Quentin T. Aten

Carbon Nanotubes as a Framework for High-Aspect-Ratio MEMS Fabrication

A class of carbon-nanotube (CNT) composite materials was developed to take advantage of the precise high-aspect-ratio shape of patterned vertically grown nanotube forests. These patterned forests were rendered mechanically robust by chemical vapor infiltration and released by etching an underlying sacrificial layer. We fabricated a diverse variety of functional MEMS devices, including cantilevers, bistable mechanisms, and thermomechanical actuators, using this technique. A wide range of chemical-vapor-depositable materials could be used as fillers; here, we specifically explored infiltration by silicon and silicon nitride. The CNT framework technique may enable high-aspect-ratio MEMS fabrication from a variety of materials with desired properties such as high-temperature stability or robustness. The elastic modulus of the silicon-nanotube and silicon nitride-nanotube composites is dominated by the filler material, but they remain electrically conductive, even when the filler (over 99% of the composites mass) is insulating.

A Tristable Mechanism Configuration Employing Orthogonal Compliant Mechanisms

ristable mechanisms, or devices with three distinct stable equiibrium positions, have promise for future applications, but the omplexities of the tristable behavior have made it difficult to dentify configurations that can achieve tristable behavior while eeting practical stress and fabrication constraints. This paper escribes a new tristable configuration that employs orthogonally riented compliant mechanisms that result in tristable mechanics hat are readily visualized. The functional principles are described nd design models are derived. Feasibility is conclusively demontrated by the successful operation of four embodiments covering range of size regimes, materials, and fabrication processes. ested devices include an in-plane tristable macroscale mechaism, a tristable lamina emergent mechanism, a tristable microechanism made using a carbon nanotube-based fabrication proess, and a polycrystalline silicon micromechanism. DOI: 10.1115/1.4000529

A Numerical Method for Position Analysis of Compliant Mechanisms With More Degrees of Freedom Than Inputs

An underactuated or underconstrained compliant mechanism may have a determined equilibrium position because its energy storage elements cause a position of local minimum potential energy. The minimization of potential energy (MinPE) method is a numerical approach to finding the equilibrium position of compliant mechanisms with more degrees of freedom (DOF) than inputs. Given the pseudorigid-body model of a compliant mechanism, the MinPE method finds the equilibrium position by solving a constrained optimization problem: minimize the potential energy stored in the mechanism, subject to the mechanisms vector loop equation(s) being equal to zero. The MinPE method agrees with the method of virtual work for position and force determination for underactuated 1-DOF and 2-DOF pseudorigid-body models. Experimental force-deflection data are presented for a fully compliant constant-force mechanism. Because the mechanisms behavior is not adequately modeled using a I-DOF pseudorigid-body model, a 13-DOF pseudorigid-body model is developed and solved using the MinPE method. The MinPE solution is shown to agree well with nonlinear finite element analysis and experimental force-displacement data.

Compliant Constant-Force Micro-Mechanism for Enabling Dual-Stage Motion

This paper describes a fully compliant constant-force micro-mechanism that enables dual-stage motion for nanoinjection. Nanoinjection is a recently developed process for delivering DNA into mouse zygotes via electrostatic accumulation and release of the DNA onto a microelectromechanical system (MEMS) lance.The fully compliant constant-force nanoinjector is a concatenation of two separate mechanisms: a six-bar mechanism with compliant lamina-emergent torsional (LET) joints to raise the lance, and a pair of constant-force crank-sliders with LET joints positioned on either side of the six-bar mechanism to drive the lance forward.The fully compliant nanoinjector exhibits self-reconfiguring metamorphic motion to first raise the lance to the midline of the zygote and then translate the lance forward with a controlled motion. This dual-stage motion is necessary for the lance to pierce the zygote without causing damage to the cell membrane.The device achieves two sequential displacement behaviors in a compliant mechanism fabricated from a single, continuous piece of material.Copyright

A self-reconfiguring metamorphic nanoinjector for injection into mouse zygotes

This paper presents a surface-micromachined microelectromechanical system nanoinjector designed to inject DNA into mouse zygotes which are ≈90 μm in diameter. The proposed injection method requires that an electrically charged, DNA coated lance be inserted into the mouse zygote. The nanoinjectors principal design requirements are (1) it must penetrate the lance into the mouse zygote without tearing the cell membranes and (2) maintain electrical connectivity between the lance and a stationary bond pad. These requirements are satisfied through a two-phase, self-reconfiguring metamorphic mechanism. In the first motion subphase a change-point six-bar mechanism elevates the lance to ≈45 μm above the substrate. In the second motion subphase, a compliant folded-beam suspension allows the lance to translate in-plane at a constant height as it penetrates the cell membranes. The viability of embryos following nanoinjection is presented as a metric for quantifying how well the nanoinjector mechanism fulfills its design requirements of penetrating the zygote without causing membrane damage. Viability studies of nearly 3000 nanoinjections resulted in 71.9% of nanoinjected zygotes progressing to the two-cell stage compared to 79.6% of untreated embryos.

High aspect ratio microelectromechanical systems: A versatile approach using carbon nanotubes as a framework

We recently developed a fabrication process for carbon nanotube templated MEMS. The fabrication process involves growing a three dimensional pattern from carbon nanotube forests and filling that forest by chemical vapor infiltration to make a solid structure. This templating process allows us to fabricate extremely high aspect ratio microscale structures from a wide variety of materials. The nanotube structures can be hundreds of microns tall with lateral pattern dimensions down to a few microns. The chemical vapor infiltration has been shown with silicon and silicon nitride but could be extended to many other materials. In this paper, we investigate the microstructure of the filling material and extend the process to the fabrication of comb actuators.

Testing of a Pumpless MEMS Microinjection Needle Employing Electrostatic Attraction and Repulsion of DNA

The ultimate goal of this work is to develop an automated MEMS-based lab-on-a-chip microinjector. This paper outlines one phase of that work: testing the feasibility of a pumpless, polysilicon MEMS microneedle for use in the proposed MEMS-based lab-on-a-chip microinjector. The pumpless MEMS microneedle operates on the principle of attraction and repulsion of DNA using electrostatic charges. Prototype microneedles were fabricated using a multi-layer surface micromachining process. DNA stained with a fluorescent dye (4‘, 6-DIAMIDINO-2-PHENYLINDOLE DIHYDROCHLORIDE or DAPI) was visualized using fluorescent illumination as the DNA was attracted to and repelled from the tips of MEMS microneedles using a 1.5 V DC source. The pumpless MEMS microneedle represents an important and significant step in the development of a self-contained, automated, MEMS-based microinjection system.Copyright

A Metamorphic Erectable Cell Restraint (MECR)

This paper introduces a metamorphic erectable cell restraint (MECR) to provide cell restraint in genetic research. A micro-electromechanical systems (MEMS) metamorphic mechanism with two phases of motion was designed to grasp individual embryos about their midplane. The first phase of motion lifts a compliant gripper approximately 40 μm (about half the diameter of an embryo). The gripper then closes in the second phase to grasp the embryo. The metamorphic mechanism includes compliant mechanism components which are analyzed here. A microscale prototype was fabricated from polysilicon and used to demonstrate the mechanism’s two phase motion.Copyright

Facets and Fissures of a Fractured SOI Wafer

This scanning electron micrograph shows a cross section of a cleaved silicon-on-insulator (SOI) wafter. The wafer cleave passed through a partially released device that included the array of etch release holes visible in this image. The patterned monocrystalline silicon layer had a different crystalline orientation than the much thicker monocrystalline silicon substrate. When the wafer was cleaved, substrate silicon fractured along a single crystalline plane, leaving a flat, smooth surface. The patterned layer did not share this crystalline plane, and fractured in many directions resulting in an irregular, multi-faceted surface.Copyright

MEMS Nanoinjector for Injecting Foreign DNA Into Living Cells

The nanoinjector is a MEMS device that has been successfully used to inject foreign genetic material into fertilized mouse egg cells (zygotes). This scanning electron micrograph shows a nanoinjector grasping a 100 μm diameter latex sphere. The sphere is roughly the size of a mouse zygote, and it can withstand the harsh environment in the electron microscope better than a mouse zygote. The nanoinjector’s two constraining mechanisms (at left and top-right) and lance mechanism (bottom right) are fabricated from two planar layers of polysilicon through MEMSCAP’s polysilicon Multi-User MEMS Processes (polyMUMPs)Copyright