K. Kalantar-zadeh

A layered SAW device based on ZnO/LiTaO/sub 3/ for liquid media sensing applications

Surface Acoustic Wave (SAW) sensors comprising a zinc oxide guiding layer deposited on a 36/spl deg/-YX lithium tantalate substrate were developed. They were found to have greater mass sensitivity than other LiTaO/sub 3/ based SAW sensors, such as the -SiO/sub 2//LiTaO/sub 3/ configuration. In this paper, the fabrication of the ZnO/LiTaO/sub 3/ sensor is described and micro-characterisation of the deposited films is presented. Sensitivity of these devices to surface mass and dielectric perturbations is then presented, followed by an analysis of temperature stability.

A novel Love mode SAW sensor with ZnO layer operating in gas and liquid media

Novel layered Surface Acoustic Wave (SAW) sensors, based on a ZnO/90/spl deg/ rotated ST-cut quartz crystal structure, were fabricated. They were employed as gravimetric sensors for immunosensing applications and as SAW conductometric sensors for gas sensing applications. These sensors are able to sense oxygen gas concentrations as low as 0.2 ppm in nitrogen gas. Their mass detection limit in liquid media is as low as 100 pgr/cm/sup 2/.

Fabrication, Structural Characterization and Testing of a Nanostructured Tin Oxide Gas Sensor

A nanostructured SnO2 conductometric gas sensor was produced from thermally evaporated Sn clusters using a thermal oxidation process. SnO2 clusters were simultaneously formed in an identical process on a Si3N4 membrane featuring an aperture created by a focused ion beam (FIB). Clusters attached to the vertical edges of the aperture were imaged using a transmission electron microscope. The original morphology of the Sn cluster film was largely preserved after the thermal oxidation process and the thermally oxidized clusters were found to be polycrystalline and rutile in structure. NO2 gas sensing measurements were performed with the sensor operating at various temperatures between 25degC and 290degC. At an operating temperature of 210degC, the sensor demonstrated a normalized change in resistance of 3.1 upon exposure to 510 ppb of NO2 gas. The minimum response and recovery times for this exposure were 45 s and 30 s at an operating temperature of 265degC. The performance of the SnO2 sensor compared favorably with previously published results. Finally, secondary ion mass spectrometry and X-ray photoelectron spectroscopy were used to establish the levels of nitrogen present in the films following exposure to NO2 gas.

Vehicle cabin air quality monitor using gas sensors for improved safety

A vehicle cabin air quality monitor using carbon monoxide (CO) and oxygen (O/sub 2/) gas sensors has been designed, developed and on-road tested. The continuous monitoring of oxygen and carbon monoxide provides added vehicle safety as alarms could be set off when dangerous gas concentrations are reached, preventing driver fatigue, drowsiness, and exhaust gas suicides. CO concentrations of 30 ppm and oxygen levels lower than 19.5% were experienced whilst driving.

A finite element approach for 3-dimensional simulation of layered acoustic wave transducers

Layered Surface Acoustic Wave (SAW) transducers were fabricated and modelled by finite-element method. A comparison of the frequency response of the measured devices and simulated structures are presented. The transducer structure is based on a two-port delay line, employing x-cut, y-propagating lithium niobate (LiNbO/sub 3/) substrate and a thin film zinc oxide (ZnO) guiding layer. A finite-element approach was employed to simulate a 3-dimensional version of the fabricated device. A transient analysis was conducted, where electrical and mechanical boundary values were applied. Simulation results show good agreement with experimental results, indicating that a finite-element approach is appropriate for modelling layered SAW transducers.

Study of layered SAW devices operating at different modes for gas sensing applications

In this paper, the behaviour of different propagation modes in layered ZnO/XZ LiNbO/sub 3/ surface acoustic wave (SAW) devices is investigated both theoretically and experimentally. Propagation properties of the structures are theoretically investigated using the multilayered spectral Greens function. The gas-sensing performance of these transducers for different ZnO layer thicknesses is observed. Additionally, the gas-sensing behaviour of different propagating modes is presented.

Spatial Sensitivity Distribution of Surface Acoustic Wave Resonator Sensors

The sensitivity distribution of surface acoustic wave (SAW) resonator sensors is investigated by theoretical and experimental means. It is shown that the sensitivity to mass loading varies strongly across the surface due to the confinement of acoustic energy toward the center of the device. A model is developed for this phenomenon based on the extraction of coupling of modes parameters from a rigorous boundary element method analysis based on a periodic Greens function. As SAW sensors for many applications include a layer covering the electrodes, a new technique is introduced to account for the mechanical interactions with buried electrodes. Using this technique, the sensitivity calculations are found to be in good agreement with measurements. It is also shown that while changes in other parameters influence sensitivity, it is velocity change that most strongly determines overall frequency change

H2 and NO2 gas sensors with ZnO nanobelts layer on 36° LiTaO3 and 64° LiNbO3 SAW transducers

Single crystal nanobelts of ZnO were synthesized and deposited onto 36deg YX LiTaO₃ and 64deg YX LiNbO₃ surface acoustic wave (SAW) devices for gas sensing applications. Sensor response, defined as the change in resonant frequency, was measured for H₂ and NO₂ between 20 and 200degC. Measured sensor responses were 3.5 kHz towards 10 ppm NO₂ for a 64deg LiNbO₃ SAW transducer operating at 160degC and 3 kHz towards 1% H₂ for a 36deg LiTaO₃ SAW transducer operating at 185degC temperature

Love mode SAW sensors with ZnO layer operating in gas and liquid media

Novel layered surface acoustic wave (SAW) sensors, based on a ZnO/90/spl deg/ rotated ST-cut quartz crystal structure, were fabricated. They were employed for liquid and gas sensing applications. Their mass detection limit in liquid media is as low as 100 pg/cm/sup 2/. Furthermore, these sensors are able to sense oxygen gas concentrations as low as 0.2 ppm in nitrogen gas.

Simulation of a Love mode surface acoustic wave transducer

A Love mode transducer equivalent circuit is presented in order to overcome limitations of previous models, which have been developed for devices with piezoelectric substrates. The model presented has the advantage of including the effect of electrical and mechanical fields in both the non-piezoelectric substrate and piezoelectric layers. Also, it can be used for various layer thicknesses, which are comparable to wavelength. Parameters of the model are calculated by a wave propagation simulator package. Admittance and transfer function of the Love mode transducer have been calculated for various material combinations for the substrate and top layers. This allows an evaluation of the device performance prior to fabrication as well as optimisation of the transducer, particularly in the cases which thickness of the layers and the choice of layer materials have substantial effect on the performance of the device.