micromachines Communication PyroMEMS as Future Technological Building Blocks for Advanced Microenergetic Systems Jean-Laurent Pouchairet and Carole Rossi *   Citation: Pouchairet, J.-L.; Rossi, C. PyroMEMS as Future Technological Building Blocks for Advanced Microenergetic Systems. Micromachines 2021, 12, 118. https://doi.org/10.3390/mi12020118 Academic Editor: Ju-Hyuck Lee Received: 6 January 2021 Accepted: 22 January 2021 Published: 23 January 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). LAAS-CNRS, University of Toulouse, 7 Avenue du Colonel Roche, 31077 Toulouse, France; jlpoucha@laas.fr * Correspondence: rossi@laas.fr; Tel.: +33-6-4753-6438 Abstract: For the past two decades, many research groups have investigated new methods for reducing the size and cost of safe and arm-fire systems, while also improving their safety and reliability, through batch processing. Simultaneously, micro- and nanotechnology advancements regarding nanothermite materials have enabled the production of a key technological building block: pyrotechnical microsystems (pyroMEMS). This building block simply consists of microscale electric initiators with a thin thermite layer as the ignition charge. This microscale to millimeter-scale addressable pyroMEMS enables the integration of intelligence into centimeter-scale pyrotechnical systems. To illustrate this technological evolution, we hereby present the development of a smart infrared (IR) electronically controllable flare consisting of three distinct components: (1) a controllable pyrotechnical ejection block comprising three independently addressable small-scale propellers, all integrated into a one-piece molded and interconnected device, (2) a terminal function block comprising a structured IR pyrotechnical loaf coupled with a microinitiation stage integrating low-energy addressable pyroMEMS, and (3) a connected, autonomous, STANAG 4187 compliant, electronic sensor arming and firing block. Keywords: microenergetics; MEMS; pyroMEMS; IR flare; nanothermite 1. Introduction In 1995, the pyroMEMS concept, which involves the integration of energetic material on an electronic chip, was introduced for medical applications using mechanical power derived from the combustion of a propellant [1] to inject drugs through the skin [2]. This original concept has led to major innovations and has inspired research that has defined the technological area called micropyrotechnics [3]. The subsequent fabrication of small pyrotechnic systems includes a wide range of applications: micropropulsion [4–10], microfluidics [11,12], electrical protection [13,14], in situ welding [13–15], safe arm and fire devices [16–18], and multipoint initiations [19,20]. The innovation of the pyroMEMS concept has been explored in several fields at many universities and research institutes: Berkeley University [21,22], Tohoku University [23], Georgia Tech [24], Sandia National Laboratory [25] and École polytechnique fédérale de Lausanne [11,26–28]. In the 2000s, pyroMEMS fabrication challenges revealed that is was necessary to replace conventional CHNO energetic materials with new, safer energetic materials com- patible with MEMS. These new materials should feature extremely high amounts of stored chemical energy that can be released quickly and safely. Nanothermites containing nanoscale metallic fuel in contact with a strong oxidizer emerged as promising candidates because their burn rate can be tuned from mm/s to m/s, and even km/s in some particular cases [29–31]. To obtain a high interfacial contact area between the fuel and the oxidizer, ultrasonication [32], electrospraying/electrospinning [33], mechanical milling [34,35], self- assembly (static electricity-based [36], ligand-based [30,37,38], sol-gel [39] and DNA-based assembly [40–42] and, recently, 3D printing [43–46] approaches have been explored with varying levels of success. An alternative technique for creating high-density, high-interface Micromachines 2021, 12, 118. https://doi.org/10.3390/mi12020118 https://www.mdpi.com/journal/micromachines