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

Self-powered sensing of the time-ofoccurrence 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. At the core of the proposed design is the integration of two self-powered modules: (a) a chipscale Fowler-Nordheim tunneling based timer array, for generating a precision, relative time-reference; and (b) a linear piezoelectricity-driven hot-electron injector acting as a floating-gate memory to record the onset of mechanical events. The paper presents measured results from a 4 × 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 hours 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 selfpowered system was measured to be 840 nJ (measured for event durations of one second) which is significantly lower than the energy that can be harvested from typical mechanical impacts. Keywords—Time reference, Self-powered Systems, Floating-gate, Piezo-floating-gate Sensors, Time-ofOccurrence.