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    Development of a compliant micro gripper : a thesis submitted in partial fulfillment for the degree of Masters of Engineering in the School of Engineering and Advanced Technology, Massey University
    (Massey University, 2019) Lofroth, Matthew
    Manipulating micro objects simply and effectively has been a widely discussed and challenging task in recent literature for many reasons. Limitations in complex micro fabrication techniques mean creating extremely small tools at the micro scale is very difficult. Adhesion forces also dominate at this scale, causing anything and everything to stick together. This means that even when these tiny structures are created and introduced to the micro world, they quickly become polluted with contaminants and struggle to pick and place particles without said particle adhering to the tool. Indirect methods for micro manipulation exist, however these can be damaging to biological material such as cells, due to unseen forces being focused into a small point. Having the ability to safely manipulate and separate these objects from a culture is crucial to understanding their individual characteristics. Therefore a safe and reliable method for micro manipulation needs to be developed. This project focuses on investigating the current methods used for micro manipulation in order to identify any possible routes towards developing a simple and yet effective means for manipulating micro objects. A modular micro gripping mechanism is proposed in this report, capable of manipulating many different types of objects such as spherical, non spherical or other arbitrary shapes. The proposed micro gripper combines traditional machining techniques with a complex micro fabrication process to produce a modular mechanism consisting of a sturdy, compliant aluminium base in which replaceable silicon and borosilicate glass end effectors are attached. This creates an easily customisable solution for micro manipulation with an array of different micro tips for different applications. A kinematic analysis for the gripper has been provided which predicts the workspace of the gripper given an input actuation. Design parameters of the gripper have also been optimised through various techniques such as FEA (finite element analysis) simulation and the effects of altering individual flexure beam lengths. The gripper is operated by a piezo actuator with a total capable expansion of 19 mm when 150 VDC is applied. This expansion is then amplified by a factor of 8.1 to a maximum tip displacement of approximately 154 mm. Displacement amplification is achieved by incorporating bridge and lever amplifying techniques into the compliant design. The complete micro gripper is then used to demonstrate manipulation tasks on several different target object types including silica micro beads (spherical and non spherical), a human eyelash and a grain of pollen. These tests are performed to investigate the effect of adhesion forces and also to demonstrate the large size range of capable pick and place objects (6 mm to 500 mm).
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    Micro implantable pressure sensors for lifetime monitoring of intracranial pressure : this dissertation is submitted for the degree of Doctor of Philosophy, School of Engineering and Advanced Technology, Massey University
    (Massey University, 2019) Sodavaram, Nireekshan Kumar
    The elevation of intracranial pressure (ICP) associated with traumatic brain injury (TBI), hydrocephalus and other neurological conditions is a serious concern. If left untreated, increased pressure in the brain will reduce cerebral blood flow (CBF) and can lead to brain damage or early death. Currently, ICP is monitored through invasive catheters inserted into the brain along with a shunt. However, insertion of catheters or shunts is an invasive procedure that introduces vulnerability to infection. In principle, the risk of infection would be overcome by a fully implantable pressure monitoring system. This would be particularly valuable for hydrocephalus patients if lifetime monitoring was available. An implantable pressure monitoring system relies on a thin flexible membrane as part of the pressure sensor. The thin film membrane displaces under load and correspondingly induces a change in a relevant electrical quantity (resistance, or capacitance). Micro-electro-mechanical system (MEMS) is the technology that helps in creating micro/nano-mechanical structures integrated with signal conditioning electronics. These micro structures can be inserted into the brain, where the thin film is exposed to a corrosive fluid (saline/blood) at a temperature of approximately 37 ◦C. The miniaturization in MEMS permits examination, sensing and monitoring from inside the patient for longer durations. However, the accuracy, particularly in terms of sensor drift over long durations, is a key concern. In general, the issue of drift is attributed to the aging and mechanical fatigue of thin film structures, particularly the thin flexible membrane. Therefore, it is essential to analyze the thin film deflection and fatigue behaviour of MEMS pressure sensors for achieving long-term reliability and accuracy. Thus, the high-level goal of this research is to identify a viable approach to producing a flexible membrane suitable for deployment as a lifetime implantable pressure measuring system. In this context, finite-element modelling (FEM) and finite-element analysis (FEA) of thin film deflection and fatigue behaviour have been conducted. The FEM was implemented in COMSOL Multiphysics with geometries resembling a capacitive type pressure sensor with titanium (Ti) thin film membrane deposited onto the silicon substrate. The mechanical behavior of thin film structures including stresses, strains, elastic strain energy density, and thin film displacements of several thicknesses (50 μm, 25 μm, 4 μm, 1 μm, 500 nm, 200 nm) have been studied. In addition, fatigue physics module has been added to the FEM to analyze the fatigue life of thin film structures. The FEA results in the form of fatigue usage factors have been plotted. Finally, to analyze the effect of fluid pressure transmission of the thin film membrane inside the closed skull, fluid-structure interaction has been modelled. The model represents a 2D fluid medium with the thin film membrane. The velocity magnitude, displacement, shear rate (1/s) and kinetic energy density (J/m3) of 4 μm and 25 μm thick Ti films has been plotted. From this analysis, 4 μm thin film membrane showed good tradeoff for thickness, pressure transmission, and mechanical behaviour. To validate the FEM, a custom designed acoustic-based thin film deflection and fatigue life experiments have been set up. The experimental design comprised of: (1) A voice coil-based multimedia speaker and subwoofer system to assist in displacing the thin film membranes, (2) A laser displacement sensor to capture the displacements, (3) A spectrum analyzer palette for generating random vibrations, (4) Dataloggers to record the input vibrations and thin film displacements, and (5) Scanning electron microscopy (SEM) to visualize the surface topography of thin film structures. Thin film titanium (Ti) foils of 4 μm and 25 μm thick were obtained from William Gregor Ltd, Ti-shop, London. The thin-film specimens were clamped to 3mm acrylic substrates and bonded to the subwoofer system. The Gaussian random vibrations generated from the spectrum analyzer loaded the voice coil of the multi-media speaker system, which assists in displacing the thin films. The SEM surface observations are divided into two regions: (1) Pre-cycle observation, where the thin film surfaces are observed before the application of any load, and (2) Post-cycle observation, where the thin films surfaces are observed after application of cyclic loadings. Based on the understanding of the FEM and experimental studies, a conceptual framework of MEMS pressure sensor has been developed. In this part of the work, initially, underlying concepts of complementary-metal-oxide silicon (CMOS) circuit simulation, MEMS modelling, and CMOS layout design have been discussed. Next the MEMS fabrication process involving deposition (sputtering), etching, and final packaging have been discussed. Finally, an optimized design process of the membrane-based sealed cavity MEMS pressure sensors has been outlined.
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    Design of analogue CMOS VLSI MEMS sensor : a dissertation presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Engineering , Integrated Circuit Design at School of Engineering and Advanced Technology, Massey University, Albany campus
    (Massey University, 2015) Sundararajan, Ananiah Durai
    There is an increasing demand of a highly sensitive and reliable pressure micro-sensor system, for implantable and non-implantable medical applications. The prerequisite of a miniaturized device for minimally invasive procedures, posed greater challenges in the complex integrated design of micro-system. Micro-sensor system designs in the recent advanced CMOS technologies are explored in this work for effective system miniaturization and improved performance. The material choices and geometry designs, which significantly influence the sensitivity and dynamic range of the micro-scale sensor devices, are well addressed. Cointegrations of MEMS devices with signal conditioning circuits that effectively reduce the parasitic effect are also performed for enhancing the overall system performance. In addition, system reliability is also improved with on-chip metal interconnections. The employed process technologies to a greater extent contributed to the high yield for these low cost micro-sensor systems. This research focuses on the design of integrated CMOS MEMS capacitive pressure sensors for diverse bio-medical applications. Two monolithically integrated capacitive pressure microsensor systems are designed, fabricated and experimentally verified. A novel micro-electromechanical capacitive pressure sensor in SiGeMEMS process, vertically integrated on top of a 0.18 μm TSMC CMOS processed die is proposed. The perforated elliptic diaphragm, which is edge clamped at the semi-major axis is developed using poly-SiGe material. High performance on-chip CMOS conditioning circuits are also designed to achieve better overall sensitivity. Experimental results indicate a high sensitivity of around 0.12 mV/hPa along with a nonlinearity of around 1% for the full scale range of applied pressure load. The L-clamp spring anchored diaphragm provided a wide dynamic range of around 900 hPa. Another integrated capacitive pressure micro-system, developed using the advanced standard IBM CMOS process in two geometrical designs is also proposed. A step-sided elliptic diaphragm that overcomes the CMOS process limitations is fabricated to achieve regulated membrane deflections and improved sensitivity. A foundry compatible post-process technique, for a lateral release length of 125 μm is also performed successfully on the 130 nm CMOS platform. A current cross mirroring technique is utilized to enhance the transconductance of an on-chip operational amplifier to achieve a high single stage gain. Sensitivities of the fluorosilicate sealed absolute pressure sensors were measured to be 0.07 mV/Pa and 0.05 mV/Pa for the elliptic and rectangular element, respectively. In addition, the linear capacitive transduction dynamic range was found to be 0.32 pF and 0.23 pF, respectively, for the elliptic and rectangular element.