U.S. patent application number 14/946295 was filed with the patent office on 2016-03-17 for methods and devices for detecting unsaturated compounds.
The applicant listed for this patent is The University of Toledo. Invention is credited to Abdul-Majeed AZAD, Robert Howard KINNER, Desikan SUNDARARAJAN.
Application Number | 20160077048 14/946295 |
Document ID | / |
Family ID | 43617994 |
Filed Date | 2016-03-17 |
United States Patent
Application |
20160077048 |
Kind Code |
A1 |
AZAD; Abdul-Majeed ; et
al. |
March 17, 2016 |
METHODS AND DEVICES FOR DETECTING UNSATURATED COMPOUNDS
Abstract
An insulated-gate field-effect transistor comprising a
semiconductor substrate, a source region, a drain region, where the
source region is spaced apart from the drain region to thereby form
a channel, and both the source region and the drain region are
located at or near one surface of the substrate, a gate insulator
deposited over said channel, and a gate electrode, said gate
electrode including a material that demonstrates appreciable change
in resistivity relative to the concentration of acetylene, where
the gate electrode covers the gate insulator.
Inventors: |
AZAD; Abdul-Majeed;
(Perrysburg, OH) ; SUNDARARAJAN; Desikan;
(Sylvania, OH) ; KINNER; Robert Howard; (Mentor,
OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The University of Toledo |
Toledo |
OH |
US |
|
|
Family ID: |
43617994 |
Appl. No.: |
14/946295 |
Filed: |
November 19, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13499963 |
Apr 3, 2012 |
9228966 |
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PCT/US10/57999 |
Nov 24, 2010 |
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14946295 |
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12626252 |
Nov 25, 2009 |
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13499963 |
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Current U.S.
Class: |
436/142 ;
257/253; 422/82.02; 438/49 |
Current CPC
Class: |
Y10T 436/216 20150115;
G01N 27/4141 20130101; G01N 33/5438 20130101; G01N 27/126 20130101;
G01N 27/12 20130101; G01N 27/125 20130101; G01N 27/403 20130101;
G01N 33/2835 20130101; Y10T 436/21 20150115; G01N 21/33
20130101 |
International
Class: |
G01N 27/414 20060101
G01N027/414 |
Claims
1. An insulated-gate field-effect transistor comprising: (i) a
semiconductor substrate; (ii) a source region; (iii) a drain
region, where the source region is spaced apart from the drain
region to thereby form a channel, and both the source region and
the drain region are located at or near one surface of the
substrate; (iv) a gate insulator deposited over said channel; and
(v) a gate electrode, said gate electrode including a material that
demonstrates appreciable change in resistivity relative to the
concentration of acetylene, where the gate electrode covers the
gate insulator.
2. An insulated-gate field-effect transistor of claim 1, further
comprising a conductive layer disposed between the gate insulator
and the gate electrode.
3. An insulated-gate field-effect transistor of claim 1, further
comprising a protective layer.
4. An insulated-gate field-effect transistor of claim 1, where said
material that demonstrates appreciable change in resistivity
relative to the concentration of acetylene is a metal salt of
nickel (II).
5. An insulated-gate field-effect transistor of claim 1, where said
material that demonstrates appreciable change in resistivity
relative to the concentration of acetylene is a metal salt of
copper (I).
6. An insulated-gate field-effect transistor of claim 1, where said
material that demonstrates appreciable change in resistivity
relative to the concentration of acetylene is nickel (II)
chloride.
7. An insulated-gate field-effect transistor of claim 1, where said
material that demonstrates appreciable change in resistivity
relative to the concentration of acetylene is copper (I)
chloride.
8. A method for fabricating an acetylene sensor, the method
comprising: (i) providing an inert substrate; (ii) placing at least
a pair of electrodes onto the surface of said substrate; (iii)
providing a solution that includes a material that demonstrates
appreciable change in resistivity relative to the concentration of
the acetylene; (iv) depositing the solution onto the substrate to
at least partially cover said electrodes; and (v) heating the
substrate having the solution deposited thereon to thereby remove
solvents associated with said solution.
9. The method of claim 8, where said material that demonstrates
appreciable change in resistivity relative to the concentration of
acetylene is a metal salt of nickel (II).
10. The method of claim 8, where said material that demonstrates
appreciable change in resistivity relative to the concentration of
acetylene is a metal salt of copper (I).
11. The method of claim 8, where said material that demonstrates
appreciable change in resistivity relative to the concentration of
acetylene is nickel (II) chloride.
12. The method of claim 8, where said material that demonstrates
appreciable change in resistivity relative to the concentration of
acetylene is copper (I) chloride.
13. The method of claim 8, where said step of heating includes
heating the substrate with the solution deposited thereon to a
temperature of about 100.degree. C. to about 150.degree. C.
14. The method of claim 8, where said solution includes water as a
solvent.
15. The method of claim 8, where said solution includes
acetonitrile as a solvent.
16. A power transformer comprising an acetylene sensor, the
acetylene sensor comprising a substrate, electrodes, and a sensor
layer, where the electrical properties of the substrate do not
change based upon any reaction or interaction with acetylene, and
where the sensor layer includes a material that undergoes and
appreciable change in resistivity based upon reaction or
interaction with acetylene.
17. The method of claim 16, where said material that undergoes an
appreciable change in resistivity based upon reaction or
interaction with acetylene is a metal salt of nickel (II).
18. The method of claim 16, where said material that undergoes an
appreciable change in resistivity based upon reaction or
interaction with acetylene is a metal salt of copper (I).
19. The method of claim 16, where said material that undergoes an
appreciable change in resistivity based upon reaction or
interaction with acetylene is nickel (II) chloride.
20. The method of claim 16, where said material that undergoes an
appreciable change in resistivity based upon reaction or
interaction with acetylene is copper (I) chloride.
21. The method of claim 16, where the acetylene sensor is in
contact with fluids contained within the power transformer.
Description
[0001] This application is a continuation of U.S. Ser. No.
13/499,963, filed on Apr. 3, 2012, which is a National Stage
application of PCT/US2010/057999, filed on Nov. 24, 2010, which is
a continuation in part of U.S. Ser. No. 12/626,252 filed on Nov.
25, 2009, which are incorporated herein by reference.
TECHNICAL FIELD
[0002] Embodiments of the invention are directed toward methods for
detecting unsaturated compounds such as acetylene.
BACKGROUND ART
[0003] In many situations there is a need to detect the presence of
small unsaturated molecules such as those including alkenylic or
alkynylic unsaturation. As those skilled in the art appreciate,
these small molecules are often gases at standard conditions, which
are the conditions under which detection is often needed. While
elaborate systems for detecting these compounds exist, there is
often a need to detect these molecules in situations or
environments where known systems are too cumbersome, too expensive,
and/or simply inoperable.
[0004] There is, therefore, a need for new techniques and/or
devices to detect small unsaturated molecules.
SUMMARY OF INVENTION
[0005] Embodiments of the present invention provide a method for
detecting an unsaturated compound, the method comprising monitoring
change in electrical properties of a substance that reacts or
interacts with unsaturated compounds.
[0006] Further embodiments of the present invention provide a
sensor for detecting acetylene gas comprising a substrate having a
surface, electrodes in electrical communication with the surface,
and a sensor layer formed of metal halide.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 cross-sectional view of a gas sensor device
schematically connected to a detection circuit according to one or
more embodiments of the invention;
[0008] FIG. 2 cross-sectional view of a gas sensor device
schematically connected to a detection circuit according to one or
more embodiments of the invention;
[0009] FIG. 3 is a schematic view of a gas sensor device according
to one or more embodiments of the invention.
[0010] FIG. 4 is a schematic view of an IGFET-type device of the
present invention.
DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS
[0011] Embodiments of the invention are based, at least in part, on
the discovery that unsaturated compounds react or interact with
certain substances and thereby alter the electrical properties of
the substance. As a result, useful techniques for detecting the
presence of unsaturated compounds are provided. In one or more
embodiments, detection devices (e.g., sensors) are provided that
operate, at least in part, based on the change in electrical
properties caused by the interaction or reaction of unsaturated
compounds with the substance.
UNSATURATED COMPOUNDS
[0012] In one or more embodiments, unsaturated compounds include
organic compounds including at least one double bond or at least
one triple bond. In one or more embodiments, unsaturated compounds
include hydrocarbons. In particular embodiments, the unsaturated
compounds include alkenes (also known as olefins) such as, but not
limited to, ethene, propene, 1-butene, 1-pentene, and 2-pentene. In
other embodiments, the unsaturated compounds include alkynes such
as, but not limited to, ethyne (also known as acetylene), propyne
(also known as methylacetylene), butyne, and pentyne. In particular
embodiments, the target unsaturated compound is acetylene. In one
or more embodiments, unsaturated compounds include those compounds
that include an alkenyl group. In these or other embodiments,
unsaturated compounds include those compounds that include an
alkynyl group. In one or more embodiments, the unsaturated
compounds may be liquids at conditions of standard pressure and
temperature. In other embodiments, the unsaturated compounds may be
gases at conditions of standard pressure and temperature.
[0013] In particular embodiments, the unsaturated compounds may be
characterized by having a relatively low molecular weight. For
example, in one or more embodiments, the molecular weight of the
unsaturated compounds may be less than 60 g/mole, in other
embodiments less than 50 g/mole, in other embodiments less than 40
g/mole, and in other embodiments less than 30 g/mole.
SUBSTANCE THAT INTERACTS WITH UNSATURATED COMPOUNDS
[0014] In one or more embodiments, the interaction between the
unsaturated compound and the substance that interacts with the
unsaturated compound results in changes in the electrical
properties of the substance. In one or more embodiments, the change
in electrical properties may be manifested, for example, in a
change in the conductivity (or resistivity) or capacitance of the
substance. Without wishing to be bound by any particular theory, it
is believed that the change in electrical properties is caused by
.pi. bonding through electrons between the unsaturated compound and
the substance. Nonetheless, for purposes of this specification, the
term interact may be used to describe the phenomena that exhibits,
demonstrates, undergoes or gives rise to the change in electrical
properties and therefore encompasses any interaction or reaction
that may occur.
[0015] In one or more embodiments, the substance that interacts
with unsaturated compounds is a transition metal compound, such as
a transition metal salt. Useful transition metals include, but are
not limited to, copper (I), copper (II), nickel (II), cobalt (II),
iron (II), zinc (II), and silver (I). Useful salts of these
transition metals include halides, such as, but not limited to,
chlorides, bromides, and iodides, as well as nitrates. Exemplary
transition metal compounds include copper (I) chloride, nickel (II)
chloride, cobalt (II) chloride, iron (II) chloride, zinc (II)
chloride, and silver nitrate (AgNO.sub.3). In particular
embodiments, the substance employed is copper (I) chloride. In
other particular embodiments, the substance employed is nickel (II)
chloride.
[0016] In particular embodiments, the purity of the substance (e.g.
metal halide) impacts that ability of the substance to interact
with the unsaturated compounds. Accordingly, in one or more
embodiments, the purity of the metal halide (e.g. cuprous chloride)
is at least 96%, in other embodiments at least 98%, and in other
embodiments at least 99%. Stated another way, in one or more
embodiments, the metal halide includes less than 5%, in other
embodiments less than 3%, and in other embodiments 1% by weight
impurity, which, for example, refers to the weight of non-cuprous
chloride atoms or molecules in the molecular arrangement or crystal
lattice of the cuprous chloride.
[0017] Advantageously, the change in electrical properties can be
monitored. For example, a voltage can be applied across the
substance and changes in the current across the substance can be
monitored. Advantageously, it has been discovered that the change
in electrical properties (e.g. resitivity) in the presence of the
unsaturated compounds is proportional to the concentration of the
unsaturated compounds in the environment in which detection of the
unsaturated compounds takes place. In one or more embodiments, the
resistivity of the substance decreases proportionally with the
increasing concentration of acetylene within the environment in
which the substance exists. Moreover, the reaction or interaction
between the substance and the unsaturated compounds is reversible.
In other words, the change in electrical properties can be reversed
as concentration of unsaturated compounds in the environment in
which a sensor is placed is reduced. For example, as a sensor is
moved from an environment having higher concentration of
unsaturated compound to an environment having lower concentration
of unsaturated compound, the conductivity of the sensor layer will
decrease proportionally to the change in concentration of
unsaturated compounds. Likewise, as the sensor is moved from an
environment having lower concentration of unsaturated compound to
an environment having higher concentration of unsaturated compound,
the conductivity of the sensor layer will increase proportionally
to the change in concentration of unsaturated compounds.
[0018] In one or more embodiments, the substance that interacts
with the unsaturated compound exhibits an initial resistance of at
least 0.1 kiloohms, in other embodiments at least 1.0 kiloohm, and
in other embodiments at least 10 kiloohms. In these or other
embodiments, the initial resistance is less than 1,000 kiloohms, in
other embodiments less than 500 kiloohms, and in other embodiments
less than 100 kiloohms. In one or more embodiments, the change in
resistivity of the substance based upon interaction with the
unsaturated compound is at least 1%, in other embodiments at least
5%, and in other embodiments at least 10% at a concentration of 1
ppm of the unsaturated compound. In one or more embodiments, the
substance that interacts with the unsaturated compound shows a
change in electrical properties in the presence of the unsaturated
compound at a temperature in the range of 20 to 130.degree. C., in
other embodiments from 50 to 120.degree. C., and in other
embodiments from 60 to 110.degree. C. In particular embodiments,
the use of nickel (II) chloride has proven to be unexpectedly
useful in the detection of acetylene. Advantageously, acetylene
interacts with nickel (II) chloride, and the interaction or
reaction unexpectedly alters the electrical properties of the
nickel (II) chloride such that the change in electrical properties
can be detected. Advantageously, the initial resistivity of nickel
(II) chloride is in the range of about 10 to about 100 kiloohms
(e.g., 20 to 80 kiloohms), and the change in resistivity is
proportional to the concentration of acetylene. And, the nickel
(II) chloride demonstrates a change in resistivity of about 10% at
a concentration of 1 ppm acetylene. This change in resistivity can
be easily monitored in view of the initial resistivity. Further,
the change in resistivity of the nickel (II) chloride in the
presence of acetylene has been found to be reversible and reliable
at temperatures up to 120.degree. C. (e.g., 100-110.degree.
C.).
DEVICE FOR DETECTING UNSATURATED COMPOUNDS
[0019] A device for detecting unsaturated compounds according to
one or more embodiments of the present invention can be generally
described with reference to FIG. 1. As those skilled in the art
will appreciate, FIG. 1, like other figures presented in this
specification, is not drawn to scale and is primarily provided to
illustrate the relationship of the various elements of the
combinations presented.
[0020] The device 10 includes a substance 12 that reacts or
interacts with unsaturated compounds and as a result exhibits a
change in electrical properties as described above with respect to
other embodiments or sub-embodiments of this invention. In
particular embodiments, substance 12 is metal halide (e.g. cuprous
chloride or nickel (II) chloride). In one or more embodiments,
substance 12 is in the form of a continuous layer that allows
electrons (i.e. a current) to travel across the layer; reference
may simply be made to layer 12 or to sensor layer 12. The thickness
of layer 12 can vary. For example, in particular embodiments, the
thickness of layer 12 can be on the atomic level (e.g. the
thickness may be one or more atoms thick) up to a thickness on the
micron level (e.g. from 1 to 1000 microns).
[0021] In one or more embodiments, sensor layer 12 is disposed on
at least a surface 17 of a substrate 16 and on at least a portion
of first and second electrodes 14 and 15, which are thereby in
electrical connection with sensor layer 12 and allow a voltage to
be applied across sensor layer 12. As shown in FIG. 1, first and
second electrodes may also be disposed on surface 17 of substrate
16. As those skilled in the art appreciate, these electrodes may be
referred to as positive and negative electrodes (e.g. positive
electrode 14 and negative electrode 15).
[0022] Substrate 16 may include or be formed from a non-conductive
or semi-conductive material. In particular embodiments, substrate
16 is inert and non-conductive, where inert refers to the fact that
the electrical properties of substrate 16 do not change as the
result of any interaction with an unsaturated compound within the
context of this specification. In these or other embodiments,
substrate 16 does not interact with unsaturated compounds.
Exemplary materials that may be used as substrate 16 include,
without limitation, alumina (Al.sub.2O.sub.3) (e.g. high-density
polycrystalline alumina), quartz (SiO.sub.2), magnesia (MgO), or
zirconia (ZrO.sub.2).
[0023] In one or more embodiments, at least a second surface 19 of
substrate 16 may be in contact with a heating device, such as a
platinum resistance heater (not shown), as well as complementary
detection and sensing devices, that can be used to heat and
maintain the temperature of device 10 at a desired temperature.
[0024] As is generally known in the art, electrodes 14 and 15 may
be fabricated from and therefore include any conductive material
including those commonly employed in the art such as platinum,
silver, and gold. Practice of the present invention is not limited
by the number or type of electrodes employed. As those skilled in
the art will appreciate, numerous electrode designs can be
configured.
[0025] In one or more embodiments, electrodes 14 and 15 may include
interdigitated electrodes (IDEs) 35 and 45 as generally shown in
FIG. 3. IDEs are generally known in the art. Practice of the
present invention is not necessarily limited by the selection of
particular IDEs. As shown, the IDEs 35 and 45 may include
interdigitated projections 37 and 47 respectively. Projections 37
and 47 may be spaced apart by gaps 50. As those skilled in the art
will appreciate, practice of the present invention is not limited
by the number of projections or the size of the gaps. These
electrodes, in a manner consistent with that described above,
include or are prepared from conductive material and are
electrically connected with device or detection circuit 18, which
may be accomplished through connection terminals (not shown) as
know in the art.
[0026] In one or more embodiments, electrical detection device 18,
which may also be referred to as a detection circuit, is in
electrical connection with electrodes 14, 15. For example,
detection device 18 may include a current meter. In one or more
embodiments, electrical detection device 18 applies a voltage
across layer 12 and monitors the change in electrical resistivity
(or conductivity) across layer 12. Practice of the present
invention is not limited by the selection of any particular
electrical detection device 18 or devices (not shown). For example,
electrical detection and monitoring may be provided by a single
device or by two or more devices working in combination with each
other (not shown). The voltage that can be applied across layer 12
may be in the form of alternating current (AC). As those skilled in
the art appreciate, this AC can be rectified to DC, filtered,
offset, and scaled to better detect changes in the electrical
properties of layer 12. As is known in the art, detection circuit
18 may include any hardware and/or software necessary for carrying
out the various detecting functions. In one or more embodiments,
detection circuit 18 may include a visual display, such as an LCD
display, or other predetermined audible, mechanical, or visual
alerts or prompts generated by detection circuit 18 when sensor
layer 12 reacts or interacts with the target unsaturated
compound.
[0027] In one or more embodiments, device 10 may include optional
permeable-protective layer 22, which may be simply referred to as
protective layer 22 or protective coating 22. Protective layer 22
may be disposed directly on sensor layer 12 as shown, or it may be
disposed on other intermediary layers disposed between sensor layer
12 and protective layer 22. In one or more embodiments, protective
layer 22 includes or is formed from a material that is permeable to
the unsaturated compound that is being detected and impermeable, or
substantially impermeable, to other compounds or constituents in
the environment that may deleteriously impact sensor layer 12 or
the ability of sensor layer 12 to react or interact with the
unsaturated compound that is being detected. For example,
protective layer 22 may be impermeable to water or organic
molecules that are larger than the unsaturated compound targeted
for detection, while it is permeable to the unsaturated compound
targeted for detection. In particular embodiments, protective layer
22 includes a hydrophobic coating.
[0028] Practice of the present invention is not necessarily limited
by the thickness of protective layer 22. In particular embodiments,
the thickness of protective layer 22 may be on the micron level;
for example, the thickness of layer 22 may be from about 2 or 4
microns to about 100 or 500 microns (e.g., up to 10 or 50
microns).
[0029] In one or more embodiments, protective layer 22 includes or
is formed from a fluorinated material. Fluorinated coatings and
coating compositions (i.e. the composition from which the coating
derives) that are useful for this purpose are known in the art. For
example, fluorinated alkyl silanes or siloxanes, which are often
referred to as FAS coatings, are known in the art as exemplified in
U.S. Publ. Nos. 2002/0081385 and 2006/0229424, which are
incorporated herein by reference.
[0030] In one or more embodiments, FAS compounds may include
compounds where a silicon atom is bonded to four chemical groups.
One or more of these groups contains fluorine and carbon atoms, and
the remaining group(s) that may be attached to the silicon atoms
may include alkyl, alkoxy, or halide group(s). Exemplary types of
FAS compounds for use in protective layer 22 include, without
limitation, CF.sub.3(CH.sub.2).sub.2Si(OCH.sub.3).sub.3 [i.e.,
3,3,3 trifluoropropyl)trimethoxysilane];
CF.sub.3(CF.sub.2).sub.5(CH.sub.2).sub.2Si(OCH.sub.2CH.sub.3).sub.3
[i.e., tridecafluoro-1,1,2,2-tetrahydrooctyl-1-triethoxysilane];
CF.sub.3(CH.sub.2).sub.2SiCl.sub.3;
CF.sub.3(CF.sub.2).sub.5(CH.sub.2).sub.2SiCl.sub.3;
CF.sub.3(CF.sub.2).sub.7(CH.sub.2).sub.2Si(OCH.sub.3).sub.3;
CF.sub.3(CF.sub.2).sub.5(CH.sub.2).sub.2Si(OCH.sub.3).sub.3;
CF.sub.3(CF.sub.2).sub.7(CH.sub.2).sub.2SiCl.sub.3;
CF.sub.3(CF.sub.2).sub.7(CH.sub.2).sub.2SiCH.sub.3Cl.sub.2; and/or
CF.sub.3(CF.sub.2).sub.7(CH.sub.2).sub.2SiCH.sub.3(OCH.sub.3).sub.2.
These FAS material may be used either alone or in any suitable
combination for protective layer 22. At least partial hydrolyzed
versions (hydrolysate) of any of these compounds may also be
used.
[0031] As noted above, the detection devices of this invention,
such as device 10, may include multiple protective layers (not
shown). Each protective layer should be permeable to the
unsaturated compound or compounds being targeted for detection, and
thereby allow the target unsaturated compounds to contact sensor
layer 12. Each of the one or more protective layers, however, may
be selectively permeable or impermeable to other constituents that
may come into contact with device 10 (i.e. are present in the
environment where the target unsaturated compounds are sought to be
detected).
[0032] Other embodiments of devices of the present invention may be
described with reference to FIG. 2. As shown, detection device 20
includes sensor layer 12, first and second electrodes 14 and 15,
substrate 16, electrical detection device 18, and optional
protective layer 22, which may be consistent with the description
provided above. In addition, detection device 20 may include
optional support layer 24, which may also be referred to as matrix
24. Support layer 24 may be disposed on first surface 17 of
substrate 16 and on at least a portion of electrodes 14 and 15.
Sensor layer 12 may then be disposed on first surface 25 of
semi-conductor layer 24. As a result of this arrangement,
electrodes 14 and 15 are in electrical contact or communication
with each other through sensor layer 12 and optionally through
matrix 24; in other words a voltage can be applied across sensor
layer 12 between electrodes 14 and 15, and optionally also across
support 24 between electrodes 14 and 15.
[0033] In one or more embodiments, support layer 24 is porous
and/or has a degree of surface roughness. In one or more
embodiments, support layer 24 is porous or partially porous with
respect to the target unsaturated compound. As a result, the
porosity, partial porosity, and/or surface roughness, at least
first surface 25 of support layer 24 has increased surface area and
may therefore provide increased surface area to sensor layer 12,
which is disposed on surface 25.
[0034] In one or embodiments, support or matrix layer 24 is a
semi-conductor, and therefore layer 24 may also be referred to, in
certain embodiments, as semi-conductor layer 24. Semi-conductor
layer may be formed from and therefore include a metal oxide such
as, without limitation, titanium dioxide (TiO.sub.2 or Ti(IV) oxide
or titania), tin dioxide (SnO.sub.2 or Sn(IV) oxide), zinc oxide
(ZnO or Zn(II) oxide), molybdenum oxide (MoO.sub.3 or Mo(VI)
oxide), tungsten oxide (WO.sub.3 or W(VI) oxide), and mixtures of
two or more of these compounds. For example, a mixture of titanium
dioxide and tin dioxide may be employed; in particular embodiments,
the ratio of titanium dioxide to tin dioxide may continuously range
from about 100:1 to about 1:100.
[0035] The thickness of support layer 24 can vary. For example, in
particular embodiments, the thickness of layer 24 can be on the
atomic level (e.g. the thickness may be one or more atoms thick) up
to a thickness on the micron level (e.g. from 1 to 1000
microns).
[0036] In these or other embodiments, any relationship that may
exist between the sensor layer 12 and the semi-conductor layer 24
may be expressed in terms of the weight of the sensor material as a
ratio to the weight of the semi-conductor material present in any
given unit of area. For example, the weight/weight ratio of sensor
material to semi-conductive material is from about 0.02 to about
100.
[0037] In one or more embodiments, the sensor devices of this
invention can be fabricated into an insulated-gate field-effect
transistor (IGFET) as shown in FIG. 4. Transistor 60 includes a
semiconductor substrate 62, a source region 64, and a drain region
66. Source region 64 is spaced apart from drain region 66, and both
may be located at or near one surface 67 of substrate 62. The
region of substrate 62 between source 64 and drain 66 is called the
channel 65. A gate insulator 68, which may include a thin layer of
insulating material, covers the surface 67 of channel 65. A gate
electrode 70, which is a sensor layer within the context of this
invention (e.g. metal halide layer), is disposed on and covers gate
insulator 68. Gate electrode 70 includes a sensor substance 71
(e.g. metal halide) and optional support material (e.g. TiO.sub.2)
72. In one or more embodiments, gate electrode 70 may also include
a conductive layer disposed between gate insulator 68 and gate
electrode 70. In those embodiments where the device includes
conductive layer 74, the device may be referred to as a metal
insulator semiconductor (MIS). The IGFET devices of this invention
may also include an optional protective layer 73.
[0038] When gate electrode 70 (e.g. metal halide sensor layer) is
exposed to an unsaturated compound (e.g. acetylene), the electric
field in gate insulator 68 is modified. The electric field attracts
or repels charge carriers, electrons or holes, in adjacent
semiconductor material 62 thereby changing the conductance of
channel 65. The change in conductance of channel 65 is related to
the concentration of unsaturated compound interacting with sensor
substance 71 and can be measured by a current meter 76 connected in
series with a potential source, source region 64, and drain region
66.
METHOD OF FABRICATING DEVICE
[0039] While practice of the present invention is not necessarily
limited by the method used to produce the device of one or more
embodiments of the present invention, the following method has been
found to be advantageous. An inert substrate, such as a thin plate
or wafer of dense (.about.100%) crystalline-alumina, can be
commercially obtained and may be optionally polished to provide at
least one relatively smooth surface. A pair or multitude of
electrodes, such as IDEs, can be placed on a surface (optionally a
polished surface) of the alumina substrate by employing techniques
known in the art of photolithography.
[0040] The substance that can interact with an unsaturated compound
may then be deposited onto at least a portion of the substrate and
onto at least a portion of each of the electrodes. In other
embodiments, one or more semiconductor layers are first deposited
onto at least a portion of the substrate and onto at least a
portion of each of the electrodes, and then the substance that can
react or interact with an unsaturated compound may then be
deposited onto the at least a portion of the semiconductor
layer.
[0041] In either event, the substance that can interact with an
unsaturated compound may be deposited by using the following
technique. In one embodiment, where cuprous chloride is employed,
cuprous chloride may be commercially obtained at purity levels that
are useful for practicing the present invention (e.g. 99%+). Where
grades are obtained that include greater levels of impurities, or
where further purification is desired, cuprous chloride may be
further purified using techniques known in the art. For example,
the cuprous chloride can be dissolved in concentrated hydrochloric
acid, which will leave impurities, such as copper-II (cupric
chloride) compounds undissolved, and allow for separation by using
techniques such vacuum filtration; the cuprous chloride can then be
precipitated out using copious amounts of water and dried using
glacial acetic acid and optional further drying in a vacuum
oven.
[0042] The cuprous chloride can be dissolved in appropriate
solvents, such as acetonitrile, to form a solution that can be
deposited onto at least a portion of the substrate and onto at
least a portion of the each of the electrodes, or in other
embodiments, onto at least a portion of the semiconductor layer and
onto at least a portion of the each of the electrodes. The
substrate can be heated (e.g. up to about 60-65.degree. C.) when
the solution of cuprous chloride is applied, or it may be
subsequently heated to drive off or evaporate the solvent.
[0043] In those embodiments where nickel (II) chloride is employed,
the nickel chloride can be dissolved in appropriate solvents, such
as water, acetonitrile or a mixture of the two, to form a solution
that can be deposited onto at least a portion of the substrate and
onto at least a portion of each of the electrodes, or in other
embodiments, onto at least a portion of the semiconductor layer and
onto at least a portion of the electrodes. The substrate can be
heated when the solution of nickel chloride is applied to drive off
the solvent, preferably above the vaporization temperature of the
solution (e.g. from about 100.degree. C.-150.degree. C. for an
acetonitrile, water mixture) for quick evaporation and dispersion
of the nickel chloride.
[0044] Where the device includes a semi-conductor layer, such as
titanium dioxide or tin oxide or other suitable oxides mention
above, the semiconductor layer may be formed from a slurry
containing the metal oxide that is deposited on the substrate, and
at least a portion of the electrodes, and subsequently fired to
obtain a porous or partially porous film with some surface
roughness. For example, titanium oxide powder that is at least
about 99.5% pure can be commercially obtained and sieved to obtain
a desirable particle size. In one or more embodiments, the metal
oxide is sieved or otherwise separated to provide particles having
a particle size of less than 200 .mu.m, in other embodiments less
than 40 .mu.m, or in other embodiments less than 1 .mu.m. The
sieved powder can be formed into a slurry using an appropriate
liquid vehicle such as 2-propanol. The slurry may then be applied
to the target surface using known techniques (e.g. brushing or
spraying), allowed to dry slowly in an air oven (e.g. overnight at
70.degree. C.) and fired at appropriate temperatures for sufficient
time (e.g. 700.degree. C. for approximately 2 hours) to achieve a
desired porous semiconductor layer.
[0045] The sensing layer can then be formed on the porous
semiconductor layer by applying the solution (e.g. cuprous chloride
in acetonitrile) described above to the surface of the
semiconductor layer.
[0046] In one or more embodiments, the solution of the cuprous
chloride is prepared and applied so as to deliver from about 1
microgram to about 200 micrograms, or in other embodiments from
about 5 micrograms to about 50 micrograms, cuprous chloride per
square mm of the substrate or semiconductor layer.
[0047] After the sensing material is applied to the substrate or
semiconductor material and appropriately dried, it may be desirable
to precondition the device. This may be accomplished by subjecting
the device to an energy source. For example, the device can be
heated in an oven under appropriate conditions. In other
embodiments, an alternating current can be applied across the
terminals (e.g. a 1-volt peak voltage at a frequency of between
10-100 Hz, although A.C. signals with other voltage magnitudes and
frequencies may be used); this voltage may be applied for extended
periods of time (e.g. 6 hours).
[0048] Protective layer(s) can be applied to the device by using
known techniques for applying these coatings. For example,
solutions of FAS coatings can be applied by using known techniques
(e.g. brushing or spraying), and the solvent within the solution
can be driven off using known techniques (e.g. heat and/or vacuum).
The protective layer can be applied before or after preconditioning
the device.
PACKAGING
[0049] As those skilled in the art appreciate, the various other
sensor configurations can incorporate the sensor layer or sensor
substance contemplated by this invention. Moreover, these various
devices can be packaged or assembled within various packages known
in the art. For example, and without limitation, these devices can
be assembled with dual in-line packages (DIPs), surface mount
packages (SMPs), and metal can packages (TO-type).
INDUSTRIAL APPLICABILITY
[0050] In one or more embodiments, the techniques and devices of
the present invention can advantageously be used to detect a number
of unsaturated compounds in diverse environments. For example,
where the unsaturated compound is in the gaseous state, the
techniques and detectors of this invention can be used in liquid or
gaseous environments. In other words, gaseous unsaturated compounds
contained in a mixture of gases can be detected where the mixture
of gases is in contact with the sensor. Or, unsaturated gaseous
compounds dissolved in a liquid can be detected where the liquid is
in contact with the sensor.
[0051] In particular embodiments, the sensors of the present
invention are employed to detect the presence of acetylene in
oil-filled electrical equipment such as power transformers. In
these embodiments, the sensor can be placed in contact with the
fluids contained in the electrical equipment (e.g. power
transformer). A voltage (e.g. about 1 volt) can be applied across
the sensor layer and/or semiconductor layer. In one or more
embodiments, the sensing device can optionally be heated (e.g. to a
temperature of about 100.degree. C.). Using known techniques, a
baseline voltage transmission can be determined for the device in
the absence of acetylene within the transformer, which represents a
degree of resistivity (or conductivity) across the device. This
degree of conductivity can be continuously or intermittently
monitored and compared to the base line. As acetylene is formed
within the transformer and the concentration of the acetylene
reaches concentrations that are detectable by the sensor, the
conductivity of the sensor changes as the acetylene reacts or
interacts with the senor layer. The change in conductivity can be
recorded on site at the transformer or communicated electronically
to a location remote from the transformer.
[0052] In other particular embodiments, the sensors of the present
invention are employed to detect the presence of acetylene or
ethylene in food applications including, but not limited to, food
ripening processes and food storage facilities.
[0053] Although the present invention has been described in
considerable detail with reference to certain embodiments, other
embodiments are possible. Therefore, the spirit and scope of the
appended claims should not be limited to the description of the
embodiments contained herein.
* * * * *