Hybrid integrated circuit for a gas sensor

Details Hybrid integrated circuit for a gas sensor Hybrid integrated circuit for a gas sensor

1999-07-26

2001-03-20

Williams, Hezron (Department: 2856)

Measuring and testing

Gas analysis

C073S025050, C073S031050, C422S088000, C422S094000

Reexamination Certificate

active

06202467

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates in general to electronic engineering and more specifically it concerns design technology for building a hybrid integrated circuit of a gas sensor.
BACKGROUND OF THE INVENTION
A thermochemical sensing transducer is known detecting the presence and concentration of various gases in the air such as air including CH
3
or Hydrogen. The known sensing transducer of prior arts provides a higher measuring accuracy due to the layer of a catalyst (platinum, palladium, or metal oxides) applied to the external surface of the sensing element, and an extended range of gases monitored which is due to the fact the sensing elements are made of different materials, have different dimensions, and make use of different catalysts. Two silicon stages are installed independently on the same substrate for two constructionally similar sensing elements (save the aforementioned basic differences). An insulating nitride layer 400 mm thick is applied to the silicon membrane of the stage. A double-meander heater is established at the center of the sensing element, said heater being made of silicon or nickel and having aluminium electric leads to the sensing element periphery. A thermocouple consisting of two meanders connected in opposition and made of different materials is applied to the heater in perpendicular with the axis thereof. A catalyst layer is applied from above, which may be coated with a protective gas-permeable layer. The aforecited sensing transducer is capable of measuring concentration variations with temperature (DE, A, 4,008,150).
However, the aforementioned construction is sophisticated and inadequately technologically manufacturable.
A structure for the gas analyzer carrier is known from prior arts, said structure enabling to obtain a mechanically strong construction of analyzers for such gases as SO
2
, H
2
S, and benzene suitable for the large-scale production. The construction of said structure appears as a square of 6×6 mm inside which another square of 2×2 mm is placed, both squares being interconnected with jumpers along the four diagonals common to both squares. The central square and partly two opposite jumpers are coated with a layer of platinum serving as a heater. The central square-shaped platinum coating is shaped as a spiral. The resultant resistor is coated with an insulating layer. Two electrodes made of platinum or gold are applied to the opposite sides of the central square, two metal strip electrodes directed along the free substrate jumpers being connected to said platinum or gold electrodes. A gas-sensitive film is applied to the central square between the electrodes (FR, A, 2,625,561).
However, the construction discussed above is sophisticated difficult to assemble, has no adequate selectivity due to an insufficient heat insulation of the central substrate portion, and is possessed of inadequate manufacturability.
SUMMARY OF THE INVENTION
The principal object of the present invention is to provide a hybrid integrated circuit of a gas sensor having such a constructive arrangement that allows to increase the selectivity, thermal isolation, and manufacturability of the gas sensor.
The foregoing object is accomplished due to the fact that in a hybrid integrated circuit of a gas sensor, comprising a substrate in the form of a mechanically strong peripheral portion and a central portion thermally insulated therefrom, both portions being interconnected through jumpers, the peripheral substrate portion is provided with film bonding pads; while the central portion carries a film heater, a gas-sensitive film, and a film electrode for connecting with a circuit for measuring the electrical resistance of the gas-sensitive film: all these being electrically, connected to the bonding pads through film conductors located on the jumpers. According to the invention, the peripheral substrate portion is ring-shaped, the central portion thereof is shaped as a disk electrically connected to the peripheral portion by three jumpers spaced 120° apart, and the jumpers have branchings at an angle of 120° at the place of connection to the peripheral portion. The gas sensor device, as placed within an outer package, is designed to have geometry with relative spacings between its portions such that the ratio between the diameter of the central portion and the inside diameter of the peripheral portion is 0.2-0.4, and the ratio between the jumper length from the center of the circuit to the branching and the inside diameter of the peripheral portion is 0.6-0.8, while the width of the jumpers is 0.05-0.15 mm and the thickness of the jumpers and of the central substrate portion is 0.15-0.25 mm.
The film heater may be placed in a recess provided on the face surface of the central substrate portion.
It is desirable that the peripheral substrate portion has through holes and is fixed on a metal base of the package in such a manner that the internal package leads are arranged in the holes of the peripheral substrate portion and are electrically connected to the bonding pads, while the cover of the package has a hole to admit the medium under analyses.
Providing the ring-shaped peripheral substrate portion and the disk-shaped central substrate portion gives an additional rigidity to the films and circuit, integrated and reduces the stress level therein.
The interconnection of the peripheral substrate portion to the central substrate portion by three jumpers spaced 120° apart is selected so as to provide the heat insulation of the central substrate portion and to compensate optimally for any mechanical stresses arising upon heating the central substrate portion.
The fact that the ratio between the diameter of the central substrate portion and the inside diameter of the peripheral portion is design selected to be 0.2-0.4, and the ratio between the jumper length from the center of the circuit to the branching and the inside diameter of the peripheral portion to be 0.6-0.8, as well as design selection of the jumper width to be 0.05-0.15 mm and of the thickness of the jumpers and of the central substrate portion to be 0.15-0.25 is explained by the desire to attain optimal circuit geometry for suitable thermal insulation, according to the invention, from the viewpoint of the better heat insulation of the central substrate portion and the strength of the film circuit construction.
The upper limits of the value of the aforementioned ratios (0.4 and 0.8, respectively) are dictated by the permissible value of the heat resistance of the jumpers at which the temperature of the central substrate portion is within the required range for providing good selectivity in device performance, that results because a required level of heat insulation is provided.
The lower limits of the value of said ratios (0.2 and 0.6, respectively) are dictated by the permissible length of the jumpers at which the mechanical strength of the circuit construction remains unaffected.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is further illustrated by a detailed description of some specific exemplary embodiments thereof to be taken with reference to the accompanying drawings, wherein:
FIG. 1
is a plan view of the filed hybrid integrated circuit of a gas sensor;
FIG. 2
is a section taken on the line II—II in
FIG. 1
;
FIG. 3
is a view of
FIG. 1
showing the respective dimensions of the circuit elements;
FIG. 4
is a section taken on the line V—V in
FIG. 3
; and
FIG. 5
is a sectional view of an alternative embodiment of the filed hybrid integrated circuit of a gas sensor.


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patent: 4596975 (1986-06-01), Reddy et al.
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