Acoustoelectric Effect of Rayleigh and Sezawa Waves in ZnO/Fused Silica Produced by an Inhomogeneous In-Depth Electrical Conductivity Profile

Caliendo, Cinzia

doi:10.3390/s23062988

Cited by 4 publications

(2 citation statements)

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“…According to the theoretical predictions of Ref. [18], it was demonstrated that the photoconductive ZnO induces a short-circuiting effect of the electric potential Φ associated with the SAW. As a result of the UV absorption from the bottom side, the electric potential of the Rayleigh wave is expected to be null at the quartz/ZnO interface, and concentrated inside the piezoelectrically active portion of the ZnO layer (not involved in the UV absorption) where it reaches a peak at the ZnO/air interface where the IDTs were located.…”

Section: Saw Uv Sensormentioning

confidence: 96%

“…It is worth mentioning that research in the field of UV SAW sensors started about 20 years ago, and since then it has continued, fueled by ever-new ideas for pursuing the goal of improving the sensors' performance, for example, by exploring different thicknesses of the UV-sensing layer, combining ZnO nanowires or nanosheets with ZnO thin films [5,6], fabricating multilayer structures [7], or exploring harmonic modes [8,9]. The last paragraph compares the performance of the ZnO-based SAW UV sensors described in the available literature (such as working frequency, sensitivity, rise and recovery time, and tested UV power range) and outlines some possible solutions to be explored to improve the sensors' performance.…”

Section: Introductionmentioning

confidence: 99%

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UV Sensor Based on Surface Acoustic Waves in ZnO/Fused Silica

Caliendo

Benetti

Cannatà

et al. 2023

Sensors

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Zinc oxide (ZnO) thin films have been grown by radio frequency sputtering technique on fused silica substrates. Optical and morphological characteristics of as-grown ZnO samples were measured by various techniques; an X-ray diffraction spectrum showed that the films exhibited hexagonal wurtzite structure and were c-axis-oriented normal to the substrate surface. Scanning electron microscopy images showed the dense columnar structure of the ZnO layers, and light absorption measurements allowed us to estimate the penetration depth of the optical radiation in the 200 to 480 nm wavelength range and the ZnO band-gap. ZnO layers were used as a basic material for surface acoustic wave (SAW) delay lines consisting of two Al interdigitated transducers (IDTs) photolithographically implemented on the surface of the piezoelectric layer. The Rayleigh wave propagation characteristics were tested in darkness and under incident UV light illumination from the top surface of the ZnO layer and from the fused silica/ZnO interface. The sensor response, i.e., the wave velocity shift due to the acoustoelectric interaction between the photogenerated charge carriers and the electric potential associated with the acoustic wave, was measured for different UV power densities. The reversibility and repeatability of the sensor responses were assessed. The time response of the UV sensor showed a rise time and a recovery time of about 10 and 13 s, respectively, and a sensitivity of about 318 and 341 ppm/(mW/cm2) for top and bottom illumination, respectively. The ZnO/fused silica-based SAW UV sensors can be interrogated across the fused silica substrate thanks to its optical transparency in the UV range. The backlighting interrogation can find applications in harsh environments, as it prevents the sensing photoconductive layer from aggressive environmental effects or from any damage caused by cleaning the surface from dust which could deteriorate the sensor’s performance. Moreover, since the SAW sensors, by their operating principle, are suitable for wireless reading via radio signals, the ZnO/fused-silica-based sensors have the potential to be the first choice for UV sensing in harsh environments.

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Section: Saw Uv Sensormentioning

confidence: 96%