Reliability Of Microelectromechanical Systems Devices Research Articles

Generalized thermoelastic analysis of thermo-optic switch multi-layer structure

Delaminating failure is the fatal failure mode of Micro Electro Mechanical Systems(MEMS) multi-layer membrane structures and severely affects the reliability of MEMS devices. In this work, a multi-layer membrane structural model of a thermo-optic switch is established under the framework of generalized thermoelastic theory, and the distribution of interlayer temperature, thermal mismatch stress and core refractive index is calculated. The effect of relaxation time on thermal mismatch stress and refractive index is discussed, and numerical results show that the thermal mismatch stress increases with the heating power. When the relaxation time rises to 10−3s magnitude, the thermal mismatch stress decreases, the core layer reaches a high steady-state temperature and the refractive index of the core layer expands. These results provide a new idea for the research and development of new devices; that is, the adoption of core layer materials with long relaxation time can improve the reliability of MEMS devices.

酸化Crバッファー層を用いた室温成膜ZnO圧電膜の開発

Due to its piezoelectric properties, the zinc oxide (ZnO) thin film is used for Micro Electro Mechanical Systems (MEMS) sensors and actuators. In order to reduce the fabrication costs and to improve the reliability of MEMS devices, a low temperature process is desired. ZnO layer is deposited on the oxidized chrome (CrO) buffer layer that is deposited on silicon substrates. Both ZnO and CrO layers are deposited by RF magnetron sputtering at room temperature. The crystalline properties of ZnO are measured with an X-ray diffraction (XRD), a scanning electron microscopy (SEM) and an atomic force microscope (AFM). The results show that varying the O2/Ar flow ratio during the deposition of CrO layer may improve the crystalline properties of ZnO. Piezoelectrically actuated cantilevers with the ZnO thin film are fabricated and tip deflection of the cantilever is measured. The piezoelectric strain constant of ZnO thin film is calculated from the tip deflection. The results show that the piezoelectric strain constant increases and saturates with the thickness of ZnO layer. The obtained piezoelectric strain constant of ZnO thin film is 3.7 pC/N which is 74% of the bulk ZnO.

Reliability assessment of a MEMS microphone under mixed flowing gas environment and shock impact loading

In this work the reliability of a Micro-Electro-Mechanical Systems (MEMS) microphone is studied through two accelerated life tests, mixed flowing gas (MFG) testing and shock impact testing. The objective is to identify the associated failure mechanisms and improve the reliability of MEMS devices. Failure analyses are carried out by using various tools, such as optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS). Finite element analysis is also conducted to study the complex contact behaviors among the MEMS elements during shock impact testing. The predicted failure sites are in agreement with the experimental findings.

Effects of Fast Neutrons on the Electromechanical Properties of Materials Used in Microsystems

Microelectromechanical systems (MEMS) technology is expected to play a significant role in avionics and in future space missions provided that the effect of radiation on the reliability of MEMS devices is well understood. Most tests, to date, have been performed on MEMS that operate based on electrostatic principles, and radiation-induced dielectric charging has been identified as a mechanism which can potentially limit the reliability of such devices. Experiments with piezoresistive and piezoelectrically actuated MEMS have also revealed changes in the operation of devices after exposure to different types of ionizing radiation. However, not many reports on the damage effects in MEMS due to fast neutrons exist. In this paper, we present results from mechanical and electrical tests on different materials which are typically used in microsystems, before and after exposure to fast neutrons. Changes were detected in the residual stress and in the resonant frequencies of silicon nitride microbeams. There was also evidence of radiation-induced charge trapping in metal-insulator-semiconductor capacitors fabricated from thermal oxide, silicon nitride, and aluminum oxide deposited by atomic layer deposition. Finally, we observed that the electrical properties of ferroelectric capacitors fabricated from lead zirconate titanate and lead strontium titanate thin films do not degrade after exposure to fast neutrons.

MEMS Reliability Review

Microelectromechanical systems (MEMS) represents a technology that integrates miniaturized mechanical and electromechanical components (i.e., sensors and actuators) that are made using microfabrication techniques. MEMS devices have become an essential component in a wide range of applications, ranging from medical and military to consumer electronics. As MEMS technology is implemented in a growing range of areas, the reliability of MEMS devices is a concern. Understanding the failure mechanisms is a prerequisite for quantifying and improving the reliability of MEMS devices. This paper reviews the common failure mechanisms in MEMS, including mechanical fracture, fatigue, creep, stiction, wear, electrical short and open, contamination, their effects on devices' performance, inspection techniques, and approaches to mitigate those failures through structure optimization and material selection.

Single-crystal-silicon-based microinstrument to study friction and wear at MEMS sidewall interfaces

Since the advent of microelectromechanical systems (MEMS) technology, friction and wear are considered as key factors that determine the lifetime and reliability of MEMS devices that contain contacting interfaces. However, to date, our knowledge of the mechanisms that govern friction and wear in MEMS is insufficient. Therefore, systematically investigating friction and wear at MEMS scale is critical for the commercial success of many potential MEMS devices. Specifically, since many emerging MEMS devices contain more sidewall interfaces, which are topographically and chemically different from in-plane interfaces, studying the friction and wear characteristics of MEMS sidewall surfaces is important. The microinstruments that have been used to date to investigate the friction and wear characteristics of MEMS sidewall surfaces possess several limitations induced either by their design or the structural film used to fabricate them. Therefore, in this paper, we report on a single-crystal-silicon-based microinstrument to study the frictional and wear behavior of MEMS sidewalls, which not only addresses some of the limitations of other microinstruments but is also easy to fabricate. The design, modeling and fabrication of the microinstrument are described in this paper. Additionally, the coefficients of static and dynamic friction of octadecyltrichlorosilane-coated sidewall surfaces as well as sidewall surfaces with only native oxide on them are also reported in this paper.

Correlating Raman peak shifts with phase transformation and defect densities: a comprehensive TEM and Raman study on silicon

AbstractSilicon is the most often used material in micro electromechanical systems (MEMS). Detailed understanding of its mechanical properties as well as the microstructure is crucial for the reliability of MEMS devices. In this paper, we investigate the microstructure changes upon indentation of single crystalline (100) oriented silicon by transmission electron microscopy (TEM) and Raman microscopy. TEM cross sections were prepared by focused ion beam (FIB) at the location of the indent. Raman microscopy and TEM revealed the occurrence of phase transformations and residual stresses upon deformation. Raman microscopy was also used directly on the cross‐sectional TEM lamella and thus microstructural details could be correlated to peak shape and peak position. The results show, however, that due to the implanted Ga+ ions in the lamella the silicon Raman peak is shifted significantly to lower wavenumbers. This hinders a quantitative analysis of residual stresses in the lamella. Furthermore, Raman microscopy also possesses the ability to map deformation structures with a lateral resolution in the submicron range. Copyright © 2009 John Wiley & Sons, Ltd.

Failure Analysis of Thermal Actuators, Comb Drives, and Other Microelectromechanical Elements

This paper reports on an investigation in which several standard Microelectromechanical Systems (MEMS) elements consisting of thermal actuators, inchworm drives, and comb drives were subjected to vibration loading representative of the environment seen in space applications. Finite-element analysis of the MEMS devices showed that sufficient margins existed under the expected environmental loading. Vibration testing, however, resulted in several failures in the devices, and analysis showed that progressive failure initiated from large local displacements. Debris transport and entrapment was another source of failure leading to shorting of thermal actuators. The results illustrate the importance of debris control and packaging design for reliable MEMS operation. Suggestions for improving the reliability of MEMS devices through practical layout and packaging guidelines are made.

FEM analysis of multilayered MEMS device under thermal and residual stress

It is essential to ensure reliability to produce a Micro-Electro Mechanical Systems(MEMS) on commercial scale. Reliability problem in inkjet printhead, one of MEMS, is also very important. To eject an ink drop, temperature of heater must be high so that ink contacting with surface reaches above 280° C on the instant. Its heater is embedded in the thin multi-layer in which several materials are deposited. MEMS processes are the main sources of residual stresses development. Residual stress is one of the factors reducing the reliability of MEMS devices. We measure residual stresses of single layers that consist of multilayer. FE analysis is performed using design of experiment. Transient analysis for heat transfer is performed to get a temperature distribution. And then static analysis is performed with the temperature distribution obtained by heat transfer analysis and the measured residual stresses to get a stress distribution in the structure. Although the residual stress is bigger than thermal stress, thermal stress is more influential on fatigue life.

Materials issues in the processing, the operation and the reliability of MEMS

In this article materials issues that arise during the processing and operation of micro-electro mechanical systems devices (MEMS), and their impact on the functionality and reliability, are discussed. The article starts with the example of an RF-MEMS switch process flow, indicating how and why certain materials are chosen. Then two specific MEMS materials issues, e.g. stiction and stress, are covered. Finally, the so-called ‘zero-level’ packaging of MEMS as well as the effect packaging can have on the device and its operation will be reviewed.

Tribology of MEMS

Because of large surface-to-volume ratios and low restoring forces, unwanted adhesion and friction can dominate the performance of microelectromechanical systems (MEMS) devices. To guarantee the function and reliability of MEMS devices, tribologists must understand the origins of adhesion, friction, and wear over a broad range of length scales from the macroscopic to the molecular. In this article, we present an overview of challenges, successes, and initial steps toward a fundamental understanding.