A CMOS Timer-Injector Integrated Circuit for Self-Powered Sensing of Time-of-Occurrence

Self-powered sensing of the time-of-occurrence of an event is challenging, because it requires access to a reliable time reference or a synchronized clock. In this paper, we propose for the first time a self-powered integrated circuit that is capable of time-stamping asynchronous mechanical events of interest. The core of the proposed design is the integration of two self-powered modules: 1) a chip-scale Fowler-Nordheim tunneling-based timer array, for generating a precision, relative time reference; and 2) a linear piezoelectricity-driven hot-electron injector acting as a floating-gate memory to record the onset of mechanical events. This paper presents measured results from a 4 \times 4 fully programmable timer array system-on-chip (SoC) and a linear injector array SoC, both of which have been prototyped in a standard double-poly CMOS process. The synchronization error of the timer array with respect to an external software clock was measured to be less than 1% over a duration of 100 h, and the average accuracy in sensing the time-of-occurrence of the event was measured to be 6.9%. The minimum activation energy of the self-powered system was measured to be 840 nJ (measured for event durations of 1 s), which is significantly lower than the energy that can be harvested from typical mechanical impacts.