Advances in Micro and Nano Manufacturing: Process Modeling and Applications

Micro- and nanomanufacturing technologies have been researched and developed in the industrial environment with the goal of supporting product miniaturization and the integration of new functionalities. The technological development of new materials and processing methods needs to be supported by predictive models which can simulate the interactions between materials, process states, and product properties. In comparison with the conventional manufacturing scale, micro- and nanoscale technologies require the study of different mechanical, thermal, and fluid dynamics, phenomena which need to be assessed and modeled.This Special Issue is dedicated to advances in the modeling of micro- and nanomanufacturing processes. The development of new models, validation of state-of-the-art modeling strategies, and approaches to material model calibration are presented. The goal is to provide state-of-the-art examples of the use of modeling and simulation in micro- and nanomanufacturing processes, promoting the diffusion and development of these technologies

Development of an electrochemical micromachining (μECM) machine

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University London.Electrochemical machining (ECM) and especially electrochemical micromachining (μECM) became an attractive area of research due to the fact that this process does not create any defective layer after machining and that there is a growing demand for better surface integrity on different micro applications such as microfluidics systems and stressfree drilled holes in the automotive and aerospace sectors. Electrochemical machining is considered as a non-conventional machining process based on the phenomenon of electrolysis. This process requires maintaining a small gap - the interelectrode gap (IEG) - between the anode (workpiece) and the cathode (tool-electrode) in order to achieve acceptable machining results (i.e. accuracy, high aspect ratio with appropriate material removal rate and efficiency). This work presents the design of a next generation μECM machine for the automotive, aerospace, medical and metrology sectors. It has 3 axes of motion (X, Y and Z) and a spindle allowing the tool-electrode to rotate during machining. The linear slides for each axis use air bearings with linear DC brushless motors and 2nmresolution encoders for ultra-precise motion. The control system is based on the Power PMAC motion controller from Delta Tau. The electrolyte tank is located at the rear of the machine and allows the electrolyte to be changed quickly. A pulse power supply unit (PSU) and a special control algorithm have been implemented. The pulse power supply provides not only ultra-short pulses (50ns), but also plus and minus biases as well as a polarity switching functionality. It fulfils the requirements of tool preparation with reversed ECM on the machine. Moreover, the PSU is equipped with an ultrafast over current protection which prevents the tool-electrode from being damaged in case of short-circuits. Two different process control algorithms were made: one is fuzzy logic based and the other is adapting the feed rate according to the position and time at which short-circuits were detected. The developed machine is capable of drilling micro holes in hard-to-machine materials but also machine micro-styli and micro-needles for the metrology (micro CMM) and medical sectors. This work also presents drilling trials performed with the machine with an orbiting tool. Machining experiments were also carried out using electrolytes made of a combination of HCl and NaNO aqueous solutions. The developed machine was used to fabricate micro tools out of 170μm WC-Co alloy shafts via micro electrochemical turning and drill deep holes via μECM in disks made of 18NiCr6 alloy. Results suggest that this process can be used for industrial applications for hard-to-machine materials. The author also suggests that the developed machine can be used to manufacture micro-probes and micro-tools for metrology and micro-manufacturing purposes.Brunel University European Commissio

Research on Mathematical Model of Composite Micromachining of Laser and Electrolysis Based on the Electrolyte Fluid

A new technology of composite micromachining of laser and electrolysis is presented through a combination of technological advantages of laser processing and electrolytic machining. The implication of its method is that laser processing efficiently removes metallic materials and that pulse electrolytic machining removes recast layer and controls shape precisely. Machining accuracy and efficiency can be improved. The impacts that electrolyte fluid effectively cools the microstructure edge in the laser machining process and that gas-liquid two-phase flow makes the electrolyte conductivity produce uneven distribution in the electrolytic processing are considered. Some approximate assumptions are proposed on the actual conditions of machining process. The mathematical model of composite micromachining of laser and electrolysis based on the electrolyte fluid is built. The validity of the model can be verified by experimentation. The experimental results show that processing accuracy meets accuracy requirements which are ±0.05 mm. Machining efficiency increases more than 20 percent compared to electrolytic processing

Development and Packaging of Microsystems Using Foundry Services

Micro-electro-mechanical systems (MEMS) are a new and rapidly growing field of research. Several advances to the MEMS state of the art were achieved through design and characterization of novel devices. Empirical and theoretical model of polysilicon thermal actuators were developed to understand their behavior. The most extensive investigation of the Multi-User MEMS Processes (MUMPs) polysilicon resistivity was also performed. The first published value for the thermal coefficient of resistivity (TCR) of the MUMPs Poly 1 layer was determined as 1.25 x 10(exp -3)/K. The sheet resistance of the MUMPs polysilicon layers was found to be dependent on linewidth due to presence or absence of lateral phosphorus diffusion. The functional integration of MEMS with CMOS was demonstrated through the design of automated positioning and assembly systems, and a new power averaging scheme was devised. Packaging of MEMS using foundry multichip modules (MCMs) was shown to be a feasible approach to physical integration of MEMS with microelectronics. MEMS test die were packaged using Micro Module Systems MCM-D and General Electric High Density Intercounect and Chip-on-Flex MCM foundries. Xenon difluoride (XeF2) was found to be an excellent post-packaging etchant for bulk micromachined MEMS. For surface micromachining, hydrofluoric acid (HF) can be used

Development of localized electrochemical deposition process for the fabrication of on-machine micro-EDM electrode

Ph.DDOCTOR OF PHILOSOPH

New Methodologies in the field of micromanufacturing

Manufacturing processes are continually improving and updating with a view towards enhancing productivity. With the rapid development of technology, the demand for miniature, lightweight and advanced products is increasing. To compensate these emerging global trends towards the miniaturization of products, the electrochemical micromachining (µECM) is a promising technique. The µECM utilizes high frequency pulses for micron to nano-scale dissolution process that can be driven by with or without feedback control systems. This thesis includes the activities performed during the last three years, as the development of electrochemical micromachining workcell, fabrication of microtools, parametric effects analysis, and fabrication of various microproducts on some noble materials. During microtool fabrication, tungsten micro shafts of 0.38 mm are electrochemically etched to fabricate the desired cylindrical tools with or without conical tips. In the fabrication of microtool, electrolyte concentrations are varied in the range to 0.08–2.0 M KOH for the applied potential differences of 3–15 V AC and different etching time. The microtool fabrication process has been monitored by measuring the size, shape and overall tool geometry. These prefabricated microtools are used in the fabrication of various microdrilling and micromilling processes, especially in the fabrication of single hole micronozzles, multiple hole micronozzles array and microhole fabrication on vitrectomy needles. A mathematical model has been developed for the analysis of material removal rate (MRR) based on pulsed electrical power applied in µECM. The parametric effects of the process are studied on applied potentials, electrolyte temperature, applied frequency and its duty cycle, the dimension of microtools. For the parametric effect analysis, material removal rate, machining time, the number of short circuits, the shape and size of the fabricated microproducts are considered as response factors. The proper experimental parameters, the relationship between the parameters and the distribution of metal removal are established from the experiments worked out. The experimental micromachining tests show that MRR increases with the increase in applied potential, duty cycle, the electrolyte temperature, and microtool diameter, whereas MRR decreases with baseline potential in a certain range, applied frequency, and tool length. Machining time shows the opposite trend of MRR for all the parameters except microtool diameter. It increases with increasing microtool diameter. The microtool feed rate also has a significant effect on the dimension of fabricated microproducts. The waveforms generated during machining are analyzed; an in-process monitoring and control process has also been developed based on the waveforms. The result shows that the shape of the waveform and its corresponding values are in good agreement with the MRR, machining time and on the dimension of fabricated microholes. The proposed monitoring technique could be employed as a predictive tool in electrochemical processing. Finally, the microtools fabricated have been used for fabricating micronozzles and micropockets on nickel plates, microholes on high grade stainless steel to realize the practical applications of microdrilling process

µECM process investigation and sustainability assessment

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonMicro electro chemical machining (µECM) as an alternative machining process gains more attraction in micro and nano industries and gradually finds its place among other non-conventional manufacturing methods. µECM same as ECM aimed at electrically conductive materials; µECM process is based on anodic dissolution of the materials at atomic level. Current progress in µECM has presented valuable improvement in the process control and monitoring, shaping accuracy, simplifying the tool design and the process stability. This makes the µECM an outstanding alternative technology to produce accurate and complex 3-dimensional micro components. However, there is still a gap in application of µECM at research level and industrial level; development and commercialisation of the µECM require huge industrial investment which still needs justification to be attractive for investors. Despite worldwide attempts to investigate and demonstrate the µECM process in full details and develop the µECM technology for the industrial applications, there is still a need for further investigation and research due to the complex and multidisciplinary nature of this process. Currently, this process is very much dependent on operator experience and trial and error approach. The lack of trained knowledgeable operators in addition to the lack of a comprehensive database (combination of materials, electrolytes and machining parameters) have increased the time and the cost of the commercialised development of this technology. A comprehensive analytical literature review highlighted three areas of knowledge gap which can be further investigated and developed. One of the main challenges in current state of this technology is initial set up for machining parameters. Current records show that the initial parameters have been set up using trial and error approach or simulation data; and there is still ongoing effort to find a better solution to set up the initial parameters. The electrode-electrolyte interface was recognised as one of the main effective parameters on µECM machining performance. The complex nature of the reaction which happens at this interface, in addition to the electrode-electrolyte structure need further investigation and analysis in order to improve the µECM machining performance. Finally, the ever increasing demand to optimise all manufacturing processes and products, has increased the need to assess the sustainability of the machining process including new developed technologies; but there is very little information available in the area of micro and nano machining sustainability assessment including µECM. Therefore, in this research it has been tried to address these three knowledge gaps and to suggest new methodologies to overcome them using a new practice consisting of laboratory experiments, mathematical analysis and simulation to investigate the initial machining parameters’ values, explore the electrode-electrolyte interface structure for stainless steel workpiece and tungsten and nickel tool electrodes. Also, to introduce a series of indicators and measures to assess the sustainability of the µECM process to justify its initial high cost in comparison with any other machining process. Laboratory experiments carried out using potentiostat (iviumstat) and mathematical analysis and simulation took place using Matlab and Simulink; and a few experiments carried out using in house built µECM machine to examine the obtained results through the laboratory and simulation works. The results suggested that combination of 6.5 to 7.5 volts, electrolyte concentration between 0.4 and 0.7 mole/L and inter-electrode gap between 22 and 27 µm generates optimum process results. Additionally, electrode-electrolyte interface structure is a useful parameter to set up the pulse on time. Finally, introduced sustainability assessment indicators and measures provides the opportunity to assess the µECM process for further optimisation. As a result, µECM is a valuable process and in claim for current manufacturing industries especially in micro and nano products which demand higher accuracy and quality, better production life cycle and lower cost. So, it is very worthy to invest for further development to bring this technology to the industrial level

Passive radiosonde transducer design for remote pressure sensing applications

Intracranial pressure can be measured to accuracies within 1 milliTorr using passive microtransponders that are micromachined using silicon as a base technology. These microtransponders can operate with either a dual-oscillator or a phase-locked loop frequency scanned control system. The current work describes the design of a totally implantable microsensor for biomedical applications with the aim to monitor and measure the epidural intracranial pressure . The implanting microsensor is basically an RLC device in which capacitance varies with fluid pressure. The resonant frequency of RLC Series connected device varies with chemically etched diaphragm electrode spacing and thereby measures the variations with pressure changes in the fluid pressure The small pressure changes are recorded by an external receiver unit which drives the implanted sensor into oscillator by means of an RF magnetic field. The pressure measurement system is expected to measure pressure with an accuracy of I Torr over the range 1 to 760 Torr. The microsensor is expected to measure pressure at distances up to 2 meters from the power source loop in any environment that is nonconductive and nonmagnetic. The one application of the present thesis is for the chronic measurement of intercranial fluid pressure following brain surgery and for eschemic brain conditions

Advanced sensors technology survey

This project assesses the state-of-the-art in advanced or 'smart' sensors technology for NASA Life Sciences research applications with an emphasis on those sensors with potential applications on the space station freedom (SSF). The objectives are: (1) to conduct literature reviews on relevant advanced sensor technology; (2) to interview various scientists and engineers in industry, academia, and government who are knowledgeable on this topic; (3) to provide viewpoints and opinions regarding the potential applications of this technology on the SSF; and (4) to provide summary charts of relevant technologies and centers where these technologies are being developed