Humidity responses of Love wave sensors based on (1 1 2¯ 0) ZnO/R-sapphire bilayer structures

Simulation of SAW Humidity Sensors Based on ( 11 2 ¯ 0 ) ZnO/R-Sapphire Structures

“…Then, the frequency responses and sensitivities of humidity sensors with Rayleigh modes and Love modes based on the structures of $\left(11\overline{2}0\right)$ZnO/R-sapphire are also simulated numerically. The simulation results agree well with previous published experimental and theoretical data [8,9,10]. Besides, the mechanical and electrical contributions of the adsorbed water layer to the sensitivities are simulated and discussed.…”

“…According to previous experimental and theoretical calculations, as the environmental humidity changes approximately from 0.01% to 90%, the corresponding water layer height on the surface of the humidity sensor changes from 1 nm to 12 nm [10,18]. The frequency shifts Δ f / f 0 of the SAW humidity sensors ( h f /λ = 0.11) against different water layer heights h w /λ are also simulated, which are obtained by the resonant frequency evaluations using Equation (1) with and without water layers as shown in Figure 8a,b for Rayleigh waves and Love waves, respectively.…”

“…In addition, due to the adsorbed water layer height is always not proportional to the environmental relative humidity [10,18], so Δ f / f 0 is also not changed linearly with the relative humidity variation.…”

“…In previous studies, several kinds of bilayered structures based on ZnO thin films deposited on sapphire substrates had been investigated and reported in order to achieve high SAW velocities and low temperature coefficients [8,9]. Considering SAWs with SH-modes are more suitable for sensing in liquid environments, a kind of Love mode sensors based on the bilayered structures of$\left(11\overline{2}0\right)$ZnO thinilmssputteredon R-sapphire substrates had been prepared and investigated experimentally [10,11]. …”

Surface acoustic wave relative humidity sensor based on sputtering SiO2 film

“…There are a bulk of materials that can be used as humidity-sensing coating, including organic polymer, [22][23][24][25][26][27][28][29] oxide, [30][31][32][33][34][35][36] nanomaterials, 1,[37][38][39][40][41][42] and composite. 17,19,20 SiO 2 has attracted interest because of its high humidity sensitivity, rich resources, low cost, and diverse synthesis methods.…”