Micro and Nanosystems - Volume 1, Issue 2, 2009

Advances in electronic materials, processing technologies, and integration schemes have resulted in phenomenal miniaturization of electronic components. Since the development of through-mask plating for thin film heads in the1960s and 1970s, an enormous amount of industrial and academic R&D effort has positioned electrochemical processing among the most sophisticated processing technologies employed in the microelectronics industry today. Electrochemical processing has thus become an integral part of advanced wafer processing and an enabling technology for nanofabrication. In this review we begin with a brief discussion of the phenomenal advances in IC based electronics and Moore's law as indicators of the paradigm shifts in microelectronics. We then highlight the important role played by electrochemical processing in the electronics industry. A detailed discussion of the dual Damascene plating technology and electroplated C4 technology form the key elements of the review. Finally, the challenges and opportunities offered by these technologies in extending Moore's law are discussed.

The use of micro and nanocomponents has increased rapidly over the last decade. The indications are that this trend is going to be sustained or even increase in the years to come due to the widespread use of these components in several micro and nanosystems. The development of such components and systems is supported by a wide range of CAD, CAM and CAE tools. These tools are either classic modeling methods already used in traditional manufacturing or modeling techniques specially developed for modeling and simulation in the micro or nanometer regime. In both cases special attention should be given to microscopic level phenomena that complicate the modeling process and increase the difficulty of applying these methods in this area. Modeling and simulation are definitely key tools employed by scientists and engineers in developing, testing, evaluating and analyzing the characteristics and performance of their micro and nanocomponents and systems. This paper reviews some of the most common techniques used in modeling and simulation of micro and nanomanufacturing; techniques such as the finite element method and molecular dynamics are analyzed. Furthermore, the application of these methods in several areas, namely micro and nanomanufacturing, nanomaterials and MEMS is discussed and the relative bibliography is presented.

A novel collection plate architecture was demonstrated for fabricating highly-aligned continuous electrospun nanofibers. This unique electrospinning platform utilizes various orientations of a three-layer stack to generate the collector plate. Through the use of multiple base plates, insulating apertures and target metal plates, the resultant electric field between the grounded base plates and charged syringe can be split. It is this divergence in the electric field that facilitates the ordered placement of the nanofibers. Ordered, continuous nanofibers have been realized for base plate separations ranging from as large as seven millimeters to as small as 1 mm. The structural properties of these aligned nanofibers are examined utilizing Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). The characterization of the aligned continuous nanofibers has revealed diameters approaching 150 nm. The appearance of standard and some new absorption bands for polypyrrole (PPy) and polyethylene oxide (PEO) confirms the composite formation.

Sensor system based on nanostructured RuO2 sensing electrode (SE) was fabricated and examined for pH and dissolved oxygen (DO) detection in water at a temperature range of 9-35°C. The electromotive force (emf) response at these temperatures was linear to the logarithm of pH (from 2.0 to 13.0 pH) and DO concentrations in the range from 0.6 to 8.0 ppm (log[O2], -4.71 to -3.59) at a neutral pH. In was also found that the response/recovery time of the sensor to DO changes is sluggish as the water temperature cools down. Sensor response time, T90, to the different DO increased from 8 min at a temperature of 23°C to about 30 min at a temperature of 9°C. The slope was -41 mV per decade for the RuO2-SE at 8.0 pH and it was closely followed the Nernst equation. However, it was found that in strong alkaline solutions sensor emf is a mixed-potential of fast and slow electrochemical reactions involving O2 -, RuO4 2- and OH- ions. X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDX) and impedance spectroscopy techniques were used to examine the morphology, crystalline structure and electrochemical behaviour of the nanostructured RuO2-SEs, respectively. Characterization analysis revealed that RuO2-SE consist of RuO2 nano-particles in the range of 100-650 nm homogeneously distributed across SE.

A newly designed three dimensional (3D) flexible circuit as a package with five IC chips has been invented, and the prototype of the 3D package using laser micromachining has been successfully demonstrated. Fabrication processes of the 3D package consist of (1) preparation of printed wiring on the flexible substrate, (2) selective polyimide material removing on contact pads using UV laser (3) component placing and soldering, and (4) preparation of bending windows by laser micromachining. The production of the so-called bending window is a unique application of laser material processing. These windows can be used in flexible circuits to define the exact position of deformation. It is done by reducing the thickness of the flexible substrate in a well-defined, narrow line. The unique feature of this newly developed package is the 2-D design for a 3D structure. According to this design, 55% area reduction can be obtained without any designing and overheating problems, which usually occur. Furthermore, the new 3D package design can simplify processes such as I/O redistribution, chip cooling, and package formation. It is proven that the mechanical integrity of the prototype 3D stacked package meets the requirements of the 85°C/85% test and JEDEC standard JESD22-B111 mechanical test.

A simple easy to use highly accurate closed-form model to determine the pull-in voltage of electrostatically actuated circular diaphragms subject to large deflection has been developed. The model takes account of the nonlinear stretching of the diaphragm during large deflection, effects of residual stress, bending stress, and the effects of fringing field capacitances. At first a linearized uniform model of the nonlinear non-uniform electrostatic force has been derived that includes the effects of the fringing field capacitances. This model is then used in conjunction with the load-deflection model of a circular diaphragm subject to large deflection to derive the closed-form model for the pull-in voltage based on the condition that at unstable equilibrium, the electrostatic force is just balanced by elastic restoring force. The model has been verified by extensive 3-D electromechanical finite element analysis (FEA) using IntelliSuite. The model is in excellent agreement with 3-D electromechanical FEA with a maximum deviation of 1.6% for a wide range of residual stress and pull-in voltage values. The model leads to an integrated design strategy to optimize the electrical and mechanical design variables for MEMS-based capacitive type sensors having circular diaphragms. The model can be used to determine pull-in voltages of MEMS capacitive type pressure sensors, capacitive micromachined ultrasound transducers (CMUT) for medical diagnostic imaging, MEMS based microphones, touch mode pressure sensors, and other application areas where electrostatically actuated circular diaphragms are used.

The performance of a two-dimensional micro synthetic jet actuator is evaluated using computational modeling and simulation. A synthetic jet is a zero net mass flux device having a cavity with an oscillating membrane as a sidewall. The motion of the membrane produces a fluctuating jet flow, which transfers linear momentum to the external domain. A Navier-Stokes solver that can run on moving and deforming meshes is used to study the membrane-driven flow in and out of the micro cavity geometry. The primary focus of the present investigation is on the delineation of a feasible design space defined by the geometric and actuation parameters that directly affect its performance. The design variables are selected to be the membrane's oscillation frequency and amplitude, the orifice's width and height, and the cavity's width and height. The results clearly indicate that, for a micro synthetic jet discharging into a quiescent medium, these variables have significant control on the vortex formation, its size, its circulation and its momentum flux. Therefore, the desired actuation can be obtained by manipulating these design variables.