Design and Electro-Thermo-Mechanical Behavior Analysis of Au/Si3N4 Bimorph Microcantilevers for Static Mode Sensing.

This paper presents a design optimization method based on theoretical analysis and numerical calculations, using a commercial multi-physics solver (e.g., ANSYS and ESI CFD-ACE+), for a 3D continuous model, to analyze the bending characteristics of an electrically heated bimorph microcantilever. The results from the theoretical calculation and numerical analysis are compared with those measured using a CCD camera and magnification lenses for a chip level microcantilever array fabricated in this study. The bimorph microcantilevers are thermally actuated by joule heating generated by a 0.4 µm thin-film Au heater deposited on 0.6 µm Si3N4 microcantilevers. The initial deflections caused by residual stress resulting from the thermal bonding of two metallic layers with different coefficients of thermal expansion (CTEs) are additionally considered, to find the exact deflected position. The numerically calculated total deflections caused by electrical actuation show differences of 10%, on average, with experimental measurements in the operating current region (i.e., ~25 mA) to prevent deterioration by overheating. Bimorph microcantilevers are promising components for use in various MEMS (Micro-Electro-Mechanical System) sensing applications, and their deflection characteristics in static mode sensing are essential for detecting changes in thermal stress on the surface of microcantilevers.

Numerical Modeling and Experimental Validation by Calorimetric Detection of Energetic Materials Using Thermal Bimorph Microcantilever Array: A Case Study on Sensing Vapors of Volatile Organic Compounds (VOCs).

Bi-layer (Au-Si3N4) microcantilevers fabricated in an array were used to detect vapors of energetic materials such as explosives under ambient conditions. The changes in the bending response of each thermal bimorph (i.e., microcantilever) with changes in actuation currents were experimentally monitored by measuring the angle of the reflected ray from a laser source used to illuminate the gold nanocoating on the surface of silicon nitride microcantilevers in the absence and presence of a designated combustible species. Experiments were performed to determine the signature response of this nano-calorimeter platform for each explosive material considered for this study. Numerical modeling was performed to predict the bending response of the microcantilevers for various explosive materials, species concentrations, and actuation currents. The experimental validation of the numerical predictions demonstrated that in the presence of different explosive or combustible materials, the microcantilevers exhibited unique trends in their bending responses with increasing values of the actuation current.

Multiplexed lipid dip-pen nanolithography on subcellular scales for the templating of functional proteins and cell culture.

Molecular patterning processes taking place in biological systems are challenging to study in vivo because of their dynamic behavior, subcellular size, and high degree of complexity. In vitro patterning of biomolecules using nanolithography allows simplification of the processes and detailed study of the dynamic interactions. Parallel dip-pen nanolithography (DPN) is uniquely capable of integrating functional biomolecules on subcellular length scales due to its constructive nature, high resolution, and high throughput. Phospholipids are particularly well suited as inks for DPN since a variety of different functional lipids can be readily patterned in parallel. Here DPN is used to spatially pattern multicomponent micro- and nanostructured supported lipid membranes and multilayers that are fluid and contain various amounts of biotin and/or nitrilotriacetic acid functional groups. The patterns are characterized by fluorescence microscopy and photoemission electron microscopy. Selective adsorption of functionalized or recombinant proteins based on streptavidin or histidine-tag coupling enables the semisynthetic fabrication of model peripheral membrane bound proteins. The biomimetic membrane patterns formed in this way are then used as substrates for cell culture, as demonstrated by the selective adhesion and activation of T-cells.

Dip Pen Nanolithography (DPN): process and instrument performance with NanoInk's NSCRIPTOR system.

Precision nanoscale deposition is a fundamental requirement for much of current nanoscience research and promises to facilitate exciting industrial applications. Tailoring chemical composition and surface structure on the sub-100 nm scale benefits researchers in topics ranging from catalysis, to biological recognition in nanoscale systems, to electronic connectivity on the nanoscale. Precision nanoscale deposition engenders applications such as additive photomask repair and nanodevice fabrication. Dip Pen Nanolithography (DPN) is a scanning-probe-based direct-write technique for generating surface-patterned chemical functionality and discrete structures on the sub-100 nm scale. In this publication we explore the effects of changing tip radius and surface roughness. We find that blunter tips lead to higher minimum line widths and that higher rms surface roughness leads to higher minimum line widths; line edge roughness also increases with substrate roughness and surface feature size. Also, we characterize the performance of the Nscriptor DPN instrument and demonstrate the placement of pattern features with precision better than 10 nm, and size control better than 15% for sub-100 nm features.

Self-leveling two-dimensional probe arrays for Dip Pen Nanolithography.

Scanning probe lithography (SPL) has witnessed a dramatic transformation with the advent of two-dimensional (2D) probe arrays. Although early work with single probes was justifiably assessed as being too slow to practically apply in a nanomanufacturing context, we have recently demonstrated throughputs up to 3x10(7) microm(2)/h--in some cases exceeding e-beam lithography--using centimeter square arrays of 55,000 tips tailored for Dip Pen Nanolithography (DPN). Parallelizing DPN has been critical because there exists a need for a lithographic process that is not only high throughput, but also high resolution (DPN has shown line widths down to 14 nm) with massive multiplexing capabilities. Although previous methods required non-trivial user manipulation to bring the 2D array level to the substrate, we now demonstrate a self-leveling fixture for NanoInk's 2D nano PrintArray. When mounted on NanoInk's NLP 2000, the 55,000 tip array can achieve a planarity of <0.1 degrees with respect to the substrate in a matter of seconds, with no user manipulation required. Additional fine-leveling routines (<2 min of user interaction) can improve this planarity to <0.002 degrees with respect to the substrate-a Z-difference of less than 600 nm across 1 cm(2) of surface area. We herein show highly homogeneous etch-resist nanostructure results patterned from a self-leveled array of DPN pens, with feature size standard deviation of <6% across a centimeter square sample. We illustrate the mechanisms and methods of the self-leveling fixture, and detail the advantages thereof. Finally, we emphasize that this methodology brings us closer to the goal of true nanomanufacturing by automating the leveling process, reducing setup time by at least a factor of 10, enhancing the ease of the overall printing process, and ultimately ensuring a more level device with subsequently homogeneous nanostructures.