“… Comparison of TCF readings between ZnO/Al SAWs in this study and ZnO based SAWs on other commonly used substrates reported in literature 16 , 22 , 23 , 25 , 33 – 39 . …”
Section: Resultsmentioning
confidence: 83%
“…This could dramatically increase the thermal expansion of the devices during heating/cooling and result in significant variations in the wave velocities with temperature. Figure 5 Comparison of TCF readings between ZnO/Al SAWs in this study and ZnO based SAWs on other commonly used substrates reported in literature 16 , 22 , 23 , 25 , 33 – 39 . …”
Section: Resultsmentioning
confidence: 87%
“…Therefore, most researchers use techniques to reduce the TCF values or achieve a temperature compensation during sensing. This can be easily implemented using an additional compensation layer such as silicon dioxide 12 – 15 or alumina 16 , 17 , both of which have positive TCFs. In contrast, for temperature sensing applications, a large absolute value of the TCF with a good linearity is desired.…”
A fundamental challenge for surface acoustic wave (SAW) temperature sensors is the detection of small temperature changes on non-planar, often curved, surfaces. In this work, we present a new design methodology for SAW devices based on flexible substrate and bimorph material/structures, which can maximize the temperature coefficient of frequency (TCF). We performed finite element analysis simulations and obtained theoretical TCF values for SAW sensors made of ZnO thin films (~5 μm thick) coated aluminum (Al) foil and Al plate substrates with thicknesses varied from 1 to 1600 μm. Based on the simulation results, SAW devices with selected Al foil or plate thicknesses were fabricated. The experimentally measured TCF values were in excellent agreements with the simulation results. A normalized wavelength parameter (e.g., the ratio between wavelength and sample thickness, λ/h) was applied to successfully describe changes in the TCF values, and the TCF readings of the ZnO/Al SAW devices showed dramatic increases when the normalized wavelength λ/h was larger than 1. Using this design approach, we obtained the highest reported TCF value of −760 ppm/K for a SAW device made of ZnO thin film coated on Al foils (50 μm thick), thereby enabling low cost temperature sensor applications to be realized on flexible substrates.
“… Comparison of TCF readings between ZnO/Al SAWs in this study and ZnO based SAWs on other commonly used substrates reported in literature 16 , 22 , 23 , 25 , 33 – 39 . …”
Section: Resultsmentioning
confidence: 83%
“…This could dramatically increase the thermal expansion of the devices during heating/cooling and result in significant variations in the wave velocities with temperature. Figure 5 Comparison of TCF readings between ZnO/Al SAWs in this study and ZnO based SAWs on other commonly used substrates reported in literature 16 , 22 , 23 , 25 , 33 – 39 . …”
Section: Resultsmentioning
confidence: 87%
“…Therefore, most researchers use techniques to reduce the TCF values or achieve a temperature compensation during sensing. This can be easily implemented using an additional compensation layer such as silicon dioxide 12 – 15 or alumina 16 , 17 , both of which have positive TCFs. In contrast, for temperature sensing applications, a large absolute value of the TCF with a good linearity is desired.…”
A fundamental challenge for surface acoustic wave (SAW) temperature sensors is the detection of small temperature changes on non-planar, often curved, surfaces. In this work, we present a new design methodology for SAW devices based on flexible substrate and bimorph material/structures, which can maximize the temperature coefficient of frequency (TCF). We performed finite element analysis simulations and obtained theoretical TCF values for SAW sensors made of ZnO thin films (~5 μm thick) coated aluminum (Al) foil and Al plate substrates with thicknesses varied from 1 to 1600 μm. Based on the simulation results, SAW devices with selected Al foil or plate thicknesses were fabricated. The experimentally measured TCF values were in excellent agreements with the simulation results. A normalized wavelength parameter (e.g., the ratio between wavelength and sample thickness, λ/h) was applied to successfully describe changes in the TCF values, and the TCF readings of the ZnO/Al SAW devices showed dramatic increases when the normalized wavelength λ/h was larger than 1. Using this design approach, we obtained the highest reported TCF value of −760 ppm/K for a SAW device made of ZnO thin film coated on Al foils (50 μm thick), thereby enabling low cost temperature sensor applications to be realized on flexible substrates.
“…ZnO thin film is an important multifunctional material, which has potential applications in many fields [1][2][3][4][5][6][7][8][9][10]. Recently, its applications in solid light-emitting devices especially attract attention [11][12][13].…”
“…During the past decade, ZnO has been extensively studied as a potential material for optoelectronic devices [16], solar cells [17] and as a catalyst material for methanol synthesis at low temperature [18], acoustic wave devices [19], photonic devices for the UV spectral region [20] and as an excellent material for UV protection [21].…”
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