Surface micromachined mechanisms and micromotors

Electric micromotors are sub-millimeter sized actuators capable of unrestrained motion in at least one degree of freedom. Polysilicon surface micromachining using heavily phosphorus-doped LPCVD polysilicon for the structural material, LPCVD silicon nitride for the electrical isolation and deposited silicon dioxide for the sacrificial material has formed the fabrication technology base for the development of these micromotors. Two polysilicon surface micromachining processes, referred to here as the center-pin and flange, have been demonstrated for the fabrication of passive mechanisms and micromotors. Passive mechanisms such as gear trains, cranks and manipulators have been implemented on silicon. Reported operational micromotors have been of the rotary variable-capacitance salient-pole and harmonic (or wobble) side-drive designs. These micromotors are capable of motive torques in the 10 pN m order of magnitude range. Preliminary progress has been made in studying the operational, friction and wear characteristics of these micromechanical devices. Typical operational voltages have been as low as 37 V and 26 V across 1.5 mu m air gap salient-pole and harmonic micromotors. These excitations correspond to electric field intensities above 10(8) Vm-1 in the micromotor air gaps. Salient-pole and wobble micromotors have been reported to operate at speeds as high as 15000 rpm and 700 rpm, respectively. Micromotor lifetimes of at least many millions of cycles over a period of several days have been reported

Development of novel micropneumatic grippers for biomanipulation

Microbjects with dimensions from 1 μm to 1 mm have been developed recently for different aspects and purposes. Consequently, the development of handling and manipulation tools to fulfil this need is urgently required. Micromanipulation techniques could be generally categorized according to their actuation method such as electrostatic, thermal, shape memory alloy, piezoelectric, magnetic, and fluidic actuation. Each of which has its advantage and disadvantage. The fluidic actuation has been overlooked in MEMS despite its satisfactory output in the micro-scale. This thesis presents different families of pneumatically driven, low cost, compatible with biological environment, scalable, and controllable microgrippers. The first family demonstrated a polymeric microgripper that was laser cut and actuated pneumatically. It was tested to manipulate microparticles down to 200 microns. To overcome the assembly challenges that arise in this family, the second family was proposed. The second family was a micro-cantilever based microgripper, where the device was assembled layer by layer to form a 3D structure. The microcantilevers were fabricated using photo-etching technique, and demonstrated the applicability to manipulate micro-particles down to 200 microns using automated pick-and-place procedure. In addition, this family was used as a tactile-detector as well. Due to the angular gripping scheme followed by the above mentioned families, gripping smaller objects becomes a challenging task. A third family following a parallel gripping scheme was proposed allowing the gripping of smaller objects to be visible. It comprises a compliant structure microgripper actuated pneumatically and fabricated using picosecond laser technology, and demonstrated the capability of gripping microobject as small as 100 μm microbeads. An FEA modelling was employed to validate the experimental and analytical results, and excellent matching was achieved

Doctor of Philosophy

dissertationPhosphate-metal complex formation is a naturally occurring toughening mechanism in underwater materials and has been incorporated into the synthetic hydrogel material discussed in this dissertation. Polyphosphate hydrogels were loaded with Ca2+ which crosslinks OPO3 groups in the hydrogel which increase the initial modulus from 0.04 to 10.3 MPa and rupture at a critical force to dissipate strain energy and act as a sacrificial network to preserve the integrity of the hydrogel. Phosphate metal crosslinks are electrostatic domains that are easily recoverable, which adds to the durability and usefulness of the hydrogels. This toughening mechanism was borrowed from the underwater caddisfly larvae, which spin a tough, adhesive silk fiber to manufacture protective mobile cases from sticks, rocks and other advantageously gathered materials. The caddisfly silk also uses serial domains of phosphates crosslinked with Ca2+ to increase modulus and produce strain induced yield, energy dissipation, and recoverability. In addition to metal ions, positively charged aminoglycoside antibiotics such as tobramycin can also be used as crosslinking agents. Due to electrostatically delayed diffusion, tobramycin is gradually released and exchanged with metal ions in biologically relevant Ca2+ and Mg2+ containing solutions. In the polyphosphate hydrogel system, tobramycin was included with and without the presence of Ca2+ to form a hydrogel with the capability to sustain tobramycin release for up to 70 days and totally eradicate pseudomonas aeruginosa biofilms within 48 hours. In the case of hydrogels loaded with Ca2+ and tobramycin, the hydrogels retained their toughness, and durability and thus may be used as structural materials in total joint replacement to reduce incidence of infection. Complex coacervation is an alternative to the polyphosphate-tobramycin hydrogel system and occurs as a phase separation where a dense coacervate of polyphosphate and tobramycin is formed. The formation of clear, fluid coacervate phase is dependent on salt concentration and is maximized at ~1M NaCl. Polyphosphate-tobramycin coacervates have a sustained release assay for up to 60 days. Additionally, the coacervate can be resuspended into micro droplets by vortex and subsequently aerosolized for pulmonary delivery of tobramycin. Aerosolized coacervate is ideal for treating chronic pulmonary infection in cystic fibrosis. It could not only improve rates of pseudomonas aeruginosa infection but also reduce the number of required doses and thus improve patient compliance

Cantilever beam microactuators with electrothermal and electrostatic drive

Microfabrication provides a powerful tool for batch processing and miniaturization of mechanical systems into dimensional domain not accessible easily by conventional machining. CMOS IC process compatible design is definitely a big plus because of tremendous know-how in IC technologies, commercially available standard IC processes for a reasonable price, and future integration of microma-chined mechanical systems and integrated circuits. Magnetically, electrostatically and thermally driven microactuators have been reported previously. These actuators have applications in many fields from optics to robotics and biomedical engineering. At NJIT cleanroom, mono or multimorph microactuators have been fabricated using CMOS compatible process. In design and fabrication of these microactuators, internal stress due to thermal expansion coefficient mismatch and residual stress have been considered, and the microactuators are driven with electro-thermal power combined with electrostatical excitation. They can provide large force, and in- or out-of-plane actuation. In this work, an analytical model is proposed to describe the thermal actuation of in-plane (inchworm) actuators. Stress gradient throughout the thickness of monomorph layers is modeled as linearly temperature dependent Δσ. The nonlinear behaviour of out-of-plane actuators under electrothermal and electrostatic excitations is investigated. The analytical results are compared with the numerical results based on Finite Element Analysis. ANSYS, a general purpose FEM package, and IntelliCAD, a FEA CAD tool specifically designed for MEMS have been used extensively. The experimental results accompany each analytical and numerical work. Micromechanical world is three dimensional and 2D world of IC processes sets a limit to it. A new micromachining technology, reshaping, has been introduced to realize 3D structures and actuators. This new 3D fabrication technology makes use of the advantages of IC fabrication technologies and combines them with the third dimension of the mechanical world. Polycrystalline silicon microactuators have been reshaped by Joule heating. The first systematic investigation of reshaping has been presented. A micromirror utilizing two reshaped actuators have been designed, fabricated and characterized

Microfabricated actuators and their application to optics

Several authors have given overviews of microelectromechanical systems, including microactuators. In our presentation we will review some of these results, and provide a brief description of the basic principles of operation, fabrication, and application, of a few selected microactuators (electrostatic and surface tension driven). We present a description of a three-level mechanical polysilicon surface-micromachining technology with a discussion of the advantages of this level of process complexity. This technology, is capable of forming complex, batch-fabricated, interconnected, and interactive, microactuated micromechanisms which include optical elements. The inclusion of a third deposited layer of mechanical polysilicon greatly extends the degree of complexity available for micromechanism design. Two examples of microactuators fabricated using this process are provided to illustrate the capabilities and usefulness of the technology. The first actuator is an example of a novel actuation mechanism based on the effect of surface tension at these micro-scale dimensions and of a microstructure within a microstructure. The second is a comb-drive-based microengine which has direct application as a drive and power source for micro optical elements, specifically, micro mirrors and micro shutters. This design converts linear oscillatory motion from electrostatic comb drive actuators into rotational motion via a direct linkage connection. The microengine provides output in the form of a continuously rotating output gear that is capable of delivering drive torque to a micromechanism

RF-MEMS Technology for High-Performance Passives (Second Edition) - 5G applications and prospects for 6G

The focus of this book develops around hardware, and in particular on low-complexity components for Radio Frequency (RF) applications. To this end, microsystem (MEMS) technology for RF passive components, known as RF-MEMS, is employed, discussing its potentialities in the application frame of 5G. The approach adopted is practical, and a significant part of the content can be directly used by scientists involved in the field, to put their hand on actual design, optimization and development of innovative RF passive components in MEMS technology for 5G and beyond applications. This update (which includes a review of the main approaches to the modelling and simulations of MEMS and RF-MEMS devices) is timely and will find a wider readership as it crosses into the translational aspects of applied research in the subject. Key features • With over 50 pages of new content, the book will be 1/3 larger than the 1st edition. • New chapter on simulation and modelling techniques. • Practical approach to the design and development of RF-MEMS design concepts for 5G and upcoming 6G. • Includes case studies. • Video figures. • Includes a review of the business landscape

Tribology of Microball Bearing MEMS

This dissertation explores the fundamental tribology of microfabricated rolling bearings for future micro-machines. It is hypothesized that adhesion, rather than elastic hysteresis, dominates the rolling friction and wear for these systems, a feature that is unique to the micro-scale. To test this hypothesis, specific studies in contact area and surface energy have been performed. Silicon microturbines supported on thrust bearings packed with 285 µm and 500 µm diameter stainless steel balls have undergone spin-down friction testing over a load and speed range of 10-100mN and 500-10,000 rpm, respectively. A positive correlation between calculated contact area and measured friction torque was observed, supporting the adhesion-dominated hysteresis hypothesis. Vapor phase lubrication has been integrated within the microturbine testing scheme in a controlled and characterized manner. Vapor-phase molecules allowed for specifically addressing adhesive energy without changing other system properties. A 61% reduction of friction torque was observed with the utilization of 18% relative humidity water vapor lubrication. Additionally, the relationship between friction torque and normal load was shown to follow an adhesion-based trend, highlighting the effect of adhesion and further confirming the adhesion-dominant hypothesis. The wear mechanisms have been studied for a microfabricated ball bearing platform that includes silicon and thin-film coated silicon raceway/steel ball materials systems. Adhesion of ball material, found to be the primary wear mechanism, is universally present in all tested materials systems. Volumetric adhesive wear rates are observed between 4x10^-4 µm^3/mN*rev and 4x10^-5 µm3/mN*rev were determined by surface mapping techniques and suggest a self-limiting process. This work also demonstrates the utilization of an Off-The-Shelf (OTS) MEMS accelerometer to confirm a hypothesized ball bearing instability regime which encouraged the design of new bearing geometries, as well as to perform in situ diagnostics of a high-performance rotary MEMS device. Finally, the development of a 3D fabrication technique with the potential of significantly improving the performance of micro-scale rotary structures is described. The process was used to create uniform, smooth, curved surfaces. Micro-scale ball bearings are then able to be utilized in high-speed regimes where load can be accommodated both axially and radially, allowing for new, high-speed applications. A comprehensive exploration of the fundamental tribology of microball bearing MEMS has been performed, including specific experiments on friction, wear, lubrication, dynamics, and geometrical optimization. Future devices utilizing microball bearings will be engineered and optimized based on the results of this dissertation

Model identification for impact dynamics of a piezoelectric microactuator

A parameterized model for the impact dynamics of a piezoelectric microactuator is proposed, and a system-identification procedure for quantifying model parameters is presented. The proposed model incorporates squeeze-film damping, adhesion and coefficient-of-restitution effects. Following parameter quantification from sample data of bouncing impacts and progressive ramped-square-wave inputs, the model is found to be effective in predicting the time response of the actuator to a range of square-wave and sinusoidal inputs. The main contributions of this paper are to show that the dynamic response to micro-scale contact can be predicted using simple lumped-parameter modeling after a proposed system-identification procedure is performed and that certain small-scale forces can be quantified. For example, for motions where bounce of the cantilever tip may occur, the range of adhesion is found to be time dependent and vary between approximately 20 and 520 nN, while the range of squeeze-film damping is estimated to be between 50 and 130 nN, depending on the input signal frequency and amplitude. The presence, absence and quantity of bounces upon impact are predicted very accurately, while oscillation amplitudes and contact durations are predicted to be between 1% and 30% error for the majority of many test cases of periodic inputs between 5 and 100 Hz.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98611/1/0960-1317_22_11_115002.pd

Mechanics of Non Planar Interfaces in Flip-Chip Interconnects

With the continued proliferation of low cost, portable consumer electronic products with greater functionality, there is increasing demand for electronic packaging that is smaller, lighter and less expensive. Flip chip is an essential enabling technology for these products. The electrical connection between the chip I/O and substrate is achieved using conductive materials, such as solder, conductive epoxy, metallurgy bump (e.g., gold) and anisotropic conductive adhesives. The interconnect regions of flip-chip packages consists of highly dissimilar materials to meet their functional requirements. The mismatches in properties, contact morphology and crystal orientation at those material interfaces make them vulnerable to failure through delamination and crack growth under various loading patterns. This study encompasses contact between deformable bodies, bonding at the asperities and fracture properties at interfaces formed by the interconnects of flip-chip packages. This is achieved through experimentation and modeling at different length scales, to be able to capture the detailed microstructural features and contact mechanics at interfaces typically found in electronic systems