Thin Film Encapsulation Methods for Large Area MEMS Packaging

The past thirty years have seen rapid growth in products and technologies based on microelectromechanical systems (MEMS). However, one of the limiting factors in commercializing MEMS devices is packaging, which can be the most costly step in the manufacturing process. A MEMS package must protect the movable parts of the device while allowing it to interact with its surroundings. In addition, the miniaturization of sensors and actuators has made it possible to integrate MEMS fabrication with that of integrated circuit (IC) processing. Due to the varying requirements for different applications, a universal standard for packaging MEMS has been elusive. However, a growing trend has been the shift away from bonding a separate sealing substrate to the device substrate and toward thin film encapsulation. The latter method has the potential to reduce costs and materials usage while increasing device throughput and yield.Two thin film encapsulation methods for creating large area packaged cavities on top of silicon substrates have been developed based on porous membrane structures. The first approach uses thin polysilicon as a permeable membrane. The polysilicon is deposited on top of a doped oxide using low pressure chemical vapor deposition (LPCVD) to a thickness less than 300 nm. High temperature annealing drives the dopant atoms from the oxide into the polysilicon film, creating gaps within the film through which hydrofluoric acid (HF) vapor penetrates and etches the buried oxide. In addition, a process of rapidly depositing oxides greater than 10 um thick without cracking due to residual stress has also been demonstrated. This is accomplished by using plasma enhanced chemical vapor deposition (PECVD) steps of 2.5 um thickness with interceding rapid thermal annealing (RTA). The permeable polysilicon membrane technology provides the foundation for wafer-level encapsulation of MEMS devices inside the cavities by depositing a thick structural layer either under vacuum or at arbitrary pressure environments.The thin permeable polysilicon technique then evolves into a broader encapsulation method in which a semi-permeable film is constructed from carbon nanotubes (CNTs) and polysilicon. The dense forest of CNTs may be grown to a height from 10 um to hundreds of um as the structural foundation for the encapsulation layer. Conformally coating the CNTs with polysilicon by LPCVD generates natural pores within the thick membrane. HF vapor penetrates the semi-permeable film to selectively etch the bottom oxide layer, after which another polysilicon deposition seals the film, rendering it impermeable. The etching behavior has been characterized as a function of the CNT height and exposure time to HF vapor. The CNT/polysilicon thickness for a given vacuum-sealed cavity area has also been designed using finite element analysis (FEA). Furthermore, large sealing areas of more than 1x1 mm^2 have been successfully demonstrated. As such, this wafer-level encapsulation technology could find potential packaging applications of MEMS devices, including large area gyroscope structures

Development of an Assessment Procedure for Integration of Mathematical and CAE Tools in Engineering Courses

In a previous study 1 the authors presented the teaching and learning experiences of integrating mathematical and CAE tools in three example undergraduate engineering courses taught at three different universities by three different instructors who share similar teaching philosophies. Integration of mathematical tools such as MATLAB, MathCAD, and Excel, and the CAE packages such as Unigraphics 2 are found to be very effective teaching and learning strategies for better understanding of the relevant course material where such tools can be incorporated. The three example courses are: Machine Component Design, (taught at Kettering University using Excel and other CAE/FEA tools), Computational and Experimental course (taught at Saginaw Valley State University using MATLAB), and Dynamic Systems and Controls (taught at Baker College using MathCAD). All these are 4-credit courses. The outcome of the previous study proved to be useful as evidenced by the student performance in these courses. Based on the experiences of the previous studies, in this paper an assessment procedure is developed to study its impact on the early implementation of those tools from the beginning of teaching of these same courses as mentioned above. One of the measures of the effectiveness of the developed assessment procedure utilizes the overall performance of the students in those courses. It is hoped that such a procedure can be used to enhance the teaching and assessment of these or other similar courses

Pediatric Venous Thromboembolism

Venous thromboembolism (VTE) occurs less often in children than adults and therefore remains underrecognized despite increasing in incidence. Due to the risk of mortality, short- and long-term morbidity, and increased healthcare costs associated with pediatric VTE, this entity merits better understanding and consideration. With this Research Topic, we aim to highlight some special considerations of pediatric VTE, namely risk factors and epidemiology, rare types of pediatric thrombosis and considerations unique to specific clinical patient subgroups, approaches to management and treatment, and preventio

Assessment of a Common Finite Element Analysis Course

This paper discusses the outcome of the common assessment of a sample introductory undergraduate/graduate level course on finite element analysis (FEA) taught at three different local four-year engineering colleges, namely, Baker College and Kettering University (Flint, MI), and Saginaw Valley State University (SVSU, Saginaw, MI). The assessment is based on the commonly used course topics and based on identifying the common course learning objectives (CLOs). CLOs are then mapped with ABET\u27s program outcomes (POs). Assessment tools such as class work, home work, quizzes, tests, as well as the final exam and/or final project work with presentations are used to assess the performance of the students. The rationale for writing this paper is to understand the variation if any in students\u27 understanding of the material on their overall performance in the class. Variation is to be expected since the student population is different (full time versus part time, graduate versus undergraduate) and the course is taught by different instructors. However, usage of common CLOs, course topics, and assessment tools used reveal that the students lack knowledge in pre-requisites and also had problems using CAE tools compared to using math tools for FEA. Finite element analysis (FEA) course typically requires pre-requisites knowledge in Statics, Mechanics of Materials and to some extent Engineering Materials, Computer Aided Modeling and Machine Design. Although many students at these colleges usually take FEA as seniors, there are a few graduate students at Kettering who take this class. Some of whom are on-campus while few others are off campus (distance learning) students. Both math and CAE tools are typically used for this course with more emphasis on finite element methods rather than finite element modeling using a CAE tool. The math tools such as MatLAB involve using matrix algebra for most part to solve the equations obtained by either direct stiffness method or by energy methods for 1D and 2D problems. CAE tools involve modeling components that involve simple or complex geometry, and solving those using SOLID EDGE/UG/ANSYS/IDEAS software. Results of assessment will be presented in the form of charts and tables and discussed in detail. A sample assessment and evaluation form will also be included in the paper