ABSTRACT Title of dissertation: PHYSICAL ASPECTS OF VLSI DESIGN WITH A FOCUS ON THREE-DIMENSIONAL INTEGRATED CIRCUIT APPLICATIONS Zeynep Dilli Doctor of Philosophy, 2007 Dissertation directed by: Professor Neil Goldsman Dept. of Electrical and Computer Engineering This work is on three-dimensional integration (3DI), and physical problems and aspects of VLSI design. Miniaturization and highly complex integrated systems in microelectronics have led to the 3DI development as a promising technological approach. 3DI offers numerous advantages: Size, power consumption, hybrid inte- gration etc., with more thermal problems and physical complexity as trade-offs. We open this work by presenting the design and testing of an example 3DI system, to our knowledge the first self-powering system in a three-dimensional SOI technology. The system uses ambient optical energy harvested by a photodiode array and stored in an integrated capacitor. An on-chip metal interconnect network, beyond its designed role, behaves as a parasitic load vulnerable to electromagnetic coupling. We have developed a spatially-dependent, transient Green’s Function based method of calculating the response of an interconnect network to noise. This efficient method can model network delays and noise sensitivity, which are involved problems in both planar and especially in 3DICs. Three-dimensional systems are more susceptible to thermal problems, which also affect VLSI with high power densities, of complex systems and under extreme temperatures. We analytically and experimentally investigate thermal effects in ICs. We study the effects of non-uniform, non-isotropic thermal conductivity of the typically complex IC material system, with a simulator we developed including this complexity. Through our simulations, verified by experiments, we propose a method of cooling or directionally heating IC regions. 3DICs are suited for developing wireless sensor networks, commonly referred to as “smart dust.” The ideal smart dust node includes RF communication circuits with on-chip passive components. We present an experimental study of on-chip inductors and transformers as integrated passives. We also demonstrate the perfor- mance improvement in 3DI with its lower capacitive loads. 3DI technology is just one example of the intense development in today’s elec- tronics, which maintains the need for educational methods to assist student recruit- ment into technology, to prepare students for a demanding technological landscape, and to raise societal awareness of technology. We conclude this work by presenting three electrical engineering curricula we designed and implemented, targeting these needs among others. PHYSICAL ASPECTS OF VLSI DESIGN WITH A FOCUS ON THREE-DIMENSIONAL INTEGRATED CIRCUIT APPLICATIONS by Zeynep Dilli Dissertation submitted to the Faculty of the Graduate School of the University of Maryland, College Park in partial fulfillment of the requirements for the degree of Doctor of Philosophy 2007 Advisory Committee: Professor Neil Goldsman, Chair/Advisor Professor Martin Peckerar Associate Professor Reza Ghodssi Associate Professor Timothy Horiuchi Associate Professor Linda Schmidt c Copyright by Zeynep Dilli 2007 Dedication To all my teachers ii Acknowledgements First and foremost I am indebted to Dr. Neil Goldsman for his invaluable support and guidance. He has been a great advisor and teacher. I am grateful to Dr. Martin Peckerar and Dr. Linda Schmidt for the privilege to work with them on different sections of this dissertation, and for joining my committee. I am grateful to Dr. Reza Ghodssi and Dr. Timothy Horiuchi for agreeing to serve in my committee, and for their time and effort. I have been lucky to collaborate with brilliant and supportive people. I must mention Dr. Akın Akt¨urk especially. I also owe thanks to Dr. Janet Schmidt, Mr. Todd Firestone, Ms. Datta Sheth, Ms. Bo Yang, Mr. Yves Ngu and Mr. Bai Yun for their assistance and collaboration, for Mr. Jay Renner and Mr. Shyam Mehrotra for technical support, and to Dr. Volkan Cevher, Mr. Susitha Jayaratne, Dr. Gary Pennington, Mr. Siddharth Potbhare and Dr. John Rodgers for very profitable discussions. Through the years I have had many inspiring teachers, and while I cannot name them all, I thank them all. I would like to thank Dr. George Metze at LPS and the Dept. of Electrical and Computer Engineering for supporting the majority of this work. My thanks and gratitude go to my mother Yıldız for teaching me how to read resistors (and for much more), to my father Budak for teaching me how to analyze filters at a glance (and for much more), and to my sister G¨ok¸cefor being the ray of sunshine she is (and for much more). I give thanks to all my extended family for iii their support and love. Size gerekti˘gikadar te¸sekk¨uredemem hi¸c. Many precious people have supported me and offered their confidence, counsel, experience and friendship during this work. Dr. Breno Imbiriba, Dr. Hilmi Volkan Demir, Mrs. Paula and Mr. Chort Montrie, Dr. Kristy Henscheid, Dr. Jeff Huo, Mrs. Maggie Brazeau, Mr. John Novak, Mrs. Loreen and Mr. Martijn de Kort, Mrs. Frederica and Mr. Herb Baer, all those who attend the Conservatory and members of Three Left Feet, all the newsgroup people, more others than I can name and once again my family—I hope I have been and will be able to give back some of all that I received from you. iv v Table of Contents List of Figures x 1 Introduction 1 1.1 Three-Dimensional Integration and Self-Powering: Motivation and Effects of VLSI Physics . 2 1.2 Issues in the Physics of VLSI Design: Interconnect Modeling . 6 1.3 Issues in the Physics of VLSI Design: Thermal Effects and Modeling . 9 1.4 Issues in the Physics of VLSI Design: Reactive Components . 12 1.5 Electrical Engineering Education: Motivation . 14 2 Three-Dimensional Integration: Physical Design of A Self-Contained Elec- tronic System 16 2.1 Introduction and Overview . 16 2.2 Example Implementation: A Self-Powering 3-D System on SOI CMOS 17 2.2.1 Design Introduction . 17 2.2.2 Process Information . 19 2.2.3 Photodiodes: Design Issues . 22 2.2.3.1 Photocurrent Calculation . 22 2.2.3.2 Photodiode Design and Layout . 28 2.2.4 Layout and Chip Microphotographs . 34 2.2.4.1 Tier 1: The Local Oscillator . 34 2.2.4.2 Tier 2: The Capacitor . 35 2.2.4.3 Tier 3: Photodiodes, Measurement Pads . 36 2.2.4.4 Chip Microphotographs . 37 2.2.5 Circuit Analysis and Simulations . 40 2.2.5.1 Circuit Operation: Qualitative Description . 40 2.2.5.2 Circuit Operation: Quantitative Analysis . 45 2.2.6 Measurement Results . 49 2.2.6.1 Rail Voltage Measurements . 49 2.2.6.2 Oscillator Output Measurements . 49 2.2.7 Concluding Remarks on the First Self-Powering SOI 3DIC . 50 2.3 Second-Generation Design . 51 2.3.1 Introduction . 51 2.3.2 Overview of of the Second-Generation Chip . 52 2.3.3 New Diode Arrays . 53 2.3.3.1 Diode Layouts with No-Silicide . 54 2.3.3.2 Diode Array with Two Serial Diodes per Branch . 55 2.3.4 Integrated Externally-Powered Amplifier . 57 2.3.5 Self-Powered Amplifier . 59 2.4 3-D Integration: Current Research, Challenges and Directions . 62 2.4.1 Sequential Fabrication Techniques for 3DI . 63 2.4.2 Parallel Fabrication Techniques for 3DI . 64 vi 2.4.2.1 Chip Stacks with Peripheral Connections . 64 2.4.2.2 Chip Stacks with Through-Wafer and Through-Die Connections . 66 2.4.2.3 Alternate Vertical Connection Methods . 68 2.4.3 An Analysis of State-of-the-Art in the Advantages and Prob- lems of 3-D Integration . 69 2.4.3.1 Gains in System Size . 69 2.4.3.2 Enabling Higher System Complexity . 70 2.4.3.3 Gains in System Speed and Power Consumption . 71 2.4.3.4 Noise and Crosstalk Problems and Proposed Solutions 72 2.4.3.5 Thermal Problems and Proposed Solutions . 73 2.4.3.6 Layout Issues . 74 2.4.3.7 New Process Requirements . 74 2.5 Recent Progress in Self-Powering Methods . 75 2.5.1 Photoelectric Methods . 76 2.5.2 Piezoelectric, Vibrational and Thermoelectric Methods . 76 2.5.3 Rectifying Antennas . 77 2.5.4 Small Batteries . 80 2.6 Summary . 80 3 Physical Aspects of VLSI Systems: A Transient Spatially-Dependent Green’s Function Approach to Modeling 3-D On-Chip Interconnect Networks 82 3.1 Introduction, Motivation and Background . 82 3.1.1 Methodology: Linear Time-Invariant Systems and Green’s Function . 83 3.2 Numerical Modeling . 85 3.2.1 Theory . 85 3.2.1.1 An Example Implementation using SPECTRE . 87 3.2.2 Computational Cost . 90 3.3 Implementation . 91 3.3.1 Interconnect Network Construction . 91 3.3.2 Impulse-Response Solver . 94 3.3.2.1 KCL Network, Equations and Discretization . 94 3.3.3 Convolution Routine . 96 3.4 Simulation Results . 97 3.4.1 Comparison with SPECTRE . 97 3.4.1.1 Convergence Test . 97 3.4.2 Example 3D Network Simulations . 100 3.5 Summary . 106 4 Physical Aspects of VLSI Systems: On-Chip Heat Generation and Dissipa- tion 107 4.1 Introduction and Motivation . 107 4.2 Background . 109 4.2.1 The Heat Equation . 109 vii 4.2.2 A Simplified Solver and the Effects of Non-Isotropic Thermal Conductivity . 111 4.2.3 A Thermal Solver with Individual IC Layers Represented . 117 4.3 Experimental Design . 119 4.3.1 Heaters . 120 4.3.2 The Temperature Sensor Array . 121 4.3.2.1 Temperature Dependence of the Diode Current . 121 4.3.2.2 Diode Array for Distributed Temperature Sensing . 124 4.3.3 Ring Oscillators as Temperature Sensors and Heat Sources .