R. Rosing

A fault simulation methodology for MEMS

Efficient built-in and external test strategies are becoming essential in microelectromechanical systems (MEMS), especially for high reliability and safety critical applications. To be realistic however, internal and external test must be properly validated in terms of fault coverage. Fault simulation is hence likely to become a critical utility within the design flow. This paper discuss methods for achieving test support based on the extension of tools and techniques currently being introduced into the mixed signal ASIC market.

Clock switching: a new design for current testability (DcT) method for dynamic logic circuits

Using an I/sub ddq/ test methodology on circuits with dynamic logic tends to be problematic, mainly due to charge leakage related problems. A new Design for current Testability (DcT) method has been developed, which overcomes these problems by switching the circuit into a static mode during test. The method referred to as clock switching is applicable to both domino logic and True Single-Phase Clock (TSPC) circuits. This paper shows that this technique can lead to higher levels of I/sub ddq/ testability and a reduced test vector set for the detection of bridging faults.

Generation of component level fault models for MEMS

Component level (nodal) simulations have been proposed to both implement closed loop simulation of complete microsystems to support the migration to shorter design cycles and implement fault models of micromechanical components. Within such a simulation environment, library cells in the form of behavioural models are used for the basic components of microelectromechanical (MEM) transducers, such as beams, plates, comb-drives and membranes. This paper presents both methodologies to generate the model parameters required for the implementation of accurate component fault models and simulation results from representative defective structures in a MEMS product.

Finite element analysis to support component level fault modeling for MEMS

Component level (nodal) simulations have been proposed to both implement closed loop simulation of complete microsystems to support the migration to shorter design cycles and implement fault models of micro-mechanical components. Within such a simulation environment, library cells in the form of behavioral models, are used for the basic components of microelectromechanical (MEM) transducers, such as beams, plates, comb-drives and membranes. This paper presents both a methodology to generate the model parameters required for the implementation of accurate component level fault models and simulation results from a number of representative defective structures in a MEMS product.

Generation of MEMS component models using Cosserat symbolic simulations

This paper describes how models of slender MEMS components can be generated using symbolic simulations based on Cosserat theory. Due to the generality of the method, models can be generated for a wide range of components under different stress conditions. The structure of the Cosserat- based models is presented, showing their concise, mathematically accurate representation. This potentially results in faster simulation results than finite element analysis, requiring detailed 3d meshed models. The use of Cosserat models in symbolic simulations enables generation of closed-form expressions for the dynamics of components with complex shapes. The influence of various stress conditions, such as package-induced and residual stress, on the behavior of the component can be included in these expressions.

Model based design optimization of micromechanical systems, based on the Cosserat theory

In this paper we present the model based design optimization on a micromechanical system which is described by a VHDL-AMS behaviour model, based on the Cosserat theory. The application is a gyroscope test structure developed by STMicroelectronics. The schematic of the microactuator is built up from component models developed in Lancaster within previous work. The equations of motion of the beam model were derived using Cosserat theory. The rigid body model was adjusted to capture the behaviour of the central disk with comb-drives of the microactuator target structure. Within the model based design optimization system MODOS developed at the University of Bremen a model optimization and a model based design optimization were performed. In this report we represent the theoretical background of the modeling and optimization process and publish the received results.

Applications of mixed-signal test strategies to next-generation microsystems

Improvements in test technology for next generation microsystems is now becoming essential, especially in sensing applications as in most cases, each sensor has a unique set of characteristics causing inevitable difficulties associated with calibration and validation. Ideally, a microsystem should generate a calibrated output and a reliability indicator. IEEE1451.2 has been developed to provide a standard interface yet research into methods of providing these features through Built-In Self-Test and On- line monitoring techniques is still needed. One of the current industrial techniques uses multiple sensor to determine faults allowing systems to be temporarily reconfigured until the problems are resolved. This technique is only economical if multiple sensors with a strong functional correlation are present within the original system. In case only one sensor is present, using redundancies within this sensor would be more economical than adding extra sensors for test purposes. The aim of this paper is to review generic properties of sensor system to identify areas where mixed signal testing techniques could be adapted for sensor test and to identify areas for further research.