Preface to the Second Edition
Eight years have passed since the first edition of this book was published. During this period, considerable research has been produced in the field of three-dimensional (3-D) integration and the first commercial products of multitier DRAM memories have appeared in the market. Furthermore, the introduction of interposers forming 2.5-D systems has enabled the integration of memory and processor modules in close proximity, supporting higher bandwidth for memory-processor communication as compared to individually packaged modules.
The intention of this second edition is to cohesively integrate and present several research milestones from different, yet interdependent, aspects of 3-D integrated circuit design, reflecting recent progress in the field. The foremost goal of the book is to describe design methodologies for 3-D circuits; methodologies that exploit the innate technological diversity existing in 3-D integrated circuits. While the focal point of this book is design and analysis techniques and related methodologies, this material also provides an overview of significant manufacturing technologies for 3-D systems, including interposer-based systems, as well as demonstration of several 3-D test circuits.
3-D or vertical integration is an exciting path to boost the performance and extend the capabilities of modern integrated systems. These capabilities are inherent in 3-D integrated circuits. The former enhancement is due to the considerably shorter interconnect length in the vertical direction, and the latter improvement is due to the ability to combine dissimilar technologies within a multitier system. It is also worth noting that vertical integration, other than the stacking process, is compatible with standard two-dimensional integrated circuit design processes that have been developed over the past several decades. These distinctive characteristics make 3-D integration highly attractive as compared to other emerging technological solutions that have been proposed to resolve the increasingly difficult issue of on-chip interconnect, which limits speed and power, while also providing heterogeneous integration of diverse and complex systems.
The new fabrication steps introduced for stacking circuits require a different business model and important shifts in the supply chain as additional stakeholders are involved in manufacturing and designing 3-D systems. Unfortunately, to date, a concrete and lucrative business model is not yet in place, the primary reason for the delay in the use of vertical systems. Beyond these nontechnical issues, the challenges of providing high performance, multi-functional heterogeneous, energy efficient, and small form factor 3-D systems are due to the lack of a complete and effective design and verification flow for these types of systems. Thus, the realization of complex 3-D systems requires advanced design technologies across multiple abstraction levels. The development of these capabilities will be better supported if the physical behavior and mechanisms that govern intertier communication and manufacturing are properly understood. The focus of this book diligently serves this purpose.
Another important objective of this second edition is to integrate the several different approaches that have been developed over the past few years in the physical design process, such as power delivery, floorplanning, placement, and synchronization. The important issue of process variability in 3-D systems that surprisingly has received minimal attention is also discussed in this book.
Recognizing the importance of the vertical interconnections in 3-D circuits, the 3-D structures are central to the content of this book. Tutorial chapters are dedicated to manufacturing processes and technological challenges, complemented by an in-depth treatment of electrical models of these structures.
The vertical wires are investigated not only as a communication medium but also as heat conduits within the 3-D system. From this perspective, novel and efficient algorithms are presented for improving the signal propagation characteristics of heterogeneous 3-D systems based on the electrical behavior of the vertical interconnects. Additionally, the important role that the vertical interconnects play in global signaling and thermal amelioration is discussed throughout this book.
As thermal issues were identified at the earliest stages as an important challenge for 3-D systems, particular emphasis is placed on thermal analysis and modeling of 3-D systems in general and the vertical wires in particular. Related thermal aware physical design techniques and architectural approaches to lower the high temperatures within these systems are also reviewed.
In all of these issues, our approach has been to cover as broadly as possible the different novel techniques and ideas that have been proposed to address these issues. Thus, the material does not follow a narrow minded approach where only the results produced by the authors are presented but rather offers full coverage of the field. Additionally, as many design methods are based on existing methods for planar (2-D) circuits, several tutorial sections are included within the appropriate chapters to provide the requisite background to ensure that the reader can more easily follow the material. Finally, another useful feature of this second edition is that techniques and methodologies are often accompanied by silicon measurements from several prototype ICs designed at the University of Rochester and fabricated by MIT Lincoln Laboratories (and other facilities).
2017