Virendra kumar*1, Shrihari Shinde2, H. Muthurajan2, SK Nema1

1Armament Research and Development Establishment, Pashan, Pune – 411 0212National Centre for Nanoscience& Nanotechnology, University of Mumbai, Mumbai – 400098

Abstract:

Electro explosive devices are widely used in both civil and military sectors. In the air-force

arena electro explosive devices are extensively used in precision-guided weapons which are

facing one shot/one kill requirements, like canopy surveillance system for pilot ejection, seat

ejection system of fighter aircraft, parachute release mechanism, air to air missiles, air to

surface missiles, cluster bomb systems, cable cutter for fast release mechanism of fighter

aircraft etc. Armament Research and Development Establishment has successfully developed

Semiconductor bridge (SCB) Detonator MK-I and Micro Electric Detonator MK-I , both of

which are in regular production. Semiconductor bridge (SCB) detonator/ igniters are widely

used as electro explosive device (EED) for the initiation of explosives and propellants in

advanced ammunitions due to its most excellent performance, low all-fire energy (requires

small quantities of electrical energy to function), fast function time (few micro sec), less

weight, small volume, low cost, immunity to EMI (Electro-magnetic interference), ESD

(Electrostatic discharge) and RF (Radio Frequency) hazards. In this paper we are presenting

the extensive electrical, optical and electron microscopy characterization of Semiconductor

bridge done at our laboratory. The stray voltage immunity as per military standard has been

tested for the Semiconductor bridge (SCB) Detonator developed by ARDE and the firing

voltage level of SCB for different capacitance of Capacitor Discharge Unit (CDU) developed

indigenously is discussed in the manuscript. The paper also briefly presents plan of

developing SCB based Slapper detonator for Electronic safety and arming for missiles.

Key words: Electro explosive devices, Semiconductor bridge igniter/ detonator.

For presentation in “International Conference on Strategies for Indigenous development of

Civil & Fighter Aircrafts” during 16-17 Sep 2014, at Hyderabad (India)

* All correspondences be mailed to dvkverma25@gmail.com , Mobile - + 91 9422513480

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Semiconductor Bridge (SCB) based highly reliable, safe and ultra-fast initiator for

fighter aircrafts and advanced armaments

SCB Detonator Mk-I

1. INTRODUCTION

The semiconductor bridge is an enabling technology which has not only changed the performance capabilities of initiators but also impacted the overall architecture of ordnance initiation systems. Semiconductor Bridge (SCB) is an advanced device which is used for ignition [1] of high energy materials such as explosives, thermite & pyro compositions. It is widely used in military and civilian fields because of its excellent properties. Advantages of SCB technology are low ignition energy, fast functioning, small size & mass, process consistency, readiness of incorporation into digital logical circuits. A typical SCB device consists of H shaped thin poly-silicon layer on SiO2 layer and two metal lands for electrical contact lying over the outer legs of the H shaped film[2]. The ‘H’ shaped polysilicon layer is highly doped with phosphorus or boron impurities to achieve 1 bridge resistance [2] The length of the bridge (e.g. 100 µm) is determined by the spacing of the aluminum lands. Typically the doped polysilicon layer is 2 µm thick, and the bridge is 380 µm wide. The H lands provide a low ohmic contact to the underlying doped layer. Typically SCB chips are fabricated on substrates such as silicon wafer or Silicon on Sapphire(SOS) film or Sapphire wafer. But despite the low energy for ignition, the substrate provides a reliable heat sink for excellent no-fire levels. The top view and cut sectional view of a typical SCB structure is shown in figure 1.

Electrical wires such as gold or aluminum wire having diameter in the range of 3 mil to 5 mil ultrasonically bonded to the lands permit a current pulse to flow from land to land through the bridge. The current pulse through the SCB causes it to burst into a bright plasma discharge that heats the energetic powder pressed or slurry against it by a convective heat transfer process that is both rapid and efficient. Consequently, SCB devices operate at very low energies and function very quickly as compared to traditional bridge wire based devises.

In view of this Armament Research and Development Establishment (ARDE) has developed SCB based detonators [4-5]. The photograph and Specifications of SCB detonator Mk-I and Micro Electric Detonator developed by ARDE are shown below

Size : Dia 8.6mm, Height 10.0 mm Shape : Cylindrical No Fire Current : 1A/1W for 5 Min All Fire Current DC : 1200mA All Fire Current AC : 14A, 2 μS Pulse All Fire Energy : 3 – 5 mJ Functioning Delay : < 60 μS

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Figure 1. Top view & Cut Section View of SCB Chip

Specifications of SCB Detonator Mk-I

Figure 2. SEM of Dual Chip SCB

2. CHARACTERIZATION OF SCB

In order to meet the advanced detonator supply demand in India, Armament Research and Development Establishment (ARDE) has indigenously designed and developed a most reliable & highly safe Semiconductor Bridge (SCB) detonator. The indigenously developed SCB detonator has undergone environmental test as per Mil Std 331B and life assessment trials have also been conducted as per ISAT B. Few of the characterization of SCB done at our lab are described briefly in the subsequent paragraph.

2.1 Scanning Electron Microscopy

The Scanning Electron Microscope image of dual chip SCB is obtained using FEI-Quanta250. The figure 2 shows the SEM image of dual chip SCB. These chips are independently connected to the conducting wire for electrical connection. The conducting wires are ultrasonically bonded to aluminuam pad. Electrical signal is passed thourgh these conducting wires to bridge for the characterization of SCB. This dual chip SCB assembly is mounted on ceramic header.In the SEM image (figure 2), we are able to view the epoxy which bind the SCB chip well with the ceramic header.

2.2 Stray Voltage Immunity

Characterization and installation by manual handling of SCB is necessary, as human produce stray voltage which may cause SCB to misfire, to validate the reliability of SCB there is need to check the immunity of SCB to stray voltage produced by Human. As per military standard Mil-DTL-23659F (June 2010) stray voltage immunity for igniters can be

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Micro Electric Detonator (MED)

tested in the laboratory by injecting 2000 pulses of 100mA constant current with 300ms of ON pulse width and 200ms of OFF pulse width.

The SCB developed by ARDE has been tested for stray voltage test as per military standard. After testing SCB it is experimentally observed that SCB is immune to stray voltage signal. During the stray voltage immunity test, the voltage across the SCB igniter is continuously monitored.

2.3 Testing of SCB using CDU

The SCB is tested with different capacitors to find optimum charging voltage and corresponding energy required by SCB to function reliably. The capacitors used for the experiments are 10μF, 47μF and 100μF. The10μF capacitor is charged for 28V using constant voltage source KEITHLEY2440 and 28V charged capacitor is discharged through 0.01Ω current viewing resistor (CVR) and semiconductor bridge (SCB). The results of SCB firing energy for different capacitors are tabulated in table 1. The discharging profiles are obtained by connecting digital storage oscilloscope (DSO) across CVR and SCB.

Table 1. SCB firing Energy for different capacitors

Sr. no

SCB resistance

Capacitor Charging Voltage

Energy stored in Capacitor

Energy through SCB

1 1.08 10 µF 28 V 3.92 mJ 1.5 mJ2 1.07 47 µF 16 V 6.016 mJ 2.23 mJ3 1.08 100 µF 14 V 16.2 mJ 3.29 mJ

2.4CDU characteristics of SCB

The current and voltage data shown in figure 3 is obtained by firing SCB using 10µF capacitor with 28V charging voltage. Current flowing through SCB is recorded by connecting current viewing resistor in series with SCB and voltage is recorded across SCB directly. This recorded current and voltage data is plotted versus time and shown in figure 3.

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Figure 3. Current & Voltage Vs Time

From figure 3 it is evident that instant rise in voltage and fall in current is at 0.9 µs (900 nano seconds). This point corresponds to vaporization of Semiconductor Bridge and time at which this occurs is denoted by burst time. For predicting the start of vaporization of SCB, the burst time is defined as time of the beginning of the current drop.

The behavior of SCB is modeled on the assumption that resistance is the unique function of energy delivered to SCB and given by.

E=∫0

t

VIdt (1)

Here, V is the voltage across SCB leads, I is current through the SCB, t is the time.

SCB resistance can be simply written using current and voltage graph as

R=∫0

t

V /I (2)

This is the classic data for the characterization of SCB. When fully charged capacitor is used to discharge through SCB the silicon material in SCB passes through various stages Extrinsic Conduction, Intrinsic conduction, Melting of bridge & Vaporization

We observed from figure 3 that burst occurs at about 1.25 mJ and resistance at burst time is 1.2 Ω. We note that initial energy stored in capacitor is 3.92 mJ which is much more than required to vaporize the bridge; hence we conclude that there is some energy loss.

The figure 4 shows resistance versus time plot. From figure 9 it is clear that there are 2 peaks in the value of resistance. The first peak in SCB resistance about 2.24 Ω is observed at about 5.04 µs and second peak is observed at 22.9 µs having peak resistance about 3.688 Ω.

Hence the behavior of SCB resistance is somewhat complicated. To simplify the characterization of SCB we have used Origin 8 data analysis software from Microcal Software. Origin software has smoothened data for current, voltage, resistance and energy as shown in figure 3, and 4. Here smoothening technique we have used is “Adjacent-Averaging” having 10 point of window and no boundary condition.

3. SCB BASED SLAPPER DETONATORS

Slapper detonators have been used since the early 1980 as a safe and reliable method of initiating insensitive explosive material in the first stage of an explosive chain. However, it requires very high energy, high voltage to trigger the system and more space. In recent years the desire to reduce the size, cost and mass of the Fire set has driven the investigation of

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Figure 4. Resistance Vs Time Plot

lower-energy slapper initiators which can reliably, safely and precisely operate at reduced firing voltages. The semiconductor bridge (SCB) is an enabling technology which will drastically reduce the high energy requirement and still maintain the safe & reliable ignition of slapper detonator. ARDE is developing SCB based slapper detonators.

4. CONCLUSION

The scanning electron microscopy image shows the independent electrical connection of conducting wire to aluminum pads for dual chip SCB mounted on Ceramic header. The experimental observation shows that the SCB designed and developed by ARDE is immune to stray voltage disturbances and it is reliable to use in stray voltage environment. The SCB can be effectively fired using different capacitors. The experimental result shows that SCB can be faithfully fired using 10μF, 47μF and 100μF with charging voltage of 28V, 16V and 14V respectively. As capacitor discharges across SCB large amount of current will flow through SCB and that is useful for quick triggering of SCB. The characterization details for CDU show that energy require to fire SCB with charging voltage of 28V and charging capacitor of 10μF is ~1.25mJ. The time require to produce plasma from bridge is ~5.04μs. These experimental results prove that SCB is fast to operate and requires less energy to function it effectively. The maximum resistance observed experimentally while firing SCB using CDU is ~3.88Ω.

ACKNOWLEDGMENTAuthors are highly grateful to Dr. KM Rajan, Director, Armament Research &

Development Establishment, Pashan, Pune for permission to publish this paper. Authors are also grateful to Shri Kapil Deo, Associate Director for constant encouragement& guidance during the course of this work.

REFERENCE

1. R. W. Bickes, Jr., “Smart Semiconductor Bridge (SCB) Igniter for Explosives,” in 3rd Canadian Symp. on Mining Automation, Montreal, Quebec, September 14–16, 1988.

2. J. D. Kim, Modeling of the current density distribution in a heavily doped semiconductor bridge, International Journal of Electronics, Vol. 80, No. 5, 623-628 (1996)

3. D. Marx, R. W. Bickes, Jr., and D. E. Wackerbarth, Characterization and Electrical Modeling of Semiconductor Bridges UC-706 Sandia Report SAND97-8246 · UC–706 Unlimited Release Printed March 1997

4. Virendra Kumar, Semiconductor Bridge (SCB) detonator and its applications, 8th National Seminar & Exhibition on Aerospace Related Mechanisms at ARDE during 06 – 08 Dec 2012

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5. Virendra Kumar, A P Agrawal, H Muthurajan, and J P Agrawal, Synthesis and Characterization of BNCP: A Novel DDT Explosive, proceedings of ‘4th National Symposium in Chemistry’ at National Chemical Laboratory, Pune, 1-3 Feb 2002

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