Organic-inorganic hybrid piezotronic bipolar junction transistor for pressure sensing

With the rapid development of the Internet of Things(IoTs),wearable sensors are playing an increasingly important role in daily monitoring of personal health and wellness.The signal-to-noise-ratio has become the most critical performance factor to consider.To enhance it,on the one hand,good sensing materials/devices have been employed;on the other hand,signal amplification and noise reduction circuits have been used.However,most of these devices and circuits work in an active sampling mode,requiring frequent data acquisition and hence,entailing high-power consumption.In this scenario,a flexible and wearable event-triggered sensor with embedded signal amplification without an external power supply is of great interest.Here,we report a flexible two-terminal piezotronic n-p-n bipolar junction transistor(PBJT)that acts as an autonomous and highly sensitive,current-and/or voltage-mediated pressure sensor.The PBJT is formed by two back-to-back piezotronic diodes which are defined as emitter-base and collectorbase diodes.Upon force exertion on the emitter side,as a result of the piezoelectric effect,the emitter-base diode is forward biased while the collector-base diode is reverse biased.Due to the inherent BJT amplification effect,the PBJT achieves record-high sensitivities of 139.7 kPa^(-1)(current-based)and 88.66 kPa^(-1)(voltage-based)in sensing mode.The PBJT also has a fast response time of<110 ms under exertion of dynamic stimuli ranging from a flying butterfly to a gentle finger touch.Therefore,the PBJT advances the state of the art not only in terms of sensitivity but also in regard to being self-driven and autonomous,making it promising for pressure sensing and other IoT applications.

Highly sensitive active-powering pressure sensor enabled by integration of double-rough surface hydrogel and flexible batteries

A conductive,elastic,and biocompatible hybrid network hydrogel was prepared by cross-linking of locust bean gum,polyvinyl alcohol,and carbon nanotubes,yielding a rough top surface and smooth bottom surface.The merging of the two pieces of hydrogel flat face to flat face forms a highly elastic hydrogel with double-rough surfaces.A piezoresistive sensor assembled with the double-rough surface hydrogel sandwiched between two carbon cloth electrodes exhibits a high sensitivity(20.5 kPa^(-1),0-1kPa),a broad detection range(0.1-100 kPa)and a reliable response for 1000 cycles.The rough contact area between the hydrogels and the carbon cloth is found critical in achieving ultra-high sensitivities in the low-pressure range.Moreover,further monolithic integration of the sensor with a flexible solid-state zinc ion battery ensures the self-powering of the sensor for various human motions detection applications.