Varying potential silicon carbide gas sensor
First Claim
1. An electronic device of semiconductor design for detecting hydrocarbon gases comprising:
- a detection layer having first and second surfaces, and forming a gate of a metal insulator field effect transistor, the detection layer comprising;
a wafer of silicon carbide;
a layer of porous silicon carbide formed at a first surface of said silicon carbide wafer by photoelectrochemical etching, the layer of porous silicon carbide for adsorbing hydrocarbon gases;
a metal grid deposited onto the porous silicon carbide layer; and
an electrode in electrical communication with the metal grid for applying a varying dissociating potential to said porous silicon carbide layer for dissociating hydrocarbon molecules adsorbed to said porous silicon carbide layer;
an insulation layer formed on a second surface of the detection layer;
a channel layer of doped silicon carbide formed on an exposed surface of the insulation layer; and
drain and source electrodes disposed on the channel layer at opposite sides thereof so that dissociation of hydrocarbons in the detection layer causes an alteration in a current flow between the drain electrode and the source electrode, a magnitude of said alteration indicating a quantity of hydrocarbon gas adsorbed to the detection layer and a magnitude of the dissociating potential indicating a type of hydrocarbon gas adsorbed to the detection layer.
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Abstract
A hydrocarbon gas detection device operates by dissociating or electro-chemically oxidizing hydrocarbons adsorbed to a silicon carbide detection layer. Dissociation or oxidation are driven by a varying potential applied to the detection layer. Different hydrocarbon species undergo reaction at different applied potentials so that the device is able to discriminate among various hydrocarbon species. The device can operate at temperatures between 100° C. and at least 650° C., allowing hydrocarbon detection in hot exhaust gases. The dissociation reaction is detected either as a change in a capacitor or, preferably, as a change of current flow through an FET which incorporates the silicon carbide detection layers. The silicon carbide detection layer can be augmented with a pad of catalytic material which provides a signal without an applied potential. Comparisons between the catalytically produced signal and the varying potential produced signal may further help identify the hydrocarbon present.
126 Citations
27 Claims
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1. An electronic device of semiconductor design for detecting hydrocarbon gases comprising:
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a detection layer having first and second surfaces, and forming a gate of a metal insulator field effect transistor, the detection layer comprising; a wafer of silicon carbide; a layer of porous silicon carbide formed at a first surface of said silicon carbide wafer by photoelectrochemical etching, the layer of porous silicon carbide for adsorbing hydrocarbon gases; a metal grid deposited onto the porous silicon carbide layer; and an electrode in electrical communication with the metal grid for applying a varying dissociating potential to said porous silicon carbide layer for dissociating hydrocarbon molecules adsorbed to said porous silicon carbide layer; an insulation layer formed on a second surface of the detection layer; a channel layer of doped silicon carbide formed on an exposed surface of the insulation layer; and drain and source electrodes disposed on the channel layer at opposite sides thereof so that dissociation of hydrocarbons in the detection layer causes an alteration in a current flow between the drain electrode and the source electrode, a magnitude of said alteration indicating a quantity of hydrocarbon gas adsorbed to the detection layer and a magnitude of the dissociating potential indicating a type of hydrocarbon gas adsorbed to the detection layer. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. An electronic device of semiconductor design for detecting hydrocarbon gases comprising:
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a detection layer having first and second surfaces, comprising; a region of porous silicon carbide formed at a first surface of said silicon carbide wafer by photoelectrochemical etching, the region of porous silicon carbide for adsorbing hydrocarbon gases; a metal grid deposited on the porous silicon carbide region; and a first electrode in electrical communication with the metal grid for applying a varying dissociating potential to said porous silicon carbide region for dissociating hydrocarbon molecules adsorbed to said porous silicon carbide region; and a second electrode deposited on a second surface of the silicon carbide wafer, the second electrode for applying a potential to said porous silicon carbide region in concert with the first electrode and for measuring changes of a current flow between the electrodes, a magnitude of the current flow indicating a quantity of hydrocarbon adsorbed to said porous silicon region and a magnitude of the dissociating potential indicating a type of hydrocarbon adsorbed to said porous silicon region. - View Dependent Claims (9, 10, 11, 12, 13)
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14. An electronic device of semiconductor design for detecting hydrocarbon gases comprising:
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a wafer of silicon carbide; a channel layer of doped silicon carbide formed on an exposed surface of the wafer with metallic drain and source electrodes disposed on the channel layer at opposite sides thereof; and an insulation layer formed on an exposed surface of the channel layer; a detection layer having a first and second surface, and forming a gate of a field effect transistor, the detection layer comprising; a layer of polycrystalline silicon carbide formed on an exposed surface of said insulation layer for adsorbing hydrocarbon gases; a metal grid deposited on the polycrystalline silicon carbide layer; and an electrode in electrical communication with the metal grid for applying a varying dissociating potential to said polycrystalline silicon carbide layer for dissociating hydrocarbon gas molecules adsorbed to the polycrystalline silicon carbide layer so that dissociation of hydrocarbon gas molecules causes an alteration in a current flow between the drain electrode and the source electrode, a magnitude of said alteration indicating a quantity of hydrocarbon gas adsorbed to the detection layer and a magnitude of the dissociating potential indicating a type of hydrocarbon gas absorbed to the detection layer. - View Dependent Claims (15, 16, 17, 18, 19)
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20. An electronic device of semiconductor design for detecting hydrocarbon gases comprising:
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a detection layer with a first surface and a second surface, comprising; a wafer of silicon carbide; a layer of polycrystalline silicon carbide formed on a first surface of said wafer for adsorbing hydrocarbon gases; a metal grid deposited on the polycrystalline silicon carbide layer; and an electrode in electrical communication with the metal grid for applying a varying dissociating potential to said polycrystalline silicon carbide region, said dissociating potential for dissociating hydrocarbon gases adsorbed to the detection layer; an insulation layer formed on a second surface of the silicon carbide wafer; and a second electrode deposited on the insulation layer, the second electrode for applying a potential to said polycrystalline silicon carbide layer in concert with the first electrode and for measuring changes of current flow between the electrodes, a magnitude of the current flow indicating a quantity of hydrocarbon adsorbed to said polycrystalline silicon carbide layer and a magnitude of the dissociating potential indicating a type of hydrocarbon adsorbed to said polycrystalline silicon carbide layer. - View Dependent Claims (21, 22)
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23. A method of employing a semiconductor device to detect hydrocarbon gases comprising the steps of:
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providing a semiconductor device with a detection layer of silicon carbide to interact with a gas sample; operating said semiconductor device at temperatures between about 100°
C. and 650°
C.;introducing a gas sample to be tested by exposure to a surface of the detection layer so that the gas sample adsorbs to the detection layer; varying a dissociating potential applied to the detection layer; measuring a change in an electrical characteristic of the semiconductor device as indicative of a quantity of hydrocarbon gas adsorbed to the detection layer; and measuring the potential at which the change in an electrical characteristic occurs as indicative of a type of hydrocarbon gas present in the detection layer. - View Dependent Claims (24, 25, 26, 27)
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Specification