Thermal measuring and testing – Determination of inherent thermal property – Thermal conductivity
Reexamination Certificate
1999-03-30
2003-01-07
Gutierrez, Diego (Department: 2859)
Thermal measuring and testing
Determination of inherent thermal property
Thermal conductivity
C374S043000
Reexamination Certificate
active
06502983
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to detectors, particularly to detectors for portable gas chromatography, and more particularly to a highly sensitive, fast response time micro-machined thermal conductivity detector utilizing a micro-machined wire on a silicon nitride window about a millimeter square in size.
In recent years, substantial effort has been directed to the development of small, portable gas chromatography systems to enable rapid response time for the detection and composition determination of various materials, such for example, as materials spilled on a highway. Portable gas chromatography systems include a carrier gas supply and control, sample gas injection means, one or more gas chromatographical columns, a detector, a recorder, and a readout, such as a chromatogram. Thus, miniaturization of the various components of the overall system have been undertaken to reduce the overall weight of the system to enable ready portability.
Recent efforts involving micro-machining of silicon gas chromatographic columns has enabled the construction of portable systems capable of testing various samples simultaneously. For example, a gas chromatograph on a silicon chip was accomplished in the early 1970s, wherein the major components (injector, separation column, and detector) were all formed on one silicon wafer, and the separation consisted of square channels anodically bonded between glass and silicon. See S. C. Terry “A Gas Chromatography System Fabricated on a Silicon Wafer Using Integrated Circutechnology”, Ph. D. dissertation, Department of Electrical Engineering, Stanford University, Stanford, Calif., 1975; and S. C. Terry et al “A Gas Chromatograph Air Analyzer Fabricated on a Silicon Wafer”, IEEE Trans. Electron Devices, Vol. ED-26, p. 1880, 1979. Since those early efforts, miniaturization efforts have been carried forward so as to result in a hand-held gas chromatograph, wherein the three above-referenced major components are fabricated separately utilizing silicon micro-machining techniques. See UCRL-JC-129689 Abs, “A Hand-held Gas Chromatograph”, Conrad Yu et al, 1998. In a portable gas chromatograph, the size of gas samples is in the order of a nanoliter, thus the thermal conductivity detector needs to be highly sensitive and with fast response time.
The present invention satisfies the need in portable gas chromatography for a thermal conductivity detector that is highly sensitive and has fast response time. These features are achieved through a micro-machined detector wherein a silicon nitride window about one millimeter square in size is formed in a silicon member and provided with a micro-sized conductive wire, such as nickel (Ni), which is in contact with the sample gas and a carrier gas, such as helium (He).
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a thermal conductivity detector for a portable gas chromatograph.
A further object of the invention is to provide a micro-machined thermal conductivity detector.
A further object of the invention is to provide a thermal conductivity detector which utilizes an electric element on a silicon nitride member, which can also be used as a heater.
Another object of the invention is to provide a thermal conductivity detector that is highly sensitive and has a fast response time.
Another object of the invention is to provide a detector which includes a silicon nitride window with a resistor formed thereon of a resistive metal conductor with a high temperature coefficient, and high temperature chemical stability under ambient conditions.
Another object of the invention is to provide a thermal conductivity detector having a structure which will hold a high temperature gradient and where most of the thermal energy is conducted away through gases passing therethrough.
Another object of the invention is to provide a micro-machined detector having a high thermal conductivity structure composed of silicon (Si) with a silicon nitride window containing a resistor composed, for example, of nickel (Ni) or tungsten (W), whereby the detector has high sensitivity and fast response time.
Other objects and advantages of the invention will become apparent from the following description and accompanying drawings. Basically, the invention involves a micro-machined thermal conductivity detector. The detector of this invention is particularly applicable for use with a portable gas chromatograph, wherein size of the gas samples is in the order of a nanoliter. The thermal conductivity detector of this invention is highly sensitive and with a fast response time, and this is compatible with small (hand-held) portable gas chromatographs. The high sensitivity and fast response time are achieved through a micro-machined silicon structure which includes a silicon nitride window about one millimeter square in size and on which is deposited a resistive conductor or resistor composed of metal, such as nickel or tungsten. The resistor patterned on a silicon nitride membrane may also be utilized as a heater for PCR applications.
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Conrad Yu, “High performance hand-held gas chromatograph,” Proceedings of the 1998 ASME International Mechanical Engineering Congress and Exposition, Nov. 15-20, 1998, pp. 481-486.
Stephen C. Terry et al, “A Gas Chromatographic Air Analyzer Fabricated on a Silicon Wafer,” IEEE Transactions on Electron Devices, US, IEEE Inc., New York, vol. Ed-26, No. 12, Dec. 1, 1979.
Carnahan L. E.
Guadalupe Yaritza
Gutierrez Diego
The Regents of the University of California
Thompson Alan H.
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