Self-sacrificial surface micromachining using poly(methyl methacrylate)

Abstract

This paper explains the idea of self-sacrificial surface micromachining. In a self-sacrificial process, there is no distinction between structural and sacrificial layers. Instead, during patterning, an in situ chemical change converts a structural material into a sacrificial material, or vice versa. This greatly increases the design space of a self-sacrificial process when compared to a traditional process with the same number of layers, as all layers can be used simultaneously for both structural and sacrificial purposes. To show the possibility of self-sacrificial surface micromachining, a concrete implementation was developed using poly(methyl methacrylate) (PMMA) as the material. Unexposed PMMA, with a high average molecular weight, was used as the structural material. Exposed PMMA, with a lower average molecular weight, was used as the sacrificial material. The in situ chemical change was caused by deep-UV irradiation at 254 nm.

Deep UV patterning of acrylic masters for molding biomimetic dry adhesives

“…Its final advantage is that it is very inexpensive per volume and per area compared with competing materials-especially silicon and glass-making larger molds more viable as a low-cost fabrication option. The ability to pattern PMMA [40,41], and acrylics [39,42] with germicidal lamps (wavelengths ∼254 nm) opens up a far different cost structure for producing microstructured surfaces over large areas, because germicidal lamps are already designed for large-area exposures of air and water for elimination of bacteria, molds and fungi. While the infrastructure to do lithography on these scales does not yet exist, functional concepts can be proven on smaller scales with commercially available or custom exposure sources.…”

“…As a result, SU-8 layers as thin as 1 μm can act as an effective blocking layer at these wavelengths. The use of SU-8 directly on acrylic avoids the metal deposition and patterning steps that were used for the production of self-sacrificial MEMS [41] and acrylic microfluidics [39] and makes the processing less expensive, as only spin-coating or spray depositions are required. A second attractive feature of SU-8 as a 254 nm blocking layer is that it is transparent to visible wavelengths, and the exact amount of undercutting during development can easily be observed, unlike with metallic layers.…”

A Large-Scale Flexible Molding Technology for Producing Biomimetic Dry Adhesives in Multiple Materials Using a Commerical Acrylic Master

“…The direct photopatterning of polymethylmethacrylate (PMMA) using 254 nm light was originally conceived as a lowcost alternative to LIGA or e-beam lithography and later on was used for self-sacrificial polymer MEMS processing [8][9]. The sensitivity of PMMA to 254 nm light is extremely low, leading to lengthy exposure times (>5 hours), but the relative low cost of this light source (used industrially as germicidal lamps) is attractive for exposing large areas.…”

“…• After exposure, the acrylic is developed using SU-8 developer at room temperature (18 °C). A slightly lower selectivity of this solvent than the IPA:H 2 O developer used earlier [8][9][10] allows for better undercutting of SU-8 features. The final fiber shape depends on the exposure dose, anti-scatter grid design and development time.…”

3D-Printed Complex Microstructures with a Self-Sacrificial Structure Enabled by Grayscale Polymerization and Ultrasonic Treatment

“…One solution to this problem relies on the use of soluble support materials. , However, a layer made of a different material needs to be deposited and then removed in the etchant by such an approach which is tedious and of low efficiency. Another way to solve such a problem is by introducing supporting structures made of the same materials as the 3D microstructures, and the sacrificial layer can be removed by deep-UV at a 254 nm or a lower degree of polymerization from lower grayscale manufacturing. , However, those previous approaches are based on the principle that the materials are soluble, which is inapplicable to most of the printable materials in reality. In the present study, the sacrificial structure and the 3D complex microstructures made of the same insoluble materials are fabricated by a projection microstereolithography (PμSL)-based 3D printing technique − at the same time.…”