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832 JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 17, NO. 4, AUGUST 2008

A Nano Initiator Realized by IntegratingAl/CuO-Based Nanoenergetic Materials

With a Au/Pt/Cr MicroheaterKaili Zhang, Carole Rossi, Marine Petrantoni, and Nicolas Mauran

Abstract—A nano initiator is developed by integrating Al/CuO-based nanoenergetic materials with a Au/Pt/Cr thin-film micro-heater realized onto a glass substrate. It is fabricated by usingstandard microsystem techniques that allow batch fabricationand high level of integration and reliability. The nano initiator ischaracterized by open-air combustion testing with an ignition suc-cess rate of 98%. The ejected combustion flame is seen clearly witha potential exceeding 2000 ◦C. The ignition power, ignition delay,and ignition energy are 1.16 W, 0.1–0.6 ms, and 0.12–0.70 mJ,

respectively. The energy output is calculated to be around60 mJ. [2008-0035]

Index Terms—Al/CuO, energetic material, heater, initiator,micro, nano.

I. INTRODUCTION

AN ELECTROPYROTECHNIC (or explosive) initiator

that is activated by the application of electrical energy is

used to initiate an explosive, burning, electrical, or mechanical

train. Electropyrotechnic initiators have found numerous civil-

ian and military applications such as triggering the inflation of

airbags in automobiles [1], [2], micropropulsion systems for

microsatellites [3]–[5], arm fire and safe-and-arm devices usedin missiles, rockets, and the like apparatus [6], and many other

ordnance systems [7]. Traditional electropyrotechnic initiators

use a bridgewire to initiate the subsequent reactions, which is

not suitable for batch fabrication and high level of integration.

Nowadays, electropyrotechnic initiators employ a semiconduc-

tor bridge (SCB) instead of a bridgewire [7]–[9]. Although the

performances are greatly improved, there are still some prob-

lems remaining such as not very high reliability, not very good

intimate contact between the SCB and the attached reactive ma-

terials, and smaller output energy compared with input energy.

Recently, nanoenergetic materials (nEMs) have received

steadily growing interests because of their improved perfor-mances in terms of energy release, ignition, and mechanical

properties compared with their bulk or micro counterparts

[10]–[18]. However, there are very few studies in the literature

to utilize nEMs in order to realize functional devices, although

this is very interesting for the practical applications of nEMs.

Manuscript received February 12, 2008. First published June 24, 2008; lastpublished August 1, 2008 (projected). Subject Editor R. Syms.

The authors are with the Laboratory for Analysis and Architecture of the Systems, French National Center for Scientific Research (CNRS), 31077Toulouse Cedex 4, France (e-mail: [email protected]; [email protected]).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/JMEMS.2008.926144

In this paper, an electropyrotechnic nano initiator is developed

by integrating Al/CuO-based nEMs with a Au/Pt/Cr thin-film

microheater realized onto a Pyrex 7740 glass substrate due to

its much lower thermal conductivity (1.18 W/mK) compared

to that of silicon substrate (141.2 W/mK). The nano initiator

is able to partially solve the problems mentioned previously.

First, the nano initiator is fabricated with standard microsystem

techniques that allow mass production and high level of inte-

gration and reliability. Second, the exothermic reaction of the

nEMs produces high-temperature products, which discharge to

a distance of several millimeters or more. The ejected products

can ignite the attached reactive materials even if the initiator

makes no physical contact to the reactive materials. Third, the

nano initiator is able to generate much more output energy than

input energy.

II. FABRICATION PROCESS AND RESULTS

The process flow of the fabrication is shown in Fig. 1. The

process starts with a 500-µm-thick double-polished 4-in Pyrex

7740 glass substrate. The substrate is cleaned by using acetoneand chromic sulfuric acid mixture (RT2), thoroughly rinsed by

deionized (DI) water, and blow dried by nitrogen. Then, the

substrate is placed into an oven at 200 ◦C for 20 min for further

drying. Positive photoresist is spin coated onto the Pyrex

glass substrate and patterned using photolithography through

a designed mask-1. The resist is exposed twice to generate a

reentrant profile. Metal films of Cr/Pt/Au with thicknesses of

20/120/800 nm are deposited by e-beam evaporation. The Cr

film acts as the adhesion layer between Pt and substrate. The Pt

film serves as the resistor, and the Au film acts as both the con-

ductor and contact pad. Metal Cr/Pt/Au liftoff is performed in

acetone with ultrasonic for 30 min. After solvent and DI watercleaning, the Pyrex glass substrate with Cr/Pt/Au metals is spin

coated with resist and patterned using photolithography by a

mask-2. After the developed resist is removed, the substrate is

put into the Au etchant. The Au in the designed area is removed,

and the Pt is exposed as the resistor. The fabricated Au/Pt/Cr

microheater on the glass substrate is shown in Fig. 2(a). The

zigzag geometry is used for the microheater because it is the

most widely employed geometry for microheater-based devices

in both commercial products and research.

A SiO2 layer with a thickness of 300 nm is deposited onto the

glass substrate by plasma-enhanced chemical vapor deposition

(PECVD). Resist is spin coated and patterned using a mask-3.

1057-7157/$25.00 © 2008 IEEE



ZHANG et al.: NANO INITIATOR REALIZED BY INTEGRATING Al/CuO-BASED nEMs WITH A MICROHEATER 833

Fig. 1. Fabrication process flow.

After removing the developed resist, the SiO2 layer that is not

covered by the resist is etched by a buffer HF solution. The

SiO2 layer is used to protect the microheater and to prevent thepotential short circuit in the following process. A 30-nm-thick

Ti thin film is then deposited onto the glass substrate, followed

by a 50-nm Cu thin-film deposition by thermal evaporation,

where the Ti film serves as the adhesion layer between Cu and

Au/Pt/Cr/glass, and the 50-nm Cu film acts as the electrical

conducting layer for the subsequent electroplating. The Cu film

with a thickness of 1 µm is then deposited by electroplating.

The substrate with Cu/Ti films is spin coated with resist and pat-

terned using photolithography by a mask-4. After the developed

resist is removed, the substrate is first put into a solution with

10-ml H2O2, 10-ml HCl, and 80-ml H2O to etch the exposed Cu

film, and then, it is put into a buffer HF solution to remove theuncovered Ti film. After this stage, the substrate with the micro-

heater, SiO2 layer, and patterned Cu film is shown in Fig. 2(b).

The glass substrate is then cleaned for 20 s in a solution

containing 10-ml HCl (37%) and 120-ml DI water to remove

the natural copper oxide formed on the Cu film surface. After

being rinsed with DI water and blow dried by N2, the substrate

is placed onto a clean silicon wafer that is put onto a quartz boat.

The quartz boat is positioned into a quartz tube that is mounted

inside a horizontal tube furnace. The substrate is then heated

in the furnace under static air at 450 ◦C for 5 h. After the heat

treatment, the color of the film is changed into black, as shown

in Fig. 2(c). During the thermal treatment, CuO nanowires grow

from the Cu thin film, as can be seen from a scanning electronmicroscopy (SEM) image in Fig. 2(d).

A 4-in double-polished silicon wafer is spin coated with

photoresist with a thickness of 10 µm and patterned using

photolithography with a mask-5. After developing the resist, the

exposed silicon wafer is etched through using deep reactive ion

etching. The silicon wafer with holes is employed as the shadow

mask for the subsequent Al deposition. Al is deposited by ther-

mal evaporation onto the glass substrate with CuO nanowires,as shown in Fig. 2(e). The deposited thickness (on average

across the substrate) of Al is set to be 1.12 µm in the thermal

evaporator. Fig. 2(f) shows the SEM image for the nanowires

after Al deposition. The SiO2 layer deposited by PECVD in

the previous step is critical to the initiator. As can be seen in

Fig. 2(e), if there was no SiO2 layer, the deposited Al (a good

conductor) will connect Pt directly, resulting in short circuit.

III. OPE N-A IR COMBUSTION TESTING

Open-air combustion testing of the nano initiator is achieved

by inputting a current to the Pt resistor through the Au contact

pads. Fig. 3 shows the optical images of two igniting samples.

After the ignition, the reaction is accompanied by a bright flash

of light, and the ejected products can be clearly seen from the

images. The high flame temperature is consistent with the large

energy release. The flame temperature in our samples may be

compared with the reported “adiabatic flame temperature” of

about 2570 ◦C for the reactions of Al and CuO/Cu2O [19].

For actual air bags in automobiles, micropropulsion systems,

and many ordnance systems, even if there is a gap (no contact)

between the initiator and the reactive material, the gap will

be very small. The small gap can be readily penetrated by

the ejected high-temperature products, as shown in Fig. 3.

However, for the bridgewire and SCB based initiators, if a smallgap exists between igniter and reactive material, the ignition of

the devices may fail due to the requirement of intimate contact

between igniter and reactive material [1]–[6], [8], and [9].

The Cu thin film is converted into bicrystal CuO nanowires

and CuO/Cu2O thin film after the thermal annealing at 450 ◦C

for 5 h in static air [17]. After Al deposition, nano Al is inte-

grated with CuO nanowires to form a core-shell nanostructure

and also deposited onto the CuO/Cu2O thin film under the

nanowires to form a layered structure. The exothermic reaction

of the Al/CuO-based nEM has been characterized by using dif-

ferential thermal analysis (DTA), as shown in Fig. 4 [17]. There

are two major exotherms associated with the thermite reaction.The first exotherm is observed with an onset temperature of

about 500 ◦C, which means that nEM reacts prior to the melting

of Al. This suggests that the first exotherm is caused by the

thermite reaction between the CuO nanowires and nano Al.

The reaction is based on the solid–solid diffusion mechanism.

The second exotherm is found with an onset temperature of

around 720 ◦C. After melting, the remaining Al reacts with the

CuO/Cu2O thin film beneath the CuO nanowires. Therefore,

the ignition temperature is estimated to be around 500 ◦C.

Fig. 5(a) shows an image of the nano initiator after com-

bustion. Part of the Pt heater covered by nEMs is exposed

again because some of the combustion products are ejected

from the heater. Fig. 5(b) shows the SEM image of some of the combustion products. Nanoparticles with average sizes of




Fig. 2. Optic and SEM images of the fabrication results. (a) Au/Pt/Cr microheater. (b) Patterned SiO2 and Cu films. (c) and (d) CuO nanowires.(e) and (f) Al/CuO nEMs.

Fig. 3. Optic images of the combustion flame.

10–50 nm are formed after the combustion due to the highly

energetic impact of the combustion wave and the high lo-

cal temperature generated. The combustion reaction between

nano Al and CuO nanowires may also be called “nano-

explosion” process, which has been used to synthesize a wide

range of multimetal oxide ceramic and metal–ceramic com-

posite nanopowders, with precise stoichiometries and uniformmorphologies [20].

Fig. 4. DTA plot of the Al/CuO-based nEM. Reproduced with permissionfrom [17]. Copyright 2007 American Institute of Physics.

IV. OPE N-A IR IGNITION POWER, IGNITION DELAY,

IGNITION ENERGY, AN D ENERGY OUTPUT

Ignition power, ignition delay, ignition energy, and energy

release are important parameters for the practical applicationsof the Al/CuO-based nEM initiator. A setup is built to determine



ZHANG et al.: NANO INITIATOR REALIZED BY INTEGRATING Al/CuO-BASED nEMs WITH A MICROHEATER 835

Fig. 5. Optic and SEM images of the combustion products.

Fig. 6. Current variation with time.

these parameters. Basically, the setup inputs a voltage to the Ptheater through the Au contact pads with a current limitation of

0.35 A. The voltage and current variations with time are re-

corded simultaneously by a digital oscilloscope. The duration

of the voltage-source power supply is set as 0.1 s. All the

devices are controlled by a computer through user interface

software.

Figs. 6 and 7 show the current and voltage variations as a

function of time for one typical sample, respectively. After the

voltage supply is triggered, the current reaches 0.35 A rapidly,

whereas the voltage increases and keeps a relatively constant

value of 3.3 V due to the current limitation. At 0.2 ms, the

thermite reaction between nano Al and CuO nanowires starts.The released heat causes the increase of the Pt resistance,

which results in the decrease of the current. At 0.24 ms, the

reaction of Al/CuO/Cu2O occurs, resulting in a further sharp

decrease of the current due to the highly energetic impact of

the combustion wave and the extremely high local temperature

generated. Consequently, the ignition power, ignition delay, and

ignition energy can be conveniently derived from the curves in

Figs. 6 and 7.

Fifty samples from the first fabrication batch were tested

under the same conditions, and one of them was not ignited.

Therefore, the ignition success rate is estimated as 98%. The ig-

nition power, ignition delay, and ignition energy are determined

as 1.16± 0.13 W, 0.1–0.6 ms, and 0.12–0.70 mJ, respectively.More precise control of the micro-/nanofabrication process is

Fig. 7. Voltage variation with time.

needed to improve the ignition repeatability and uniformity.

The heat release of the thermite reaction of the Al/CuO-based

nEMs has been roughly determined as 2950 J/g by using DTA

(see Fig. 4) and differential scanning calorimetry experiments

in [17]. For one nano initiator, the Cu surface area is 1.2 ×

1.2 mm, and the deposited Cu and Al thicknesses are 1 and

1.12 µm, respectively. Therefore, the mass of the Al/CuO-based

energetic materials is estimated to be 2.043× 10−5 g. As a

result, the energy output is roughly determined as 60 mJ. The

energy output can be further increased without changing the

ignition energy by several ways such as increasing the mass

of the deposited materials, annealing Cu for longer time or

under a N2/O2 gas flow to obtain pure CuO, and tuning the

Al deposition to reach a stoichiometric reaction [17], [21].

V. CONCLUSION

Al/CuO-based nEMs are integrated with a Au/Pt/Cr thin-

film microheater realized onto a Pyrex 7740 glass substrate to

achieve a nano initiator. The nano initiator is fabricated by using

standard microsystem technologies and simple nanofabrication,

which are suitable for batch fabrication and high level of inte-

gration. Combustion of the nEMs is accompanied by a brightflash of light, which is due to the high reaction temperature with




a potential of more than 2000 ◦C. The ejected high-temperature

products can ensure the successful ignition of the attached

reactive materials even if the contact between the nano initiator

and the reactive materials is not very intimate. The ignition

power, ignition delay, and ignition energy are determined as

1.16± 0.13 W, 0.1–0.6 ms, and 0.12–0.70 mJ, respectively.

The ignition success rate of the nano initiator is estimated as98%. The released energy is roughly estimated to be 60 mJ with

further potential improvement without increasing the energy

input. The nano initiator is supposed to have many interesting

applications in both civilian and military areas such as air bags

in automobiles, micropropulsion systems, and many ordnance

systems.

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Kaili Zhang received the B.S. degree in mechanicalengineering from Dong Hua University, Shanghai,China, in 1997, and the Ph.D. degree in micro-systems from the National University of Singapore,Singapore, in 2006.

Since 2006, he has been with the Laboratoryfor Analysis and Architecture of the Systems,French National Center for Scientific Research(CNRS), Toulouse, France, where he has been work-ing on nanosystems as a Postdoctoral Researcher.His current research interests include nanoenergetic

materials, nanometals, nanometal oxides, nanocatalysis, micropropulsion,microigniters, solar cells, fuel cells, and hydrogen storage.

Carole Rossi received the engineer degree in physicsand the Ph.D. degree in electrical engineering fromthe National Institute for Applied Science, Toulouse,France, in 1994 and 1997, respectively.

After her postdoctoral research at the Universityof California, Berkeley, under the supervision of Prof. Pister, she joined the French National Centerfor Scientific Research (CNRS), Toulouse, to de-velop her research at the Laboratory for Analysisand Architecture of the Systems (LAAS). She is

currently leading the power MEMS research areaat LAAS, with her team proposing new concepts for actuation and energyon a chip. Her research interests include nanoenergetics, micropyrotechnicalsystems, and power MEMS for electrical generation.

Marine Petrantoni received the Engineerdegree from the Department of Materials,“Polytech’Grenoble,” an engineering school that ispart of Joseph Fourier University, Grenoble, France,in 2006. She is currently working toward the Ph.D.degree in the Laboratory for Analysis and Architec-ture of the Systems (LAAS), MEMS Department,Toulouse, France. LAAS is a national laboratory

under the French National Center for ScientificResearch (CNRS).

Her Ph.D. topic concerns the integration of nano-energetic materials via microelectronic technologies.

Nicolas Mauran wasbornin Muret, France, in 1974.He received the Engineer degree in instrumentationfrom the Conservatoire National des Arts et Métiers,Toulouse, France, in 2003.

He has been with the Laboratory for Analysis andArchitecture of the Systems, French National Centerfor Scientific Research (CNRS) since 1996, wherehe is currently responsible for the Semiconductor

Electrical Characterization Center, Toulouse.

kaili zhang et al- a nano initiator realized by integrating al/cuo-based nanoenergetic materials...

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