Daniel Hilbich

Bidirectional magnetic microactuators for uTAS

We present the design, fabrication and characterization of a novel bidirectional magnetic microactuator. The actuator has a planar structure and is easily fabricated using processes based on laser micromachining and soft lithography, allowing it to be readily integrated into microfluidic, microelectromechanical systems (MEMS) and lab-on-a-chip (LOC) designs. The new microactuator is a thin magnetic membrane with a central magnet feature. The membrane and magnet are both composed of a magnetic nanocomposite polymer (M-NCP) material that is fabricated by embedding magnetic powder in a polydimethysiloxane (PDMS) polymer matrix. The magnetic powder (MQP-12-5) has the chemical composition of (Nd0.7Ce0.3)10.5Fe83.9B5.6, and contains grains that are 5-6 microns in size. The powder is uniformly dispersed at a weight percentage of 75 wt-% in the PDMS matrix, and micropatterned using soft lithography micromolding to realize magnetic microstructures, which sit on a thinner magnetic PDMS membrane of the same material. The molds are fabricated by laser-etching into Poly (methyl methacrylate) (PMMA) using a Universal Laser Systems VersaLASER© laser ablation system. The PDMS-based M-NCP is then poured and spun over the mold patterns, producing a thin polymer membrane to which the polymer micromagnets are attached, forming a one-piece actuator. The M-NCP is initially un-magnetized, but is then magnetized by placing it in a 2.5T magnetic field to produce permanent bidirectional magnetization that is polarized in the specified direction. To characterize the bidirectional actuators, a uniform magnetic field is established via a Helmholtz coil pair, and is characterized by applying varying currents. The magnetic field (and thus the actuator deflection) is controlled by regulating the current in the Helmholtz pair. Using this apparatus, deflection versus field characteristics are obtained, with maximum deflections varying as a function of actuator dimensions and the applied magnetic field. Permanent rare earth magnets are used to produce supplemental fields for higher magnetic fields and higher deflections. Deflections of 100 micrometers and more are observed for 3 to 8 mm square membranes with central magnetic features ranging from 0.8 to 3.6 mm squares, in magnetic fields ranging from 52 to 6.2 mT. In addition, smaller membranes (1 mm and 2 mm with 0.4 mm and 0.6 mm central magnets, respectively) also deflect 20 and 50 microns, respectively, under 72 mT fields.

A new low-cost, thick-film metallization transfer process onto PDMS using a sacrificial copper seed

We present a new low cost microfabrication technology that utilizes a sacrificial conductive paint transfer method to realize thick film copper microstructures that are embedded in polydimethylsiloxane (PDMS). This process has reduced fabrication complexity and cost compared to existing metal-on-PDMS techniques, which enables large scale rapid prototyping of designs using minimal laboratory equipment. This technology differs from others in its use of a conductive copper paint seed layer and a unique transfer process that results in copper microstuctures embedded in PDMS. By embedding microstructures flush with PDMS surface, rather than fabricating the microstructures on the substrate surface, we produce a metallization layer that adheres to PDMS without the need for surface modifications. The fabrication process begins with the deposition of the seed layer onto a flexible substrate via airbrushing. A dry film photoresist layer is laminated on top and patterned using standard techniques. Electroplated copper is grown on the seed layer through the photoresist mask and transferred to PDMS through a unique baking procedure. This baking transfer process releases the electroplated copper from the seed layer, permanently embedding it into the cured PDMS without cracking or otherwise deforming it. We have performed initial characterizations of the copper microstructures in terms of feature size, film thickness, surface roughness, resistivity, and reliability under flexing. Initial results show that we can achieve films 25-75 micrometers in thickness, with reliable feature sizes down to 100 micrometers and a film resistivity of approximately 7.15 micro-Ω-cm. Process variants and future work are discussed, as well as large scale adaptations and rapid prototyping. Finally, we outline the potential uses of this technology in flexible electronics, particularly in high power applications.

Manipulation of permanent magnetic polymer micro-robots: a new approach towards guided wireless capsule endoscopy

We present the initial experimental results for manipulating micro-robots featuring permanent magnetic polymer magnets for guided wireless endoscopy applications. The magnetic polymers are fabricated by doping polydimethylsiloxane (PDMS) with permanent isotropic rare earth magnetic powder (MQFP 12-5) with an average particle size of 6 μm. The prepared magnetic nanocomposite polymer (M-NCP) is patterned in the desired shape against a plexiglass mold via soft lithography techniques. It is observed that the fabricated micro-robot magnets have a magnetic field strength of 50 mT and can easily be actuated by applying a field of 8.3 mT (field measured at the capsule’s position) and moved at a rate of 5 inches/second.

Stretchable electronics for wearable and high-current applications

Advances in the development of novel materials and fabrication processes are resulting in an increased number of flexible and stretchable electronics applications. This evolving technology enables new devices that are not readily fabricated using traditional silicon processes, and has the potential to transform many industries, including personalized healthcare, consumer electronics, and communication. Fabrication of stretchable devices is typically achieved through the use of stretchable polymer-based conductors, or more rigid conductors, such as metals, with patterned geometries that can accommodate stretching. Although the application space for stretchable electronics is extensive, the practicality of these devices can be severely limited by power consumption and cost. Moreover, strict process flows can impede innovation that would otherwise enable new applications. In an effort to overcome these impediments, we present two modified approaches and applications based on a newly developed process for stretchable and flexible electronics fabrication. This includes the development of a metallization pattern stamping process allowing for 1) stretchable interconnects to be directly integrated with stretchable/wearable fabrics, and 2) a process variation enabling aligned multi-layer devices with integrated ferromagnetic nanocomposite polymer components enabling a fully-flexible electromagnetic microactuator for large-magnitude magnetic field generation. The wearable interconnects are measured, showing high conductivity, and can accommodate over 20% strain before experiencing conductive failure. The electromagnetic actuators have been fabricated and initial measurements show well-aligned, highly conductive, isolated metal layers. These two applications demonstrate the versatility of the newly developed process and suggest potential for its furthered use in stretchable electronics and MEMS applications.