Abstract
Piezoelectricity-driven hot-electron injectors (p-HEI) are used for self-powered monitoring of mechanical activity in biomechanical implants and structures. Previously reported p-HEI devices operate by harvesting energy from a piezoelectric transducer to generate current and voltage references which are then used for initiating and controlling the process of hot-electron injection. As a result, the minimum energy required to activate the device is limited by the power requirements of the reference circuits. In this paper we present a p-HEI device that operates by directly exploiting the self-limiting capability of an energy transducer when driving the process of hot-electron injection in a pMOS floating-gate transistor. As a result, the p-HEI device can activate itself at input power levels less than 5 nW. Using a prototype fabricated in a 0.5-μm bulk CMOS process we validate the functionality of the proposed injector and show that for a fixed input power, its dynamics is quasi-linear with respect to time. The paper also presents measurement results using a cadaver phantom where the fabricated p-HEI device has been integrated with a piezoelectric transducer and is used for self-powered monitoring of mechanical activity.
Highlights
Piezoelectricity driven hot-electron injectors (p-HEI) have been shown to be attractive for long-term, autonomous and self-powered structural health monitoring (SHM) applications [1], [2] where the use of batteries or remote powering is considered to be impractical
While a detailed explanation and verification of the p-HEI device physics have been presented in [9], we briefly introduce the generic working principle of a p-HEI device in Fig. 1(a) using a simplified energy-band diagram
As the piezoelectric transducer is periodically excited, more electrons are injected onto the floating-gate and the total amount of charge stored on the floating gate is a function of the duration and the magnitude of the mechanical excitation
Summary
Piezoelectricity driven hot-electron injectors (p-HEI) have been shown to be attractive for long-term, autonomous and self-powered structural health monitoring (SHM) applications [1], [2] where the use of batteries or remote powering is considered to be impractical. This source of energy could be delivered either using a plug-and-play interface [4], or using a radio-frequency telemetry link [11] or using an ultrasonic telemetry link [12]. An embedded piezoelectric accelerometer with a tip-mass of 1 mg and an oscillation speed 1 cm/s could generate electrical power only in the range of a few nanowatts
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