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Cavities fabricated on the microscale have a wide variety of applications, from microwells for cell cultures, microfluidic channels for drug delivery systems to waveguide structures for RF applications. Micro-cavities are particularly useful for sensing applications, such as cavity-based pressure sensors and gap-based capacitive sensors. Cavity structures have been widely demonstrated in MEMS devices using typical semiconductor processing. However, the development of similar structures for flexible applications poses additional challenges. While flexible cavity structures have been fabricated in laboratory environments, challenges arise when these structures are integrated into a larger flexible sensing device or flexible hybrid electronics system. An additive manufacturing approach to cavity formation is presented which utilizes a 3D screen-printing process and in-situ cure. Patterned micro-structures are formed by building up layers of dielectric ink interspersed as needed with printed conductive traces. A proof-of-concept microfluidic channel-based capacitor is fabricated to demonstrate the potential sensing applications for the fabricated microcavities. 

Abstract Ferroelectric hafnium zirconium oxide (HZO) holds promise for nextgeneration memory and transistors due to its superior scalability and seamless integration with complementary metal‐oxide‐semiconductor processing. A major challenge in developing this emerging ferroelectric material is the metastable nature of the non‐centrosymmetric polar phase responsible for ferroelectricity, resulting in a coexistence of both polar and non‐polar phases with uneven grain sizes and random orientations. Due to the structural similarity between the multiple phases and the nanoscale dimensions of the thin film devices, accurate measurement of phase‐specific information remains challenging. Here, the application of 4D scanning transmission electron microscopy is demonstrated with automated electron diffraction pattern indexing to analyze multiphase polycrystalline HZO thin films, enabling the characterization of crystallographic phase and orientation across large working areas on the order of hundreds of nanometers. This approach offers a powerful characterization framework to produce a quantitative and statistically robust analysis of the intricate structure of HZO films by uncovering phase composition, polarization axis alignment, and unique phase distribution within the HZO film. This study introduces a novel approach for analyzing ferroelectric HZO, facilitating reliable characterization of process‐structure‐property relationships imperative to accelerating the growth optimization, performance, and successful implementation of ferroelectric HZO in devices. 

Abstract Micrometer scale arbitrary hollow geometries within a solid are needed for a variety of applications including microfluidics, thermal management and metamaterials. A major challenge to 3D printing hollow geometries using stereolithography is the ability to retain empty spaces in between the solidified regions. In order to prevent unwanted polymerization of the trapped resin in the hollow spaces—known as print-through—significant constraints are generally imposed on the primary process parameters such as resin formulation, exposure conditions and layer thickness. Here, we report on a stereolithography process which substitutes the trapped resin with a UV blocking liquid to mitigate print-through. We investigate the mechanism of the developed process and determine guidelines for the formulation of the blocking liquid. The reported method decouples the relationship between the primary process parameters and their effect on print-through. Without having to optimize the primary process parameters to reduce print-through, hollow heights that exceed the limits of conventional stereolithography can be realized. We demonstrate fabrication of a variety of complex hollow geometries with cross-sectional features ranging from tens of micrometer to hundreds of micrometers in size. With the framework presented, this method may be employed for 3D printing functional hollow geometries for a variety of applications, and with improved freedom over the printing process (e.g. material choices, speed and resulting properties of the printed parts). 

Abstract 3D printing using conventional stereolithography is challenging because the polymerized layers adhere to the solid constraining interface. The mechanical separation forces lead to poor process reliability and limit the geometrical design space of the printed parts. Here, these challenges are overcome by utilizing a static inert immiscible liquid below the resin as the constraining interface. We elucidate the mechanisms that enable the static liquid to mitigate stiction in both discrete layer-by-layer and continuous layerless growth modes. The inert liquid functions as a dewetting interface during the discrete growth and as a carrier of oxygen to inhibit polymerization during the continuous growth. This method enables a wide range of process conditions, such as exposure and resin properties, which facilitates micrometer scale resolutions and dimensional accuracies above 95%. We demonstrate multi-scale microstructures with feature sizes ranging from 16 μm to thousands of micrometers and functional devices with aspect ratios greater than 50:1 without using sacrificial supports. This process can enable additive 3D microfabrication of functional devices for a variety of applications.