Measuring and testing – Gas analysis – By vibration
Reexamination Certificate
1998-10-05
2001-03-06
Williams, Hezron (Department: 2856)
Measuring and testing
Gas analysis
By vibration
C073S031060
Reexamination Certificate
active
06196052
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to a piezoelectric gas sensing device including a piezoelectric sensing element such as a quartz crystal microbalance or a surface acoustical wave (SAW) element.
2. Description of the Related Art
In the semiconductor manufacturing industry and in other industrial process and manufacturing fields, a number of systems and techniques have been developed for monitoring a fluid, e.g., a process stream or an ambient environment in a plant facility, for the presence of specific gas components. Applications in which such fluid monitoring is carried out include monitoring of ion implant cabinets for hydride and acid gases, monitoring of process streams to determine the end point utility of a scrubber medium employed for treatment of such streams to remove hazardous gas components therefrom, and monitoring of room air for toxic gas components.
In such fluid monitoring applications, piezoelectric devices have been used for gas sensing. Examples include the use of a surface acoustical wave (SAW) element to sense concentration of a dopant species, as described in U.S. Pat. No. 4,936,877 issued Jun. 26, 1990 to Steven J. Hultquist and Glenn M. Tom for “Dopant Delivery System for Semiconductor Manufacture,” and the use of quartz microbalance systems for gas stream monitoring and environmental sensor applications, as described in U.S. patent application Ser. No. 08/678,572 filed Jul. 12, 1996 in the name Glenn M. Tom and Cynthia A. Miller for “Piezoelectric End Point Sensor for Detection of Breakthrough of Fluid, and Fluid Processing Apparatus Comprising Same,” U.S. patent application Ser. No. 08/679,258 filed Jul. 12, 1996 in the names of Glenn M. Tom and Cynthia A. Miller for “Piezoelectric Environmental Fluid Monitoring Assembly and Method,” and U.S. patent application Ser. No. 08/785,342 filed Jan. 17, 1996 in the names of Glenn M. Tom and Cynthia A. Miller for “Piezoelectric Sensor for Hydride Gases, and Fluid Monitoring Apparatus Comprising Same,” the disclosures of which hereby are incorporated herein by reference in their entireties.
In these applications, the piezoelectric element is coated with an affinity coating which is selective for particular gas species. For example, quartz crystal microbalances when used as gas sensing elements are provided with electrode coating materials that are selective for interaction with one or more gas species. Surface acoustical wave elements when employed as gas sensing elements are likewise are coated with materials selective for interaction with a desired gas species, typically as a film of the affinity coating on the top surface of the piezoelectric crystal between the respective electrode structures of the device.
In these applications, the permeability and thickness characteristics of the affinity coatings are critical to the sensitivity and speed of response of the piezoelectric device. In general, the affinity coating (which may comprise a physical adsorbent material or a chemisorbent material) should be highly available to the gas species of interest, to maximize the speed of binding or reaction of the gaseous species with the sorptive or chemically reactive sites in the affinity coating, and to maximize speed of response.
It is known to utilize porous material coatings on a quartz microbalance to provide a high surface area affinity coating, as described in the aforementioned U.S. patent application Ser. No. 08/785,342 filed Jan. 17, 1996 in the names of Glenn M. Tom and Cynthia A. Miller for “Piezoelectric Sensor for Hydride Gases, and Fluid Monitoring Apparatus Comprising Same.”
The art has continued to seek improvements in piezoelectric devices for gas sensing applications.
It would be a substantial advance in the art, and is an object of the present invention, to provide an improved piezoelectric device substrate providing an enhanced interaction with the gas species of interest.
It is another object of the present invention to provide an improved surface acoustical wave device of such type.
It is a further object of the invention to provide a quartz microbalance device of such type.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.
SUMMARY OF THE INVENTION
The present invention relates generally to a piezoelectric gas sensing device, comprising:
(a) a piezoelectric element arranged for gas sensing exposure to a gas environment;
(b) a layer of a gas-retentive support medium on the piezoelectric element which is retentively effective for a gas component potentially present in the gas environment; and
(c) a gas-interactive material associated with (e.g., deposited on, impregnated in, etc.) the retentive support medium, and sorptively effective to form a solid interaction product in interaction with said gas component potentially present in the gas environment, said solid interaction product imparting a changed frequency response to the piezoelectric gas sensing device, in relation to a corresponding piezoelectric gas sensing device in the absence of said solid interaction product resulting from presence of said gas component in said gas environment.
In such gas sensing device the support medium may for example comprise a sol gel or polymeric material. Such a polymeric material may comprise a polymer having a glass transition temperature below the temperature of said gas sensing exposure.
As used in such context, the term “retentively effective” means that the gas-retentive support medium on the piezoelectric element takes up the gas component potentially present in the gas environment with which the gas-interactive material deposited on or otherwise associated with the retentive support medium is interactive. In other words, the gas-retentive support medium acts to retain the gas component for interaction of the gas component with the gas-interactive material, so that the overall interaction of the gas-interactive material is increased over the level of interaction that would exist in the absence of the gas-retentive support medium.
The gas-interactive material is a different material from the gas-retentive support medium. The gas-interactive material is sorptively effective—i.e., physically adsorptive and/or chemically reactive (chemisorptive) with respect to the gas component—to form a solid interaction product in interaction with such gas component when present in the gas environment. The solid interaction product imparts a changed frequency response to the piezoelectric gas sensing device, in relation to a corresponding piezoelectric gas sensing device that is devoid of the solid interaction product that otherwise results from the presence of the gas component in said gas environment.
The gas-interactive material may comprise any suitable material that generates a solid reaction product in interaction with the gas component sought to be detected in the gaseous environment, which alters the frequency response of the gas sensing device as a result of such interaction. Examples include metals, metal oxides and involatile organic and inorganic compounds. The gas-interactive material may be widely varied in the practice of the invention, depending on the gas component sought to be detected in the gaseous environment being sampled or monitored.
By use of appropriate apparatus to monitor the frequency response of the piezoelectric crystal, the presence of the gas component of interest can be detected by the change in the output frequency of the piezoelectric device or the rate of such output frequency change.
A further aspect of the invention relates to a method of detecting a gas component in a gaseous environment, by deployment of a gas sensing device of the type described hereinabove.
Other aspects, features and embodiments of the invention will be more fully apparent from the ensuing disclosure and appended claims.
REFERENCES:
patent: 4111036 (1978-09-01), Frechette et al.
patent: 4399686 (1983-08-01), Kindlund et al.
patent: 4936877 (1990-06-01), Hultquist et al.
patent: 5065
May Iain
Tom Glenn M.
Advanced Technology & Materials Inc.
Hultquist Steven J.
Miller Rose M.
Williams Hezron
Zitzmann Oliver A. M.
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