Tuning the Ignition Performance of a Microchip Initiator by Integrating

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Tuning the ignition performance of a micro-chip initiator by integrating various Al/ MoO3 RMFs on a semiconductor bridge Jianbing Xu, Yu Tai, Chengbo Ru, Ji Dai, Yinghua Ye, Ruiqi Shen, and Peng Zhu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b14662 • Publication Date (Web): 17 Jan 2017 Downloaded from http://pubs.acs.org on January 23, 2017

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ACS Applied Materials & Interfaces

Tuning the Ignition Performance of a Micro-Chip Initiator by Integrating Various Al/ MoO3 RMFs on a Semiconductor Bridge Jianbing Xu, Yu Tai, Chengbo Ru, Ji Dai, Yinghua Ye*, Ruiqi Shen and Peng Zhu Department of Applied Chemistry, School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing, 210094, China

ABSTRACT:

Reactive multilayer films (RMFs) can be integrated into semiconducting

electronic structures with the use of microelectromechanical systems (MEMS) technology, and represent potential applications in the advancement of microscale energy-demanding systems. In this study, aluminum/ molybdenum trioxide (Al/MoO3) -based RMFs with different modulation periods were integrated on a semiconductor bridge (SCB) using a combination of image reversal lift-off process and magnetron sputtering technology. This produced an energetic semiconductor bridge (ESCB)-chip initiator with controlled ignition performance. The effects of the Al/MoO3 RMFs with different modulation periods on ignition properties of ESCB initiator were then systemically investigated in terms of flame duration, maximum flame area and RMFs’ reaction ratio. These micro-chip initiators achieved flame duration of 60~600µs, maximum flame areas of 2.85~17.61 mm2, RMFs’ reaction ratios of 14%~100% (discharged with 47µF/30V) by simply changing the modulation periods of Al/MoO3 RMFs. This behavior was also consistent with a one-dimensional diffusion reaction model. The micro-chip initiator exhibited a high level of integration and proved to have tuned ignition performance, which can potentially be used in civilian and military applications.

KEYWORDS:

Reactive multilayer films (RMFs); Microelectromechanical systems (MEMS);

Magnetron sputtering; Aluminum/ Molybdenum trioxide (Al/MoO3); Energetic semiconductor bridge (ESCB)

1. INTRODUCTION Reactive multilayer films (RMFs) consisting of alternating layers of two or more different materials show excellent performance in many aspects, such as ignition, energy release rates, and other properties acted as energetic materials1-3. These reactive materials can also be integrated into semiconducting electronic devices by using micro-electromechanical systems (MEMS) 1

ACS Paragon Plus Environment


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technology which can apply into “nanoenergetics-on-a-chip” (NOC) technology4-6. NOC has a wide range of potential applications in the miniature of energy-demanding devices, such as micro-ignition4, 7-9, micro-propulsion10-11, micro-safe and arm12, and electro-explosive devices13-15. Semiconductor bridge (SCB) is a type of advanced electro-pyrotechnic initiator device which is concentrated within semiconductor devices, MEMS technology and energetic materials

16

. SCB

was firstly invented by Hollander in 196817, but it did not garner much attention until 198718 when its ignition performance was greatly improved by the Sandia National Laboratory. Since its invention, the SCB device has been used in civilian and military applications due to its high degree of safety, rapid response time, and low energy input as well as its high level of integration19-21 compared to traditional electro-pyrotechnic initiators which use a bridge wire to initiate subsequent reactions. For a typical SCB, a plasma is generated by an electrical explosive reaction caused by high voltage being placed across the bridge area. The heated plasma then rapidly spreads to the charges and initiates ignition17, 22. The duration time and size of the flame accompanying the plasma both play a key role in the successful ignition of the charge. This fact has triggered extensive research into how to improve the duration time and size of the flame without increasing input energy. Indeed, researchers studied various kinds of SCB in attempts to improve ignition performance, including single metal film-SCB23-24, multilayer metal-film-SCB25 and reactive multilayer film-SCB7, 26-27. However, all of the above-mentioned researches focus solely on improvement of ignition performance. It will be more worthwhile to tune the ignition performance by controlling the duration time and the size of the stimulated plasma to initiate charges with different sensitivity levels. Thermite RMFs systems are mixtures of nano-Al films and metal oxide films such as CuO28-30, MoO327, 31, and NiO32-33. The exothermic reactions of thermite RMFs systems have high energy density and high adiabatic temperatures to make up for heat loss and allows thermite RMFs to maintain self-sustaining combustion at the microscale, as shown in Table 134. Based on the advantages listed above, thermite RMFs systems are promising structures for integrating energetic layers onto a SCB chip, which increases the duration time and size of the flame accompanying the chemical reaction. Therefore, it is easy to tune ignition performance of the SCB-chip initiator integrated with RMFs because the reactivity of these RMFs can be easily controlled by changing 2


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the thickness of each layer and the number of layers.35. In this study, an Al/ MoO3 RMFs was selected because it is characterized by a much higher reaction energy and adiabatic temperature than other RMFs such as Al/Ni RMFs (Table 1). Three kinds of energetic semiconductor bridge (ESCB) initiators were fabricated using MEMS technology which allowed us to create large batches of the ESCB. Tuning of the ignition performance of the ESCB initiators were systematically investigated by varying the internal structures of the Al and MoO3 multilayers accumulated on the surface of the SCB. The ignition performance of the given ESCB initiators have been exhibited in terms of the flame duration, maximum flame area and RMFs’ reaction ratio when ignited. Table 1. Theoretical energy release of energetic materials Energetic

Mass energy density

Volume energy density

Adiabatic temperature

materials

(cal/g)

(cal/cm3)

(K)

Al/CuO

974.1

4976

2843

Al/MoO3

1124

4297

3253

Al/Fe2O3

945.4

3947

3135

Al/NiO

822.3

4288

3187

Al/Ni

330

1710

>1910

B/Ti

652

2560

>2452

2. EXPERIMENTS 2.1. The fabrication of ESCB initiators The

SCB

chips

are

fabricated

using

conventional

complementary

metal

oxide

semiconductor(CMOS) procedure19. More than 1000 SCB patterns can be defined on a 4-in. diameter wafer, and then diced into individual chips. In this experiment, n-type doped polysilicon was applied in order to create SCB chips. Figure 1a shows a digital image of a fabricated SCB. The SCB had a heating area of a “double-V” (with the angles of 90º) shaped bridge and the size was 380µm (width) ×80µm (length) × 2.5µm (thickness). Two rectangle-shape Au/Ti electrodes with a size of 1 mm × 1.96 mm were adopted to connect to SCB. Image reversal lift-off process is used for the patterned RMFs, because the inverted trapezoid profile of the photoresist is beneficial for fabricating thick film graphics with high accuracy. The process is illustrated schematically in Figure 1b. The SCB chip was cleaned with acetone, alcohol, 3



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and de-ionized water in an ultrasonic bath for 10 minutes. Then the cleaned SCB chip was placed in an oven for 1.5 hours at 100°C. Next, an image reversal photoresist (PR; AZ5200NJ) was spin coated on the SCB chip substrate at 3000rpm for 10 seconds and soft-baked in an oven for 2 minutes at 100°C. Afterwards, the PR layer was partially exposed to ultraviolet (UV) radiation with an intensity of 20mJ/cm2 through a mask using an ultraviolet lithography system (URE_2000A). The UV-exposed region of the PR layer was cross-linked by reversal baking in an oven for 3 minutes at 115 °C. Subsequently, the processed PR layer was entirely exposed to the UV radiation (no filtering was used) in order to solubilize the non-cross-linked region. Then, an inverted trapezoid profile was generated by dissolving the non-cross-linked region using a developer (AZ400K), which revealed the SCB. Next, the RMFs were deposited on prepared photoresist structure of the inverted trapezoid profile using magnetron sputtering technology. Finally, the patterned RMFs were defined by removing unnecessary portions of the deposited RMFs’ thin film in an ultrasonic bath containing acetone. As mentioned above, thermite RMFs systems are a new type of nano thermite consisting of alternating nano layers of Al and metal oxide, respectively. To obtain Al/MoO3 RMFs with different modulation periods, magnetron sputtering is used because it has the advantages of low-temperatures and high-speeds, which meet the requirements for the preparation of multiple alternating depositions on the nanometer scale, and also provide accurate control over layer thickness in composite films. Figure 1c shows a magnetron sputtering setup for RMFs deposition. The Al target (purity>99.999%) was direct-current (DC) sputtered at 150 W and the MoO3 target (purity>99.999%) was radiofrequency (RF) sputtered at 200W to maintain an optimized film quality. The base pressure of the chamber was 9×10-4Pa, while the working pressure for all two types of targets was selected to be 0.4Pa. Ultrahigh purity argon (99.99%) was employed as the working gas with a flux of 12 sccm. A rotating substrate table was employed to realize multiple alternating depositions and a baffle switch was controlled by setting computer program to adjust the thickness of the RMFs. The selected modulation periods in various RMFs were 50nm, 150nm and 1500nm at theory stoichiometric ratio, respectively, and the total thickness was 3ߤm. For the convenience of writing, the ESCB initiators with different modulation periods were denoted as 4


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ESCB-50nm, ESCB-150nm, ESCB-1500nm.

Figure 1. (a) The photographs and optical microscope images of the SCB; (b) the schematic representation of the MEMS-based processes used for fabricating the ESCB; (c) the magnetron sputtering system and RMFs-deposited ESCB initiator.

2.2. Characterization methods For investigating the electrical explosion characteristics of Al/MoO3–ESCB initiators, a capacitor (47ߤF) discharge firing circuit test system is adopted to apply the current across the Al/MoO3–SCB initiator, as shown in Figure 2. In the experiment, switch A was closed firstly to charge the capacitor to the settled voltage. Then switch A was disconnected and switch B was closed. Multiple tests were performed with the charging voltage ranging from 30V to 50V at 5V increment. Under each identical condition, three samples of each kind of initiators were initiated, and then the results were averaged. The ignition process was recorded using a high-speed camera (HG-100 K) that captured 50000 frames per second. At the same time, voltage and current were recorded synchronously with an oscilloscope. The surface roughness measurements of the MoO3 and Al layers were performed using atomic force microscopy (AFM, Solver P47). Structural microscopic characterization was performed using scanning electron microscopy (SEM, S-4800Ⅱ). The multilayer composition was determined using Energy Dispersive Spectrometer (EDS, NORAN System SIX). To examine the exothermic reaction temperatures in the various Al/MoO3 RMFs, a glass wafer (Φ50mm×H1mm) was spin coated with a layer of photoresist prior to deposition, so that the Al/MoO3 RMFs could be easily peeled afterwards by dissolving the photoresist. Then differential scanning calorimetry (DSC, NETZSCH STA 449 C) was carried out at temperatures ranging from 30°C to 900 °C under N2 flow. And the activation energy of the exothermic reaction was determined with DSC experiments at heating rate from 5 °C⋅min

−1

to

20 °C⋅min −1.

Figure 2. Schematic drawing of the test circuit used to generate pulses across a sample bridge and provide data on bridge current, voltage and ignition process.

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3. RESULTS AND DISCUSSION 3.1. The structure and layers morphology of Al/MoO3 RMFs AFM indicated a roughness of 5.03 nm and 5.21 nm for the MoO3 and Al thin layers (respectively), with a scan area of 10µm×10µm, as illustrated in Figure 3a and Figure 3b. EDS analysis was performed using 3µm Al/MoO3 RMFs deposited on a native oxidized silicon substrate. The Al, Mo, O, and Si (Figure 3c) confirmed the presence of each expected element in RMFs.

Figure 3. AFM images of (a)Al film surface and (b) MoO3 film surface; (c) EDS patterns on the RMFs.

Figure 4. Schematic of the various assembled RMFs on the SCB and the cross-sectional SEM images of the RMFs. Figure 4 shows the conceptual schematics and SEM images of the cross-sectional area of various Al/MoO3 RMFs. First, a thin layer of MoO3 (300nm) was deposited on the bottom to act as an insulating layer and avoid short-circuits of the SCB of before ignition. Subsequently, Al layer and MoO3 layer were deposited alternately using a magnetron sputtering process. Each modulation period was 1500 nm (Al/MoO3:900nm/600nm, 2 period, Φ=1), 150nm (Al/MoO3:90nm/60nm, 20 period, Φ=1), and 50nm (Al/MoO3:20nm/30nm, 60 period, Φ=1), receptivity, where Φ was stoichiometric ratio. The final thickness of all of the Al/MoO3 RMFs was approximately 3µm. The modulation period of RMFs is a crucial parameter, because it significantly influences chemical reactions of Al/MoO3. Moreover, the heat flow and reaction velocity can be easily changed by controlling the modulation period of RMFs with fixed thickness at theory stoichiometric ratio 28-29. Therefore, the ignition performance of the ESCB initiators can be tuned by varying the structure of the Al/MoO3 RMFs. As shown in Figure 4, the cross sectional SEM images of the Al/MoO3 RMFs showed that the Al and MoO3 layers had distinct boundary lines for the Al/MoO3 RMFs (i.e.1500nm, 150nm). The visible division between layers was distinct for larger modulation periods of Al/MoO3 RMFs because the layers themselves were thick, 6


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whereas the visible division between Al/MoO3 RMFs was less distinct in the case of 50nm modulation periods of Al/MoO3 RMFs because each layer was getting thinner.

Figure 5. DSC plots of Al/MoO3 RMFs with different modulation periods at heating rate of 20 °C⋅min −1. DSC analysis was performed at heating rate of 20 °C⋅min−1 to examine the effects of the various modulation periods on the exothermic reaction temperature of the Al/MoO3 RMFs, as shown in Figure 5. The exothermic peak of RMFs with modulation period of 50nm, 150nm were 556.6°C, 589.8°C, respectively (as shown in the shadow area). For the thickest modulation period of Al/MoO3 RMFs (1500 nm), there were two endothermic peak at 703.1°C and 736.3°C after the melting point of metal Al at 660°C (as shown in the dotted line). The exothermic peak increased with increase in the modulation periods of the Al/MoO3 RMFs. This suggested that reactivity was higher for smaller modulation period of Al/MoO3 RMFs because an increasing in the interfacial contact area between the Al films and the MoO3 films significantly affected the chemical reactivity of the RMFs.

Figure 6 DSC plots of Al/MoO3 RMFs at various heating rate and the fitting curves used for calculating activation energy of exothermic peak by Kissinger method. (a) Al/MoO3 50nm, (b) Al/MoO3 150nm, (c) Al/MoO3 1500nm. (Here, β is the heating rate and Tmax is the temperature of exothermic peak.) To obtain the activation energy of exothermic peak, the Kissinger method was used to calculated it. Figure 6 shows the DSC plots of Al/MoO3 RMFs at various heating rate from 5 °C⋅min−1 to 20 °C⋅min−1 and the fitting curves by Kissinger method. The activation energy of Al/MoO3 RMFs with modulation period of 50nm, 150nm were calculated at 75.65kJ/mol, 80.09kJ/mol, respectively. For Al/MoO3 RMFs with modulation period of 1500nm, there were two endothermic peak at 703.1°C and 736.3°C at the heating rate of 20 °C⋅min−1, while only one endothermic peak at lower heating rate. The mainly endothermic peak was selected and the activation energy was calculated at 74.99kJ/mol. It seems that the modulation periods of Al/MoO3 had little effect on the activation energy of exothermic reaction. 7



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3.2. The ignition performance for three kinds of ESCB initiators

Figure 7. The ignition processes of the SCB and various ESCB initiators and their microscope images after ignition. (a) SCB, (b) ESCB-1500nm, (c) ESCB-150nm, (d)ESCB- 50nm. The ignition processes of ESCB-1500nm, ESCB-150nm and ESCB-50nm were qualitatively measured using a high speed camera. Figure 7 shows a sequence of high-speed video frames of the burst action for SCB, ESCB-1500nm, ESCB-150nm and ESCB-50nm all discharged with 47µF/30V. The interval between adjoining pictures is 20 µs. The right side frames correspond to the optical microscope images after ignition. By comparing the size of the glowing emissions and projected streaks, it was evident that the height and duration time of flames significantly increased as the modulation periods decrease. This was a result of enhanced reactivity. Initially, plasma was generated at 20 µs in each initiator. After generation, the plasma became weaker because of no RMFs on the SCB. Without RMFs on SCB, plasma can last for 60µs. The maximum flame area was measured at 2.85mm2. Flames didn’t have a long duration time or a large flame area, which indicated a low ignition performance. However, for the ESCB, the reaction of RMFs was stimulated by the generated plasma, which resulted in a combustion process with large quantities of product particles bursting forth. The reaction rates varied by the structure of the RMFs and the duration time of flame can reach about 600 µs for ESCB-50nm, with a maximum flame area of 17.61mm2.

Table 2. Ignition properties of the SCB and Various ESCB Initiators discharged with 47 µF/30 V Initiator

Ignition duration(µs)

SCB ESCB-1500nm ESCB-150nm ESCB-50nm

60 140 440 600

Time to maximum flame(µs) 20 40 120 140

Maximum flame height(mm)

Maximum flame width(mm)

Maximum flame area(mm2)

Reaction ratio(%)

1.9 2.4 3.6 7.0

1.7 1.4 2.3 4.8

2.85 3.23 6.52 17.61

-14 22 100

Table 2 summarizes the ignition properties of SCB, ESCB-1500nm, ESCB-150nm and ESCB-50nm discharged with 47µF/30V, including their reaction duration, duration to maximum flame, and maximum flame height, width, area as well as reaction ratio of the RMFs. The ignition 8


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durations of SCB, ESCB-1500nm, ESCB-150nm and ESCB-50nm were recorded at 60µs, 140µs, 440µs and 600µs, respectively, and their maximum flame areas were measured at 2.85 mm2, 3.23 mm2, 6.52 mm2 and 17.61mm2, respectively. In addition, the reaction ratios of various RMFs were calculated from the right picture after ignition. The images clearly indicated that the reaction zones of the RMFs increased with decrease in modulation periods. Moreover, the images showed that the RMFs completely reacted for ESCB-50nm. Therefore, ESCB-50nm resulted in longer reaction duration time, relatively larger maximum flame area and higher reaction ratio. The maximum flame height for ESCB-50nm can reach at 7.0mm, which had a wide application in the field of non-contact ignition.

Figure 8. Critical explosive energy (a) and ignition duration (b) of SCB, ESCB-1500nm, ESCB-150nm, ESCB-50nm at different discharge voltages. (Here, Ec is the critical explosive energy and tl is ignition duration.) The voltage and current of ESCB initiators were recorded using an oscilloscope. The second voltage peak is defined as the critical explosive temporal of the SCB because it corresponded to the emergence of plasma20. Figure 8a shows the critical explosive energy (Ec) for each ESCB discharged with different discharge voltages. From this experiment, it was determined that discharge voltage had no effect on the Ec for ESCB with the same modulation period; however, the Ec increased with the increase in the modulation periods of the RMFs. The reason may be that the Ec was only related to the structure of the SCB, while the energy used for melting and gasifying the SCB remained consistent. Moreover, the RMFs may absorb heat from the SCB as a result of an extension of the Ec in the ESCB initiators. Furthermore, the heat conductivity of film decreased with thickness36-38, which explained the minimum Ec for thinnest films (ESCB-50nm) among various ESCB initiators because of lower loss of heat in the RMFs(50nm). Figure 8b shows the duration time (tl) of flame after ignition for various ESCB initiators. For SCB, the tl only reached about 100µs, while the tl can reach about 400µs, 600µs for ESCB-150nm and ESCB-50nm respectively with discharge voltage from 30V to 50 V. And the ESCB-1500nm had tl from 150µs to 400µs with discharge voltage from 30V to 50 V. This suggested that the ignition performance of the ESCB micro-chip initiators can be easily controlled by designing the 9



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accumulation structures of the Al/ MoO3 RMFs.

3.3. The ignition model for RMFs Based the above results, the RMFs’ modulation period has a direct effect on the ignition process. A one-dimensional diffusion reaction model39 is proposed to study the effect of number of interface of RMFs on the reaction ignition (Figure 9). The Al/MoO3 RMFs was ignited by the generated plasma, as shown in Figure 9a. The interface of Al/MoO3 was assumed to dominate the reactivity and oxygen atoms diffused from MoO3 layer to Al layer through the interface, as shown in Figure 9b.

Figure 9. Schematic of ignition model for RMFs. (a) the ignition process of Al/MoO3 RMFs, (b) the diffusion reaction at the interface of Al/MoO3, (c) the concentration gradient at the interface of Al/MoO3. Analysis energy conservation equation with the equation of state of ideal condition,

dT 1 & Qrxn = dt C p

(1)

relates the temporal change in temperature to the rate of heat generation by reaction (Q̇rxn) divided by the heat capacity (Cp). And the heat generated is evaluated in eq 2,

Q& rxn = nA∆H rnx J

(2)

where n is the number of interfaces, A(m2) is the surface area of each interface, ∆Hrxn (J/mol) is the energy released from each mol of reaction, and J (mol/(s·m2)) is the flux of oxygen through each interface. The interfacial area, A, can be calculated based on the heat area of SCB with 380×80µm2. The number of interfaces is related to the number of modulation periods(N) of RMFs through n=2N−1. Eq 3 is the Fickian diffusion flux through each interface,

J =− where

∂C − E / RT D0 e( a ) ∂x

(3)

∂C (mol/m4) is the concentration gradient across the interface, D0 is the pre-exponential to ∂x

the diffusivity, and Ea is its activation energy. The concentration gradient is based on O atoms going from zero to the concentration in MoO3 over the length of a typical interfacial barrier layer (3~5nm29) to be 8.14×1012 mol/m4, as shown in Figure 9c. The electrical-explosive process of 10


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SCB achieved in 10µs~100µs and produced high temperature plasma about 3000K. As such, the film temperature rapidly increased above that of the plasma.

dT 103 K = = 108 ~ 109 K / s dt 10 ×10−6 s ~ 100 ×10−6 s

(4)

For this reason, the ignition temperature (Tign) is define as the point at which the temperature rise from reaction (eq 1) exceeds the heating rate from the plasma (108~109K/s). Combining eq 1−3 and solving for ignition temperature gives

Tign

  8  9 − Ea   (10 ~ 10 K / s ) C p   = ln   R   nA∆H ∂C D   rnx 0   ∂x  

−1

(5)

Garth C. Egan39 calculated the ignition temperature of thermite nanolaminates with the value (Ea= 20 kJ/mol, D0= 9.0×10−13m2/s) firstly, and the final result of the iterative refinement was obtained with the value (Ea= 49 kJ/mol, D0= 2.9×10−10m2/s ). The Ea of Al/MoO3 RMFs with modulation period of 50nm, 150nm,1500nm in this experiment were measured at 75.65kJ/mol, 80.09kJ/mol, 74.99kJ/mol, respectively. The average Ea=76.91kJ/mol, D0=2.9×10−10m2/s was selected to calculated the ignition temperature. The modeled ignition temperature is shown in Figure 10. When the number of modulation period (N) is in the range of 0~15, the ignition temperature of RMFs decreased rapidly with the amplitude of the number of modulation period, while the ignition temperature of RMFs decreased slowly when the N in the range of 15~60. This result clearly indicates the change of chemical reactivity with different modulation period of the RMFs, which is greatly consistent with the change of ignition performance for various ESCB initiators.

Figure 10. The relationship of modeled ignition temperature with number of modulation period.

4. CONCLUSIONS In this study, three kinds of ESCB-chip initiators (ESCB-1500nm, ESCB-150nm, ESCB-50nm) were proposed by depositing Al/MoO3 RMFs with different modulation periods (1500nm, 150nm, 50nm) on a SCB. The ESCB-chip initiators were fabricated using a combination of MEMS-based processes with image reversal lift-off and magnetron sputtering technology. The as-deposited 11



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Al/MoO3 RMFs with different modulation periods were identified with SEM and DSC. SEM showed the distinct layer structure for the Al/MoO3 RMFs (i.e.1500nm, 150nm), while less distinct in the case of smaller modulation periods of Al/MoO3 RMFs (i.e.50nm). And the mainly exothermic peak of RMFs with modulation period of 50nm, 150nm, 1500nm were 556.6°C, 589.8°C, 736.3°C, respectively at the heating rate of 20°C/min. The ESCB-chip initiators can produce fierce flame when a voltage was supplied to the SCB. The ignition durations of the SCB, ESCB-1500nm, ESCB-150nm and ESCB-50nm were recorded at 60µs, 140µs, 440µs and 600µs, respectively, and their maximum flame areas were measured at 2.85mm2, 3.23mm2, 6.52mm2 and 17.61mm2, respectively, both discharged with 47µF/30V. Furthermore, this behavior is consistent with a one-dimensional diffusion reaction model. In short, the ESCB-chip initiator detailed in this report exhibited controlled ignition performance and can potentially be used in civilian and military applications, especially in non-contact ignition, such as air bags in automobiles, micro propulsion systems, and many ordnance systems.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation (U1230115), and the Ordinary University Graduate Student Scientific Research Innovation Projects of Jiangsu Province (KYLX15_0351).

REFERENCES (1) Rossi, C.; Zhang, K.; Esteve, D.; Alphonse, P.; Tailhades, P.; Vahlas, C. Nanoenergetic Materials for MEMS: A Review. J. Microelectromech. Syst. 2007, 16, 919-931. (2) Zhou, X.; Torabi, M.; Lu, J.; Shen, R.; Zhang, K. Nanostructured Energetic Composites: Synthesis, Ignition/Combustion Modeling, and Applications. ACS Appl. Mater. Interfaces 2014, 6, 3058-3074. 12


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Tuning the Ignition Performance of a Micro-Chip Initiator by Integrating Various Al/ MoO3 RMFs on a Semiconductor Bridge Jianbing Xu, Yu Tai, Chengbo Ru, Ji Dai, Yinghua Ye*, Ruiqi Shen and Peng Zhu Department of Applied Chemistry, School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing, 210094, China

ABSRACT:

Reactive multilayer films (RMFs) can be integrated into semiconducting

electronic structures with the use of microelectromechanical systems (MEMS) technology, and represent potential applications in the advancement of microscale energy-demanding systems. In this study, aluminum/ molybdenum trioxide (Al/MoO3) -based RMFs with different modulation periods were integrated on a semiconductor bridge (SCB) using a combination of image reversal lift-off process and magnetron sputtering technology. This produced an energetic semiconductor bridge (ESCB)-chip initiator with controlled ignition performance. The effects of the Al/MoO3 RMFs with different modulation periods on ignition properties of ESCB initiator were then systemically investigated in terms of flame duration, maximum flame area and RMFs’ reaction ratio. These micro-chip initiators achieved flame duration of 60~600s, maximum flame areas of 2.85~17.61 mm2, RMFs’ reaction ratios of 14%~100% (discharged with 47F/30V) by simply changing the modulation periods of Al/MoO3 RMFs. This behavior was also consistent with a onedimensional diffusion reaction model. The micro-chip initiator exhibited a high level of integration and proved to have tuned ignition performance, which can potentially be used in civilian and military applications.

KEYWORDS: Reactive multilayer films (RMFs); Microelectromechanical systems (MEMS); Magnetron sputtering; Aluminum/ Molybdenum trioxide (Al/MoO3); Energetic semiconductor bridge (ESCB)

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FIGURES

Figure 1. (a) The photographs and optical microscope images of the SCB; (b) the schematic representation of the MEMS-based processes used for fabricating the ESCB; (c) the magnetron sputtering system and RMFs-deposited ESCB initiator.

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Figure 2. Schematic drawing of the test circuit used to generate pulses across a sample bridge and provide data on bridge current, voltage and ignition process.

Figure 3. AFM images of (a)Al film surface and (b) MoO3 film surface; (c) EDS patterns on the RMFs.

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Figure 4. Schematic of the various assembled RMFs on the SCB and the cross-sectional SEM images of the RMFs.

Figure 5. DSC plots of Al/MoO3 RMFs with different modulation periods at heating rate of 20 °Cmin −1. 4


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Figure 6 DSC plots of Al/MoO3 RMFs at various heating rate and the fitting curves used for calculating activation energy of exothermic peak by Kissinger method. (a) Al/MoO3 50nm, (b) Al/MoO3 150nm, (c) Al/MoO3 1500nm. (Here, β is the heating rate and Tmax is the temperature of exothermic peak.)

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Figure 7. The ignition processes of the SCB and various ESCB initiators and their microscope images after ignition. (a) SCB, (b) ESCB-1500nm, (c) ESCB-150nm, (d)ESCB- 50nm.

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Figure 8. Critical explosive energy (a) and ignition duration (b) of SCB, ESCB-1500nm, ESCB150nm, ESCB-50nm at different discharge voltages. (Here, Ec is the critical explosive energy and tl is ignition duration.)

Figure 9. Schematic of ignition model for RMFs. (a) the ignition process of Al/MoO3 RMFs, (b) the diffusion reaction at the interface of Al/MoO3, (c) the concentration gradient at the interface of Al/MoO3. 7



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Figure 10. The relationship of modeled ignition temperature with number of modulation period.

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Tuning the Ignition Performance of a Microchip Initiator by Integrating

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