Development of a high sensitive pH sensor based on shear horizontal surface acoustic wave with ZnO nanoparticles

• The new pH sensor based on Surface Acoustic Wave (SAW) was developed.
• To increase the sensitivity, ZnO Nanoparticles (NPs) was employed as a sensitive layer.
• To improve stability, shear horizontal wave was used to improve stability of the sensor.
• The measured frequency shift and linearity were 144 kHz and 0.957, respectively.
• The developed sensor exhibited good chemical resistance and pH stability.

This study proposes a new pH sensor with a 230 MHz center frequency based on surface acoustic wave (SAW). It consists of piezoelectric substrate, input and output interdigital transducer (IDT) and ZnO Nanoparticles (NPs) used for sensitive layer. The change in conductivity of ZnO NPs induced by pH solutions affects SAW velocity and attenuation. By measuring the frequency shift induced by change in SAW velocity, we can determine the pH value in a target solution. To improve sensitivity and stability of the sensor, we used ZnO Nanoparticles (NPs) and shear horizontal wave. ZnO NPs has some advantages over ZnO films, such as low price and simple fabrication procedure. The SH wave is suitable for layered structure and measurement in liquid. An optimal device structure was designed using coupling of mode (COM) analysis. Depending on the different pH values, a change in the center frequency was clearly observed. The measured frequency shift and linearity between pH 7 to pH 2 of the sensor with 1 μm thick ZnO NPs were 144 kHz and 0.957, respectively. In addition, the developed sensor exhibited good chemical resistance and pH stability.

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