EP0914587B1 - Thin layer igniter element for active pyrotechnic materials and method for the production thereof - Google Patents

Abstract

The thin layer igniter elements used to ignite active pyrotechnic materials generally have high ignition voltages or involve very high amounts of initialization energy. Said elements are mainly based on a purely thermal coupling of a hot material and a volatile material forming a bridging material for ignition. By using hafnium hydride and/or titanium hydride as a bridging material for ignition (2) and by employing a method of production which is compatible with semi-conductors, large quantities of ignition elements requiring low-range initialization voltages can be produced in an extremely simple manner. A hafnium hydride and/or titanium hydride decomposition process is activated at a low heating temperature, resulting in the release of reactive hydrogen and the formation of plasma. The inventive igniter elements provide simplified control circuits for passenger protection devices such as airbags in motor vehicles.

Description

The invention relates to a thin-layer ignition element for pyrotechnic active materials according to the preamble of claim 1 and method for its production according to the preamble of claim 11.

From DE 42 22 223 C1 is an electrical igniter according to the preamble of Claim 1 known.

In conventional ignition elements, a thin wire bridge is reduced Resistor (2Ω) heated and evaporated by a current pulse. Through this one thermal impulse is then ignited the pyrotechnic active mass. In DE 42 22. 223 C1 becomes a thin-film ignition bridge made of titanium, titanium nitride or one Alloy containing predominantly titanium is proposed as titanium or titanium nitride due to their high thermal conductivity and their compared to conventional ignition bridge materials higher electrical resistance when melting one Ensure large and uniform heating of the pyrotechnic active mass. However, the ignition energy required for this is very high because titanium has a melting point over 1660 ° Celsius; Titanium nitride over 2900 ° Celsius and common titanium alloys are still above.

Another variant, preferably using the semiconductor material Polysilicon, the principle of which is also thermal in nature, is described in US 4,708,060. Here, the one that occurs at an elevated temperature negative temperature coefficient of the resistance material exploited. This leads to Ignition moment in addition to the heat transfer to form a thin plasma and one convective pressure effect. The structure is comparable to a resistance bridge.

Another ignition principle, described in US 5,080,016, is based on the use of a Metallhydridfolie. A plastic strip is applied to this self-supporting film due to the thermal decomposition of the hydride layer (gas pressure development) as a result of Voltage pulse and parts of the plastic strip (flyer) are accelerated and meet the pyrotechnic active mass arranged at a distance, whereby this is ignited by the pressure effect (shock wave) of the impacting plastic part becomes. The electrical energy supplied is thus initially converted into thermal energy and Pressure implemented, which in turn leads to a kinetic energy of the flyer, which this converts into pressure and heat when it hits the pyrotechnic active material. Due to this multiple energy conversion, however, considerable Efficiency losses, so that the voltage used for ignition is in the kV range must lie. The patent US 5,080,016 names the elements titanium, zirconium, Nickel and palladium are suitable metals for storing hydrogen accordingly.

In general, hydrogen storage in metal hydrides can also be regarded as known, however, which is mostly a negative effect on the strength of the metal (hydrogen disease) is undesirable. This effect can also be used for the targeted storage of Hydrogen can be used (see Bergmann / Schäfer: Textbook der Experimental Physics, Vol. 6 1992, p. 452 f.).

The object of the present invention is to develop a thin-layer ignition element, which can be ignited by a low initialization energy and this with the lowest possible loss of efficiency passes on to the pyrotechnic ignition compound. The thin-layer ignition element should also be simple and in large numbers be producible.

This object is achieved with the features of the first claim and by Method for manufacturing according to the features of claim 15 solved.

Characteristic of the present invention is the coupling of physical, chemical and thermal energy input from the hafnium hydride directly into the pyrotechnic active mass with significantly smaller amounts of initialization energy. In addition to ignition bridge layers made of hafnium, a mixture with titanium is also available Linking their positive properties.

Low-voltage voltages <50 V and an initialization energy in the range are sufficient a few millijoules to start the ignition. Essential for that Energy saving is the property of the hafnium hydride, which is already at a local temperature about 450 ° to 800 degrees Celsius, meanwhile one Melting temperature of about 1660 ° Celsius had to be applied. With increasing The proportion of hafnium increases with mixtures of hafnium and titanium hydride Decomposition temperature.

However, when the hafnium hydride or hafnium / titanium hydride mixture is decomposed atomic hydrogen released, resulting in a significant increase in pressure between Ignition bridge layer and pyrotechnic active mass leads. The atomic also works Hydrogen itself as an igniter (chemical reaction with oxygen and Constituents of the pyrotechnic active mass). It can also be used for training of a plasma.

The metallic component titanium, which is preferably used in a supplementary manner, can be used easy to master in terms of process technology and has the basic mode of operation, so that in addition to the effect of the reactive hydrogen released during the decomposition as well as the effect of the resulting plasma and the energy input by the heated metal atoms is high, which accelerates the ignition process.

The metallic component hafnium used is characterized by a higher specific atomic weight, so that in addition to the effect of the decomposition released reactive hydrogen as well as the effect of the resulting plasma also the energy input through the heavy metal atoms is particularly high, which Ignition process accelerated. More advantageous compared to other metal hydride layers is the high thermal stability with regard to the out diffusion of the hafnium hydride Hydrogen and the even higher compared to the already quite good titanium Decomposition temperature of the metal hydride layer, which has a favorable effect on the stability against thermal environmental influences and on the overall service life of the Ignition element affects.

This coupling of energy inputs leads to a very fast, in Ignition of the pyrotechnic active mass, which is at microsecond range almost all practical applications of ignition elements is extremely advantageous.

Due to the low ignition voltage and initialization energy, car batteries are sufficient etc. directly and without complex voltage amplifiers for power supply. Therefore, these ignition elements can be used particularly advantageously as igniters for airbags and other occupant protection devices are used.

The thermal insulation layer under the ignition bridge layer reduces energy losses through the heat dissipation into the carrier substrate and thus increases the direction of the pyrotechnic active mass flowing and thus effective amount of energy. By Variation of the structure geometry and in particular thickness of the thermal Insulation layer can therefore also the ignition time and the minimum required Ignition voltage can be influenced.

By using a semiconductor process compatible manufacturing process as well the use of a semiconductor substrate as a carrier substrate is the integration of Sensors for monitoring the functionality (e.g., moisture and Temperature sensors) as well as control and monitoring electronics in one microelectronic switching possible in the smallest space. circuit engineering Measures to protect the ignition element against high-frequency interference pulses and EMC influences can also be realized advantageously.

In order to minimize the contact resistance between the ignition bridge and the Ensuring contacts are first across from the ignition bridge layer the ignition bridge formed large-area contact surfaces and these as completely as possible touch the metallization layers of the contacts. In addition to the separation of the Metallization layer on the ignition bridge layer is also a face-down contact possible from interconnect areas integrated in the carrier substrate, the ignition bridge layer to contact from the opposite side. The ignition bridge layer can then on the carrier substrate surface or optionally also on the interposed structured metallization layer is deposited.

A spark plug layer between 0.2 and 2 µm allows for a specific one Resistance of the titanium hydride of approx. 0.50 µΩ m is a quite large surface area of the Ignition bridge and good variation possibilities by length and width of the ignition bridge in the preferred range of total electrical resistance of the ignition bridge layer of 0.5 to approx. 200 Ω.

The method required to manufacture an ignition element according to the invention is described in claim 11, in particular the opposite conventional tempering processes quite low temperature of about 350 ° Celsius is very advantageous for hydrogen storage. During the process time at lower temperatures (below 300 ° Celsius) rise significantly, higher temperatures Temperatures (over 400 ° Celsius) already the process of decomposition of the titanium hydride, so that the storage of hydrogen is not or only under considerably more difficult Process conditions (printing ect.) Becomes possible. With a high proportion of hafnium the Temperature strength.

In connection with this, the further training according to claim 13 should also be considered, after which the ignition bridge layer is cooled when the metallization layer is deposited so that the local temperature does not exceed 350 ° Celsius.

All manufacturing steps are compatible for manufacturing in semiconductor factories designed and can thus for a variety of igniter elements simultaneously can be realized by using a silicon wafer as the carrier substrate is sawn after all manufacturing steps.

The invention is described below with the aid of exemplary embodiments and associated ones Drawings explained in more detail.

Fig. 1

Anzündelement mit abgeschiedender und strukturierter Zündbrückenschicht (0,2<x<2) auf einem Trägersubstrat mit einer thermischen Isolationsschicht,

Fig.1a

als Draufsicht ohne Kontaktmetallisierung,

Fig.1b

als Draufsicht mit Kontaktmetallisierung und

Fig.1c

als Schnittdarstellung

Fig.2

Anzündelement mit abgeschiedender und strukturierter Zündbrückenschicht (0,2<x<2) auf einem Trägersubstrat mit einer thermischen Isolationsschicht,

Fig.2a

als Draufsicht ohne Kontaktmetallisierung,

Fig.2b

als Draufsicht mit Kontaktmetallisierung und

Fig.2c

als Schnittdarstellung

Fig.3

thermodynamisch wirksame Länge I und Breite b der Zündstruktur

Fig.4

Prinzipschaltbild des Zündstromkreises

Fig.5

Anzündelement mit abgeschiedender und strukturierter Zündbrückenschicht (0,2<x<2) auf einem Trägersubstrat ohne eine thermische Isolationsschicht und mit einer direkt aufgebrachten pyrotechnischen Wirkmasse

Fig.6

Anzündelement mit abgeschiedender und strukturierter Zündbrückenschicht (0,2<x<2) auf einem Trägersubstrat mit einer thermischen Isolationsschicht sowie mit einer in geringem Abstand aufgebrachten pyrotechnischen Wirkmasse

Figur 7

Anzündelement mit aus dem Trägersubstrat herausgeführten Kontaktierung der Zündbrückenschicht

Figur 8

Anzündelement mit einer Dämmschicht auf der Zündbrücke

Show it:

Fig. 1

Ignition element with a deposited and structured ignition bridge layer (0.2 <x <2) on a carrier substrate with a thermal insulation layer,

1a

as a top view without contact metallization,

1b shows

as a top view with contact metallization and

Figure 1C

as a sectional view

Fig.2

Ignition element with a deposited and structured ignition bridge layer (0.2 <x <2) on a carrier substrate with a thermal insulation layer,

2a

as a top view without contact metallization,

2b

as a top view with contact metallization and

Figure 2c

as a sectional view

Figure 3

thermodynamically effective length I and width b of the ignition structure

Figure 4

Block diagram of the ignition circuit

Figure 5

Ignition element with a deposited and structured ignition bridge layer (0.2 <x <2) on a carrier substrate without a thermal insulation layer and with a directly applied pyrotechnic active compound

Figure 6

Ignition element with a deposited and structured ignition bridge layer (0.2 <x <2) on a carrier substrate with a thermal insulation layer and with a pyrotechnic active compound applied at a short distance

Figure 7

Ignition element with contacting of the ignition bridge layer led out of the carrier substrate

Figure 8

Ignition element with an insulation layer on the ignition bridge

Of fundamental importance for all of the exemplary embodiments shown below is that all manufacturing steps and layers are compatible with semiconductor processes. It only one thin-film ignition element is shown; however, this is done with a A large number of identical ignition elements are realized on a semiconductor substrate wafer. In principle, however, it is also possible to use another one instead of one semiconductor substrate Carrier substrate, for example. To use a glass or ceramic surface. The representation of the Layer thicknesses, widths and lengths are schematic and not to scale.

FIG. 1 shows an ignition element with a deposited, structured and hydrogenated ignition bridge layer 2 made of hafnium hydride HfH _{x; (0.025 <x <2)} or a mixture of hafnium hydride with TiH _{x; (0.2 <x <2)} on a carrier substrate 4 with a thermal insulation layer 3.

In this exemplary embodiment, the thermal insulation layer 3 is designed as a closed epitaxially deposited SiO ₂ layer. In principle, however, this can also be produced by oxidation of a silicon substrate surface. In addition, other materials for thermal insulation are also suitable. It is essential for the function, however, that it is neither electrically short-circuited by the thermal insulation layer 3 nor by the carrier substrate 4, if the thermal insulation layer 3 is dispensed with.

The contact surfaces 21 (see FIG. 1a) of the ignition bridge layer are widened designed to have the lowest possible contact resistance to the To reach contacts 1. Accordingly, the contacts 1 as an Al layer or another layer made of a highly conductive material realized (see Fig.1b and Fig.1c) to facilitate contacting. The Dimensions of the contact surfaces 21 depend on the respective required contacting conditions. In Figure 1c, the Sequence of layers on average clearly, the variable thickness d of thermal insulation layer 3 the ignition timing and the at least required ignition voltage affects. Namely, the ignition bridge layer 2 flowed through by the current, so is the time to reach the critical decomposition temperature essentially from the thermal conductivity the insulation layer 3 dependent. Can a larger amount of heat flow off over the insulation layer 3 to the carrier substrate 4, so delayed the ignition point or a higher power must be implemented what a higher ignition voltage means.

As FIG. 2 shows as a second exemplary embodiment, the hafnium and / or Titanium hydride layer 2 also directly on the carrier substrate 4 be deposited if there is a delay in the ignition timing desired or the ignition voltage is selected to be correspondingly high and in addition, the carrier substrate is not electrically conductive. The contacts 1 are again on the structured ignition bridge layer 2 deposited (see. Fig. 2b and 2c).

FIG. 3 illustrates the ultimately effective surface of the ignition bridge layer 2. Also in this FIG. 3, a rectangular structure of the ignition bridge 2 with the effective length I and width b was selected. This structure is particularly easy to calculate theoretically using the known equations R = ρ I / A and P = U ² / R and is also easy to dimension in terms of production technology. The critical ignition properties, such as ignition times and ignition voltages can be adjusted.

Figure 4 shows the basic circuit diagram of the ignition circuit. The ignition takes place by applying an electrical voltage U in the low-voltage range to the metallized contacts 1. As a result of the onset of current flow there is a Joule heating of the ignition bridge 2, which then through their warming and chemical decomposition (Release of reactive hydrogen) and a plasma discharge Ignition process in the directly lying pvrotechnical active mass 5 (cf. Fig. 5) initiated. The hot metal atoms and the pressure lead to one widespread inflammation.

The arrangement of the pyrotechnic active mass 5 can on the one hand directly of the ignition bridge layer 2 (see FIG. 5) in addition to the hydrogen reaction and plasma effects also use direct heat conduction. Or it becomes an ignition bridge layer by means of distance-determining intermediate layers 6 2 realizes a small distance 7 (see FIG. 6) in order primarily to use the pure plasma effect.

Figure 7 now shows yet another embodiment in which the ignition bridge layer 2 in the area of the contact surfaces 21 from the lower one opposite pyrotechnic active mass is contacted. The Contacts 1 are embedded in the top of the carrier substrate, for example. Between contacts 1 and under the effective area of the ignition bridge layer 2, the thermal insulation layer 3 is provided, which the Ignition bridge layer 2 thermally and electrically from the carrier substrate 4 isolated. The carrier substrate points toward interconnect regions toward the contacts 1 4.1, which are made, for example, of highly doped carrier substrate material (Si). The two interconnect areas 4.1 are separated by an isolation trench 4.2 Carrier substrate 4 isolated from each other. Advantage of this embodiment is the omission of an Al layer and external connections to the Contacts. In addition, the contact between pyrotechnic Active mass and ignition bridge layer simplified and improved.

In addition to those described above and shown in the figures Embodiments are particularly other, for example circular configurations of the ignition bridge layer are conceivable.

In Figure 8, in turn, an embodiment of another Further development of the invention is shown, after which on the ignition bridge layer 2 in the effective area of the ignition bridge between contacts 1 an insulation layer 7 is deposited. Through such, for example Oxide material existing insulation layer 7 can the heating process of the ignition bridge layer to the temperature required for the decomposition a pressure increase can be accelerated. The thickness of the layer and its Structure (local tapering of the insulation layer 7 as a predetermined breaking point ect.) Is chosen so that after the release of the reactive hydrogen and the beginning of expansion, the insulation layer 7 at a previously defined Pressure opens and the hot hydrogen gas as well as the hot particles of the Ignition bridge layer and, if developing, the plasma on or in the pyrotechnic active mass 5 can reach.

Preferably, the insulation layer 7 is only so thick that it directly at Beginning of the reaction of the ignition bridge layer 2 is destroyed. The Insulation layer 7 can consist of a material or a sequence of layers exist in which at least the directly on the ignition bridge layer 2 lying must be electrically insulating so that the ignition bridge layer 2 is not bridged. A partial metal deposition as the top layer of the Insulation layer 7 is conceivable, however, because of the reflection on the metallized top layer the heat before the destruction of the insulation layer 7 is reflected back into the ignition bridge layer 2 and thus this heated faster.

Claims (19)

1. A thin-film ignition element for igniting pyrotechnically active materials (5) consisting of a carrier substrate (4) upon which two electrical contacts (1) are interconnected via a chemically and thermally active ignition bridge layer (2) which is ignited as a result of a voltage (U) being applied to the contacts (1) thereof, characterised in that the ignition bridge layer (2) is a hydrogenated layer of hafnium or a titanium-hafnium mixture.
2. A thin-film ignition element in accordance with Claim 1, characterised in that the ignition bridge layer (2) is ignited by means of a plasma discharge.
3. A thin-film ignition element in accordance with Claim 1 or 2, characterised in that a thermally insulating layer (3) is located below the ignition bridge layer (2) towards the carrier substrate (4).
4. A thin-film ignition element in accordance with any of the preceding Claims, characterised in that the contacts (1) are in the form of two metallised layers which make contact over a large surface area with contact surfaces (21) formed from the ignition bridge layer (2).
5. A thin-film ignition element in accordance with any of the preceding Claims, characterised in that the ignition time and the minimum necessary ignition voltage (U) are set directly by varying the structural geometry and by varying the thickness of the ignition bridge layer (2).
6. A thin-film ignition element in accordance with Claim 5, characterised in that the ignition bridge layer (2) has an approximately constant thickness of 0.2 to 2 µm.
7. A thin-film ignition element in accordance with any of the preceding Claims, characterised in that the ignition time and the minimum necessary ignition voltage (U) are set directly by varying the structural geometry and by varying the thickness of the thermally insulating layer (3) that is located below the ignition bridge layer (2).
8. A thin-film ignition element in accordance with Claim 7, characterised in that the thermally insulating layer (3) has an approximately constant thickness of 0.5 to 3 µm and consists of silicon oxide.
9. A thin-film ignition element in accordance with any of the preceding Claims, characterised in that, for the purposes of varying the ignition time and the minimum necessary ignition voltage, the structural geometry and the thickness of the ignition bridge layer (2) are set in such a manner that the ohmic resistance of the ignition bridge layer (2) amounts to between 0.5 and 200 Ω, and preferably approximately 20 Ω, and the area of the surface of the ignition bridge layer (2) towards the pyrotechnically active material (5) and the thermally insulating layer (3) amounts to between 25 and 100,000 µm².
10. A thin-film ignition element in accordance with any of the. preceding Claims, characterised in that the ignition bridge layer (2) consists of hafnium without a titanium component and in that the atomic compound ratio (x) of hydrogen/hafnium in the hydrogenated hafnium layer (Hf H_x) lies in the range 0.025 to 2.0.
11. A thin-film ignition element in accordance with Claim 10, characterised in that the percentile content of hydrogen in the hydrogenated hafnium layer lies in the range of 2.25 to 66.4 percent.
12. A thin-film ignition element in accordance with any of the preceding Claims 1 to 9, characterised in that the ignition bridge layer (2) consists of a hydrogenated hafnium-titanium mixture.
13. A thin-film ignition element in accordance with any of the preceding Claims, characterised in that a thermally and electrically insulating isolating layer (7) is applied to the ignition bridge layer (2) towards the pyrotechnic material (5), the material and structure of said isolating layer being such that it is destroyed when reaching a defined pressure by virtue of the reaction of the ignition bridge layer (2).
14. A thin-film ignition element in accordance with any of the preceding Claims, characterised in that the carrier substrate (4) is a semiconductor substrate having components integrated therein for controlling the ignition process, and the contact surfaces (21) of the ignition bridge layer (2) are connected to regions of conductive tracks (4.1) that are integrated in the carrier substrate (4).
15. A method of manufacturing a thin-film ignition element in accordance with any of the preceding Claims, characterised in that

    a) a layer of hafnium or of a titanium/hafnium mixture is initially deposited and is structured in correspondence with the selected structural geometry of the ignition bridge layer (2) and the contact surfaces (21), and

    b) hydrogen is then stored by means of a tempering process the temperature being preferably maintained at approximately 350° Celsius during the tempering process.
16. A method in accordance with Claim 15, characterised in that a micro-electronic circuit in the carrier substrate (4) and the thermally insulating layer (3) are initially implemented utilising a semiconductor process prior to the deposition of the hafnium or titanium/hafnium mixture.
17. A method in accordance with Claim 16, characterised in that, following the hydrogenation of the hafnium or titanium-hafnium mixture, an aluminium layer is deposited and is then structured as contacts (1) in correspondence with the shape of the contact surfaces (21) of the ignition bridge layer (2), the arrangement consisting of the carrier substrate (4) and the ignition bridge layer (2) preferably being locally cooled in such a manner that the temperature of the ignition bridge layer (2) remains below 350° Celsius.
18. A method in accordance with Claim 17, characterised in that a plurality of ignition elements are implemented on the carrier substrate (4) which is in the form of a silicon wafer.
19. The use of a thin-film ignition element in accordance with any of the Claims 1 to 14 as an igniter for occupant protection devices, and especially for airbags in motor vehicles.

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