Detonator, solid state type I film bridge

A solid state detonator is made using a silicon chip with appropriate surnding sections to provide the resistance path necessary to detonate a primary explosive. The chip is set on a metal-to-glass-to-metal header to provide uniformity of current and insulation capabilities. A gold mesh is used as a conductor connected to a chromium-silicon resistor film. This provides a uniform annular heating ring for detonation purposes. The silicon chip may be doped for high conductivity and low resistance. This arrangement provides fast function with moderate power pulses while the thermal design permits high no-fire current levels.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention is for electro-explosive devices. In particular, this 
invention is for electro-explosive devices with large area uniform 
detonation surfaces and high safety and reliability with fast response 
times. 
2. Description of the Prior Art 
Electro-explosive devices, EEDs, fall into one of two basic groups in 
current technology. The first group is electro-thermally initiated devices 
which respond to relatively low electrical energies. The second group is 
electro-shock initiated devices which include exploding wire and foil 
designs requiring very high energy levels. 
The shock initiated devices have the advantages of very fast and repeatable 
function times and very high resistance to inadvertent initiation. The 
greatest disadvantage of the second group of EEDs is the large and 
expensive electrical systems required to initiate them. The 
electro-thermally initiated group, while operating at much lower input 
energy requirements, have not matched the inherent input safety 
characteristics or response time of the shock initiated group. Typical 
response times for the thermally initiated group range from about 10 
microseconds to several milliseconds, while the shock initiated EEDs 
function in less than one microsecond. 
In order to obtain environmental tolerance with long shelf-life for 
military and aerospace systems, both types are usually designed with 
hermetically sealed housings. These additional requirements plus those of 
ensuring adequate safety in handling and system assembly require that the 
thermally initiated group be able to withstand reasonable unintended 
currents without firing. This problem does not arise in the shock 
initiated EED group because the currents required for firing are typically 
several thousand amps. However, thermally initiated designs have problems 
with this respect since any current will produce some heating of the 
bridgewire and most designs have limited capability to conduct this heat 
away from the thermally sensitive primary explosive. The previous approach 
to achieve no-fire currents above a few hundred milliamps is to use a 
large diameter bridgewire and thermally conductive header dielectrics. 
This tends to extend function time for many applications and frequently 
becomes the unacceptable limit. Thus, there is a need for hermetic header 
designs which permit high no-fire currents in combination with very fast 
function times for reasonable firing currents representative of 
traditional hot-wire EEDs. Ideally, a new device capable of no-fire 
currents above one amp at one watt with function times of approximately 
one microsecond at current levels of twenty amps is desired. None of the 
previous detonators in either group satisfy these requirements. 
SUMMARY OF THE INVENTION 
The present invention uses a metal-to-glass-to-metal header as a base 
support. This metal-to-glass-to-metal header amounts to having a metal pin 
within a glass tube within a metal sleeve. The pin part of the header is 
connected to a conductive material such as gold mesh which in turn is 
electrically connected to a resistive film. Because of the circular 
symmetry of the metal-to-glass-to-metal header the resistive film can form 
a ring connected through the middle by the conductive pad to the metal 
pin. The resistor film is mounted on a silicon chip. The appropriate metal 
bridge is connected to the metal sleeve of the header. When a power supply 
is connected across the metal sleeve and metal pin a current path is 
formed which passes through the silicon chip with its resistor film. 
Because of the circular symmetry the complete resistive film ring is 
permitted to heat providing a large surface area for the primary explosive 
to be packed against. The large surface in effect permits spurious low 
level currents to generate heat which is absorbed by the silicon chip and 
the primary explosive over a relatively diffuse area. Thus, typical low 
level currents will generate far less heat per volume into the primary 
explosive than in previous models. By the same token, when sufficient heat 
due to a high enough current is produced in the resistor film a much 
larger surface area of primary explosive is receiving this heat thus 
producing more reliability in the triggering of the detonation.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The FIGURE shows the present invention in side view with a header 10. 
Header 10 is comprised of a pin 12, a ring 14, which can be considered a 
glass tube surrounding pin 12, and a sleeve 16 which in turn surrounds 
ring 14. Ring 14 serves as an insulator between pin 12 and sleeve 16. 
Surrounding sleeve 16 is a ring 18. Ring 18 forms a cup to hold explosive. 
Ring 18 and sleeve 16 can be made of stainless steel or other highly 
conductive metal combinations. Current in lead 20 is provided by a power 
source 22 which in turn is connected to pin 12. Power source 22 can be a 
battery or other source of electrical current. Obviously a current will 
flow whenever a conductive path is present between sleeve 16 and pin 12. 
A solid state bridge is connected between sleeve 16 and pin 12 via a 
silicon chip 24 which has a thickness determined by mechanical, thermal, 
and electrical constraints. Chip 24 may be made of various materials other 
than silicon which will readily conduct an electric current. Chip 24 may 
be doped to provide desired semiconductor current limitations. Chip 24 is 
usually doped for high conductivity level and low resistance. Deposited 
around chip 24 is an insulating layer 26, such as SiO.sub.2. Header 10 is 
polished prior to attaching chip 24. As shown in the FIGURE, the layer's 
thickness as compared to the thickness of the chip itself are not drawn to 
scale. Holding silicon chip 24 to sleeve 16 is a conducting material 28 
which can also contact ring 18 as shown. Conductive material 28 can be a 
gold glass frit or thick gold film which transmits electrical current from 
metal sleeve 16. To isolate the electrical path, an insulating ring 30, 
which can also be silicon dioxide, SiO.sub.2, serves as an insulating 
coating on silicon chip 24 similar to insulating layer 26. Current passes 
from conductive material 28 through silicon chip 24 to a resistor film 
bridge 32 which can be a chromium-silicon, CrSi, composite material or 
some other appropriate resistor material. Current passes through this 
resistor film but due to the increased resistance inherent in the material 
a heating effect is caused throughout resistor film bridge 32. Insulating 
layer 26 and insulating ring 30 may be deposited as a single coating with 
openings etched in each side of the SiO.sub.2. 
Resistor film bridge 32 is connected to a conductive cap 34 via a 
metallurgical joint 36. Conductive cap 34 may be a gold mesh and 
metallurgical joint 36 can be a solid gold pad. A protective layer 38, 
such as silicon dioxide, SiO.sub.2, or other material that is corrosion 
resistant, is placed over resistor film 32. Protective layer 38 also 
serves as a conducting layer for heat generated in resistor film 32. 
Protective layer 38 provides corrosion protection because it is inert and 
prevents the explosive from reacting with a metal surface. Primary 
explosive 40 is packed within ring 18 on top of protective layer 38 and 
conductive cap 34 to fill in the top of this detonator. 
Because of the circular symmetry involved, resistor film bridge 32 is an 
annular ring. The large amount of surface area permits relatively low 
currents to dissipate their heat over a wide surface area producing very 
little heat absorption by primary explosive 40 per unit volume. Primary 
explosive 40 may be lead azide or some other suitable compound. Thus, the 
low current problem of earlier thermal detonators is avoided due to the 
large increase in surface area which permits the actual heat caused by the 
spurious current to be dissipated due to its thermal dissipation 
characteristics. However, when the normal detonating current is present in 
resistor film bridge 32, adequate heat is generated such that a large 
detonating surface area in primary explosive 40 is created which is a far 
greater working surface area than anything previously used in a thermal 
initiated detonator. As a result of this, far more energy is transferred 
with a greater efficiency which permits significantly reduced reaction 
times. 
Conductive cap 34 is electrically connected to pin 12 via a frit filled 
hole 42 which permits electrical contact between connective cap 34 and pin 
12. A seal 44, which can be a glass frit, is placed across ring 14 to 
assure a mechanical support, a thermal path, and an insulating boundary 
between sleeve 16 and pin 12 except for a current path which goes through 
silicon chip 24, resistor film bridge 32, metallurgical joint 36 and 
conductive cap 34. Thus, a series electrical circuit is formed by power 
source 22, sleeve 16, conductive material 28, chip 24, resistor film 
bridge 32, pads 36 and cap 34, and pin 12. A switch, not shown, to be 
closed at a predetermined time for the circuit to be active, is added in 
series with power source 22 and sleeve 16. 
This invention replaces the wire bridge of traditional EEDs with a 
deposited metallic film bridge. Unlike other film bridge detonators, there 
is no requirement for extremely fine polishing of the header surface. This 
is due to the film not being deposited directly on the header. 
Construction techniques made feasible by the use of silicon substrate also 
permit a major advantage in this invention. It can be readily arranged 
that the metallic bridge be thermally clamped to the header structure in a 
way very advantageous to conduct heat generated by inadvertent currents 
away from the primary explosive. By interposing between the bridge and the 
substrate a very thin film of much less thermally conductive silicon 
dioxide, no more than a negligible fraction of the heat from an intended 
firing pulse will be conducted away into the header before ignition 
occurs. Yet when considering the lower levels and much longer time 
duration of an inadvertent or stray current, after the first few 
microseconds of application, the thin insulating film will not present a 
barrier to conducting the generated heat away from the header. Most of 
this heat due to stray currents is conducted away via the thin film into 
the chip and then into the leads. Thus, lower energy density is conducted 
safely away while higher energy densities cause ignition. 
Among the several advantages of this invention are the very fast function 
times attainable with moderate firing energies while still able to absorb 
unusually large stray currents without firing. Ease in production due to 
uniform resistance of bridges and improved hermetic seal permit use of 
modern solid state technology for most critical features. 
It is obvious to those skilled in the art that modifications to the above 
device can be made.