Adaptive Cooling Of Integrated Circuits Using Digital Microfluidics

Thanks to increasing power consumption and component density, localized hot spots are becoming a serious challenge in IC (integrated circuit) chip design - so serious, in fact, that Intel recently had to yank a circuit because it was literally burning. For IC engineers grappling with high power dissipation and thermal issues, new droplet-based cooling techniques using digital microfluidics technology could provide the solution. This definitive guide paves the way, with design and implementation methodologies and prototypes for utilizing this groundbreaking technology. After reviewing cooling principles and current bulk cooling methods, the book brings engineers up to speed on emerging droplet-based architectures. Amply illustrated, this milestone work will prove invaluable in tackling IC heat issues that existing methods can no longer address.

The recent development of microfluidics has lead to the concept of lab-on-a-chip, where several functional blocks are combined into a single device that can perform complex manipulations and characterizations on the microscopic fluid sample. However, integration of multiple functionalities on a single device can be complicated. This a cutting-edge resource focuses on the crucial aspects of integration in microfluidic systems. It serves as a one-stop guide to designing microfluidic systems that are highly integrated and scalable. This practical book covers a wide range of critical topics, from fabrication techniques and simulation tools, to actuation and sensing functional blocks and their inter-compatibility. This unique reference outlines the benefits and drawbacks of different approaches to microfluidic integration and provides a number of clear examples of highly integrated microfluidic systems.

Thermal management in electronics is an ever-growing challenge which needs constant innovations to regulate hotspots in integrated circuits for safe operation within its Thermal Design Power (TDP) envelope. As the number of transistors increase due to advancements in photolithography to enable die shrink, portable electronics are on the rise and so is the demand for microscale cooling systems because conventional cooling components like heat sinks, heat pipes and fans are not capable of meeting design requirements for cooling solutions. In addition to the benefits enjoyed by microscale cooling systems like compact and lightweight design along with simple operation, electrowetting on dielectric (EWOD) based digital microfluidic (DMF) hotspot cooling promises an innovative and novel cooling based on valveless and pumpless motion of coolant droplets directly on hotspots. Along with reduction in thermal resistance, this technology is also useful for site specific cooling by moving droplets to multiple hotspots on chip. In this research, Indium Tin Oxide (ITO), a transparent conducting material, was patterned on glass substrates to emulate hotspots and also provide the electric field for EWOD pumping of droplets. Two cooling systems were designed, fabricated and tested for demonstrating temperature drop, namely Ionic Liquids (ILs) and De-Ionized (DI) water, using Liquid Crystals and ITO Resistance Temperature Detectors (RTDs) as the temperature sensing techniques. ILs were initially used as coolants to suppress evaporation but turned out to have poor cooling capability than DI water from LCT results. Apart from conduction and convection heat transfer from the hotspot to the droplet, phase-change was also responsible in achieving cooling for DI water. To facilitate detailed study of hotspot cooling, an innovative approach to regulate hotspot temperature was demonstrated by creating a hydrophilic spot (H-spot) on the heater which retains a small droplet while the main coolant droplet passes over the hotspot. High-speed video was taken and synchronized with RTD data to identify different phases of droplet motion and observations were made to explain the heat transfer modes in each phase of motion. Transient heat transfer simulations in COMSOL Multiphysics including emulation of phase-change effects were performed for varying thermal diffusivity values of the droplet to understand its effect on the heater temperature. Finally, an analytical model was proposed based on literature which related droplet evaporation on the H-spot to the overall heat transfer coefficient. The evaporation rate was also calculated experimentally and compared with the ideal values used in the COMSOL simulations which resulted in the evaporation rates being in good agreement with each other.

This book provides a comprehensive methodology for automated design, test and diagnosis, and use of robust, low-cost, and manufacturable digital microfluidic systems. It focuses on the development of a comprehensive CAD optimization framework for digital microfluidic biochips that unifies different design problems. With the increase in system complexity and integration levels, biochip designers can utilize the design methods described in this book to evaluate different design alternatives, and carry out design-space exploration to obtain the best design point.

Heat removal technologies are among the most critical needs for three-dimensional (3D) stacking of high-performance microprocessors. This research reports a 3D integration platform that can support the heat removal requirements for 3D integrated circuits that contain high-performance microprocessors in the 3D stack. :This work shows the use of wafer-level batch fabrication to develop advanced electrical and fluidic three-dimensional interconnect networks in a 3D stack. Fabrication results are shown for the integration of microchannels and electrical through-silicon vias (TSVs). A compact physical model is developed to determine the design trade-offs for microchannel heat sink and electrical TSV integration. An experimental thermal measurement test-bed for evaluating a 3D inter-layer liquid cooling platform is developed. Experimental thermal testing results for an air-cooled chip and a liquid-cooled chip are compared. Microchannel heat sink cooling shows a significant junction temperature and heat sink thermal resistance reduction compared to air-cooling. The on-chip integrated microchannel heat sink, which has a thermal resistance of 0.229 °C/W, enables cooling of>100W/cm2 of each high-power density chip, while maintaining an average junction temperature of less than 50°C. Cooling liquid is circulated through the 3D stack (two layers) at flow rates of up to 100 ml/min. :The ability to assemble chips with integrated electrical and fluidic I/Os and seal fluidic interconnections at each strata interface is demonstrated using three assembly and fluidic sealing techniques. Assembly results show the stacking of up to four chips that contain integrated electrical and fluidic I/O interconnects, with an electrical I/O density of ~1600/cm2.

The first book offering a global overview of fundamental microfluidics and the wide range of possible applications, for example, in chemistry, biology, and biomedical science. As such, it summarizes recent progress in microfluidics, including its origin and development, the theoretical fundamentals, and fabrication techniques for microfluidic devices. The book also comprehensively covers the fluid mechanics, physics and chemistry as well as applications in such different fields as detection and synthesis of inorganic and organic materials. A useful reference for non-specialists and a basic guideline for research scientists and technicians already active in this field or intending to work in microfluidics.

Heat Transfer - Advances in Fundamentals and Applications explores new knowledge in the domain of fundamental and applied advances in heat transfer. This book specifically emphasizes advanced topics of heat transfer. Professionals, researchers, and academics working in various areas of heat transfer will find this a useful reference for finding new solutions to heat transfer problems. The book is organized into two sections on the fundamental advances in heat transfer and advances in applications of heat transfer. Chapters address inverse conduction problems, heat transfer enhancement during internal flows, shell-and-tube heat exchangers, heat transfer mechanisms in petroleum and geothermal wellbores, and other topics in the field.

Supported with over 280 illustrations and over 160 equations, the book offers cutting-edge guidance on designing integrated circuits for wireless biosensing, body implants, biosensing interfaces, and molecular biology. You discover innovative design techniques and novel materials to help you achieve higher levels circuit and system performance.