Nano-Bio- Electronic, Photonic and MEMS Packaging

With the phasing out of lead-bearing solders, electrically conductive adhesives (ECAs) have been identified as one of the environmentally friendly alternatives to tin/lead (Sn/Pb) solders in electronics packaging applications. In particular, with the requirements for fine-pitch and high-performance interconnects in advanced packaging, nanoconductive adhesives are becoming more and more important due to the special electrical, mechanical, optical, magnetic, and chemical properties that nano-sized materials can possess. There has been extensive research for the last few years on materials and process improvement of ECAs, as well as the advances of nanoconductive adhesives that contain nano-filler such as nanoparticles, nanowires, or carbon nanotubes and nanomonolayer graphenes. In this chapter, recent research trends on electrically conductive adhesives (ECAs) and their related nanotechnologies are discussed, with the particular emphasis on the emerging nanotechnology, including materials development and characterizations, processing optimization, reliability improvement, and future challenges/opportunities identification. The state of the art on nanoisotropic/anisotropic conductive adhesives incorporated with nanosilver, carbon nanotubes, and nanonickel, and their recent studies on those for flexible nano/bioelectronics, transparent electrodes, and jettable processes are addressed in this chapter. Future studies on nanointerconnect materials are discussed as well.

This chapter addresses fundamentals on biomimetic nano Lotus surfaces, their chemistry, and nanostructure texture physics. In addition, preparation methodologies for various nano-textured superhydrophobic surfaces, their applications, and future researches are presented.

A brief review on CNT structure, electrical property, heat transport, and synthesis methods, CNT applications as electrical interconnects and TIMs, CNT integration into circuits and packaging, with focus on CNT transfer technology, are presented. In comparison with CNT/polymer composites, nanographite/polymer composites are more promising for TIM applications, which is discussed together with current thermal measurement techniques, commercialized and non-commercialized.

NanoSpray Combustion™ processing is a versatile and cost-effective manufacturing method for a wide range of materials, including nanopowders and nanostructured thin films. The NanoSpray process is used in combustion chemical vapor condensation (nCCVC) mode for making metal oxide, metal phosphate, and select metal nanopowders while combustion chemical vapor deposition (nCCVD) is used to make thin films. In this chapter, we will use NanoSpray Combustion process as a benchmark and review its capabilities to that of other nanomaterials’ fabrication processes. Examples will mostly be of nanopowders synthesized using nCCVC. Applications of the nanomaterials in the electronic and energy sectors will be discussed.

Manipulation of nanostructured electrode material can provide versatile strategies toward improving the electrochemical properties. The nanostructure promotes fast Li-ion pathways for lithium ion transport and electronic conduction. Better rate capabilities are due to that the distance over which Li⁺ must diffuse in the solid state dramatically decreases in the nanostructured electrode. Recently, there are growing applications of these materials in the area of micro-potable electronics, such as micro-robots, sensor nods, active radio frequency identification (RF-ID) tag, etc. Fast charging time and longer may be essential for these applications, and 1D-nanowire materials may enable to realize much more faster charging speeds than those achieved using conventional bulk materials, without significant degradation in storage capacity.

This chapter reviews a novel technology that uses piezoelectric nanowires to harvest nanoscale mechanical energy. Wurtzite ZnO nanowires were first applied for this purpose. Due to the bending of nanowires, the piezoelectric effect induces positive and negative potentials on the stretched surface and compressed surface, respectively. This effect has been proved by using a conductive AFM tip to deflect individual wurtzite ZnO and CdS nanowires as well as vertically aligned ZnO nanowire arrays. On the basis of this phenomenon, a prototype nanodevice (nanogenerator) has been successfully developed to convert ultrasonic wave energy into electricity. After optimization, the nanogenerator’s output has reached ∼83 nW/cm², which shows a great potential to power nanosensors. A flexible substrate and textile fibers were also integrated with the ZnO nanowire array for harvesting energy from low-frequency perturbations. At the end of this chapter, several pathways are suggested for further performance improvements.

Lead-free solder, tin, tin/silver (SnAg) and tin/silver/copper (SnAgCu) alloy nanoparticles with various sizes were synthesized via a low temperature chemical reduction method and their thermal properties were studied by differential scanning calorimetry. The particle size dependency of the melting temperature and the latent heat of fusion was observed. The wetting test for the as-prepared SnAg and SnAgCu alloy nanoparticle pastes on a Cu surface showed the typical Cu₆Sn₅ intermetallic compound (IMC) formation. These low melting point SnAg or SnAgCu alloy nanoparticles could be used for low reflow temperature lead-free interconnect applications.

This chapter discusses state of the art in nanoengineered integrated passives. In particular, the chapter elaborates nanoparticle-based integrated passives that are being developed using various thin and thick films processes, such as printing. The discussion provides need for next generation of integrated passives and opportunities offered by the nanotechnology to meet those needs. This is a novel area of research and the chapter shares results for integrated capacitors, inductors, and resistors for materials selection, deposition processes, and testing for integrated applications.

The heat dissipation problem is becoming a crucial barrier in the continuous process of electronic devices and systems miniaturization, and thermal interface materials play a key role in transport at all level microelectronics packaging. In this chapter, thermally conductive composites, as one of the main types of thermal interface materials are discussed. Such composites consist of the polymer base material matrix and thermally conducting filler. In modern bio- and micro-electronics, the thermal conductivity of the filler material ought to be as high as possible and its size—in the nanometer range. For this purpose, the nanosized particles of metals (mostly silver) or carbon allotropies (mostly carbon nanotubes) are used. Unfortunately, even when the fillers with thermal conductivity in the range of hundreds or more W/m×K are applied, the conductivity of nanocompostes elaborated currently are not higher than a few W/m×K. The analysis of heat transport in filled composites shows that the reason of such limitation of the heat transport is related with thermal contact resistance between filler’s particles. The way of the thermal conductivity improvement is discussed; however, in order to evaluate this progress correctly, the proper measurement methods have to be used. Currently there are many technical solutions to measure thermal conductivity which are based on either steady-state or transient techniques, but for relatively low thermal conductivity of nanocomposites, only few methods can be applied. Here the analysis of the thermal conductivity measurement is presented.

Carbon nano-tubes (CNTs) and carbon nano-fibers (CNFs) are characterized by a number of unique and extraordinarily attractive physical/mechanical properties. Examples are high Young’s modulus, high tensile strength, low coefficient of thermal expansion (CTE), and high thermal conductivity. These unique properties of CNTs and CNFs lead to many potentially attractive applications of these quasi-one-dimensional nano-structural elements in many fields of applied science and engineering. One of such applications is the use of CNT/CNF arrays as thermal interface materials (TIM) in electronic, opto-electronic, and photonic systems. In order to be employed in such a capacity, CNTs/CNFs must possess not only high thermal conductivity but also a number of other crucial physical/mechanical properties: be able to make good contact with attaching (usually hot) surface, possess good “anchoring” strength at their root cross-sections (i.e., good “adhesion” to their substrate), withstand high pressure (up to100 psi), exhibit acceptable consistency in their heights and diameters, demonstrate adequate mechanical performance in the post-buckling conditions, exhibit good wettability to the embedding low-modulus material, if any, etc. Good manufacturability and low cost of CNT/CNF-based heat-spreaders and other heat removing devices are also necessary for practical applications in high-power electronic devices.

In this chapter we address several major experimental techniques that have been developed during the last decade and are being used to characterize the physical/mechanical properties of the individual CNTs/CNTs and CNT/CNF arrays, and to understand their physical (mechanical and thermal) behaviors and performance. We also discuss some results that have been obtained using these techniques. In the extension part of this chapter, we show how analytical stress modeling can be used to describe the mechanical behavior of CNTs/CNFs embedded into low-modulus elastic media. This is done to improve both the thermal and the mechanical performance of the CNT/CNF arrays. The developed models can be employed for the analysis and rational physical design of the structures in question.

The rapid emergence of nanoelectronics, with the consequent rise in transistor density and switching speed, has led to a steep increase in die heat flux and growing concern over the emergence of on-chip “hot spots.” The application of on-chip high heat flux cooling techniques provides a viable direction for the thermal management of such nanoelectronic components. Following a review of the relevant passive and active thermal management techniques, the physical phenomena underpinning the most promising on-chip thermal management approaches are described. Attention is devoted to thin-film and miniaturized thermoelectric coolers, orthotropic TIMs/heat spreaders, and phase-change microgap coolers for hot-spot remediation and thermal management of these nanoelectronic chips.

Systems for energy conversion, heat rejection, and sensing and control often incorporate heat exchange devices. Recent developments in microfabrication and assembly methods have led to significant miniaturization of these systems. Miniaturized heat exchange devices have commonly utilized microchannel flow passages. This chapter reviews the fundamental flow and heat-transfer phenomena in microchannels, the most common numerical and experimental characterization techniques, microfabrication methods, and the application of microchannels in thermal management of high heat flux electronics. The range of channel hydraulic diameters covered in this chapter is from a few micrometers to a few millimeters where the larger diameter transport characteristics become valid.

The ability to visualize in real time the expression dynamics and localization of specific RNAs in vivo offers tremendous opportunities for biological and disease studies including cancer detection. However, quantitative methods such as real-time polymerase chain reaction (PCR) and DNA microarrays rely on the use of cell lysates thus not able to obtain important spatial and temporal information. Fluorescence proteins and other reporter systems cannot image endogenous RNA in living cells. Fluorescence in situ hybridization (FISH) assays require washing to achieve specificity, therefore can only be used with fixed cells. Here we review the recent development of nanostructured probes for living cell RNA detection and discuss the biological and engineering issues and challenges of quantifying gene expression in vivo. In particular, we describe methods that use oligonucleotide probes, combined with novel delivery strategies, to image the relative level, localization, and dynamics of RNA in live cells. Examples of detecting endogenous messenger RNAs, as well as imaging their subcellular localization are given to illustrate the biological applications, and issues in probe design, delivery, and target accessibility are discussed. The nanostructured probes promise to open new and exciting opportunities in sensitive gene detection for a wide range of biological and medical applications.

In the last two decades, fundamental and application-driven research on microfluidics and bio-micro-electro-mechanical systems (BioMEMS) has flourished in academia and industries and has begun to make impact on medicine and biosciences. Packaging of these systems is an integral if not critical part of the device/system design and function. Because the applications and the designs of the chips are wide ranging, it is difficult to achieve a universal packaging scheme that meets the requirements of all applications. Instead, research and manufacturing practices of each type of biochip have come up with specialty techniques. This chapter will review these techniques in the specific contexts of the chip applications, as well as materials requirements. In addition, we will highlight common and advanced practices and point out research needs in these areas.

Packaging of microsensors is not standardized and highly customized depending upon the requirements for a specific application. This chapter reviews selected illustrative examples for chemical and biosensors for a range of applications. Approaches range from modified semiconductor device packages, fully customized packages to packages produced by rapid prototyping stereolithography. Packaging for room temperature operation of sensors, such as ion selective FETs, microelectrochemical sensors, microcantilever sensors, in addition to sensors which operate at higher temperatures including microhotplate sensors and electrochemical gas sensors is discussed. Also biomedical sensors and microfluidic devices including microneedles, soft lithography for microchannel fabrication, bonding, and packaging materials are discussed.

Define bioelectronics, nanobioelectronic sensors, and their applications.

Describe fundamentals of biology related to interfacing biological material with electronic systems.

Present the elements or building blocks of nanobioelectronic sensors, and fabrication methodologies.

Describe functionality of nanobioelectronic sensors and nanopackaging

Identify the challenges in interface mechanisms between biosensor element and transducer; signal transduction, processing, and monitoring.

The nanobiosensor technology, an integral part of bioelectronics, is revolutionizing the health care industry, forensic medicine, home-land security, food and drink industries, environmental protection, genome analysis of organisms and communications. In this chapter, the biosensing electronics building blocks such as biosensing, signal conversion and signal processing, and biosensing mechanisms have been described. The use of smart nanomaterials such as Zinc oxide (ZnO) nanowire and carbon nanotubes (CNTs) in fabrication of biosensors has been described. A critical account on biological probe design, probe preparation and interfacing with signal transducer element of the biosensor is given. Various transducer elements and biosensing methods have been enumerated. The application of nanochemistry for biosensing packaging, with special reference to surface modification and biofunctionalization of sensor devices, and integration of biosensor system with system-on packaging (SOP) are detailed. Finally, the chapter concludes with future trends in biosensor technologies and a brief summary.

Development of integrated circuits (IC) and semiconductor chips has narrowed dimensions of electronic components to length scales of nanometer size. However, design and manufacture of nano-scale electronic components need extensive understanding of material properties at small length scales, preferably at the atomistic level. Behavior of materials at nanometer scale is significantly influenced by size effects; behaviors of materials significantly change at nanometer level compared in macroscopic world due to size effects. As a result, electronic packaging has to adopt significant design requirements associated with the tremendous reduction in size.

Molecular dynamics (MD) simulation [1–5] was invented as a tool to account for the interactions between basic particles, generally atoms, in small systems of interest. Many attributes of materials can be obtained from MD simulation, at least on a qualitative level and sometimes in more quantitative manner. MD has been utilized as a powerful tool to narrow the number of possible candidate materials for many components in electronic packaging, based on the critical requirements on the material, such as resistance of materials to moisture, stress and thermal cycling, and strength of interfaces. This is achieved by understanding the behavior of the materials with hypothetical structure and composition, reducing or eliminating the need for synthesizing these materials at least during the initial material selection process. Thus, in addition to understanding material behavior, MD can be used to address the inverse problem of designing materials with specific properties for a chosen end use.

In the past decade, MD procedure has experienced explosive growth in its usage in a variety of areas. Here, we give a brief review of MD simulation procedure with particular emphasis to its applications in electronic packaging.

Among all the micro-scale or nano-scale simulation methods (MD, Monte Carlo methods and quantum mechanics), MD serves as a major simulation tool in electronic packaging area. Selection of an appropriate simulation method depends on the length scale of the systems under consideration and the time scale associated with the process of interest that the system is subjected to. Many problems of interest in the packaging area fall within the length scale limits of MD as it is comparable to the relevant size of many electronic packaging devices. Compared to other methods, MD can model most properties and processes at the equilibrium state as well as many nonequilibrium phenomena (such as water diffusion, heat transfer, mechanical deformation) in the packaging area. In addition, MD can be coupled with (1) Monte Carlo methods to incorporate complementary effects within the MD time/length scale domain, (2) quantum mechanics to capture events even at smaller scale and the effects of changes in electronic structures from the changes in atomic positions or structure, and (3) with finite element methods to embed quantum and molecular effects with continuum structural behavior for a material or a device. Depending on the particular property, in most cases molecular simulations can give excellent qualitative results and in many cases very good quantitative results as well. Since there are limitations on time and domain size in MD simulations, one may find difficulties in accurately simulating some of the properties that are realized in a larger domain and longer duration in real materials.

Digital image correlation (DIC) technique with the aid of scanning probe microscopes has become a very promising tool for deformation analysis of micro- and nanoscale components. The scanner drift of the atomic force microscope (AFM) is a great disadvantage to the application of digital image correlation to micro/nanoscale deformation measurements. This chapter has addressed the image distortion induced by the scanner drifts and developed a method to reconstruct AFM images for the successful use of AFM image correlation. The proposed AFM/DIC method is to generate a corrected image from two correlated AFM images scanned at the angle of 0° and 90°, respectively. The method has been validated by two simple AFM/DIC experiments. The application of this AFM/DIC technique was demonstrated by the deformation measurement on the micro-interconnection in a micro thermoelectric cooler. AFM images of the scan region of interest were obtained separately when the microelectronic device was before and after operating at both its cooling and heating stages. The AFM images were then used to obtain the in-plane deformation fields in the observed region of the micro-assembly. AFM image correlation is performed for nanoscale deformation analysis using the authors’ AFM–DIC program. The results show that the observed region was subjected to cyclic strains when the device worked between its cooling and heating stages, and cyclic strain in the vertical direction was found to be significant deformation mode. The thermally induced deformation behavior of the micro-assembly device was modeled by finite element analysis (FEA). Both thermal-electric analysis and thermal stress analysis were conducted on a 3D finite element model of the device. It is shown that the experimental results were able to validate the finite element analysis results.

The studies on advanced materials at sub-micron scales have become a popular subject in engineering sciences and technology development in the past decade. In general, experimental investigations at this scale are very difficult and may be unreliable. Therefore, analytical and computational modeling appears to be rather critical and important in such studies. The objective of this chapter is to review two state-of-the-arts approaches for modeling advanced materials at the nano- and the atomistic scales, respectively.

The first part of this chapter introduces a unit cell model for the analysis of composites with carbon nanotubes (CNTs) and epoxy resin using finite element method (FEM). Varying CNT orientation is considered in order to describe the behaviors of the randomly oriented CNTs inside the epoxy matrix. Composite loss factors are calculated based on the average ratio of the unit cell energy loss to the unit cell energy input. Calculated loss factors under different strain levels are compared to experimental data. With the validated model, parametric study is thereafter performed. Parameters such as CNT dimension and CNT alignment orientation are studied. Those factors lead to higher composite damping capacity are identified.

The second part of this chapter proposes a novel atomistic–continuum mechanics which is a hybrid method for coupling continuum mechanics and interatomic potential function to predict the mechanical behavior of nano-scale single crystal silicon under uniaxial tensile loading. The atomistic–continuum mechanics is based on the transformation of chemical bonds between atoms in molecular mechanics into appropriate elements in finite element method and continuum mechanics. There are many methods used in nano-structure analysis such as molecular dynamics (MD) and ab initio calculation; the molecular dynamics simulation is one of the most promising methods for investigating the mechanical properties of structure and material at nano-scale. However, it requires extensive computing time and cost. Furthermore, in traditional continuum mechanics, the finite element method (FEM) is widely used to model and simulate the mechanical behaviors of solid/discrete body; it is a mature technology after decades of development. Compared with MD simulation, the continuum mechanics can be very efficient as it can provide results quickly in an accurate range. In the hybrid approach, the total energy of the nano-structure is formed by each individual potential energy of bi-atom, once the total potential is assembled the FEM could take the minimization of the total energy, which includes the potential energy and external works, and to solve the structure by conventional way. Therefore, this study employs FEM to explore the mechanical properties of nano-scale single crystal silicon. This research also utilizes an interatomic potential function to describe the interaction of each atom. A general form of Stillinger–Weber potential function was used for interaction between the silicon atoms in the simulations. Based on atomistic–continuum simulation results, the Young’s modulus of single crystal silicon in various crystallographic planes could be estimated. The results obtained from the present modeling approach are in reasonable agreement with the experiment and simulation results reported in the literature.