A Shock-Optimized SECE Integrated Circuit

This paper presents a fully integrated, self-starting shock-optimized synchronous electric charge extraction (SECE) interface for piezoelectric energy harvesters (PEHs). After introducing a model of the electromechanical system under shocks, we prove that the SECE is the most appropriate electrical interface to maximize the harvested energy from our PEH. The proposed interface is then presented, both at system and transistor levels. Thanks to a dedicated sequencing, its quiescent current is as low as 30 nA. This makes the proposed interface efficient even under time-spaced shocks occurring at sporadic and unpredictable rates. The circuit is, for instance, able to maintain its self-powered operation while harvesting very small shocks of 8 μJ for every 100 s. Our chip was fabricated in CMOS 40-nm technology and occupies a 0.55-mm2 core area. The measured maximum electrical efficiency under shocks reaches 91%. Under shocks, the harvested energy by the proposed shock-optimized SECE interface is 4.2× higher than using a standard energy harvesting circuit, leading to the best shock figure of merit (FoM) among the prior art.