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Directing neurons to form predetermined circuits with the intention of treating neurological disorders and neurodegenerative diseases is a fundamental goal and current challenge in neuroengineering. Until recently, only neuronal aggregates were studied and characterized in culture, which can limit information gathered to populations of cells. In this study, we use a substrate constructed of arrays of strain-induced self-rolled-up membrane 3D architectures. This results in changes in the neuronal architecture and altered growth dynamics of neurites. Hippocampal neurons from postnatal rats were cultured at low confluency (∼250 cells mm–2) on an array of transparent rolled-up microtubes (μ-tubes; 4–5 μm diameter) of varying topographical arrangements. Neurite growth on the μ-tubes was characterized and compared to controls in order to establish a baseline for alignment imposed by the topography. Compared to control substrates, neurites are significantly more aligned toward the 0° reference on the μ-tube arra...

Radio-frequency (RF) integrated circuits are used for wireless communications and require transformers capable of transferring electrical energy at RF/microwave frequencies. Traditional on-chip RF transformer designs have complex fabrication schemes and offer limited performance scalability. Here we report on-chip RF/microwave transformers that are based on a self-rolled-up membrane platform. The monolithic nature and versatility of this platform allows us to create high-performance transformers while maintaining an ultra-compact device footprint and by using only planar processing. We also show that the performance of the three-dimensional RF transformers improves with scaling, which is in contrast to conventional planar designs. In particular, we observe a continuous rate of increase in the index of performance of our RF transformers as we scale up the turns ratio. This behaviour is attributed to the almost ideal mutual magnetic coupling inherent to the self-rolled-up membrane three-dimensional architecture.

On-chip copper (Cu) based self-rolled-up membrane (S-RuM) inductors are demonstrated for the first time. Compared to the gold (Au) based S-RuM inductor, device structures and fabrication processes are re-designed to realize CMOS compatibility by switching conduction metal to Cu and overcoming related processing challenges. Performance enhancements include ∼44% reduction of conduction layer resistivity compared to Au-based with the same thickness, and a clear path to 100% fabrication yield are achieved. RF measurement shows as high as ∼ 61nH/mm2 inductance density with just a 2-turn structure for these air-core S-RuM inductors. The achieved inductance is in the range from 0.3nH to 1nH. The best self-resonant-frequency (SRF) and quality factor (Q factor) of 1nH device is ∼23GHz and ∼2.4@5GHz, respectively. Much better performance can be readily obtained by rolling up more turns and integrating soft magnetic material thin film and core. Results show that Cu S-RuM inductor is very promising to replace on-chip planar inductor with better performance as a new industry standard.

In neural interface platforms, cultures are often carried out on a flat, open, rigid, and opaque substrate, posing challenges to reflecting the native microenvironment of the brain and precise engagement with neurons. Here we present a neuron cell culturing platform that consists of arrays of ordered microtubes (2.7–4.4 μm in diameter), formed by strain-induced self-rolled-up nanomembrane (s-RUM) technology using ultrathin (

Inductors are essential components of radio frequency integrated circuits (RFICs). While the active devices in RF systems downscale steadily, inductors have not been able to keep up with the pace of continual miniaturization because of the trade-off between size and performance as well as fabrication complexity. Strain-induced self-rolled-up nanotechnology allows the formation of three-dimensional (3D) architectures, such as multiple-turn spiral tubes, through planar processing. Here, we report on using 3D SiN(x) tubular structures with accompanying prepatterned metal layers, as a novel on-chip tube inductor design platform. We found, by an equivalent lumped circuit and electromagnetic modeling, that the 3D metal spiral structure has the ability to significantly better confine magnetic field compared to conventional planar spiral on-chip inductors. More than 100× reduction in footprint can be realized using this platform while achieving excellent electrical performance, including large inductance, high quality (Q) factor, and high self-resonance frequency (f(0)).

An outstanding challenge for humanity is to continue to understand how our brain works and invent technology to restore neural circuit functionalities. Many neural interfaces used for neuron cell cultures are flat, open, rigid, and opaque, posing challenges to reflecting the native microenvironment of the brain and precise engagement with neurons. Here we present a novel neural interface consisting of silicon nitride microtube arrays formed by a new nanotechnology platform that simply relies on strain-induced self-rolled-up membrane (S-RUM) mechanism [1]. We have found that these microtubes provide robust physical confinement and unprecedented guidance effect towards outgrowth of primary cortical neurons [2]. What is more surprising is that a dramatic increase (20x) of the growth rate inside the microtube compared to regions outside the microtubes has been observed [2]. The outgrowth of hippocampal neurons is also explored using identical platforms with the intent of integrating both networks on the same chip. The unique characteristics of these S-RUM microtubes that enabled the cell guidance and acceleration will be discussed in detail: (1) True 3D geometrical confinement: the perfect cylindrical geometry of the S-RUM microtubes with tunable diameters and ultra-thin walls, the same type of small and confined spaces neurons grow in vivo, provides conformal 3D adhesion tailored to different kinds of cells. (2) Electrostatic adhesion: the deposited SiN x thin films are found to have a high density of trapped positive charges that naturally attract the axon towards the microtube opening. The ability of the microtube array to control the speed and direction of axonal extension provides a key element in arranging patterned neural networks that have both short and long range connections. (3) Optically transparent: having the ability to see through both the tube and the underlying substrate enabled direct observation of how cells transition from the flat regions to different parts of the tube.

In this work, we present recent results on several novel applications including optically monitoring the dissolution of biodegradable materials proposed for use in biological electronic implants, the self-assembly of microtubes during semiconductor etching, and the expansion and deformation of palladium structures for use in hydrogen sensing applications. The measurements are done using diffraction phase microscopy (DPM), a quantitative phase imaging (QPI) technique, which uses the phase of the imaging field to reconstruct a map of the sample’s surface. It combines off-axis and common-path geometries allowing for single-shot, high-speed dynamics with sub-nanometer noise levels.

Formation of three-dimensional (3D) mesostructures in advanced functional materials is of growing interest due to the widepread envisioned applications of devices that exploit 3D architectures. Mechanically-guided assembly based on compressive buckling of 2D precursors represents a promising method, with applicability to a diverse set of geometries and materials, including inorganic semiconductors, metals, polymers and their heteogenous intergration. This paper introduces ideas that extend the levels of control and and the range of 3D layouts that are achievable in these systems. Here, thin, patterned layers with well-defined residual stresses influence the process of 2D to 3D geometric transformation. Systematic studies through combined analytical modeling, numerical simulations and experimental observations demonstrate the effectiveness of the proposed strategy through ~20 example cases with a broad range of complex 3D topologies. The results elucidate the ability of these stressed layers to alter the energy landscape associated with the transformation process and, specifically, the energy barriers that separate different stable modes in the final 3D configurations. A demonstration in a mechanically tunable micro-balance illustrates the utility of these ideas in a simple structure designed for mass measurement.

This study presents the superior structural versatility of strained silicon nitride (SiNx) membranes as a platform for three-dimensional (3D) hierarchical tubular architectures. The effects of compressive and tensile stressed SiNx layer thickness on the self-rolled-up tube curvature, the sacrificial layer etching anisotropy on rolling direction and chirality, and stress engineering by localized thickness control or thermal treatment, are explored systematically. Using strained SiNx membranes as an electrically insulating and optically transparent mechanical support, compact 3D hierarchical architectures involving carbon nanotube arrays and passive electronic components are demonstrated by releasing the functional structures deposited and patterned in 2D. These examples highlight the uniqueness of this platform that exploits 2D processing and self-assembly to achieve highly functional 3D structures.