Challenges in fabrication and testing of piezoelectric MEMS with a particular focus on energy harvesters

In this paper an overview of some of the challenges encountered in the fabrication and testing of MEMS-based piezoelectric devices is presented. All major steps involved in developing piezoelectric MEMS, with particular focus on energy harvesters, are examined in three main sections: Microfabrication, Packaging and Testing. Although the main focus of this paper are the challenges involved with vibration based piezoelectric energy harvesters, most of these challenges apply to other piezoelectric MEMS devices. Various techniques reported for each individual fabrication step are categorized to provide a summary of required information. This allows new researchers to estimate the overall fabrication process, available resources and equipment to prepare accordingly. In addition, challenges of each technique are pointed out explicitly with solutions from literature and our own research. These challenges are typically overlooked in results-based technical papers. Some of the technical solutions discussed were achieved in our experimental work. For other solutions found in literature, references are provided to address issues more in detail. Packaging piezoelectric energy harvesters can be especially challenging. Although a variety of packaging solutions exist for MEMS, these solutions are generic and must be adapted to fit the specific needs of the energy harvesters. This paper illustrates some packaging schemes that have been developed in our research to overcome these challenges. In addition, testing challenges and equipment requirements are discussed with sample results demonstrated. This article explores all fabrication steps, reviews literature, points out challenges and provides solutions with regard to developing piezoelectric MEMS.