High sensitivity humidity sensors using flexible surface acoustic wave devices made on nanocrystalline ZnO/polyimide substrates

Annealing Effect on Structural, Functional, and Device Properties of Flexible ZnO Acoustic Wave Sensors Based on Commercially Available Al Foil

“…SAW devices are usually fabricated on rigid substrates such as silicon, quartz, LiNbO3 [11], and LiTaO3 [12], which are not suitable to fabricate flexible SAW devices. It was reported that polymers could be used as the flexible substrates for fabrication of bendable or flexible SAW devices [13], and some results about humidity sensing [14] and UV sensing [15] have been published. However, because of significant attenuation and dissipation of acoustic wave and energies, poor film crystallinity and poor adhesion of thin film on the polymer substrates, there are significant challenges to realize efficient acoustic microfluidics and high precision sensing functions using these polymer substrates [16].…”

Distilling determination of water content in hydraulic oil with a ZnO/glass surface acoustic wave device

“…A 3-μm-thick ZnO thin film was deposited on the glass as piezoelectric layer by direct current (dc) reactive magnetron sputtering method. The deposition conditions were optimized (Zhou 2013;He et al 2013): substrate temperature of 100 °C, deposition pressure of 2 Pa, O 2 /Ar mixture gas at a ratio of 50/100 sccm, sputtering power of 200 W, and bias voltage of −75 V. Figure 1 shows a SEM picture of the ZnO thin film on the glass substrate. A clear columnar structure with large grain sizes indicates c-axis orientation of the ZnO film, which is crucial for the performance of SAW devices.…”

“…SAW devices have been widely studied to use as a sensor to detect gas, humidity and moisture owing to their high sensitivity, small size, and ability to be interfaced with passive wireless systems, etc (Zhou et al 2013;Zhou 2013). For instance, Khan et al studied SAW device based fluorine gas sensor integrated on ZnO nano thin film with palladium (Pd) on top as sensing layer (Khan et al 2015).…”

Flexible and bendable acoustofluidics based on ZnO film coated aluminium foil

“…Using commercially available large area Al foils and thin film process, mass-production or roll-to-roll processes with a low-cost could be realized to fabricate high performance flexible/deformable acoustic wave sensors and microfluidic devices. However, there is not any report on flexible acoustofluidics using Al foils as substrates, although Al foil has been used as flexible electrodes on rigid LiNbO 3 based SAW substrates [24].…”

“…Acoustic wave (AW) technologies, especially thin film surface acoustic wave (SAW) devices, have been investigated extensively for integrated lab-on-chip and μTAS applications [14][15][16][17][18][19][20][21]. ZnO thin film based SAW microfluidic devices fabricated on the flexible polymer substrates have also been demonstrated [22][23][24]. However, there are significant challenges with realizing efficient acoustic microfluidic functions on these polymer substrates, including significant attenuation and dissipation of acoustic wave and energies into polymer, poor film crystallinity and poor adhesion of thin film on the polymer substrates.…”