Microfluidics-based biochips are soon expected to revolutionize clinical diagnosis, deoxyribonucleic acid (DNA) sequencing, and other laboratory procedures involving molecular biology. In contrast to continuous-flow systems that rely on permanently etched microchannels, micropumps, and microvalves, digital microfluidics offers a scalable system architecture and dynamic reconfigurability; groups of unit cells in a microfluidics array can be reconfigured to change their functionality during the concurrent execution of a set of bioassays. As more bioassays are executed concurrently on a biochip, system integration and design complexity are expected to increase dramatically. This paper presents an overview of an integrated system-level design methodology that attempts to address key issues in the synthesis, testing and reconfiguration of digital microfluidics-based biochips. Different actuation mechanisms for microfluidics-based biochips, and associated design-automation trends and challenges are also discussed. The proposed top-down design-automation approach is expected to relieve biochip users from the burden of manual optimization of bioassays, time-consuming hardware design, and costly testing and maintenance procedures, and it will facilitate the integration of fluidic components with a microelectronic component in next-generation systems-on-chips (SOCs).

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Microfluidics-Based Biochips: Technology Issues, Implementation Platforms, and Design-Automation Challenges

Modern electronics testing has a legacy of more than 40 years. The introduction of new technologies, especially nanometer technologies with 90nm or smaller geometry, has allowed the semiconductor industry to keep pace with the increased performance-capacity demands from consumers. As a result, semiconductor test costs have been growing steadily and typically amount to 40% of today's overall product cost. 

This book is a comprehensive guide to new VLSI Testing and Design-for-Testability techniques that will allow students, researchers, DFT practitioners, and VLSI designers to master quickly System-on-Chip Test architectures, for test debug and diagnosis of digital, memory, and analog/mixed-signal designs.

KEY FEATURES
* Emphasizes VLSI Test principles and Design for Testability architectures, with numerous illustrations/examples.
* Most up-to-date coverage available, including Fault Tolerance, Low-Power Testing, Defect and Error Tolerance, Network-on-Chip (NOC) Testing, Software-Based Self-Testing, FPGA Testing, MEMS Testing, and System-In-Package (SIP) Testing, which are not yet available in any testing book.
* Covers the entire spectrum of VLSI testing and DFT architectures, from digital and analog, to memory circuits, and fault diagnosis and self-repair from digital to memory circuits.
* Discusses future nanotechnology test trends and challenges facing the nanometer design era; promising nanotechnology test techniques, including Quantum-Dots, Cellular Automata, Carbon-Nanotubes, and Hybrid Semiconductor/Nanowire/Molecular Computing.
* Practical problems at the end of each chapter for students.

System-on-Chip Test Architectures: Nanometer Design for Testability

Composite microsystems that integrate mechanical and fluidic components are fast emerging as the next generation of system-on-chip designs. As these systems become widespread in safety-critical biomedical applications, dependability emerges as a critical performance parameter. In this paper, we present a costeffective concurrent test methodology for droplet-based microelectrofluidic systems. We present a classification of catastrophic and parametric faults in such systems and show how faults can be detected by electrostatically controlling and tracking droplet motion. We then present tolerance analysis based on Monte-Carlo simulations to characterize the impact of parameter variations on system performance. To the best of our knowledge, this constitutes the first attempt to define a fault model and to develop a test methodology for droplet-based microelectrofluidic systems.

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Testing of droplet-based microelectrofluidic systems

Author(s): Tang, William; Zhang, Xia | Abstract: A systematic experimental study of viscous air damping in laterally moving planar microstructures is reported. Previous studies indicated that Couette and Stokes flow models underestimate microstructural damping. To investigate this discrepancy, a series of lateral resonant microstructures with different damping plates and combs was fabricated by polysilicon surface micromachining. The resonant frequencies and quality factors of the structures were measured electrically. By analyzing these data, the damping effects due to different geometries were elucidated and compared to theory. The results indicated that if edge and finite-size effects are included in the model, reasonably accurate predictions of the quality factors can be obtained even for small geometries and comb drives. An empirical formula that predicts the quality factor for a range of plate sizes and comb designs was derived. The damping effects as functions of structural thickness and structure-to-substrate separation are also reported.

Viscous air damping in laterally driven microresonators

Advances in microfluidics technology offer exciting possibilities in the realm of enzymatic analysis, DNA analysis, proteomic analysis involving proteins and peptides, immunoassays, implantable drug delivery devices, and environmental toxicity monitoring. Microfluidics-based biochips are therefore gaining popularity for clinical diagnostics and other laboratory procedures involving molecular biology. As more bioassays are executed concurrently on a biochip, system integration and design complexity are expected to increase dramatically. This paper presents different actuation mechanisms for microfluidics-based biochips, as well as associated design automation trends and challenges. The underlying physical principles of eletrokinetics, electrohydrodynamics, and thermo-capillarity are discussed. Next, the paper presents an overview of an integrated system-level design methodology that attempts to address key issues in the modeling, simulation, synthesis, testing and reconfiguration of digital microfluidics-based biochips. The top-down design automation will facilitate the integration of fluidic components with microelectronic component in next-generation system-on-chip designs.

Design automation for microfluidics-based biochips

Microelectromechanical systems (MEMS) are miniature electromechanical sensor and actuator systems developed from the mature batch-fabricated processes of VLSI technologies. Projected growth in the MEMS market requires significant advances in CAD and manufacturing for MEMS. These advances must be accompanied with testing methodologies that ensure both high quality and reliability. We describe our approach for developing a comprehensive testing methodology for a class of MEMS known as surface micromachined sensors. Our first step involving manufacturing process and low-level mechanical simulations is illustrated by studying the effects of realistic contaminations on the folded-flexure comb-drive resonator. The simulation results obtained indicate that realistic contaminations can create a variety of defective structures that result in a wide spectrum of faulty behaviors.

Development of a MEMS testing methodology

We have enhanced the process simulator CODEF (1996) into a tool called CARAMEL (Contamination And Reliability Analysis of MicroElectromechanical Layout) for analyzing the impact of contamination particles on the geometrical and material properties of microelectromechanical systems (MEMS). CARAMEL accepts as input a microelectromechanical layout, a particulate description, and a process recipe. CARAMEL produces a mesh description of the defective layout that is completely compatible with the electromechanical simulator ABAQUS (1995). Analysis of CARAMEL's output indicates that a wide range of defective structures are possible due to the presence of contaminations. Moreover, electromechanical simulations of CARAMEL's mesh representations of defective layout has revealed that a wide variety of faulty behaviors are associated with these defects. In this paper, we describe CARAMEL and its application to the development of realistic fault models for MEMS.

MEMS fault model generation using CARAMEL

Wafer-level testing of surface-micromachined sensors provides new challenges to the test community. Currently, there is no method available for performing direct measurements to assess faulty micromechanical structures. Most commercial methods use electrical measurements to deduce the physical source of failures in the micromechanical structure. As a result, the process of identifying various failure modes (electrical measurements) and accurately mapping them to the underlying physical failure mechanisms of the mechanical sensor becomes highly complex. Several sources of failures that include particulates and stiction complicate the situation even more. Here, we provide a case study of the Analog Devices ADXL75 Accelerometer. One failure category called stuck/tipped beams is investigated and a methodology is developed to uniquely distinguish failures either caused by stuck or tipped beams. The proposed method is easy to implement and the information obtained can be critical for yield improvement.

Failure modes for stiction in surface-micromachined MEMS

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A. Kolpekwar

Papers

Development of a MEMS testing methodology

MEMS fault model generation using CARAMEL

Failure modes for stiction in surface-micromachined MEMS

Fault Model Generation for MEMS