High-frequency stability oscillator for surface acoustic wave gas sensor

• Published in: Acoustical Science and Technology Vol. 30; no. 1; pp. 7 - 12
• Main Authors: He, Shitang, Wang, Wen, Li, Shunzhou, Pan, Yong, Liu, Minghua
• Format: Journal Article
• Language: English
• Published: Tokyo ACOUSTICAL SOCIETY OF JAPAN 01.01.2009; Acoustical Society of Japan; Japan Science and Technology Agency
• Subjects: Delay line; Exact sciences and technology; Frequency stability; Gas sensor; General equipment and techniques; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Measurements common to several branches of physics and astronomy; Metrology, measurements and laboratory procedures; Oscillator; Physics; Sensitivity; Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing; Surface acoustic wave; Time and frequency; Acoustic wave device; Mode coupling; Sensitivity; 43.60.Lg; Threshold detection; Acoustic surface waves; Coatings; Electrodes; Oscillator; Detection limit; Bandwidth; Modelling; Frequency response; Surface instability; Measurement sensor; Comb configuration; Experimental study; Quartz; Surface acoustic wave; 43.66.Jh; Surface waves; Insertion loss; Delay lines; Coupled modes; Gas sensor; Temperature control; High frequency; Delay line; Gas detector; Frequency stability
• ISSN: 1346-3969; 1347-5177
• DOI: 10.1250/ast.30.7

We present a 300 MHz surface acoustic wave (SAW) oscillator for gas sensor application. As the oscillator element, SAW delay lines on an ST-X quartz substrate with low insertion loss and single-mode-selection capability were developed. And they were structured by Electrode Width Control Single Phase Unidirectional Transducer (EWC/SPUDT) configuration and comb transducer. The coupling of modes (COM) model was used to predict device performance prior to fabrication. The measured frequency response S12 showed a good agreement with simulated results; a low insertion loss of less than 9 dB and a linear phase in the 3 dB bandwidth were observed. The experimental results show that the baseline noise of the fabricated oscillators was typically up to ∼0.7×10−7 in a laboratory environment with temperature control. The oscillator was successfully applied to a gas sensor coated with fluoroalcoholpolysiloxane (SXFA) as the sensor material for O-isopropyl methyphosphonofluoridate (GB) detection, and a superior threshold detection limit was obtained (<<0.4 mg/m3).