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1. Molecular layer deposition of an Al-based hybrid resist for electron-beam and EUV lithography

   https://doi.org/10.1117/12.2657636  

   Ravi, Ajay; Shi, Jingwei; Lewis, Jacqueline; Bent, Stacey F. (May 2023, Proc. SPIE 12498, Advances in Patterning Materials and Processes XL)

   Guerrero, Douglas; Amblard, Gilles R. (Ed.)

   As lithographic techniques advance in their capabilities of shrinking microelectronics devices, the need for improved resist materials, especially for extreme ultraviolet (EUV), has become increasingly pressing. In this work, we study the molecular layer deposition (MLD) of an Al-based hybrid thin film resist, known as “alucone,” extending our previous research that tested the Hf-based hybrid thin film “hafnicone” as an EUV resist. Alucone is grown at 100 ºC using the metal precursor trimethylaluminum and the organic precursor ethylene glycol. Like hafnicone, alucone behaves as a negative tone resist that can resolve 50-nm line widths, though preliminary data suggest that alucone’s line patterns are more sharply defined than those of hafnicone. Whereas hafnicone’s sensitivity is 400 μC/cm2 using 3 M HCl as the developer, alucone’s sensitivity is not yet as good (4800 μC/cm2 using 0.125 M HCl). Our study of alucone offers new insight into structural features of an MLD film that can lead to desired EUV-responsive behavior. This insight may accelerate the development of vapor-deposited inorganic resists for use in electron-beam and EUV lithography. 

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2. Parallelizable microfluidic dropmakers with multilayer geometry for the generation of double emulsions

   https://doi.org/10.1039/c9lc00966c  

   Nawar, Saraf; Stolaroff, Joshuah K.; Ye, Congwang; Wu, Huayin; Nguyen, Du Thai; Xin, Feng; Weitz, David A. (January 2020, Lab on a Chip)

   null (Ed.)

   Microfluidic devices enable the production of uniform double emulsions with control over droplet size and shell thickness. However, the limited production rate of microfluidic devices precludes the use of monodisperse double emulsions for industrial-scale applications, which require large quantities of droplets. To increase throughput, devices can be parallelized to contain many dropmakers operating simultaneously in one chip, but this is challenging to do for double emulsion dropmakers. Production of double emulsions requires dropmakers to have both hydrophobic and hydrophilic channels, requiring spatially precise patterning of channel surface wettability. Precise wettability patterning is difficult for devices containing multiple dropmakers, posing a significant challenge for parallelization. In this paper, we present a multilayer dropmaker geometry that greatly simplifies the process of producing microfluidic devices with excellent spatial control over channel wettability. Wettability patterning is achieved through the independent functionalization of channels in each layer prior to device assembly, rendering the dropmaker with a precise step between hydrophobic and hydrophilic channels. This device geometry enables uniform wettability patterning of parallelized dropmakers, providing a scalable approach for the production of double emulsions. 

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3. Layer-by-layer fabrication of 3D hydrogel structures using open microfluidics

   https://doi.org/10.1039/c9lc00621d  

   Lee, Ulri N.; Day, John H.; Haack, Amanda J.; Bretherton, Ross C.; Lu, Wenbo; DeForest, Cole A.; Theberge, Ashleigh B.; Berthier, Erwin (February 2020, Lab on a Chip)

   Patterned deposition and 3D fabrication techniques have enabled the use of hydrogels for a number of applications including microfluidics, sensors, separations, and tissue engineering in which form fits function. Devices such as reconfigurable microvalves or implantable tissues have been created using lithography or casting techniques. Here, we present a novel open-microfluidic patterning method that utilizes surface tension forces to form hydrogel layers on top of each other, into a patterned 3D structure. We use a patterning device to form a temporary open microfluidic channel on an existing gel layer, allowing the controlled flow of unpolymerized gel in device-regions. After layer gelation and device removal, the process can be repeated iteratively to create multi-layered 3D structures. The use of open-microfluidic and surface tension-based methods to define the shape of each individual layer enables patterning to be performed with a simple pipette and with minimal dead-volume. Our method is compatible with unmodified (native) biological hydrogels, and other non-biological materials with precursor fluid properties compatible with capillary flow. With our open-microfluidic layer-by-layer fabrication method, we demonstrate the capability to build agarose, type I collagen, and polymer–peptide 3D structures featuring asymmetric designs, multiple components, overhanging features, and cell-laden regions. 

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4. Surface Functionalization of 4D Printed Substrates Using Polymeric and Metallic Wrinkles

   https://doi.org/10.3390/polym15092117  

   Agyapong, Johnson N.; Van Durme, Bo; Van Vlierberghe, Sandra; Henderson, James H. (May 2023, Polymers)

   Wrinkle topographies have been studied as simple, versatile, and in some cases biomimetic surface functionalization strategies. To fabricate surface wrinkles, one material phenomenon employed is the mechanical-instability-driven wrinkling of thin films, which occurs when a deforming substrate produces sufficient compressive strain to buckle a surface thin film. Although thin-film wrinkling has been studied on shape-changing functional materials, including shape-memory polymers (SMPs), work to date has been primarily limited to simple geometries, such as flat, uniaxially-contracting substrates. Thus, there is a need for a strategy that would allow deformation of complex substrates or 3D parts to generate wrinkles on surfaces throughout that complex substrate or part. Here, 4D printing of SMPs is combined with polymeric and metallic thin films to develop and study an approach for fiber-level topographic functionalization suitable for use in printing of arbitrarily complex shape-changing substrates or parts. The effect of nozzle temperature, substrate architecture, and film thickness on wrinkles has been characterized, as well as wrinkle topography on nuclear alignment using scanning electron microscopy, atomic force microscopy, and fluorescent imaging. As nozzle temperature increased, wrinkle wavelength increased while strain trapping and nuclear alignment decreased. Moreover, with increasing film thickness, the wavelength increased as well. 

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5. MEMS analogous micro-patterning of thermotropic nematic liquid crystalline elastomer films using a fluorinated photoresist and a hard mask process

   https://doi.org/10.1039/c7tc03958a  

   Ditter, David; Chen, Wei-Liang; Best, Andreas; Zappe, Hans; Koynov, Kaloian; Ober, Christopher K.; Zentel, Rudolf (January 2017, Journal of Materials Chemistry C)

   In this work, we present a method to pattern liquid crystal elastomers (LCEs) in the micrometer range without using any mechanical processing steps to prepare micron sized LCE actuators compatible with microelectromechanical system (MEMS) technology. Multi-layer spin-coating processes are developed to synthesise and structure 300–3500 nm thick LCE films. A water soluble sacrificial layer, a photoalignment layer and a LCE formulation, which is polymerised and crosslinked in its liquid crystal phase, are spin-coated successively onto a substrate. A fluorinated photoresist layer is used to structure LCE films with thicknesses up to 700 nm in a photolithographic and etching process. For thicker LCE films a hard mask process, using hydrogen silsesquioxane (HSQ) as hard mask, is used. Film thicknesses and homogeneities are analysed with profilometry. Actuation motions of LCE layers are investigated before and after patterning and LCE patterns are investigated via (polarised optical) microscopy (POM), scanning electron microscopy (SEM) and profilometry. A resolution of 1.5–2.0 microns is achieved with the described techniques, which make deformable micron sized LCE actuators of variable shape and director orientation accessible. The presented results demonstrate the potential of LCEs in MEMS devices. 

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