Mr. Alexandru C. Fechete Profile

Mr. Alexandru C. Fechete

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PROCEEDINGS ARTICLE | January 5, 2006

Comparative study of surface acoustic wave based hydrogen sensors with: InO_x/SiN_x/36° YX LiTaO₃ structure

Proc. SPIE. 6035, Microelectronics: Design, Technology, and Packaging II

KEYWORDS: Thin films, Gas sensors, Sensors, Sputter deposition, Hydrogen, Plasma enhanced chemical vapor deposition, Wave sensors, Magnetic sensors, Acoustics, Indium oxide

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Layered Surface Acoustic Wave (SAW) based sensors with: InO_x / SiN_x / 36° YX LiTaO₃ structure were developed for sensing different hydrogen (H₂) concentrations between 0.06% (600ppm) and 1% H₂ in synthetic air. This paper presents a comparative study of the sensors performances in terms of response time, recovery time and response magnitude as a function of operational temperature. The SAW devices consist of metal interdigitated electrodes fabricated on lithium tantalate (LiTaO₃) piezoelectric substrate forming the input and output Interdigital Transducers (IDTs). A 1 μm thick silicon nitride (SiN_x) intermediate layer was deposited over these finger pairs, either by Plasma Enhanced Chemical Vapour Deposition (PECVD) or by r.f. magnetron sputtering. A 100 nm thin film of indium oxide (InO_x) deposited by r.f. magnetron sputtering provides the selectivity towards hydrogen. The highest sensitivity for the sensor with r.f. magnetron sputtered SiN_x intermediate layer was recorded at 190° C, when the frequency shift of 361 KHz for 1% H₂ in synthetic air was recorded. However larger responses were obtained for the sensor with the PECVD SiN_x intermediate layer at 290° C, when the large frequency shift of 516 KHz was recorded for the same H₂ concentration. Microstructural characterization of the InO_x and SiN_x films by Atomic Force Microscopy (AFM) and X-Ray Photoelectron Spectroscopy (XPS) is also presented.

PROCEEDINGS ARTICLE | February 23, 2005

Surface acoustic wave based ozone sensor with an InOx/Si3N4/36-degree YX LiTaO3 structure

Proc. SPIE. 5650, Micro- and Nanotechnology: Materials, Processes, Packaging, and Systems II

KEYWORDS: Thin films, Sensors, Sputter deposition, Silicon, Oxygen, Sensor performance, Acoustics, Ozone, Indium oxide, Temperature metrology

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A layered Surface Acoustic Wave (SAW) device based on an InO_x/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 (InO_x) sensing layer was deposited over the Si₃N₄ layer. Both layers were deposited by RF magnetron sputtering. InO_x 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.

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