A layered Surface Acoustic Wave (SAW) hydrogen gas sensor, based on a delay line structure with 64 finger pairs on input and output port, is fabricated on 64° Y-cut, X-propagating LiNbO3 substrate. A guiding layer of ZnO is used to increase the sensitivity of the structure. A WO3 selective layer is employed to H2 gas sensing applications at different operating temperatures between room temperature and 300°C. In this paper, the fabrication process of WO3/ZnO/64° YX LiNbO3 sensor is described and the sensor’s response features are analyzed. The improvement of the response with the addition of a gold catalytic layer on the sensor surface is also investigated.
A layered Surface Acoustic Wave (SAW) device based on an InOx/Si3N4/36° YX LiTaO3 structure is investigated for sensing ozone in air at different operating temperatures and concentrations. These concentrations are between 25 ppb and 150 ppb. Layered SAW devices are of a great interest as they show a remarkable performance for liquid and gas sensing applications. This structure is a single delay line SAW device with 64 input and output finger pairs, having periodicity of 24 μm. They were fabricated on a 36° Y-cut X-propagating lithium tantalate (LiTaO3) piezoelectric substrate. A 1 μm thick silicon nitride (Si3N4) layer was deposited over the finger pairs and a 100 nm indium oxide (InOx) sensing layer was deposited over the Si3N4 layer. Both layers were deposited by RF magnetron sputtering. InOx was chosen as it has a remarkable sensitivity towards ozone. Si3N4 was chosen as it is inert and has stable characteristics at high temperature. The sensor performance is analysed in terms of response time, recovery time and response magnitude as a function of operational temperature. The operational temperature ranges between 185°C and 205°C. The sensor shows repeatability, reversibility, fast response and recovery time. At approximately 190°C the highest sensitivity was observed. A frequency shift of 5.0 kHz at 25 ppb, 6.5 kHz at 50 ppb ozone was recorded. The presented results show this structure is promising for gas sensing applications.
A comparison between the performance of conductometric and layered surface acoustic wave (SAW) hydrogen sensors is presented. Both sensor structures employ an R.F. magnetron sputtered tungsten trioxide (WO3) thin film as a selective layer for hydrogen (H2) sensing applications. The conductometric device is based on an alumina substrate, while the layered SAW device structure is fabricated on a 36° Y-cut, X-propagating LiTaO3 substrate with a zinc oxide (ZnO) guiding layer. The sensors were investigated for different operational temperatures and various concentrations of H2 in synthetic air.
A multi-layered surface acoustic wave (SAW) transducer employing an R.F. magnetron sputtered tungsten trioxide (WO3) thin film as a selective layer, for low concentration nitrogen dioxide (NO2) gas sensing is presented. The layered SAW device structure is fabricated on a 36° Y-cut, X-propagating LiTaO3 substrate with a zinc oxide (ZnO) guiding layer. The dominant mode of acoustic propagation in the sensor is a combination of mainly a shear and a longitudinal displacement types. Such a structure has the advantage of confining the acoustic wave energy to the surface of the device, which increases the sensitivity of the system. A frequency shift of 30 kHz is shown for a concentration of 500ppb of NO2 in synthetic air, highlighting the possibility of such a sensor being targeted towards the sub-ppb levels of NO2.
A finite-element method is employed to model layered Surface Acoustic Wave (SAW) two port delay lines, with a zinc oxide (ZnO) thin film guiding layer. The structure is based on x-cut, y-propagating LiNbO3 substrate. Conditions that model the realistic electrical and mechanical boundary values are applied to the structure to analyze the electromechanical properties of the SAW device. Transient analyses are performed and the frequency responses are calculated using the FFT. Simulation results show good agreement with experimental results, indicating that a finite-element method is an appropriate approach for modeling layered SAW devices.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.