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Research Papers

J. Micro Nano-Manuf. 2016;5(1):011001-011001-8. doi:10.1115/1.4034634.

One of the major challenges in nanoscale manufacturing is defect control because it is difficult to measure nanoscale features in-line with the manufacturing process. Optical inspection typically is not an option at the nanoscale level due to the diffraction limit of light, and without inspection high scrap rates can occur. Therefore, this paper presents an atomic force microscopy (AFM)-based inspection system that can be rapidly implemented in-line with other nanomanufacturing processes. Atomic force microscopy is capable of producing very high resolution (subnanometer-scale) surface topology measurements and is widely utilized in scientific and industrial applications, but has not been implemented in-line with manufacturing systems, primarily because of the large setup time typically required to take an AFM measurement. This paper introduces the design of a mechanical wafer-alignment device to enable in-line AFM metrology in nanoscale manufacturing by dramatically reducing AFM metrology setup time. The device consists of three pins that exactly constrain the wafer and a nesting force applied by a flexure to keep the wafer in contact with the pins. Kinematic couplings precisely mate the device below a flexure stage containing an array of AFM microchips which are used to make nanoscale measurements on the surface of the semiconductor wafer. This passive alignment system reduces the wafer setup time to less than 1 min and produces a lateral positioning accuracy that is on the order of ∼1 μm.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2016;5(1):011002-011002-6. doi:10.1115/1.4034645.

This paper presents the development process of a new coating method for micro pencil grinding tools (MPGTs). MPGTs, applied for microgrinding, consist of a base body, abrasives, and a metallic bond. The manufacturing process of these microtools presents two challenges. The first being in finding a method to embed the abrasives with a uniform grit distribution and the second finding the correct parameters, required for a bond with adequate grit retention forces. In this research, an electroless plating process is presented. Both the abrasive grit distribution method and the plating parameters will be presented in this paper.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2017;5(1):011003-011003-14. doi:10.1115/1.4035389.

A hybrid thermoplastic forming process involving sequential micromolding and microdrawing operations is developed to manufacture the multifacet/curvilinear geometries found on most surgical blades. This is accomplished through an oblique drawing technique, i.e., drawing with a nonzero inclination angle. By applying time-varying force profiles during the drawing operation, a wide range of complex blade geometries is possible. Experiments have exhibited positive results across several multifacet and curvilinear blade geometries. Manufacturing process capabilities are quantitatively evaluated and experimental results have measured the bulk metallic glass (BMG) blade cutting edge radii to be consistently less than 15 nm, rake face surface roughness Ra to be on the order of 20 nm, and edge straightness deviations to be less than 5 μm root-mean-square (RMS) while retaining an amorphous atomic structure.

Topics: Blades
Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2017;5(1):011004-011004-7. doi:10.1115/1.4035390.

Microstructured surfaces have extensive applications in a wide array of fields due to their improved functional performance. Existing manufacturing methods for these surfaces fall short of efficiency for volume production or are only applicable to a specific class of materials. In this paper, an innovative and highly efficient machining method, elliptical vibration texturing (EVT), is proposed for rapid generation of microdimples on planar engineered surfaces. The cutting tool of the EVT process vibrates along an elliptical trajectory. The elliptical vibrations, when coupled with a high cutting velocity, impose microdimples onto workpiece surfaces while machining. The high productivity is achieved by adopting a newly designed tertiary motion generator, which is able to deliver required elliptical vibrations at an ultrasonic frequency. The shape and distribution of the generated dimple patterns have been theoretically analyzed and predicted by a proposed simulation model. Preliminary texturing results using aluminum and brass as workpieces are given to validate the process principle and simulation model.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2017;5(1):011005-011005-5. doi:10.1115/1.4035474.

In this paper, a finite element model is developed, and experimentally validated, for predicting the force required to produce a compression seal between a polycarbonate sealing boss and a 25-μm thick elastoviscoplastic hemodialysis membrane. This work leverages previous efforts to determine the conditions for hermetic sealing in a microchannel hemodialyzer fabricated using hot-embossed polycarbonate microchannel laminae containing sealing boss features. Methods are developed for mechanically characterizing the thin elastoviscoplastic hemodialysis membrane. The experimental data for assessing the depth of penetration into the membrane as a function of force show an R2 value of 0.85 showing good repeatability. The average percent error was found to be −8.0% with a range between −21.9% and 4.4% error in the strain region of interest.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2017;5(1):011006-011006-8. doi:10.1115/1.4035392.

A novel directional freezing based three-dimensional (3D) printing technique is applied to fabricate graphene aerogel (GA). Thermal property of the graphene ink is one of the key impacts on the material morphology and process efficiency/reliability. We develop a heat transfer model to predict temperature evolution of the printed materials and then estimate layer waiting time based on it. The proposed technique can not only improve the process efficiency and reliability but also serve as a flexible tool to predict and control the microstructure of the printed graphene aerogels. Both the simulation and experiment results demonstrate the efficiency and effectiveness of the proposed approach.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2017;5(1):011007-011007-7. doi:10.1115/1.4035397.

Ceramics and semiconductors have many applications in optics, micro-electro-mechanical systems, and electronic industries due to their desirable properties. In most of these applications, these materials should have a smooth surface without any surface and subsurface damages. Avoiding these damages yet achieving high material removal rate in the machining of them is very challenging as they are extremely hard and brittle. Materials such as single crystal silicon and sapphire have a crystal orientation or anisotropy effect. Because of this characteristic, their mechanical properties vary significantly by orientation that makes their machining even more difficult. In previous works, it has been shown that it is possible to machine brittle materials in ductile mode. In the present study, scratch tests were accomplished on the monocrystal sapphire in four different perpendicular directions. A laser is transmitted to a diamond cutting tool to heat and soften the material to either enhance the ductility, resulting in a deeper cut, or reducing brittleness leading to decreased fracture damage. Results such as depth of cut and also nature of cut (ductile or brittle) for different directions, laser powers, and cutting loads are compared. Also, influence of thermal softening on ductile response and its correlation to the anisotropy properties of sapphire is investigated. The effect of thermal softening on cuts is studied by analyzing the image of cuts and verifying the depth of cuts which were made by using varying thrust load and laser power. Macroscopic plastic deformation (chips and surface) occurring under high contract pressures and high temperatures is presented.

Commentary by Dr. Valentin Fuster
J. Micro Nano-Manuf. 2017;5(1):011008-011008-7. doi:10.1115/1.4035473.

This paper presents the design and characteristics of a new two-dimensional nonresonant tertiary motion generator which is based on the flextensional structure. A tool holder connects two perpendicularly placed flextensional actuators with flexure hinges which decouple the motion outputs from the two actuators. Piezoelectric stacks, which are preloaded through precision screws, are used to provide input displacements. By balancing the requirements of driving current, stiffness, and the displacement amplification ratio, the proposed design is targeted to operate at above 10 kHz with two-dimensional vibrations amplitude of 10 μm in each direction. Technical difficulties in driving a nonresonant mode piezoelectric actuator at a high frequency are discussed. The solutions and optimization procedures are presented in this paper. The design is optimized by finite-element simulation; and the results are presented and verified by our prototype design.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Micro Nano-Manuf. 2017;5(1):014501-014501-6. doi:10.1115/1.4035388.

In micro-stereolithograhy (μSL), high-speed fabrication is a critical challenge due to the long delay time for refreshing resin and retaining printed microfeatures. Thus, the mask-image-projection-based micro-stereolithograhy (MIP-μSL) using the constrained surface technique is investigated in this paper for quickly recoating liquid resin. It was reported in the literature that severe damages frequently happen in the part separation process in the constrained-surface-based MIP-μSL system. To conquer this problem, a single-layer movement separation approach was adopted, and the minimum delay time for refreshing resin was experimentally characterized. The experimental results verify that, compared with the existing MIP-μSL processes, the MIP-μSL process with single-layer movement separation method developed in this paper can build microstructures with complex geometry, with a faster build speed.

Commentary by Dr. Valentin Fuster

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