Abstract
A comprehensive overview of PowderMEMS—a novel back-end-of-line-compatible microfabrication technology—is presented in this paper. The PowderMEMS process solidifies micron-sized particles via atomic layer deposition (ALD) to create three-dimensional microstructures on planar substrates from a wide variety of materials. The process offers numerous degrees of freedom for the design of functional MEMSs, such as a wide choice of different material properties and the precise definition of 3D volumes at the substrate level, with a defined degree of porosity. This work details the characteristics of PowderMEMS materials as well as the maturity of the fabrication technology, while highlighting prospects for future microdevices. Applications of PowderMEMS in the fields of magnetic, thermal, optical, fluidic, and electrochemical MEMSs are described, and future developments and challenges of the technology are discussed.
Highlights
The fabrication of 3D microstructures with dimensions between several tens and several hundreds of microns, on planar substrates such as silicon or glass wafers, is of considerable interest for MEMSs
The individual methods are often dedicated to specific materials, such as deep reactive-ion etching (DRIE) for silicon [1] or laser-induced deep etching (LIDE) for glass [2]
The photoresist mask used for mold etching remains on the wafer as a DRIE in the MEMS cleanroom, the substrates are transferred into a dedicated laboratory
Summary
The fabrication of 3D microstructures with dimensions between several tens and several hundreds of microns, on planar substrates such as silicon or glass wafers, is of considerable interest for MEMSs. Powder-based techniques such as selective laser beam sintering [16] or melting [17] allow the generation of organic-free microstructures that do not suffer from low thermal stability. Both techniques are widely applied to create free-standing parts, their implementation on planar substrates is a challenge. Compared to other state-of-the-art processes, this technique fulfills a unique set of requirements for the integration of 3D functional microstructures at the substrate level: a multitude of dielectric, metallic, or semi-conducting materials can be used; structures with thicknesses of several hundreds of micrometers can be obtained; porous and magnetic volumes can be fabricated; and integration is performed at the substrate level via a batch-enabled, low-temperature process.
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