U.S. patent application number 11/555990 was filed with the patent office on 2007-03-15 for titanium semiconductor bridge igniter.
This patent application is currently assigned to SCB TECHNOLOGIES, INC.. Invention is credited to Martin C. Foster, Bernardo Martinez-Tovar.
Application Number | 20070056459 11/555990 |
Document ID | / |
Family ID | 23867228 |
Filed Date | 2007-03-15 |
United States Patent
Application |
20070056459 |
Kind Code |
A1 |
Martinez-Tovar; Bernardo ;
et al. |
March 15, 2007 |
TITANIUM SEMICONDUCTOR BRIDGE IGNITER
Abstract
A titanium semiconductor bridge igniter (10, 10') has a
substrate (12, 12') on which is carried a pair of spaced-apart pads
(18a, 18b) connected by a bridge (20). The pads (18a, 18b) and
bridge (20) are made of a layer of polysilicon (22) or crystalline
silicon (22') covered by a layer of titanium (24). Metal lands
(26a, 26b) overlie the pads (18a, 18b) but leave the bridge (20)
exposed so that it can be placed in contact with an energetic
material charge (42). A method of stabilizing the titanium
semiconductor bridge igniter (10, 10') against temperature-induced
variations in electrical resistance of bridge (20) includes heating
the titanium semiconductor bridge igniter (10, 10') to an elevated
temperature, e.g., from about 37.degree. C. to about 250.degree.
C.
Inventors: |
Martinez-Tovar; Bernardo;
(Albuquerque, NM) ; Foster; Martin C.; (Placitas,
NM) |
Correspondence
Address: |
CANTOR COLBURN, LLP
55 GRIFFIN ROAD SOUTH
BLOOMFIELD
CT
06002
US
|
Assignee: |
SCB TECHNOLOGIES, INC.
Albuquerque
NM
|
Family ID: |
23867228 |
Appl. No.: |
11/555990 |
Filed: |
November 2, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09470343 |
Dec 22, 1999 |
|
|
|
11555990 |
Nov 2, 2006 |
|
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Current U.S.
Class: |
102/202.7 |
Current CPC
Class: |
F42B 3/13 20130101 |
Class at
Publication: |
102/202.7 |
International
Class: |
F42C 19/12 20060101
F42C019/12 |
Claims
1. A semiconductor bridge igniter comprising: a substrate; an
electrical bridge structure disposed on the substrate, the bridge
structure comprising a bridge section and pad sections, the bridge
section extending between and connecting the pad sections, the pad
sections each comprising a layer of semiconductor material on the
substrate and a layer of titanium disposed on the semiconductor
material, and the bridge section consisting of a layer of
semiconductor material and a layer of titanium disposed on the
semiconductor material; and a pair of electrically conductive lands
each overlying a respective one of the pad sections and being
spaced apart from each other to leave the bridge section
exposed.
2. The igniter of claim 1 wherein the igniter has a lower input
energy requirement for initiation than an identically sized
semiconductor bridge igniter layer that comprises a bridge section
that includes a layer of tungsten.
3. A semiconductor bridge igniter comprising: a substrate; an
electrical bridge structure disposed on the substrate, the bridge
structure comprising a bridge section and pad sections, the bridge
section extending between and connecting the pad sections, the pad
sections and bridge section each comprising a layer of
semiconductor material on the substrate and a layer of metal
disposed on the semiconductor material, the layer of metal
consisting of titanium and the bridge section being free of a layer
of tungsten; and a pair of electrically conductive lands each
overlying a respective one of the pad sections and being spaced
apart from each other to leave the bridge section exposed.
4. The igniter of claim 1 wherein the pad sections each consist of
a layer of semiconductor material.
5. The semiconductor bridge igniter of any one of claims 1, 2, 3 or
4 further comprising a pair of electrical leads, one connected to a
respective one of the electrically conductive lands.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of co-pending patent
application Ser. No. 09/470,343, filed Dec. 22, 1999, and entitled
"Titanium Semiconductor Bridge Igniter".
FIELD OF THE INVENTION
[0002] The present invention relates to a titanium semiconductor
bridge igniter of a type used to initiate an energetic material by
passing an electric current through the semiconductor bridge to
generate therefrom a plasma which ignites the energetic
material.
RELATED ART
[0003] U.S. Pat. No. 4,708,060, issued Nov. 24, 1987 to R. W.
Bickes, Jr., et al., and entitled "Semiconductor Bridge (SCB)
Igniter" discloses a semiconductor bridge igniter comprising an
electrical material having a negative temperature co-efficient of
electrical resistivity at elevated temperature. The electrical
material comprises doped silicon, is mounted on a non-electrically
conducting substrate, and defines a pair of spaced pads connected
by a bridge. The area of each of the pads is much larger than the
area of the bridge, the resistance of which must be less than about
3 ohms. Metallized layers, such as aluminum lands, overlie the
pads. An energetic material is placed in contact with the
semiconductor bridge and the passage of a low level of electric
current through the semiconductor bridge is attained by connecting
the lands in an electrical circuit. The electric current is said to
result in the formation of plasma from the bridge material, which,
with a resultant convective shock effect, initiates the energetic
material.
[0004] U.S. Pat. No. 4,976,200, issued Dec. 11, 1990 to D. A.
Benson et al., and en-titled "Tungsten Bridge for the Low Energy
Ignition of Explosive and Energetic Materials". This patent
discloses a device similar to the above-mentioned '060 patent, but
one in which the doped silicon semiconductor bridge of the '060
patent is replaced by a composite bridge comprised of a first layer
of silicon in contact with the insulating substrate and a second
layer overlying the first layer, the second layer being tungsten.
One difficulty with the tungsten thin-film bridge of U.S. Pat. No.
4,976,200 is the difficulty and expense of applying the thin film
of tungsten to the silicon bridge by the chemical vapor deposition
process suggested in the patent.
[0005] Devices such as the silicon semiconductor bridge igniter of
U.S. Pat. No. 4,708,060 and the tungsten-coated semiconductor
bridge of U.S. Pat. No. 4,976,200 require intimate contact of, and
significant pressure between, the bridge and the energetic material
they are intended to ignite, in order to provide reliable
initiation. If intimate contact and significant pressure are not
maintained between the bridge and the energetic material, the
device may be rendered unreliable and/or the activation energy must
be increased in order to avoid a decrease in initiation reliability
of the device.
SUMMARY OF THE INVENTION
[0006] In accordance with the present invention there is provided a
titanium semiconductor bridge device comprising a substrate and an
electrical bridge structure disposed on the substrate and
electrically insulated therefrom. The bridge structure comprises a
layer of a material having a negative coefficient of electrical
conductivity at temperatures above ambient temperature and having
disposed thereover a layer of titanium, the bridge structure
comprising a bridge section extending between and connecting
spaced-apart pad sections, each pad section being of larger area
than the bridge section. A pair of electrically conductive lands
each overlies a respective one of the pad sections and is spaced
apart from the other land to leave the bridge section exposed.
[0007] In one aspect of the invention, the titanium semiconductor
bridge device further comprises a pair of electrical leads, each
connected to a respective one of the electrically conductive
lands.
[0008] The present invention also provides one or more of the
following features, separately or in combination: the titanium
semiconductor bridge device may further include a source of
electrical energy connected to each of the electrical leads to
define an electrical circuit extending from one lead to one of the
aluminum lands, through the bridge section, thence to the other
aluminum land and to the other electrical lead; the substrate may
comprise silicon on which is disposed a layer of silicon dioxide on
which is disposed the electrical bridge structure and,
alternatively, the substrate may comprise sapphire.
[0009] Other aspects of the invention provide one or more of the
following features, separately or in combination: the material
having a negative coefficient of electrical conductivity may
comprise crystalline silicon or polysilicon, in which case, the
polysilicon may be an undoped film; and the titanium semiconductor
bridge device may be disposed in contact with an energetic material
charge contained within the header of an igniter assembly. The
silicon may be pure, or small impurities may be present without
degrading the effectiveness of the invention.
[0010] In a method aspect of the present invention, there is
provided a method for making the titanium semiconductor bridge
igniter, which method includes preconditioning the titanium
semiconductor bridge igniter by heating it to an elevated
temperature to stabilize it against temperature-induced variations
in bridge electrical resistance, for example, a method in which the
igniter is heated to an elevated temperature of from about
37.degree. C. to about 250.degree. C., e.g., from about 100.degree.
C. to 250.degree. C.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic plan view of a titanium semiconductor
bridge igniter in accordance with one embodiment of the present
invention;
[0012] FIG. 2 is a schematic view in cross section taken along line
II-II of FIG. 1;
[0013] FIG. 3 is a schematic cross-sectional view of an igniter
assembly utilizing one embodiment of a titanium semiconductor
bridge igniter of the present invention;
[0014] FIG. 3A is a view, enlarged relative to FIG. 3, of
approximately the portion of FIG. 3 enclosed by the rectangular
area A; and
[0015] FIG. 4 is a view corresponding to FIG. 2 showing a second
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION AND SPECIFIC EMBODIMENTS
THEREOF
[0016] The titanium semiconductor bridge igniter of the present
invention provides a significant improvement over the prior art
semiconductor bridge igniters described above. Generally, it is
desired that semiconductor bridge igniters provide highly reliable
initiation of energetic material while requiring less energy input,
and yet not be sensitive to unintended, stray currents. It is
further desirable that such devices be relatively simple and
inexpensive to manufacture and lend themselves to mass production
techniques.
[0017] In addition to the drawbacks noted above, the
tungsten-covered silicon bridge of U.S. Pat. No. 4,976,200 poses
another difficulty due to the fact that the melting point of
tungsten, 3695.degree. Kelvin (".degree. K."), is higher than the
vaporization temperature (2628.degree. K.) of silicon. This impedes
the effectiveness of the plasma formed from the silicon in igniting
the energetic material, because the tungsten layer of the bridge
overlies the silicon and is therefore interposed as a solid layer
between the vaporizing silicon and the energetic material charge
against which the semiconductor bridge igniter is placed. The
resulting absorption of energy by the solid tungsten lessens the
efficiency of tungsten bridge devices.
[0018] The titanium semiconductor bridge igniter of the present
invention utilizes a thin film of titanium deposited on the silicon
bridge and thereby provides a product which is greatly superior to
the tungsten-layered silicon bridge of U.S. Pat. No. 4,976,200. The
melting point of titanium (1660.degree. C.) is only slightly higher
than that of silicon (1420.degree. C.) and much lower than
silicon's vaporization point of 2628.degree. K., so that when the
bridge is activated by an electrical current, or an electrical
discharge from a capacitor, the titanium layer interposed between
the silicon bridge and the energetic material charge melts well
before the silicon vaporizes at 2628.degree. K. The molten titanium
does not impede the plasma generated from the silicon bridge from
impinging upon and igniting the energetic material charge against
which the titanium semiconductor bridge igniter is placed.
[0019] Further, as the titanium thin film is heated, it reacts with
oxygen and/or nitrogen present in the environment of the energetic
material charge in an exothermic reaction which enhances the energy
output of the vaporizing silicon bridge. Thus, reaction of the
titanium with atmospheric oxygen and/or nitrogen enclosed within an
igniter assembly supplements the energy derived from the electrical
energy input to the titanium semiconductor bridge igniter to
vaporize and generate a plasma from the silicon bridge. The
titanium layer of the bridge therefore provides initiation of the
energetic material charge at lower energy input to the device than
do the silicon or tungsten/silicon semiconductor bridges of the two
prior art patents noted above. Specifically, the use of a thin-film
titanium overlayer as part of the bridge of the titanium
semiconductor bridge igniter results in a lower input energy
requirement for initiation than do identically sized semiconductor
bridge igniters such as the silicon bridge of U.S. Pat. No.
4,708,060, or the tungsten/silicon bridge of U.S. Pat. No.
4,976,200.
[0020] Not only does the titanium silicon bridge of the present
invention require lower energy input for initiation than a
comparably sized bridge of the prior art but, because the titanium
enters into an exothermic reaction with atmospheric oxygen and/or
nitrogen, the energy output is supplemented and the requirement for
high-pressure intimate contact of the titanium semiconductor bridge
igniter with the energetic material charge is lessened. Thus,
because of its pyrophoric activity, the titanium layer in the
bridge generates hot particles as the silicon bridge heats up and
vaporizes, the hot particles further aiding in reliability of
initiation of the energetic material.
[0021] In terms of manufacturing, the titanium layer can be readily
deposited on the titanium semiconductor bridge igniter by standard
vacuum deposition techniques, such as evaporation or sputtering.
The titanium layer can be produced in the desired patterns by
standard semiconductor fabrication techniques which readily lend
themselves to mass production of the igniters.
[0022] One drawback associated with the use of titanium is that the
bridge electrical resistance of the igniter increases with
increasing temperature, and part of this increase appears to be
irreversible, i.e., return to lower temperature does not return the
material to lower resistance. Without wishing to be bound by any
particular theory, it is believed that oxidation of the surface of
the titanium and/or oxygen impurities within the titanium film
causes the irreversible increase in electrical resistance.
Therefore, titanium semiconductor bridge igniters containing a
thin-film layer of titanium on a silicon bridge in accordance with
the present invention, and which were subjected in transportation
or use to high temperatures after leaving the factory, e.g.,
temperatures of about 37.degree. C. to about 250.degree. C., might
offer a higher electrical resistance than that for which they were
rated at the factory. However, this difficulty can be readily
overcome simply by heating the devices after, or as part of, the
manufacturing process in order to precondition them. Thus, if the
titanium semiconductor bridge igniters are heated to a temperature
of, for example, about 250.degree. C., there will be no increase of
resistivity of the igniters if they encounter temperatures up to
250.degree. C. in storage, transportation or use. Generally, during
the preconditioning step the igniters may be heated to, or close
to, the highest temperatures they can sustain without risk of
damage, in order to stabilize them against temperature-induced
changes in bridge resistance.
[0023] Referring now to FIGS. 1 and 2, there is shown a titanium
semiconductor bridge igniter 10 comprising a substrate 12. In the
illustrated embodiment, substrate 12 is an insulator and comprises
silicon 16 on which is disposed a silicon dioxide layer 14. (All
the Figures are schematic and are not drawn to scale.) Pads 18a and
18b (FIG. 1) are connected to each other by a bridge 20. The pads
18a, 18b and bridge 20 are comprised, as shown in FIG. 2, of a
polysilicon layer 22 surmounted by a thin-film titanium layer 24.
Preferably, the titanium layer 24 should be deposited over the
entirety of the polysilicon layer 22. Pads 18a, 18b and portions of
bridge 20 adjacent thereto are surmounted by a pair of metal, e.g.,
aluminum, lands 26a, 26b. Any suitably conductive metal or
combination of metals may be substituted for the aluminum of
aluminum lands 26a, 26b; for example, gold, silver, chromium or
other metals may be utilized. As shown in FIG. 1, aluminum (or
other metal) lands 26a, 26b are connected by electrical leads 28a,
28b (FIG. 1) to a DC energy source 30 which may comprise a battery
or other source of DC current, a capacitor or the like. A switch 31
is shown in the electrical circuit.
[0024] The titanium semiconductor bridge igniter 10 of FIGS. 1 and
2 is shown in FIG. 3 as a component of an igniter assembly 32 which
is comprised of an electrically insulating header base 36, which
may be made of, for example, ceramic or glass. Header base 36 is,
however, preferably made of metal for good thermal conductivity and
is electrically insulated from the electrical leads passing through
it, typically by glass insulation. In any case, header base 36 is
contained within a receptacle 38. Titanium semiconductor bridge
igniter 10, as best seen in FIG. 3A, is mounted on the top surface
36a of header base 36. Header base 36 has a pair of passageways
(unnumbered) formed therein for the passage therethrough of
electrical leads 28a, 28b (FIGS. 3 and 3A). The unnumbered
passageways in header base 36 are sealed by a suitable sealant, as
is well known in the art, in order to prevent the ingress of
moisture, liquids or other contaminants therethrough. Electrical
leads 28a, 28b are connected in electrical contact to the aluminum
lands 26a, 26b of the titanium semiconductor bridge igniter 10 by
wire bonds 34a, 34b. The ends of electrical leads 28a, 28b which
emerge from header base 36 will be connected to a suitable source
of electrical energy such as the DC energy source 30 of FIG. 1.
[0025] Receptacle 38 defines an enclosure within which is contained
titanium semiconductor bridge igniter 10 and an energetic material
charge 42 comprised of a compacted powder of energetic material,
e.g., a pyrotechnic material such as zirconium potassium
perchlorate. Any suitable energetic material may, of course, be
used, such as titanium subhydride potassium perchlorate, lead azide
or zirconium potassium perchlorate.
[0026] In use, upon closing of switch 31, electrical current flows
through the circuit established by leads 28a, 28b (FIGS. 2 and 3)
aluminum lands 26a, 26b and, initially, titanium layer 24 of bridge
20. Either the DC current or the discharge of a capacitor provides
the requisite electrical energy. At room temperature the undoped
polysilicon layer 22 exhibits high electrical resistance and the
current flow is through the titanium layer 24. As the undoped
polysilicon layer 22 is heated by the joule heating of the
titanium, its electrical resistance decreases due to its negative
coefficient of electrical resistivity, which is characteristic of
the material, until its resistivity equals, or is less than, that
of the titanium layer 24. At that point, most of the electric
current, and therefore most of the energy, is passing through the
polysilicon layer 22. The titanium layer 24 of the bridge 20
becomes heated and melts before the polysilicon layer 22 of the
bridge vaporizes to generate a plasma. Because the titanium layer
24 has melted, it does not interpose a solid barrier between the
energetic material charge 42 and the plasma generated upon
vaporization of the polysilicon layer 22 of bridge 20. The silicon
plasma therefore impinges directly upon the energetic material
charge 42. Further, the molten titanium will react with any oxygen
or nitrogen present in an exothermic reaction which further
contributes energy to the initiation of energetic material charge
42. Therefore, effective and reliable initiation of energetic
material charge 42 is attained.
[0027] The titanium semiconductor bridge igniter of the invention
may be used in the same applications as known semiconductor bridge
igniters, for example, to initiate a charge to inflate automobile
airbags or to initiate other larger explosive charges. The igniter
assembly 32 will, in use, therefore be securely fastened by means
(not shown) so as to cause the initiation of energetic material
charge 42 to effectuate its intended purpose upon the passage of a
suitable electric current through the circuitry schematically
illustrated in FIG. 1.
[0028] FIG. 4 is a view corresponding to FIG. 2, but showing a
semiconductor bridge igniter 10' in accordance with another
embodiment of the present invention. Titanium semiconductor bridge
igniter 10' utilizes a sapphire substrate 12' in lieu of the
substrate 12 of the FIG. 2 embodiment. Crystalline silicon layer
22' replaces polysilicon layer 22. All other components of the
titanium semiconductor bridge igniter 10' of FIG. 4 are identical
to those of the FIG. 2 device and are identically numbered.
Accordingly, the description thereof is not repeated here.
[0029] The following examples illustrate the benefits obtained by a
particular embodiment of the present invention.
EXAMPLE 1
[0030] A titanium semiconductor bridge igniter as schematically
illustrated in FIG. 1 was prepared using standard semiconductor
processing equipment and techniques. The numerals utilized in FIGS.
1 and 2 are used in this example to help identify components of the
titanium semiconductor bridge igniters tested. The titanium layer
24 was deposited by vacuum evaporation on an undoped polysilicon
layer 22. Immediately after cessation of deposition of the titanium
layer, aluminum metallization was deposited without breaking the
vacuum conditions in the evaporation chamber, in order to ensure a
clean interface between the resultant aluminum lands 26a, 26b and
titanium layer 24. Conventional masking and etching techniques were
employed to configure the polysilicon layer 22 and the titanium
layer 24 in the "bow-tie" pattern illustrated in FIG. 1. The
aluminum lands 26a, 26b are configured to expose the bridge 20, but
overlie the pads 18a, 18b. The exposed bridge 20 was 39 micrometers
long by 78 micrometers wide. The titanium layer 24 had a thickness
of 0.35 micrometers and the aluminum lands 26a, 26b had a thickness
of 1.5 micrometers. The final tested resistance of the bridge 20
was 3 ohms. These parts were manufactured on a wafer, as is
conventional, and the parts were then diced and mounted onto
standard TO-46 headers substantially as illustrated in FIG. 3.
Five-mil diameter aluminum wire was used for electrical leads 28a,
28b (FIGS. 1 and 3) and were thermosonically wire-bonded in
electrical contact with aluminum lands 26a, 26b (FIGS. 1 and 2), as
indicated by wire bonds 34a, 34b (FIG. 3). The parts were tested
using a standard Sensit test for destructible parts: firing voltage
being varied for each test firing based on analysis of preceding
test firings, using an algorithm which determines firing statistics
(mean firing voltage, standard deviation) with a relatively small
number of firings.
[0031] Two samples of 20 such parts, loaded with zirconium
potassium perchlorate ("ZPP") were pressed at 12,000 psi and 6,000
psi, respectively, and were tested using the statistical methods of
the Sensit test. A capacitive discharge fireset was used, with a
120 microfarad capacitor, and a 1.5 ohm series resistance, in
addition to the resistance of the devices under test. The test
results show a mean firing voltage of 5.59 volts and a sigma of
0.055 volts for the parts pressed to 6,000 psi and a mean firing
voltage of 5.50 volts and a sigma of 0.116 volts for the parts
pressed to 12,000 psi.
COMPARATIVE EXAMPLE 2
[0032] By comparison, two twenty-unit samples of parts manufactured
with the silicon bridge of U.S. Pat. No. 4,708,060 were assembled
with the same ZPP pressed to the same pressures. The bridge areas
and volumes were identical for both the silicon bridge and the
titanium bridge. The data for the silicon bridge parts showed a
mean firing voltage of 6.07 volts and a sigma of 0.124 volts for
the parts pressed to 12,000 psi and a mean firing voltage of 6.5
volts and a sigma of 0.246 volts for the parts pressed to 6,000
psi. The results are shown in table form below. TABLE-US-00001
Bridge Type/ Titanium Bridge Comparative Silicon Consolidation
Pressure Embodiment (Example 1) Bridge (Example 2) 6,000 psi Mean =
5.59 V Mean = 6.50 V Sigma = 0.055 V Sigma = 0.246 V 12,000 psi
Mean = 5.50 V Mean = 6.07 V Sigma = 0.116 V Sigma = 0.124 V
[0033] A comparison of the data of Examples 1 and 2 shows that the
igniters of the present invention required less input energy and a
lower voltage to attain initiation than did the identically sized
comparative igniters of U.S. Pat. No. 4,708,060. These results
support the belief that the exothermic reaction of the titanium
layer supplements the electrical energy input into the system with
the energy of the exothermic reaction of the titanium layer, to
more efficiently attain initiation of the energetic material
charge. The advantages enjoyed by the embodiment of the present
invention over the comparative examples of the prior art are
especially pronounced in the samples prepared with the lower
consolidation pressure, where ignition reliability is lower than
for the examples prepared with higher consolidation pressure.
[0034] While the invention has been described with reference to
specific preferred embodiments thereof, it will be appreciated
that, upon a reading and understanding of the foregoing, numerous
alterations to those embodiments will occur to those skilled in the
art, and it is intended to include all such variations within the
scope of the appended claims.
* * * * *