Three-Dimensional Tetrapodal ZnO Microstructured Network Based Flexible Surface Acoustic Wave Device for Ultraviolet and Respiration Monitoring Applications

Abstract

Sensitivity of flexible surface acoustic wave (SAW) sensors to ultraviolet (UV) light is enhanced by application of micro-and nano-structured ZnO networks as sensing layers. In this study, the influence of three dimensional (3D) tetrapodal ZnO microstructured networks spin coated onto Al foil/ZnO piezoelectric film SAW devices on the sensor performance under stimulus of UV light irradiation and influencs of relative humidity was investigated. The UV light sensitivity is increased from -3.03×10 −6 cm 2 mW -1 to -5.25×10 −6 cm 2 mW -1 with the application of 3D tetrapodal ZnO microstructured networks. Likewise, the humidity sensitivity is enhanced by a factor of 2.9 at 90% relative humidity, which is explained by the porous structure of tetrapodal ZnO microstructured networks. In addition, the measured sensitivity to UV light intensity is demonstrated to be significantly modified under a bent condition, because the surface of ZnO piezoelectric film is relatively denser in the case of bending. This study also demonstrates that the sensing performance of respiratory characteristics is increased by nearly a factor of 1.7 under bent

Flexible and Integrated Sensing Platform of Acoustic Waves and Metamaterials based on Polyimide-Coated Woven Carbon Fibers

“…According to eq 1 , the frequency shift caused by the UV light is mainly composed of two parts: i.e., (a) from the conductivity change of ZnO thin films; and (b) from the increase of the temperature. For the frequency shift due to the changes of conductivity, the following equation is generally applied 37 , 38 where k 2 is the coupling coefficient, C s is the capacitance per unit length of the surface, and σ s the sheet conductivity. By measuring the current–voltage ( I – V ) curves of the device under different intensities of the UV illumination (see Figure SI2 in the Supporting Information), the obtained sheet conductance G s is shown in Figure 5 c, and the readings increase with the UV intensity.…”

“…We have previously explored this effect for Al-foil-based flexible SAW sensors and explained how the measurements can be decoupled. 37 , 38 …”

Ultrathin Glass-Based Flexible, Transparent, and Ultrasensitive Surface Acoustic Wave Humidity Sensor with ZnO Nanowires and Graphene Quantum Dots

“…20 Tao et al further used aluminum foils/sheets as the substrate to make flexible SAW devices for various sensing (including humidity) and respiration monitoring. 21 However, it is well-known that these Al foil/sheet substrates are easily plastically deformed without a good flexibility, thus often unable to easily recover to their original states when they have been bent. Therefore, at present, there is still great challenge to develop flexible SAW devices with high performance and good flexibility, for flexible lab-on-a-chip applications.…”

Bending behaviors of flexible acoustic wave devices under non-uniform elasto-plastic deformation

“…Recently, flexible acoustic wave devices (FAWDs) based on different substrates have been investigated, including ultra-thin glass 12 and silicon 18 , LiNbO3 thin film 19 , polyethylene terephthalate (PET) 20 , polyimide (PI) 10 and polyethylene naphthalate (PEN) films 21 . We have recently fabricated flexible SAW devices by depositing ZnO piezoelectric thin films on low-cost and commercially available aluminum (Al) thin sheets, demonstrating excellent performance for both sensing and acoustofluidics applications [22][23][24][25] .…”

“…and K denotes the stiffness matrix of this layer, which is an eight-order matrix determined by material properties, angular frequency and wave vector. For a layered media, the recurrence relation of K can be expressed by 24 :…”