System-level reliability assessment of mixed-signal convergent microsystems

The next-generation convergent microsystems, based on system-on-package (SOP) technology, require up-front system-level design-for-reliability approaches and appropriate reliability assessment methodologies to guarantee the reliability of digital, optical, and radio frequency (RF) functions, as well as their interfaces. Systems approach to reliability requires the development of: i) physics-based reliability models for various failure mechanisms associated with digital, optical, and RF Functions, and their interfaces in the system; ii) design optimization models for the selection of suitable materials and processing conditions for reliability, as well as functionality; and iii) system-level reliability models understanding the component and functional interaction. This paper presents the reliability assessment of digital, optical, and RF functions in SOP-based microsystems. Upfront physics-based design-for-reliability models for various functional failure mechanisms are presented to evaluate various design options and material selection even before the prototypes are made. Advanced modeling methodologies and algorithms to accommodate material length scale effects due to enhanced system integration and miniaturization are presented. System-level mixed-signal reliability is discussed thorough system-level reliability metrics relating component-level failure mechanisms to system-level signal integrity, as well as statistical aspects.     

Interconnect Lifetime Prediction for Reliability-Aware Systems

Thermal effects are becoming a limiting factor in high-performance circuit design due to the strong temperature dependence of leakage power, circuit performance, IC package cost, and reliability. While many interconnect reliability models assume a constant temperature, this paper analyzes the effects of temporal and spatial thermal gradients on interconnect lifetime in terms of electromigration, and presents a physics-based dynamic reliability model which returns reliability equivalent temperature and current density that can be used in traditional reliability analysis tools. The model is verified with numerical simulations and reveals that blindly using the maximum temperature leads to too pessimistic lifetime estimation. Therefore, the proposed model not only increases the accuracy of reliability estimates, but also enables designers to reclaim design margin in reliability-aware design. In addition, the model is useful for improving the performance of temperature-aware runtime management by modeling system lifetime as a resource to be consumed at a stress-dependent rate     

Hybrid reliability assessment for packaging prototyping

The paper presents a physics-based hybrid approach to assist the assessment of thermally induced packaging reliability. This method is applicable to prototypes at different stages of development. The approach realizes the efficiency and effectiveness through some special capabilities in identifying reliability critical locations and evaluating deformation and failure mechanisms. These capabilities are facilitated by the computer vision techniques for multi-scale measurement, including, the digital speckle correlation and the phase-shifted shadow moiré. The techniques combine to become three-dimensional and capable of locating failure prone sites and obtaining failure related parameters at desired spatial resolution. The novelty comes as the experimental measurement is integrated with numerical and analytical modeling. An apparent merit is that the approach can bypass some uncertain issues that could cause deficiency of an assessment if a pure modeling or testing is employed. Following an introduction to the experimental techniques and procedures, application examples are presented to demonstrate the feasibility and the potential of the approach.     

Physics-based integration of multiple sensing modalities for sceneinterpretation

The fusion of multiple imaging modalities offers many advantages over the analysis, separately, of the individual sensory modalities. In this paper we present a unique approach to the integrated analysis of disparate sources of imagery for object recognition. The approach is based on physics-based modeling of the image generation mechanisms. Such models make possible features that are physically meaningful and have an improved capacity to differentiate between multiple classes of objects. We illustrate the use of physics-based approach to develop multisensory vision systems for different object recognition application domains. The paper discusses the integration of different suites of sensors, the integration of image-derived information with model-derived information and the physics-based simulation of multisensory imagery     

A New NBTI Model Based on Hole Trapping and Structural Relaxation in MOS Dielectrics

Negative bias temperature instability (NBTI) is one of the major reliability concerns for analog and digital MOS devices. NBTI understanding and modeling is receiving a growing interest for failure prediction, depending on the temperature and duty cycle of dynamic-stress conditions. In this framework, we present a new NBTI model based on hole trapping and thermally activated relaxation. The model unifies previous concepts of hole tunneling/trapping and structural relaxation initiated by hole trapping. Simulation results can account for the time and temperature dependence of NBTI stress, NBTI recovery, and the dependence on thickness and nitridation technology of the gate dielectric. The numerical model may be used for physics-based reliability predictions of NBTI effects as a function of time, temperature, and stress regime.      

Analysis of temperature dependence of linearity for SiGe HBTs in the avalanche region using Volterra series

In this paper, linearity characteristic of silicon germanium (SiGe) heterojunction bipolar transistors (HBTs) at different temperatures in the avalanche regime is investigated by the Volterra approach incorporating with a physics-based breakdown network for the first time. Third-order intermodulation distortion (IMD₃) decreases with increasing temperature in the impact ionization region due to lower nonlinear contributions from individual nonlinearity according to the Volterra analysis results. Calculated gain, output power, and efficiency of SiGe HBTs are in good agreement with measurement results in the avalanche region. This analysis with respect to temperature can benefit the reliability study of linearity for SiGe HBTs in the avalanche regime.     

Physics-based electron device modelling and computer-aided MMICdesign

On overview on the state of the art and future trends in physics-based electron device modelling for the computer-aided design of monolithic microwave ICs is provided. After a review of the main physics-based approaches to microwave modeling, special emphasis is placed on innovative developments relevant to circuit-oriented device performance assessment, such as efficient physics-based noise and parametric sensitivity analysis. The use of state-of-the-art physics-based analytical or numerical models for circuit analysis is discussed, with particular attention to the role of intermediate behavioral models in linking multidimensional device simulators with circuit analysis tools. Finally, the model requirements for yield-driven MMIC design are discussed, with the aim of pointing out the advantages of physics-based statistical device modeling; the possible use of computationally efficient approaches based on device sensitivity analysis for yield optimization is also considered     

Reliability Modeling and Assessment of Embedded Capacitors in Organic Substrates

Understanding and quantifying the RLC characteristics of the embedded passives under thermomechanical deformation during fabrication and accelerated thermal conditions is necessary for their successful implementation. Embedded passives are composite layers with dissimilar material properties compared to the neighboring layers in the integral substrate. The ongoing project explores the fabrication, multifield physics-based reliability modeling and accelerated testing of embedded passive test vehicles. As a first step, in this paper, the effect of thermomechanical deformation on the electrical characteristics of embedded capacitors is studied at frequencies from 100 KHz to 2 GHz using two test vehicles. Test vehicles with embedded passives were fabricated and were subjected to accelerated thermal cycles between -55degC to 125degC, between -40degC to 125degC and high humidity and temperature conditions of 85degC/85% RH. Significant changes in the electrical parameters of the embedded capacitors are observed. The fabrication process mechanics with multiphysics global-local modeling methodology is demonstrated to study the effect of thermal cycling on the electrical characteristics of embedded capacitors. The results obtained from the multiphysics global-local modeling methodology are validated against the measured electrical characteristics of the fabricated functional test boards. The effect of changes in electrical parameters of embedded passives on system performance of low-pass filters is presented     

Universal fatigue life prediction equation for ceramic ball grid array (CBGA) packages

A traditional approach to predicting solder joint fatigue life involves finite-element simulations in combination with experimental data to develop a Coffin–Manson type predictive equation. The finite-element simulations often require good understanding of finite-element modeling, physics-based failure models, and time-, temperature-, and direction-dependent material constitutive behavior. Also, such simulations are computationally expensive and time-consuming. Microelectronic package designers often do not have the time and the expertise to perform such simulations. The traditional solder joint fatigue predictive equations fall short of ideal because: (1) they are not applicable to others due to numerical modeling issues, (2) they require a mature understanding of mechanics, numerical modeling, and reliability theory, and (3) they are difficult to implement into the design process. This includes both design of an individual electronic component and selecting which type of existing component to include in an application.Therefore, this work develops universal predictive equations that are: (1) simple, quick, and accurate, (2) require only a basic understanding of reliability and mechanics, (3) require no special software; easy to implement in a spreadsheet or current reliability tools, (4) information rich in regards to design parameters, and (5) maximize available information from experimental tests and numerical models. Using experimental data and finite-element simulations as a basis, this work has developed a predictive equation for solder joint fatigue life in lead-containing ceramic ball grid array (CBGA) package. The developed equation has been validated with other experimental data with good success. Efforts are underway to develop similar equations for other packages and Pb-free CBGAs.     

Nonlinear integral modeling of dual-gate GaAs MESFET's

A nonlinear integral approach is adopted for the modeling of Dual-Gate GaAs MESFET's (DGFET's) in the framework of Harmonic-Balance circuit analysis. In particular, the model enables the computation of the large-signal performance of DGFET's directly on the basis of DC characteristics and small-signal bias-dependent admittance parameters without requiring complex procedures for parameter extraction. The validity of the approach is confirmed by accurate physics-based numerical simulations of a DGFET mixer     

Dual approach for bipolar transistor thermal impedance determination

This paper presents a dual approach for a coherent determination and validation of heterostructure bipolar transistor (HBT) thermal impedance. This study relies both on an experimental characterization method and a 3D finite element simulation approach. One section reminds briefly the experimental approach. Another describes the 3D device modeling used for the physics-based thermal simulation. Thereafter, details on the reduction method used for the numerical computation of the thermal impedance are given. As complement to pure thermal simulation, an electrothermal distributed model is proposed and gives an interpretation of the distributed effects in multi-finger devices.     

Integrated physics-oriented statistical modeling, simulation, andoptimization [MESFETs]

Physics-based modeling of MESFETs is addressed from the point of view of efficient simulation, accurate behavior prediction and robust parameter extraction. A novel integration of a large-signal physics-based model into the harmonic balance equations for simulation of nonlinear circuits, involving an efficient Newton update, is presented and exploited in a gradient-based FAST (feasible adjoint sensitivity technique) circuit optimization technique. For yield-driven MMIC design a relevant physics-based statistical modeling methodology is presented. Quadratic approximation of responses and gradients suitable for yield optimization is discussed. The authors verify their theoretical contributions and exemplify their computational results using built-in and user-programmable modeling capabilities of the CAE systems OSA90/hope and HarPE. Results of device modeling using a field-theoretic nonlinear device simulator are reported     

A TCAD approach to the physics-based modeling of frequencyconversion and noise in semiconductor devices under large-signal forcedoperation

The paper presents a novel, unified technique to evaluate, through physics-based modeling, the frequency conversion and noise behavior of semiconductor devices operating in the large-signal periodic regime. Starting from the harmonic balance (HE) solution of the spatially discretized physics-based model under (quasi) periodic forced operation, frequency conversion at the device ports in the presence of additional input tones is simulated by application of the small-signal large-signal network approach to the model. Noise analysis under large-signal operation readily follows as a direct extension of classical approaches by application of the frequency conversion principle to the modulated microscopic noise sources and to the propagation of these to the external device terminals through a Green's function technique. An efficient numerical implementation is discussed within the framework of a drift-diffusion model and some examples are finally provided on the conversion and noise behavior of rf Si diodes     

The missing kink to seamless simulation [nanometer CMOS ULSI]

This paper reviews the trends and needs in multilevel modeling in the context of nanometer CMOS ULSI systems, with an emphasis from the model/tool developer's perspective. A dual representation of the transistors/circuit is proposed and demonstrated through physics-based compact modeling and a single-engine circuit simulator based on subcircuit expansion. Extension to process correlation and block-level representation is also proposed, which will be the key to studying process effects on system performance. This consistent dual representation allows detailed physics captured at a lower level to be propagated to the higher level of abstraction. The key idea is to build a physics-based device compact model (CM) based on technology characterization, which serves as the building block for an implicit multilevel circuit simulator based on a subcircuit-expansion approach. In this way, process variation can be captured through device CMs, and its effects on circuit/system performance can be linked to a consistent hierarchy of abstractions within the same simulator engine.     

Knee surgery assistance: patient model construction, motion simulation, and biomechanical visualization

We present a new system that integrates computer graphics, physics-based modeling, and interactive visualization to assist knee study and surgical operation. First, we discuss generating patient-specific three-dimensional (3-D) knee models from patient's magnetic resonant images (MRIs). The 3-D model is obtained by deforming a reference model to match the MRI dataset. Second, we present simulating knee motion that visualizes patient-specific motion data on the patient-specific knee model. Third, we introduce visualizing biomechanical information on a patient-specific model. The focus is on visualizing contact area, contact forces, and menisci deformation. Traditional methods have difficulty in visualizing knee contact area without using invasive methods. The approach presented here provides an alternative of visualizing the knee contact area and forces without any risk to the patient. Finally, a virtual surgery can be performed. The constructed 3-D knee model is the basis of motion simulation, biomechanical visualization, and virtual surgery. Knee motion simulation determines the knee rotation angles as well as knee contact points. These parameters are used to solve the biomechanical model. Our results integrate 3-D construction, motion simulation, and biomechanical visualization into one system. Overall, the methodologies here are useful elements for future virtual medical systems where all the components of visualization, automated model generation, and surgery simulation come together.     

Modeling real-time 3-d lung deformations for medical visualization.

In this paper, we propose a physics-based and physiology-based approach for modeling real-time deformations of 3-D high-resolution polygonal lung models obtained from high-resolution computed tomography (HRCT) images of normal human subjects. The physics-based deformation operator is nonsymmetric, which accounts for the heterogeneous elastic properties of the lung tissue and spatial-dynamic flow properties of the air. An iterative approach is used to estimate the deformation with the deformation operator initialized based on the regional alveolar expandability, a key physiology-based parameter. The force applied on each surface node is based on the airflow pattern inside the lungs, which is known to be based on the orientation of the human subject. The validation of lung dynamics is done by resimulating the lung deformation and comparing it with HRCT data and computing force applied on each node derived from a 4-D HRCT dataset of a normal human subject using the proposed deformation operator and verifying its gradient with the orientation.     

A new analytical method of solving 2D Poisson''s equation in MOS devices applied to threshold voltage and subthreshold modeling

In this paper we present a new theoretical approach in MOS modeling to derive analytical, physics-based model equations for the geometry and voltage dependence of threshold voltage and for the subthreshold behavior of short-channel MOSFETs. Our approach uses conformal mapping techniques to analytically solve the two-dimensional Poisson equation, whereby inhomogeneous substrate doping is taken into account. The presented model consists of analytical equations in closed form and uses only physically meaningful parameters. Therefore, the results are not only useful in circuit simulators but also in calculations of scaling behavior, where planned processes can be investigated. Comparison with numerical device simulation results and measurements confirm the high accuracy of the presented model.     

Cross-cell interference variability aware model of fully planar NAND Flash memory including line edge roughness

The main reliability issue of highly scaled floating gate NAND Flash memories is the cross-cell interference phenomenon. This is an active area of research in microelectronics engineering. In the last decade, there has been much progress and there are already proposed models for extraction of parasitic capacitive couplings within floating gate transistors. However, most of simulation-based methodologies for evaluation of the impact of cross-cell interference on the electrical behavior rely on deterministic capacitive coupling, neglecting the variability effects. This approach ignores the variable nature of the capacitive couplings caused by technological limitations such as line edge roughness (LER) in advanced technological nodes. The aim of this work is to present an alternative approach of modeling threshold voltage disturbance propagation in a raw NAND Flash memory array, sourced by variability-affected parasitic capacitive couplings.The major contribution of this work is the introduction of probabilistic framework to link the process technology and system level.