Self-powered CMOS impact-rate monitors for biomechanical implants

We have previously reported a novel self-powered piezo-floating-gate sensor that can be used for long-term monitoring of strain levels in biomechanical implants. In this paper, we extend this work to monitor impact-rates (rate of change of strain levels) which is important for predicting mechanical fatigue. We augment the piezo-floating-gate sensor with a filtering and triggering circuit that activates the ionized-hot-electron-injection (IHEI) only when the impactrates exceed predetermined threshold levels. Using multiple prototypes fabricated in a 0.5-mum standard CMOS process we characterize the performance of the sensor for mismatch and for its variability under different biasing conditions. Experimental results obtained using the prototypes demonstrate that the sensor can record different impact-rate levels over a duration of 105 cycles.