Conducting metal oxides integrated with the surface acoustic wave (SAW) sensor platform
Inventors
Ohodnicki, Jr., Paul R • Fryer, Robert • Devkota, Jagannath
Assignees
Publication Number
US-10976287-B2
Publication Date
2021-04-13
Expiration Date
2038-11-28
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Abstract
One or more embodiments relates a single port surface acoustic wave sensor (SAW) device adapted for use in a wide range of operational temperatures and gas phase chemical species. The device includes a piezoelectric crystal substrate; at least one interdigitated electrode/transducer (IDT) positioned on the piezoelectric crystal substrate; and at least one conducting metal oxide film positioned on the piezoelectric crystal substrate and in communication with at least the IDT.
Core Innovation
The invention relates to a single port surface acoustic wave sensor (SAW) device that is adapted for use in a wide range of operational temperatures and gas phase chemical species. The device comprises a piezoelectric crystal substrate; at least one interdigitated electrode/transducer (IDT) positioned on the substrate; and at least one conducting metal oxide (CMO) film positioned on the substrate and in communication with the IDT. The use of conducting metal oxides enables tuning the absolute electronic conductivity of the gas sensing material, thereby allowing the SAW device to be tuned for gas sensitivity in arbitrary conditions.
The problem solved by the invention is the limited operational window for conductivity in conventional SAW sensors using standard metal oxides, which restricts their sensitivity only to certain gas/temperature conditions. The SAW device parameter monitored, resonant frequency or phase, depends on the film's surface electrical conductivity, but only within a narrow absolute conductivity range determined by the piezoelectric substrate properties. Film conductivity changes outside this range yield no significant device response. Conventional metal oxides such as ZnO, SnO2, or TiO2 used as gas sensing materials on SAW devices have conductivities that fall outside this narrow range in many conditions, limiting their effectiveness.
This invention addresses this limitation by utilizing conducting metal oxides with tunable absolute electronic conductivity, achieved through doping, controlled film processing, or other treatments. These CMOs exhibit greater conductivity modulation in response to gas interactions compared to standard metal oxides, allowing enhanced sensitivity and adaptability of the SAW devices over a wide range of temperatures and gas environments. The device thus enables real-time, sensitive, wireless, and passive gas sensing across harsh environments including temperatures up to 1000° C. and diverse chemical species.
Claims Coverage
The patent includes three independent claims covering the SAW device with conducting metal oxide films and the method of forming such devices with tailored electronic conductivity.
Surface acoustic wave sensor device with conducting metal oxide film
A SAW device comprising a piezoelectric crystal substrate, at least one interdigitated electrode/transducer (IDT), and a conducting metal oxide (CMO) film selected from FI-doped SnO (FTO), Sn-doped In2O3 (ITO), Al-doped ZnO (AZO), and Nb-doped TiO2 (NTO) positioned on the substrate and communicating with the IDT, adapted for use in operational temperatures and gas phase chemical species.
Acoustic wave sensor device for detecting fuel and oxidizing gases with correlated electronic oxides
A SAW device configured to detect fuel gas concentrations and monitor oxidizing gas concentrations, including a piezoelectric crystal substrate, at least one IDT, and a CMO film selected from the group consisting of FI-doped SnO (FTO), Sn-doped In2O3 (ITO), Al-doped ZnO (AZO), Nb-doped TiO2 (NTO), and correlated electronic oxides such as (La,Sr)MnO3, LaFeO3, LaCoO3, SrFeO3, SrCoO3, LaMnO3, SrMnO3, La(Co,Fe)O3, (La,Sr)(Co,Fe)O3, BaFeO3, BaTiO3, and CaFeO3.
Method of forming a SAW device with tailored conducting metal oxide film conductivity
A method comprising selecting at least one CMO film with electronic conductivity in the range required for measurable acoustoelectric effect from a specified group of correlated electronic oxides; positioning the CMO film on a piezoelectric crystal substrate with at least one IDT so the film communicates with the IDT; and tailoring the absolute electronic conductivity of the CMO film for operational temperatures and gas phase chemical species by means including chemical doping, controlled pre-treatments in non-ambient atmospheres, temperature treatments, and controlled deposition processes.
The independent claims cover SAW devices incorporating selected conducting metal oxide films with conductivity tuned for measurable acoustoelectric responses in gas sensing applications, as well as methods to form these devices by tailoring the electronic conductivity of the CMO films to optimize sensitivity across operational conditions and chemical environments.
Stated Advantages
Ability to tune the absolute electronic conductivity of conducting metal oxide films to place it within the optimal range for maximizing SAW device sensitivity.
Enhanced sensitivity and easier-to-read changes in measured resonant frequency or phase due to greater conductivity modulation from film-gas interactions compared to standard metal oxides.
Enables SAW devices to operate effectively across a wide range of temperatures (up to about 1000° C.) and gas phase chemical species.
Compatibility with the advantages of SAW platforms such as miniature size, wireless and passive operation, and multi-sensor interrogation by a single antenna.
Flexibility in tuning each sensor individually for specific operational temperature and gas compositions, reducing fabrication complexity and cost.
Documented Applications
Use in power generation systems for detecting fuel gas concentrations (e.g., H2, CO, CO2) and monitoring oxidizing gases (e.g., O2, NOx) for in-situ feedback and optimized process control.
Chemical monitoring for subsurface applications such as carbon sequestration, oil and gas recovery, and natural gas infrastructure monitoring.
Applications in harsh environments such as industrial manufacturing processes, chemical processing, aerospace, and natural gas and oil industries.
Selective monitoring of reducing gas species including H2S, a toxic and corrosive gas commonly found in natural gas or petroleum.
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