Multicomponent patterning of nanocomposite polymer and nanoparticle films using photolithography and layer-by-layer self -assembly

In this dissertation, the fabrication, characterization, and application examples of 3D multicomponent nanocomposite micropatterns (MNMs) with precise spatial arrangements are described. The ability to produce such small-scale 3D structures with versatility in composition and structure is a new development based on the integration of nanoscale layer-by-layer (LbL) self-assembly and microscale photolithographic patterning, enabling construction of surfaces with microscale patterns that possess nanotopographies. The techniques used here are analogous to surface micromachining, except that the deposition materials are polymers, biological materials, and colloidal nanoparticles used to produce 3D MNMs. A key feature of the resulting 3D MNMs is that the physical and chemical properties of the multilayer nanofilms may be finely tuned using the versatile LbL assembly process, which makes them attractive for many applications requiring polymeric structures with small features. The work presented here involves development of techniques for the fabrication, characterization, and applications of 3D MNMs, and evaluation of the process parameters involved in the developed techniques. These results clearly demonstrate the feasibility of the polymer 3D MNMs for biotechnological applications; specifically, they have potential as tailored surfaces for direct comparison of cell-material interactions on a single substrate, and for co-culture systems. In reality, the approach described here may enable study of and control over cell-biomaterial and cell-cell interactions in a whole new fashion. The techniques developed in this work represent a major advancement of nanoscale engineering through the integration of nanoscale LbL self-assembly and microscale photolithographic patterning for constructing 3D MNMs with varying physical and chemical properties in precise spatial arrangements. A major finding of this work, related to the applicability of the developed techniques, is that most of the seemingly harsh processes involved in constructing the 3D MNMs have minimal or no deleterious effects on the biological models used here. The exception is the resist developer (MF319), which due to its highly basic nature, results in disintegration of nanofilms exposed to it directly. Nevertheless, the methods developed here are not limited by the photoresists and resist developers used here; biocompatible photoresists and aqueous base developers could potentially be used. This work has pursued the development of organic and inorganic nanofilm scaffolds which can eventually be combined to achieve functionality desired for specific applications. It is anticipated that the 3D MNMs developed in this work will provide general platforms for studying biological processes, which will not only impact stem cell research in general but also provide useful information in support of biomedical device development, and tissue engineering. Although the intended purpose for developing 3D MNMs is to produce novel bioactive systems, their applicability is more general and may find use in a broad range of applications including electronics, photonics, optoelectronics, and chemical and biochemical sensors

3D complex shaped- dissolvable multi level micro/nano mould fabrication

There is growing interest in the development of fabrication techniques to cost effectively mass-produce high-resolution (micro/nano) 3D structures in a range of materials. Biomedical applications are particularly significant. This work demonstrates a novel technique to simultaneously fabricate a sacrificial mould having the inverse shape of the desired device structure and also create the desired device structure using electroplating deposition techniques. The mould is constructed of many thin layers using a photoresist material that is dissolvable and sensitive to UV light. At the same time the device is created in the emerging mould layers using Gold electroplating deposition technique. Choosing to fabricate the mould and the 3D structures in multiple thin layers allows the use of UV light and permits the potential cost-effective realization of 3D curved surfaces, the accuracy and geometric details of which are related to the number of layers used. In this work I present a novel idea to improve the LIGA process when using many masks to deposit multi thin layer over each other. Moreover, this technique can be utilized to produce a curved surface in the vertical direction with any diameter. Practically, a 2 µm thickness of layer is applied in the proposed technique. However, a layer of 0.5 µm or less can be deposited. An example is provided to explain the novel fabrication process and to outline the resulting design and fabrication constraints. With this technique, any structure could be made and any material used. The work employs conventional techniques to produce a 3D complex shape. By using conventional techniques with multi layers to produce a 3D structure, many problems are expected to occur during the process. Those problems were mentioned by many researchers in general but have not been addressed correctly. Most researchers have covered those problems by leaving the conventional and using a new technique they invented to produce the required product. However, in my work I have addressed those problems for the first time and I offered a new and effective technique to improve the MEMS technology and make this technology cheaper. This was achieved by using a research methodology requiring a rigorous review of existing processes, as outlined above, then by proposing a concept design for an improved process. This novel proposed process was then tested and validated by a series of experiments involving the manufacture of demo-devices. The conclusion is that this new process has the potential to be developed into a commercially implementable process

3D laser scanner based on surface silicon micromachining techniques for shape and size reconstruction of the human ear canal

2005/2006As technology advances, hearing aids can be packaged into increasingly smaller housings. Devices that fit entirely within the deeper portion of the external auditory canal have been developed, called completely-in-the-canal (CIC). These aids are custom moulded and have high cosmetic appeal because they are virtually undetectable. They also have several acoustic advantages: reduced occlusion effect, reduced gain requirements, and preservation of the natural acoustic properties of the pinna and external ear. However, CIC hearing aids require proper fitting of the hearing aid shell to the subject ear canal to achieve satisfactory wearing comfort, reduction in acoustic feedback, and unwanted changes in the electro-acoustic characteristics of the aid. To date, the hearing aid shell manufacturing process is fully manual: the shell is fabricated as a replica of the impression of the subject ear canal. Conventional impression acquisition method is very invasive and imprecise, moreover the typical post-impression processes made on the ear impression leaves room for error and may not accurately represent the structural anatomy of patient’s ear canal. There are some laser approaches able to perform a 3D laser scanning of the original ear impression but, the entire shell-making process is completely dependent on the ear impression and often is the sole cause of poor fitting shell. Therefore, direct ear canal scanning is the only way to perform accurate and repeatable measurements without the use of physical ear impression. The conventional optical elements are not able to enter in the inner part of the ear and perform a scanning of the cavity. This work is devoted to the direct scanning of human external auditory canal by using electromagnetically actuated torsion micromirror fabricated by micromachining technique as scanner. This is the first ever demonstration of actual scanning of human external auditory canal by a single integral Micro-Electro-Mechanical System (MEMS). A novel prototype 3D scanning system is developed together with surface reconstruction algorithm to obtain an explicit 3D reconstruction of actual human auditory canal. The system is based on acquisition of optical range data by conoscopic holographic laser interferometer using electromagnetically actuated scanning MEMS micromirror. An innovative fabrication process based on poly(methylmethacrylate) (PMMA) sacrificial layer for fabrication of free standing micromirror is used. Micromirror actuation is achieved by using magnetic field generated with an electromagnetic coil stick. Micromirror and electromagnet coil assembly composes the opto-mechanical scanning probe used for entering in ear auditory canal. Based on actual scan map, a 3D reconstructed digital model of the ear canal was built using a surface point distribution approach. The proposed system allows noninvasive 3D imaging of ear canal with spatial resolution in the 10 μm range. Fabrication of actual shell from in-vivo ear canal scanning is also accomplished. The actual human ear canal measurement techniques presented provide a characterization of the ear canal shape, which help in the design and refining of hearing aids fabrication approaches to patient personalized based.XIX Ciclo197

Fabrication of ceramic and ceramic composite microcomponents using soft lithography

This PhD project is set out to develop a high precision ceramic fabrication approach suitable for mass production, and to meet the needs of microengine application. A group of new processes have been developed and the results are characterized for fabrication of high precision ceramic oxides and composite microcomponents using soft lithography and colloidal powder processing. The materials chosen in the research are alumina, yttria stabilised zirconia and their composite for their excellent properties at high temperature

Air-suspended single-mode polymer waveguides towards highly sensitive optofluidic sensors

In this thesis, a polymer lamination method is presented that enables efficient light coupling into air-suspended polymer waveguides by grating couplers which can then be exploited for research towards a large range of applications in the field of microfluidics, optics and optofluidics. This approach is especially useful for highly sensitive integrated optofluidic sensors as has been demonstrated in this work. Due to the low refractive index contrast available between various polymer materials, the efficiency of miniaturized polymer photonic and optofluidic devices is often limited. In this work, a new lamination technique is presented that allows the bonding of unstructured and structured layers of SU-8 photoresist down to sub-micron thicknesses onto microchannels fabricated in KMPR photoresist using a flexible PDMS carrier stamp. This approach enables the creation of air-suspended SU-8 structures with the highest possible refractive index contrast. Such layers can be bonded down to a thickness of 0.5 µm which in principal allows guidance of light of infrared wavelengths within the single-mode regime. In order to exploit this approach for highly sensitive optofluidic sensing applications, light needs to be coupled into such layers. In this work light coupling is achieved using air-suspended SU-8 rib waveguides and butt coupling, as well as using air-suspended SU-8 surface grating couplers. Particularly, air-suspended SU-8 grating couplers are very interesting. After numerical simulations, air-suspended SU-8 grating couplers have been fabricated based on the developed lamination method. Transmission measurements have shown that a single grating coupler exhibits approximately 8 dB coupling loss at a centre wavelength of 1557 nm indicating a coupling efficiency of about 16%. In addition, the thermal sensitivity of the air-suspended SU-8 grating couplers has been studied by numerical simulations followed by experimental evaluation. Even though the achieved coupling efficiencies are lower than for SOI couplers, mainly due to current fabrication limits of the master structures, the fabrication method employing widely used polymer materials has the advantage that multiple air-suspended structures can directly be created in only one simple lamination process without the need of additional etching steps. Finally, different optofluidic sensor concepts are proposed based on the demonstrated SU-8 bonding method and the air-suspended SU-8 waveguide grating couplers. Experimental transmission measurements have shown that a first sensor concept exhibits a refractive index sensitivity of approximately 400 nm RIU-1 according to the wavelength shift and 17 dB RIU-1 due to the intensity loss which is similar to the results of the numerical simulations. In comparison to previously shown sensing applications using grating coupler structures, the analytes can directly be probed in-line due to the combination of a microfluidic channel and air-suspended grating couplers making the proposed sensor concept highly applicable for in-line polymer optofluidics and suitable for low-cost optofluidics and photonics sensor concepts. However, in order to detect even the smallest differences in analytes, higher sensitivities would be required. Therefore, a second sensor concept aims to increase the sensitivity by introducing a long-period grating into an air-suspended SU-8 waveguide in order to enhance the light-matter interaction strength. Numerical simulations have been carried out to obtain a set of parameters for a multi-mode long-period grating sensor for TE polarized light at a resonance wavelength of 1550 nm. Transmission calculations as a function of wavelength have shown that such sensor can exhibit a very high refractive index sensitivity of about 6000 nm RIU-1. In summary, this thesis introduces a new polymer lamination method for thin, structured air-suspended SU-8 films down to sub-micron thicknesses. In fact, such films are thin enough to provide single-mode guidance of light in planar waveguides in the infrared wavelength regime. By exploiting air-suspended SU-8 grating couplers, light can be efficiently coupled into such waveguides. Different applications in the fields of microfluidics, optics and optofluidics are introduced in this thesis and it appears that the thin air-suspended SU-8 films can be robust enough even for the realisation of real world applications

A microgripper for single cell manipulation

This thesis presents the development of an electrothermally actuated microgripper for the manipulation of cells and other biological particles. The microgripper has been fabricated using a combination of surface and bulk micromachining techniques in a three mask process. All of the fabrication details have been chosen to enable a tri-layer, polymer (SU8) - metal (Au) - polymer (SU8), membrane to be released from the substrate stress free and without the need for sacrificial layers. An actuator design, which completely eliminates the parasitic resistance of the cold arm, is presented. When compared to standard U-shaped actuators, it improves the thermal efficiency threefold. This enables larger displacements at lower voltages and temperatures. The microgripper is demonstrated in three different configurations: normally open mode, normally closed mode, and normally open/closed mode. It has-been modelled using two coupled analytical models - electrothermal and thermomechanical - which have been custom developed for this application. Unlike previously reported models, the electrothermal model presented here includes the heat exchange between hot and cold arms of the actuators that are separated by a small air gap. A detailed electrothermomechanical characterisation of selected devices has permitted the validation of the models (also performed using finite element analysis) and the assessment of device performance. The device testing includes electrical, deflection, and temperature measurements using infrared (IR) thermography, its use in polymeric actuators reported here for the first time. Successful manipulation experiments have been conducted in both air and liquid environments. Manipulation of live cells (mice oocytes) in a standard biomanipulation station has validated the microgripper as a complementary and unique tool for the single cell experiments that are to be conducted by future generations of biologists in the areas of human reproduction and stem cell research