Laser direct-write fabrication of Micro-electromechanical systems

Thesis: Ph. D., Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2019Cataloged from PDF version of thesis.Includes bibliographical references (pages 147-162).Micro-electromechanical systems (MEMS) have many applications in healthcare, consumer electronics, and automobile industry. Unfortunately, the development of novel MEMS is significantly hindered by the limitations of the state-of-the-art MEMS microfabrication processes such as high cost of equipment ownership, long development time, and limited choice of fabrication material selection and integration. Recent developments in alternate MEMS fabrication processes such as PCB-MEMS, laminate MEMS, pop-up book MEMS, and soft-MEMS have reduced fabrication cost, increased material choice, and facilitated material integration. However, MEMS fabricated using these methods have large feature size and low aspect ratio as compared to MEMS produced utilizing conventional deep reactive ion etching (DRIE) microfabrication process. Moreover, fabricating MEMS with six degrees of freedom (DOF) free-standing microstructures using these processes is challenging.Finally, the choice of fabrication material is fairly limited and each material requires a separate manufacturing process. This thesis presents a novel MEMS fabrication process called multi-lamina assembly of laser micromachined laminates (MALL), which can fabricate MEMS comparable to DRIE, enable creating free-standing microstructures with six degrees of freedom, and further expand the choice of fabrication material. Moreover, the proposed approach offers a single microfabrication method to process a wide range of materials. A novel microfabrication process called laser-assisted material phase-change and expulsion (LAMPE) micromachining is developed. Using this process, the fabrication of high aspect ratio structures with lateral features as small as 10Lm, and aspect ratio as large as 10:1 is demonstrated in metals, silicon and diamond.Previously, such high aspect ratio and small lateral feature structures could be fabricated in silicon alone using the deep reactive ion etching process. The LAMPE micromachining process is used to manufacture individual layers of a MEMS. Subsequently, the micromachined laminates are stack assembled and bonded to construct MEMS devices. Using the MALL process, fabrication of six degrees of freedom free-standing structures as thin as 10[mu] is demonstrated. In addition, the gap between the free-standing structure and the substrate can be as small as 12.5pm. The utility of the MALL process is demonstrated by fabricating three MEMS. First, an electrostatic comb-drive actuator is fabricated using copper as the structural material. The distance between the comb-drive fingers is 10[mu], and the thickness of the fingers is 100[mu]. This is the first demonstration of using a metal to fabricate comb-drive structure with such small lateral feature and high aspect ratio.Second, a MEM relay for high-current switching application is demonstrated. The current carrying capacity of the MEM relay is higher than OOmA. Finally, development of high-aspect-ratio diamond rotors for enhancing the resolution of magic-angle spinning nuclear magnetic resonance spectroscopy (MAS-NMR) is presented. This is the first demonstration of micromachining such ultra-deep (5 mm), and ultra-high aspect ratio (10:1) holes in diamond. The MALL process can manufacture MEMS comparable to conventional DRIE microfabrication process. Moreover, the manufacturing cost per device in MALL is less than DRIE. However, DRIE offers high part production rate than MALL. The part production rate in MALL can be matched with DRIE using multiple laser sources. For matching the part production rate, the investment required to purchase a laser micromachining tool with multiple lasers is comparable to the cost of a DRIE tool.Thus, equal investment in MALL and DRIE results in equal part production rate. The MALL process significantly reduces the time required for material integration, process development, and design iteration. As a result, the MEMS device development time is reduced from many months (in DRIE) to a day. The MALL process empowers rapid testing of new MEMS concepts and theory. Moreover, MALL can be used to fabricate one-of-a-kind MEMS devices and used for low-volume production, where initial high investment can not be justified. The MALL process enables greater material selection and integration, rapid development, and integrated packing, thereby empowering a new paradigm in MEMS design, functionality, and application. The tools and material cost of MALL fabrication can be as low as $25,000, which is affordable to a wider scientific community. The low capital investment and use of low-cost of materials enables MEMS fabrication for masses and can expedite the development of novel MEMS.by Prashant Patil.Ph. D.Ph.D. Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Science