Flexible Piezoelectric Energy-Harvesting Exploiting Biocompatible AlN Thin Films Grown onto Spin-Coated Polyimide Layers

Abstract

The increasing demand of piezoelectric energy harvesters for wearable and implantable applications requires biocompatible materials and careful structural device design, paying special attention to the conformability characteristics, properly tailored to scavenge continuously electrical energy even from the tiniest body movements. This paper provides a comprehensive study on a flexible and biocompatible aluminum nitride (AlN) energy harvester based on a new alternative fabrication approach, exploiting a thin polyimide (PI) substrate, prepared by spin coating of precursors solution. This strategy allows manufacturing substrates with adjustable thickness to meet conformability requirements. The device is based on a piezoelectric AlN thin film, sputtered directly onto the soft PI substrate, without poling/annealing processes and patterned by simple and low cost microfabrication technologies. AlN active layer, grown on soft substrate, exhibits good morphological and structural properties with roughness root mean squared (R rms ) of 6.35 nm, columnar texture and (002) c-axis orientation. Additionally, piezoelectric characterization has been performed and the extracted piezoelectric coefficient value of AlN thin film resulted to be 4.93 ± 0.09 pm/V. The fabricated flexible AlN energy harvester generates an output peak-to-peak voltage of ∼1.4 V and a peak-to-peak current up to 1.6 μA, under periodical deformation, corresponding to a current density of 2.1 μA/cm 2 , and providing a maximum generated power of 1.57 μW under optimal resistive load. Furthermore, the AlN energy harvester exhibits high elasticity and resistance to mechanical fatigue. High quality AlN piezoelectric layers on elastic substrates with tunable thicknesses pave the way for the development of a straightforward technological platform for wearable/implantable energy harvesters and biomechanical sensors.

Direct Scaling of Measure on Vortex Shedding through a Flapping Flag Device in the Open Channel around a Cylinder at Re∼103: Taylor’s Law Approach

“…The multi-layered thin films structure consists of a piezoelectric layer of Aluminum Nitride (AlN, 1 μm thick) sandwiched between two Molybdenum films (Mo, 200 nm of thickness) acting as electrodes. AlN is a dielectric material presenting interesting electrical and a natural piezoelectricity due to its crystal symmetry [ 16 , 20 , 21 , 28 ]. Since the device will be employed as an underwater sensor, it needs to be fully electrically insulated.…”

“…In the context of fluid dynamics, the microcantilever has already found application as a rheological sensor to measure the properties of Newtonian and non-Newtonian fluids in real time [ 14 ] and for sensing of both the flow rate and the flow direction [ 15 ]. On the other hand, the piezoelectric cantilever is also used to harvest energy [ 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ], in the Internet-of-Things field [ 20 , 25 , 26 ], to realize piezoelectrochemical hydrogen production [ 27 ], for biochemical sensing, parallel multicantilever Atomic Force Microscopy (AFM) measurements and nanometer range manipulation [ 28 ]. The strengths of this device are low cost, easily manufactured; although intrusive, it is well suited for small scale models and can be used as a self-powering sensor.…”

Progress in lead-free piezoelectric nanofiller materials and related composite nanogenerator devices

“…It has been importantly studied for micro-electromechanical systems (MEMS) and biomedical devices because AlN has high biocompatibility and chemical resistivity as well as facile thin lm processability with the feature of well crystalline texturing and lowtemperature fabrication. [111][112][113] Relatively, AlN syntheses of nanopowder and nanostructures have not been studied deeply in elds of piezoelectric properties and applications. Because the syntheses and fabrications of wurtzite materials are relatively easy and very broadly known, it is not the main topic in this review.…”

Reliability of Protective Coatings for Flexible Piezoelectric Transducers in Aqueous Environments

“…Photo and expanded view of the layered structure of the first group of piezoelectric micro-devices employed for energy harvesting in fluid environments. The thin films were deposited by reactive sputtering, as described in [15,16]. …”