Thin-film PMUTs: A Review of 40 Years of Research

A concise review on the thin-film PMUTs, which has been one of the rather important research topics amongst microultrasound experts is being reported. It has been rigorously surveyed, scrutinized, and perceived that the work in this direction began nearly 44 years ago, with the primitive development of functional piezoelectric thin-film material, and now there are already three major companies commercializing them on a bulk scale. This fascinating fact illustrates the enormous contribution made by more than 70 different centers, research institutes, and agencies spread across 4 different continents to develop the vast know-how of these devices design, make, and function. This review covers such important contributions in a short but comprehensive fashion and in particular, intends to educate the readers about the global scenario of PMUTs, the principles governing their design, the ways following their make, all non-conventional useful PMUT designs, and lastly, category wise applications. Crucial comparison charts in terms of thin-film piezoelectric material used in PMUTs, and in terms of targeted applications are also depicted and discussed, which is believed to enlighten any MEMS designer planning to begin working with PMUTs. Moreover, each relevant section is provided with a crisp future forecast, from the authors past knowledge and expertise in this very field of research along with the elements of a careful literature survey. In short, this review can be considered a one-stop time-efficient guide for whoever is interested in knowing about these small devices.