There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

생체의 모델링과 Simulation

Polymer based MEMS and microfluidic devices have the advantages of mechanical flexibility, lower fabrication cost and faster processing over silicon based ones. Also, many polymer materials are considered biocompatible and can be used in biological applications. A valuable class of polymers for microfabricated devices is piezoelectric functional polymers. In addition to the normal advantages of polymers, piezoelectric polymers can be directly used as an active material in different transduction applications. This paper gives an overview of piezoelectric polymers based on their operating principle. This includes three main categories: bulk piezoelectric polymers, piezocomposites and voided charged polymers. State-of-the-art piezopolymers of each category are presented with a focus on fabrication techniques and material properties. A comparison between the different piezoelectric polymers and common inorganic piezoelectric materials (PZT, ZnO, AlN and PMN?PT) is also provided in terms of piezoelectric properties. The use of piezopolymers in different electromechanical devices is also presented. This includes tactile sensors, energy harvesters, acoustic transducers and inertial sensors.

https://iopscience.iop.org/article/10.1088/0964-1726/23/3/033001/pdf

A review of piezoelectric polymers as functional materials for electromechanical transducers

We investigated the folding of rectangular stimuli-responsive hydrogel-based polymer bilayers with different aspect ratios and relative thicknesses placed on a substrate. It was found that long-side rolling dominates at high aspect ratios (ratio of length to width) when the width is comparable to the circumference of the formed tubes, which corresponds to a small actuation strain. Rolling from all sides occurs for higher actuation, namely when the width and length considerably exceed the deformed circumference. In the case of moderate actuation, when both the width and length are comparable to the deformed circumference, diagonal rolling is observed. Short-side rolling was observed very rarely and in combination with diagonal rolling. On the basis of experimental observations, finite-element modeling and energetic considerations, we argued that bilayers placed on a substrate start to roll from corners due to quicker diffusion of water. Rolling from the long-side starts later but dominates at high aspect r...

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Shape-programmed folding of stimuli-responsive polymer bilayers.

Since its introduction in the nineties, the negative resist SU-8 has been increasingly used in micro- and nanotechnologies. SU-8 has made the fabrication of high-aspect ratio structures accessible to labs with no high-end facilities such as X-ray lithography systems or deep reactive ion etching systems. These low-cost techniques have been applied not only in the fabrication of metallic parts or molds, but also in numerous other micromachining processes. Its ease of use has made SU-8 to be used in many applications, even when high-aspect ratios are not required. Beyond these pattern transfer applications, SU-8 has been used directly as a structural material for microelectromechanical systems and microfluidics due to its properties such as its excellent chemical resistance or the low Young modulus. In contrast to conventional resists, which are used temporally, SU-8 has been used as a permanent building material to fabricate microcomponents such as cantilevers, membranes, and microchannels. SU-8-based techniques have led to new low-temperature processes suitable for the fabrication of a wide range of objects, from the single component to the complete lab-on-chip. First, this article aims to review the different techniques and provides guidelines to the use of SU-8 as a structural material. Second, practical examples from our respective labs are presented.

SU-8 as a structural material for labs-on-chips and microelectromechanical systems.

We have developed a new polymer MEMS process that shows enormous flexibility in design parameters. This process uses entirely spin-on layers for structural and sacrificial materials. Further, this process flow is designed for multiple users to fabricate as many devices as possible on the same wafer which up to this point has not been demonstrated with polymer MEMS technologies. In this process, all structural layers are fabricated out of negative tone SU-8 photoresist and all sacrificial and separation layers are defined by a thin film of polystyrene. Using entirely spin-on layers for structural and sacrificial materials provides an easy way to select layer thicknesses without having to significantly alter the materials or processing techniques. A metal thin-film deposition step is also incorporated that allows electrical connection to the microstructures and actuators in this process. To characterize the robustness and flexibility of this technology we have fabricated a variety of in-plane and out-of-plane microstructures including chevron-type thermal actuators and tested their mechanical and electromechanical operation. The entire process sequence is accomplished at temperatures below 200 °C, making this technology compatible for post-processing integration of MEMS on an electronics circuit wafer.

Polymer MEMS processing for multi-user applications

The effect of processing conditions on the curvature of SU-8 cantilevers up to 6400 µm long is determined by experimental methods. Our observations suggest that a zero curvature condition can be achieved by controlling the exposure dose and post-exposure baking time for any given SU-8 thickness. The curvature of SU-8 cantilevers processed with different exposure doses and post-exposure baking times has been measured and reveals that the gradient of crosslinking density throughout the SU-8 film is the cause of out-of-plane stress. A general model for the SU-8 cantilever curvature is developed which explains the behavior of SU-8 structures that have been processed with different conditions and can be used to predict the general effect on the SU-8 cantilever curvature for different SU-8 thicknesses and process parameters.

https://iopscience.iop.org/article/10.1088/0960-1317/17/5/032/pdf

Control of the out-of-plane curvature in SU-8 compliant microstructures by exposure dose and baking times

A novel design for hingeless out-of-plane microstructures is presented. These structures can be assembled to 90° by a single-point actuation, which can be provided by, for example, a microelectronics wirebonder or a microprober station. Both wirebonders and microprober stations are commonly available to microfabrication facilities, and therefore the assembly method described here introduces a practical and economical approach to the creation of out-of-plane structures. The microstructure designs can be used in many types of microfabrication processes, and in particular have been fabricated using both PolyMUMPs and an SU-8 technology developed at Simon Fraser University. In addition to the fabricated devices, we will present the results of finite element analysis (FEA). Also reported here are tests for positional repeatability and reliability.

https://iopscience.iop.org/article/10.1088/0960-1317/17/7/014/pdf

Automated assembly of hingeless 90° out-of-plane microstructures

This paper reports on two novel 3-axis thermal accelerometers based on different mechanical structures that are fabricated using polyimide PI-2611, and assembled using a standard wire-bonder. One accelerometer design has an un-amplified linear DC sensitivity of plusmn45 muV/g, plusmn60 muV/g, and plusmn35 muV/g on the X, Y, and Z axes respectively. The second design has a sensitivity of plusmn17 muV/g, plusmn8.5 muV/g, and plusmn14 muV/g respectively. Both accelerometers are assembled by applying a lateral push to each of the out-of-plane parts using an unmodified wire-bonder. This paper will detail the fabrication, design, assembly, and functional results of the two 3-axis thermal accelerometer designs.

Monolithically fabricated polymermems 3-axis thermal accelerometers designed for automated wirebonder assembly

A novel electrothermal micro-actuator capable of actuation after being rotated 90 out of plane is presented. The actuator is fabricated and characterized using the Micragem silicon-on-insulator (SOI) process developed by Micralyne Inc. The actuator is designed to be rotated out of plane by means of a serpentine spring design that provides electrical contact to the substrate while applying a downward force to hold the actuator in place. The eventual purpose of this actuator is to adjust the position of a micromirror at a 90 angle to the substrate. The actuator performs as expected in the horizontal position and can be assembled using standard microprobes. The actuator performance and the theory of spring operation are presented using an analytical heat transfer model, finite element modelling, and device measurements.

See-Ho Tsang

Papers

Polymer MEMS processing for multi-user applications

Control of the out-of-plane curvature in SU-8 compliant microstructures by exposure dose and baking times

Automated assembly of hingeless 90° out-of-plane microstructures

Monolithically fabricated polymermems 3-axis thermal accelerometers designed for automated wirebonder assembly

Out-of-plane electrothermal actuators in silicon-on-insulator technology