Linearization of CMOS Hot-Electron Injectors for Self-Powered Monitoring of Biomechanical Strain Variations

In our previous work we demonstrated that by eliminating regulation and rectification modules from the energy harvesting pathway, the minimum activation power of a piezoelectricity-driven hot-electron injector (p-HEI) can be reduced down to a few nanowatts. As a result the p-HEI device could be used for self-powered, in-vivo recording of biomechanical strain variations. However, for large magnitudes of input strain energy, the response of the modified p-HEI sensor was found to be quasi-linear with respect to the number of loading cycles, which made the calibration of the sensor difficult across a wide variety of biomedical applications. In this paper we propose a compensation circuit that is able to linearize the response of the p-HEI injector over a wide range of input power while maintaining a low activation threshold. The compensation circuit uses a combination of a storage capacitor and a non-linear resistor which produces a compressive input-output response required for linearization. Using prototypes fabricated in a 0.5-mu m bulk CMOS process we validate the functionality of the injector and demonstrate that it can achieve a linear injection response for input power ranging from 5 nW to 1.5 mu W.