Towards an integrated atom chip

The field of atom chips is a relatively new area of research which is rapidly becoming of great interest to the scientific community. It started out as a small branch of cold atom physics which has quickly grown into a multidisciplinary subject. It now encompasses topics from fundamental atomic and quantum theory, optics and laser science, to the engineering of ultra sensitive sensors.In this thesis the first steps are taken towards a truly integrated atom chip device for real world applications. Multiple devices are presented that allow the trapping, cooling, manipulation and counting of atoms. Each device presents a new component required for the integration and miniaturisation of atom chips into a single device, capable of being used as a sensor.Initially, a wire trap was created capable of trapping and splitting a cloud of BoseEinstein condensate (BEC) for use in atom interferometry. Using this chip a BEC has been successfully created, trapped and coherent splitting of this cloud has been achieved.Subsequently, the integration and simplification of the initial trapping process was approached. In all the experiments to date, atoms are initially collected from a warm vapour by a magneto-optical trap (MOT). This thesis presents a new approach in which microscopic pyramidal MOTs’ are integrated into the chip itself. This greatly reduces the number of optical components and helps to simplify the process significantly.Also presented is a method for creating a planar-concave micro-cavity capable of single atom detection. One such cavity consists of a concave mirror fabricated in silicon and the planar tip of an optical fibre. The performance of the resonators is highly dependent on the surface roughness and shape profile of the concave mirrors therefore a detailed study into the fabrication technique and its effects on these parameters was undertaken. Using such cavities single atom detection has been shown to be possible. These cavities have also been sccessfully integrated into an atom wire guide.Finally a co-sputtered amorphous silicon/titanium (a-Si/Ti) nanocomposite material was created and studied for its use as a novel structural material. This material is potentially suitable for integrated circuitry (IC)/Micro-electromechanical- systems (MEMS) integration. The material’s electrical and structural properties were investigated and initial results suggest that a-Si/Ti has the potential to be a compelling structural material for future IC/MEMS integration.To build all of these devices, a full range of standard microfabrication techniques was necessary as well as some non standard processes that required considerable process development such as the electrochemical deposition.This thesis presents a tool box of fabrication techniques for creating various components capable of different tasks that can be integrated into a single device. Each component has been successfully demonstrated in laboratory conditions. This represents a significant step toward a real world atom chip device

MEMS Devices for Circumferential-scanned Optical Coherence Tomography Bio-imaging

Ph.DDOCTOR OF PHILOSOPH

A disposable bio-nano-chip usuing agarose beads for protein analysis

This thesis reports on the fabrication of a disposable bio-nano-chip (BNC), a microfluidic device composed of polydimethylsiloxane (PDMS) and thiolene-based optical epoxy which is both cost-effective and suitable for high performance immunoassays. A novel room temperature (RT) bonding technique was utilized so as to achieve irreversible covalent bonding between PDMS and thiolene-based epoxy layers, while at the same time being compatible with the insertion of agarose bead sensors, selectively arranged in an array of pyramidal microcavities replicated in the thiolene thin film layer. In the sealed device, the bead-supporting epoxy film is sandwiched between two PDMS layers comprising of fluidic injection and drain channels. The agarose bead sensors used in the device are sensitized with anti-C-reactive protein (CRP) antibody, and a fluorescent sandwich-type immunoassay was run to characterize the performance of this device. Computational fluid dynamics (CFD) was used based on the device specifications to model the bead penetration. Experimental data revealed analyte penetration of the immunocomplex to 100μm into the 280μm diameter agarose beads, which correlated well with the simulation. A dose response curve was obtained and the linear dynamic range of the assay was established over 1ng/mL to 50ng/mL with a limit of detection less than 1ng/mL

Scanning micro interferometer with tunable diffraction grating for low noise parallel operation

Large area high throughput metrology plays an important role in several technologies like MEMS. In current metrology systems the parallel operation of multiple metrology probes in a tool has been hindered by their bulky sizes. This study approaches this problem by developing a metrology technique based on miniaturized scanning grating interferometers (μSGIs). Miniaturization of the interferometer is realized by novel micromachined tunable gratings fabricated using SOI substrates. These stress free flat gratings show sufficient motion (~500nm), bandwidth (~50 kHz) and low damping ratio (~0.05). Optical setups have been developed for testing the performance of μSGIs and preliminary results show 6.6 μm lateral resolution and sub-angstrom vertical resolution. To achieve high resolution and to reduce the effect of ambient vibrations, the study has developed a novel control algorithm, implemented on FPGA. It has shown significant reduction of vibration noise in 6.5 kHz bandwidth achieving 6x10-5 nmrms/√Hz noise resolution. Modifications of this control scheme enable long range displacement measurements, parallel operation and scanning samples for their dynamic profile. To analyze and simulate similar optical metrology system with active micro-components, separate tools are developed for mechanical, control and optical sub-systems. The results of these programs enable better design optimization for different applications.Ph.D.Committee Chair: Degertekin, Levent; Committee Co-Chair: Kurfess, Thomas; Committee Member: Adibi, Ali; Committee Member: Danyluk, Steven; Committee Member: Hesketh, Pete

Integrated polymer photonics : fabrication, design, characterization and applications

[no abstract

Polymer Pen Printing: A Tool for Studying 2D Enzymatic Lithography and Printing 3D Carbon Features

Polymer Pen Lithography (PPL) is a promising molecular printing approach which combines the advantages of both microcontact printing (low cost, high-throughput) and the dip pen lithography (DPN) (arbitrary writing, high-resolution) into one cohesive lithography method to create 2 dimensional (2-D) patterns with micro/nano-features on different substrates. The goal of this dissertation is to design and develop a new tool based upon PPL, which is not limited to forming 2D parallel patterns, but can also create 3D complex microstructures, finding applications in both biotechnology and Micro-Electro-Mechanical systems (MEMS) technology. This novel approach is named Polymer Pen Printing. Different from PPL using traditional dry-ink printing methods, an inking step is added to each printing repetition in the polymer pen printing process. Thus a wide range of ink materials with diverse viscosities can be transferred to substrates to create functional 2D and 3D microstructures. The polymer pen printing apparatus used in this thesis has been accomplished and introduced in Chapter 2. As a preliminary attempt, the single polymer pen printing approach was developed by simply attaching a solid polydimethylsiloxane (PDMS) pen tip to a multi-axis robot for small microarray fabrication. Compared to the single pen printing method, multi-pen printing can create large arrays of features. Therefore, an improved apparatus for polymer pen printing with high-throughput was discussed and built. Silicon molds, which consist of hundreds of uniform pyramidal openings, were photolithographically defined and etched using hydrofluoric acid (HF) followed by potassium hydroxide solution; after surface-modification with fluorosilane, these silicon molds were used to cast arrays of PDMS pyramidal pen tip. The cast PDMS pen array was mounted to a hollow holder with a 45° mirror inside. Therefore, each PDMS pen can be observed and monitored from the microscope on the side. To achieve prints less than 1 micron across, a Z axis stage with nanometer resolution was incorporated; and to control the compression of PDMS pen tips, a force gauge was also incorporated to detect 1 mg of applied force from the tips. The printing process for the multi-pen system is almost the same as single pen system. PDMS pens are coated with ink solution before each printing cycle by dipping into an inkwell and then brought into contact with the substrate surface. Thus multiple patterns, one from each tip, are created in parallel simultaneously. Furthermore, with control of the printing force, feature sizes could be controlled over the range submicron to tens of microns. Three ink candidates have been printed by polymer pen printing approach to fabricate 2D&3D microstructures. The first ink material is Barium Strontium Titanate (BST) nanocrystallites dispersed in a furfuryl alcohol (FA), which was printed by the single PDMS pen with 100 μm tip diameter (Chapter 3). After printing, samples were heated to crosslink FA monomers, forming a stable polymeric matrix with embedded BST nanocrystallites. Without shear-thinning properties, BST/FA ink cannot be used to build 3D posts, but it has the capability to create circular patterns with different thickness by the single or multi-tier deposition method. It was found that the thickness of film increased linearly with the number of deposits without changing the diameter significantly. This encouraging result could enable the formation of microcapacitors with multi-tiered structure. Moreover, the study of printing parameters, including printing height and ink pick-up position, shows that changes to the pen positions in the ink reservoir or substrate have essentially no impact on deposit thickness or diameter. Beyond that, the effect of surface chemistry of PDMS pen and silicon wafer have also been studied. The plasma treated hydrophilic PDMS pen can pen transfer more BST/FA than untreated one; and the larger diameters with smaller thickness were obtained on a hydrophilic silicon wafer. The second ink candidate is a dilute aqueous solution of enzyme Candia antartica lipase B (CALB), which is known to catalyze the decomposition of poly (ε-caprolactone) (PCL) films. By bringing enzymes into contact with pre-defined regions of a surface, a polymer film can be selectively degraded to form patterned features that are requited for applications in biotechnology and electronics. This so-called enzymatic lithography is an environmentally friendly process as it does not require any actinic radiation or synthetic chemicals to develop required features. But the need to restrict the mobility of the enzyme in order to maintain control of feature sizes poses a significant challenge. In Chapter 4, after writing 2D enzyme patterns onto a spin-cast PCL film by single pen printing, samples with CALB were incubated at 37 ℃ and 95% relative humidity (RH) for up to 7 days to develop features. The CALB selectively degraded the PCL film during incubation, forming openings through the film. The size of these features (10 to 50 μm diameter) is well suited for use as biocompatible micro-reactors. Previous study of patterning CALB by single polymer pen printing technique resulted in slow etch rates, low throughput and poor image quality. In Chapter 5, I present an improved enzymatic lithography approach, still based on enzyme CALB and PCL system, which can resolve fine-scale features (\u3c 1 μm across) in thick (0.1 - 2.0 μm) polymer films after 5 minutes to 2 hours of incubation at 37 ℃ and 87% RH. Immobilization of the enzyme on the polymer surface was monitored using fluorescence microscopy by labeling CALB with FITC. The crystallite size in the PCL films was systematically varied; small crystallites resulted in significantly faster etch rates (20 nm/min) and the ability to resolve smaller features (as fine as 1 μm). The effect of printing conditions and RH during incubation is also presented. Patterns formed in the PCL film were transferred to an underlying copper foil demonstrating a Green approach to the fabrication of printed circuit boards. In parallel, the third ink material is a mixture of 25 wt% graphite dispersed in a high viscosity phenolic resin n-methyl-2-pyrrolidone (NMP) solution, which can be converted into carbon/carbon composites after a pyrolysis process. The 3D polymeric posts were created by depositing multilayers of thixotropic phenolic ink on a silicon substrate by single polymer pen printing method with a 10 μm radius PDMS pen tip (Chapter 6). After pyrolysis at 1000 ℃ in a nitrogen (N2) atmosphere, the polymeric features were converted to the glassy carbon/graphite features with a high aspect ratio (\u3e2). These features may be used as microelectrodes. Last, arrays of needle-shaped glassy carbon have been developed by a drawing approach using multi-pen printing technique followed by simple pyrolysis process (Chapter 7). To build polymeric needles with ultra-high aspect ratio, the polymeric ink was prepared by dissolving phenolic resin in the high boiling point (204 ℃) solvent NMP without fillers to achieve good printability and suitable viscosity. By slowly lifting up the print head from substrate, liquid needle structures were formed and then solidified on silicon substrates or gold electrodes due to the solvent evaporation. In addition, suspended resin fibers connected to two electrodes have also been fabricated by precisely controlling the movement of the PDMS pen. After pyrolysis, these resin features were converted to glassy carbon and the 3D structures remained. The electrical characterization results showed that glassy carbon made by this method had relatively low resistivity (2.5 x 10-5 Ωm). Therefore the glassy carbon based microneedles are well-suited to be electrodes for electrochemical sensors for biological applications

Study of advanced resonant photonic gratings in the mid-infrared spectrum for the chemical sensing applications

This dissertation focuses on developing advanced Mid-IR optical devices for chip-scale chemical sensing. Various Mid-IR techniques based on Beer-Lambert’s law offer valuable insights into molecular interactions but suffer from bulkiness and high cost. Towards the compact and cost-effective sensing purpose, many efforts have been made in light sources (e.g., QCLs), photodetectors (e.g., PbSe, MCT detectors), and gas sampling chambers via on-chip photonic waveguides. Despite the progress achieved through these new technologies, there is still plenty of room for enhancing the performance and cost-effectiveness of miniaturized Mid-IR gas sensing systems. Thus, this dissertation explores new photonic engineering pathways to address existing challenges through on-chip integration and downsizing in three core mid-IR gas sensing components, including the light source, detector, and interaction path. In this dissertation, a simple yet versatile and powerful resonant grating platform has been utilized as the foundation to develop innovative engineering methods. Herein, due to the nontrivial properties of High Contrast Gratings (HCGs), such as broadband reflectivity, and high Q factor resonance, I focus mostly on these types of grating resonators. Through a new design, HCGs are used to enhance absorption in uncooled PbSe-based photodetectors. Moreover, for shrinking the interaction path, a high Q factor HCG resonator was designed, showing 600 times light absorption enhancement in a micro-size path length. Furthermore, integrating active HCGs with Parity-Time (PT) symmetry concept offers near-zero bandwidth photonic resonant emission with application in Mid-IR light sources. Besides the exploration of new photonic design methods, another important aspect of this work has been focused on the development of a suitable mid-IR material platform to allow the implementation of the aforementioned photonic design methods. Specifically, a modified chemical deposition method is used to synthesize Oriented-Attached (OA) PbSe nanocrystals (NCs) on amorphous substrates with strong quantum confinement and broad size-tunability. This optimized and cost-effective growth technique demonstrates promising illumination in the Mid-IR range, contributing to the potential of OA PbSe NCs synthesized by this novel method as a material for fabricating Mid-IR photonic components. At the end of this dissertation, an experimental exploration of a low-cost and large-area patterning nanofabrication method is also presented as an extended effort from the core photonic design and novel material synthesis works towards the overarching goal to develop smaller, cost-effective, and efficient on-chip mid-IR optical devices for chemical sensing applications

Integration of Micro Patterning Techniques into Volatile Functional Materials and Advanced Devices

Novel micro patterning techniques have been developed for the patterning of volatile functional materials which cannot be conducted by conventional photolithography. First, in order to create micro patterns of volatile materials (such as bio-molecules and organic materials), micro-contact printing and shadow mask methods are investigated. A novel micro-contact printing technique was developed to generate micro patterns of volatile materials with variable size and density. A PDMS (Polydimethylsiloxane) stamp with 2-dimensional pyramidal tip arrays has been fabricated by anisotropic silicon etching and PDMS molding. The variable size of patterns was achieved by different external pressures on the PDMS stamp. A novel inking process was developed to enhance the uniformity and repeatability in micro-contact printing. The variable density of patterns could be obtained by alignment using x-y transitional stage and multiple stamping with a z-directional moving part. Second, for direct patterning of small molecule organic materials (e.g. pentacene), a novel shadow mask method has been developed with a simple and accurate alignment system. To make accurate dimensions of patterning windows, a silicon wafer was used for the shadow mask since a conventional semiconductor process gives a great advantage for accurate and repeatable fabrication processes. A sphere ball alignment system was developed for the accurate alignment between the shadow mask and the silicon substrate. In this alignment system, four matching pyramidal cavities were fabricated on each side of the shadow mask and silicon wafer substrate using an anisotropic silicon bulk etching. By placing four steel spheres in between the matching cavities, the self-alignment system could be demonstrated with 2-3um alignment accuracy in x-y directions. For OTFT (Organic thin film transistor) application, an organic semiconducting layer was directly deposited and patterned on the substrate using the developed shadow mask method. On the other hand, novel embedding techniques were developed for enabling conventional semiconductor processes including photolithography to be applied on the small substrate. The polymer embedding method was developed to provide an extended processing area as well as easy handling of the small substrate. As an application, post CMOS (Complementary metal-oxide-semiconductor) integration of a relatively large microstructure which might be even larger than the substrate was demonstrated on a VCO (Voltage-controlled oscillator) chip. In addition, micro patterning on the optical fiber was demonstrated by using a silicon wafer holder designed to surround and hold the optical fiber. The micro Fresnel lens could be successfully patterned and integrated on the optical fiber end

Two-dimensional microscanners with t-shaped hinges and piezoelectric actuators

For a wide range of application areas such as medical instruments, defense, communication networks, industrial equipment, and consumer electronics, microscanners have been a vibrant research topic. Among various fabrication methodologies, MEMS (microelectromechanical system) stands out for its small size and fast response characteristics. In this thesis, piezoelectric actuation mechanism is selected because of its low voltage and low current properties compared with other mechanisms, which are especially important for the target application of biomedical imaging. Although 1- and 2-dimensional microscanners with piezoelectric actuators have been studied by several other groups, this thesis introduces innovative improvements in design of the piezoelectric MEMS microscanner. A novel T-shaped hinge geometry is proposed, which is flexible in whole six directions and also free from the crosstalk issue found in the earlier designs by other groups. The piezoelectric actuator of the microscanner is comprised of five layers; a top electrode, a piezoelectric layer (lead zirconate titanate or PZT), a bottom electrode, a dielectric layer, and a mechanical support. The microscanners were analyzed using both analytical formulas and numerical simulations. Based on the analysis, the microscanners were designed and fabricated with four mask levels¯top electrodes, bottom electrodes, bonding pads, and substrate etching windows. During the silicon substrate wet etching process in KOH, ProTEK@ B3 was coated in the front to protect the devices. Polarization-voltage (P-V) measurement of deposited PZT was performed using RT66B. Actuation of the piezoelectric cantilevers were observed under a microscope by applying voltage