SNR] improvement over existing commercial directional microphones, and roughly 100x smaller in volume). Furthermore, as demonstrated in Phase I, the microphones have an inherently directional response with the benefit of focusing on a speaker or event of interest while rejecting ambient background noise. These attributes make this innovation ideal for addressing an emerging need of high volume consumer communication device manufactures who are looking for acoustic sensing innovations with the unique combination of high performance + low manufacturing cost. The objective of this Phase II innovation is to continue prototyping efforts from Phase I to the point of pilot scale manufacture. This effort will entail finite element modeling and design optimization of the new device structure, fabrication of 2nd generation prototypes, and experimentation in collaboration with customers from several different microphone sectors including hearing aids and cellular phones.
The broader impact/commercial potential of this project is based on an enabling capability: the introduction of advanced audio features (e.g. directionality and high fidelity) into a suite of consumer communication devices. The primary customer focus for this innovation is high volume consumer communication device manufacturers. New applications on their horizon demand improvements in microphone component performance. There are presently several commercial suppliers of MEMS microphones. All use variations of a traditional microphone architecture which has proven incapable of addressing high SNR applications. Additional markets and applications for this innovation include acoustic instrumentation, performance audio, military and defense, intelligence gathering, speech recognition (e.g. in laptop computers), and hearing aids. Addressing hearing aid markets will have a societal impact as well, as patient satisfaction with hearing aid devices is presently very low. Innovations at the microphone and signal processing level have the potential to improve this greatly. The innovation is also expected to have other audiological applications including use in hearing health monitoring systems based on otoacoustic principles. Clinical tools and instruments based on this innovation will serve to enhance scientific and technological understanding in many fields of acoustics.
This Small Business Innovation Research Phase II project investigated the commercial feasibility of a novel MEMS microphone with out-of-plane directivity. The microphone is open at front and back sides of the package so that it is configured to respond to pressure differences in space (i.e. pressure gradients) rather than absolute sound pressure. Both optical and piezoelectric embodiments were explored, with the final embodiment employing piezoelectric detection. Two generations of prototypes were realized, with the second batch successfully demonstrating the anticipated performance. In each case, the fabrication was performed on silicon wafers. Etching processes were used to define a 2mm diameter diaphragm anchored to a rigid substrate through four circumferential springs. Wet microfabrication processes were used to deposit piezoelectric material on the surface of the springs. Upon deflection of the diaphragm due to differential sound pressure, the stress in the springs created an electric field in the piezoelectric film which is read as on open-circuit voltage signal proportional to differential sound pressure. The prototypes were micromachined at UT’s Microelectronics Research Center (MRC), part of NSF’s Next-Generation National Nanotechnology Infrastructure Network (NNIN). Measurements in an anechoic test chamber on UT’s main Austin campus demonstrated the anticipated figure-of-8 directivity and also a noise floor limited by dielectric loss in the piezoelectric material. The measurements, summarized in a forthcoming Applied Physics Letter, summarize a performance 15dB better than that achievable with the existing state of the art. Voice and music recordings were also obtained for qualitative demonstration of functionality. In the future, a third generation of prototypes will be made with the same size and form-factor as existing MEMS microphones, and these prototypes will be shared with interested third parties.
