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Sensitivity is a key parameter for microspeakers, especially in low-power applications such as consumer electronics, medical devices and Internet of Things. However, the sensitivities of most reported piezoelectric MEMS speakers are inferior to those of commercially available electrodynamic speakers. Design of high-sensitivity piezoelectric MEMS speakers requires an analytical expression of sensitivity, which is not yet available. In this paper, the analytical expression is derived, and an ultrahigh-sensitivity piezoelectric MEMS speaker is designed, fabricated and characterized. The sensitivities of the speaker in an ear simulator are 107 dB/mW, 104 dB/mW and 105 dB/mW at 250 Hz, 1 kHz and 10 kHz, respectively, which are the highest among piezoelectric MEMS speakers. The analytical calculation results and measurement data are perfectly matched. Furthermore, the speaker is based on thin-film AlN instead of commonly used thin-film PZT. This work demonstrates that the ultrahigh-sensitivity piezoelectric AlN MEMS speaker consumes 10 times less power than a typical 6 mm electrodynamic speaker; and the developed analytical expressions provide valuable design insights into piezoelectric MEMS speakers for high sensitivity and low power. [2022-0063] [ABSTRACT FROM AUTHOR]

Cardiac auscultation is an orthodox method to prevent and diagnose cardiovascular diseases. Traditional stethoscopes cannot offer a highly reliable diagnosis, and electronic stethoscopes suffer from low signal-to-noise ratio (SNR) and high cost. This paper reports an electronic stethoscope based on piezoelectric bimorph MEMS transducers for cardiac sound monitoring. The stethoscope prototype, measuring 37 $\times 28\times12$ mm3, contains a preamplifier, holders and polydimethylsiloxane (PDMS) packaging. The transducer is designed using a lumped element model, fabricated by MEMS process, packaged, and assembled for final use. A triangular cantilever is chosen as a basic element for the transducer, with analytical analysis showing high sensitivity per unit area as a figure of merit (FoM). Performance parameters such as sensitivity and noise are experimentally characterized and consistent with simulation results. Owing to the outstanding receiving performance of the aluminum nitride (AlN) material and bimorph triangular cantilever structure of the transducer, compared with the commercial electronic stethoscopes, the proposed stethoscope demonstrates real-time phonocardiogram (PCG) with higher SNR. With its small size, high performance and low cost, the stethoscope is developed for portable and wearable cardiac sound monitoring. [2022-0007] [ABSTRACT FROM AUTHOR]