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Review
. 2020 Sep 8;20(18):5118.
doi: 10.3390/s20185118.

ZnO Metal Oxide Semiconductor in Surface Acoustic Wave Sensors: A Review

Izabela Constantinoiu  1 , Cristian Viespe  1
Affiliations
Review

ZnO Metal Oxide Semiconductor in Surface Acoustic Wave Sensors: A Review

Izabela Constantinoiu et al. Sensors (Basel). .

Abstract

Surface acoustic wave (SAW) gas sensors are of continuous development interest to researchers due to their sensitivity, short detection time, and reliability. Among the most used materials to achieve the sensitive film of SAW sensors are metal oxide semiconductors, which are highlighted by thermal and chemical stability, by the presence on their surface of free electrons and also by the possibility of being used in different morphologies. For different types of gases, certain metal oxide semiconductors are used, and ZnO is an important representative for this category of materials in the field of sensors. Having a great potential for the development of SAW sensors, the discussion related to the development of the sensitivity of metal oxide semiconductors, especially ZnO, by the synthesis method or by obtaining new materials, is suitable and necessary to have an overview of the latest results in this domain.

Keywords: ZnO; gas; metal oxide semiconductor; sensor; surface acoustic wave.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Scheme of a surface acoustic wave (SAW) delay line [44].
Figure 2
Figure 2
Scanning Electron Microscope (SEM) images for different types of morphologies obtained for ZnO: nanorods (a) [122], nanosheets (b) [132], nanotubes (c) [133], nanoflowers (d) [1], microspheres (e) [134], nanoplates (f) [113], nanoflakes (g) [135], nanowires (h) [136], and nanofibers (i) [137]. Reproduced (2020) with permission from Elsevier and ACS Publications.
Figure 3
Figure 3
Field scanning electron microscope (FESEM), cross-section of ZnO-Nanoroads (NRs) (a), closer cross-sectional view of ZnO-NRs (b), 25° lateral (c) and top view of ZnO-NRs [122] (d). Reproduced (2020) with permission from Elsevier.
Figure 4
Figure 4
The selectivity of ZnO and Pd@ZnO nanorod sensors at 500 ppm concentrations of different types of gases. [122]. Reproduced (2020) with permission from Elsevier.
Figure 5
Figure 5
Scheme of the proposed detection mechanism for ZnO and ZnO-SnO2 [99]. Reproduced (2020) with permission from Elsevier.
Figure 6
Figure 6
SEM images for ZnO obtained by the hydrothermal method for different morphologies: nanoflowers (a,c) [84,164], nanowires (b,d) [91]. Reproduced (2020) with permission from Elsevier.
See this image and copyright information in PMC

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