Carole Rossi

Nanoenergetic Materials for MEMS: A Review

New energetic materials (EMs) are the key to great advances in microscale energy-demanding systems as actuation part, igniter, propulsion unit, and power. Nanoscale EMs (nEMs) particularly offer the promise of much higher energy densities, faster rate of energy release, greater stability, and more security (sensitivity to unwanted initiation). nEMs could therefore give response to microenergetics challenges. This paper provides a comprehensive review of current research activities in nEMs for microenergetics application. While thermodynamic calculations of flame temperature and reaction enthalpies are tools to choose desirable EMs, they are not sufficient for the choice of good material for microscale application where thermal losses are very penalizing. A strategy to select nEM is therefore proposed based on an analysis of the material diffusivity and heat of reaction. Finally, after a description of the different nEMs synthesis approaches, some guidelines for future investigations are provided.

A Nano Initiator Realized by Integrating Al/CuO-Based Nanoenergetic Materials With a Au/Pt/Cr Microheater

A nano initiator is developed by integrating Al/CuO-based nanoenergetic materials with a Au/Pt/Cr thin-film microheater realized onto a glass substrate. It is fabricated by using standard microsystem techniques that allow batch fabrication and high level of integration and reliability. The nano initiator is characterized by open-air combustion testing with an ignition success rate of 98%. The ejected combustion flame is seen clearly with a potential exceeding 2000 . 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 around 60 mJ.

Synthesis of large-area and aligned copper oxide nanowires from copper thin film on silicon substrate

Large-area and aligned copper oxide nanowires have been synthesized by thermal annealing of copper thin films deposited onto silicon substrate. The effects of the film deposition method, annealing temperature, film thickness, annealing gas, and patterning by photolithography are systematically investigated. Long and aligned nanowires can only be formed within a narrow temperature range from 400 to 500°C. Electroplated copper film is favourable for the nanowire growth, compared to that deposited by thermal evaporation. Annealing copper thin film in static air produces large-area, uniform, but not well vertically aligned nanowires along the thin film surface. Annealing copper thin film under a N2/O2 gas flow generates vertically aligned, but not very uniform nanowires on large areas. Patterning copper thin film by photolithography helps to synthesize large-area, uniform, and vertically aligned nanowires along the film surface. The copper thin film is converted into bicrystal CuO nanowires, Cu2O film, and also perhaps some CuO film after the thermal treatment in static air. Only CuO in the form of bicrystal nanowires and thin film is observed after the copper thin film is annealed under a N2/O2 gas flow.

Development of a nano-Al∕CuO based energetic material on silicon substrate

Nanoenergetic materials (nEMs) have improved performances compared to their bulk counterpart or microcounterpart. The authors propose an approach to synthesize an Al∕CuO based nEM that has several advantages over previous investigations such as enhanced contact, reduced impurities and Al oxidation, tailored dimensions, and easier integration into microsystem. CuO nanowires are synthesized by thermally annealing Cu film deposited onto silicon. Nano-Al is integrated with the nanowires to realize an Al∕CuO based nEM. The synthesized nEM is characterized by scanning electron microscopy, high resolution transmission electron microscopy, x-ray diffraction, differential thermal analysis, and differential scanning calorimetry.

Realization and performance of thin SiO2/SiNx membrane for microheater applications

Abstract There is considerable interest in thin-film microheaters for decreasing the power consumption in portable applications. In this paper, we present the study of new stacked thin membranes (SiO 2 /SiN 1.2 ) supporting the heating element (polysilicon resistor). The great interest of using SiN 1.2 deposited onto a SiO 2 layer is the improvement in mechanical properties of the membrane, leading to a fabrication yield very close to 100%. Microheaters fabricated with a 1.6 mm × 1.6 mm square and 0.7 μm thick SiO 2 /SiN 1.2 membrane give promising results in terms of power consumption; 230°C is reached with an electrical power of 50 mW.

Multilayered Al/CuO thermite formation by reactive magnetron sputtering: Nano versus micro

Multilayered Al/CuO thermite was deposited by a dc reactive magnetron sputtering method. Pure Al and Cu targets were used in argon–oxygen gas mixture plasma and with an oxygen partial pressure of 0.13 Pa. The process was designed to produce low stress (<50 MPa) multilayered nanoenergetic material, each layer being in the range of tens nanometer to one micron. The reaction temperature and heat of reaction were measured using differential scanning calorimetry and thermal analysis to compare nanostructured layered materials to microstructured materials. For the nanostructured multilayers, all the energy is released before the Al melting point. In the case of the microstructured samples at least 2/3 of the energy is released at higher temperatures, between 1036 and 1356 K.

Theoretical and experimental study of silicon micromachined microheater with dielectric stacked membranes

Abstract In this paper, we model first the heating performance of a silicon micromachined microheater. The pros and cons of the use of a stacked dielectric membranes instead of p ++ -Si membranes are discussed, either in terms of electrical consumption, or in terms of emperature homogeneity. Then, we realize and characterize two examples among the simulated structures. This allows some practical problems during the fabrication, essentially due to mechanical breakdown, to be demonstrated. A general agreement between results is found. This study shows significant promise in the development of stacked dielectric membranes.

Design, fabrication and modelling of MEMS-based microthrusters for space application

With the development of microspacecraft technology micropropulsion concepts are introduced for course correction and orbit insertion as well as attitude control of the microspacecraft. In this context, we have introduced a new concept of MEMS-based technology microthruster responding to the spatial constraints (volume constraints, high level of integration) and MEMS characteristics (miniaturization, low cost, mass production). The originality of these new thrusters is the use of only one solid propellant loaded in a small tank micromachined in a ceramic, glass or silicon substrate and the fabrication of arrays of N independent microthrusters in the same chip. The structure consists of a sandwich of three micromachined silicon substrates: nozzles, igniters and propellant chambers. The thrust force generated can be set from a few hundred µN to a few tens of mN by geometrical and dimensional considerations. In this paper we present the fabrication and assembly of one prototype: it is an array of 36 microthrusters that proved the technological feasibility of this new concept of small-scale thrusters. We also investigate the influence of nozzle geometry on the performances of our thruster.

Pyrotechnic actuator: a new generation of Si integrated actuator

Abstract Mechanical micro actuators on silicon is playing a major role in the development of microsystems. In this context, many structures have been performed on electrostatic, piezo electric or pneumatic actuators. However, limitations remain when energetic micro actuations have to be created. We propose in this paper, a new original type of actuation based on the force generated by the combustion of an explosive. It consists of a micromachined silicon microheater (3 mm×3 mm×0.3 mm) on which a thin film of propellant (2 mm×2 mm×0.2 mm) is deposited. Its functioning principle is based on a hot gas emitted by the auto combustion of the propellant when its temperature reaches 300°C locally. In this paper, we present the results of a study (by modelling and experimental) of the ignition and combustion of a very small quantity of explosive onto a Si-micromachined microheater. We conclude by presenting two examples of applications showing the promising interest of this energetic actuator: the first application is the biomedical field. The second one, today is used for microspace craft attitude control.

Interfacial Chemistry in Al/CuO Reactive Nanomaterial and Its Role in Exothermic Reaction

Interface layers between reactive and energetic materials in nanolaminates or nanoenergetic materials are believed to play a crucial role in the properties of nanoenergetic systems. Typically, in the case of Metastable Interstitial Composite nanolaminates, the interface layer between the metal and oxide controls the onset reaction temperature, reaction kinetics, and stability at low temperature. So far, the formation of these interfacial layers is not well understood for lack of in situ characterization, leading to a poor control of important properties. We have combined in situ infrared spectroscopy and ex situ X-ray photoelectron spectroscopy, differential scanning calorimetry, and high resolution transmission electron microscopy, in conjunction with first-principles calculations to identify the stable configurations that can occur at the interface and determine the kinetic barriers for their formation. We find that (i) an interface layer formed during physical deposition of aluminum is composed of a mixture of Cu, O, and Al through Al penetration into CuO and constitutes a poor diffusion barrier (i.e., with spurious exothermic reactions at lower temperature), and in contrast, (ii) atomic layer deposition (ALD) of alumina layers using trimethylaluminum (TMA) produces a conformal coating that effectively prevents Al diffusion even for ultrathin layer thicknesses (∼0.5 nm), resulting in better stability at low temperature and reduced reactivity. Importantly, the initial reaction of TMA with CuO leads to the extraction of oxygen from CuO to form an amorphous interfacial layer that is an important component for superior protection properties of the interface and is responsible for the high system stability. Thus, while Al e-beam evaporation and ALD growth of an alumina layer on CuO both lead to CuO reduction, the mechanism for oxygen removal is different, directly affecting the resistance to Al diffusion. This work reveals that it is the nature of the monolayer interface between CuO and alumina/Al rather than the thickness of the alumina layer that controls the kinetics of Al diffusion, underscoring the importance of the chemical bonding at the interface in these energetic materials.