University of Texas at Austin

Sponsored by Elsevier and the NJIT Granular Science Laboratory

For more information about this lecture, and to access the video, go to http://www.journals.elsevier.com/mechanics-research-communications/journal-news/distinguished-lecture-sponsored-by-elsevier/

Abstract:

Early applications of the finite element method to crack problem was
developed by Swedlow and et al. Even though they could get reasonable
accuracy about 5 to 10%, later study showed that solutions in the
vicinity of the crack tip cannot be guranteed to be accurate regardless
of the mesh density around tip. In order to overcome this problem,
people developed special crack tip elements.

In this term paper, I'm going to present 1) Finite Element Method in
Fracture Mechanics and 2) NewFinite Element technique so called Extended Element Method.

One of the most common problems in older people is the fragility of the bones. Human bones are prone to fracture, and fracture of certain bones in the body such as the cortical bone may be fatal. Understanding of the fracture mechanism of bones is essential for the medical profession, and plays a major role in the study of osteoporosis as well.  

Abstract: 

Abstract

With the scaling of VLSI, ultra low-k dielectrics with porosity are being introduced to reduce the capacitance coupling. But due to the weak bonding strengths, low-k dielectrics may fail by environmental-assisted subcritical cracking, fracture at stresses far below the loads required for catastrophic failure, causing reliability issues. In this term paper, several references are reviewed to investigate the mechanism of subcritical cracking at multiscale levels.

A double cantilever beam (DCB)
specimen is created by affixing the two halves together using a bi-layer of
PC-3 prostate cancer cells. The specimen is pinned at a bottom corner, and the
upper corner on the same end is displaced with the force-displacement profile
being recorded. This upper corner is displaced until the crack, a portion of
the specimen where cell grown has been selectively inhibited, propagates
through the cell layer. The critical value of force at which the crack
propagates through the cell layer is used, in conjunction with the initial
crack length, to determine the toughness via the compliance-energy method (Ripling, et al. 1971). A method for performing a FE analysis of the

Stress-induced voiding (SIV) is investigated in Cu-based, deep-submicron, dual damascene technology. Two failure modes are revealed by TEM failure analysis. For one mode, voids are formed under the via when the via connects a wide metal lead below it. For the via which is instead under a wide metal line, voids are formed right above the via bottom. The void source results from the supersaturated vacancies which develop when Cu is not properly annealed after electroplating and before being constrained by dielectrics. The driving force comes from the stress built up due to grain growth and the thermal expansion mismatch (CTE) between Cu interconnect and dielectrics. A diffusion model is introduced to investigate the voiding mechanism primarily for the vias connected to wide metal leads.

Dislocations are common in epitaxial systems. For a thin film epitaxially grown on a substrate with coherent interface, it may have spontaneously-formed dislocations when its thickness is larger than certain value, i.e. critical thickness. The presence of dislocations can have an adverse effect on electrical performance of semiconductor materials, providing easy diffusion paths for dopants to lead to short circuits, or recombination centers to reduce carrier density. And, formation of dislocations is one of the most observed mechanisms of relaxation of mismatch strain. However, in optoelectric applications, strain alters the electronic bandgap and band edge alignment, and should be maintained. So, controlling formation of dislocations is very important in the manufacture of microelectronic and optoelectronic devices.

This term paper will review some basic concepts and try to produce some understanding about the control dislocation formation.

Today low-k dielectric materials are integrated into computer chips to improve the operation speed and reduce the cross-talk noise. Due to weak mechanical properties of low-k dielectric materials, cohesive failure is subjected to occur. Channel cracking is one common mode of cohesive failure. In this term paper, several potential issues relevant to channel cracking of low-k dielectric thin films are reviewed.

For films or coatings deposited on substrate at high temperature, residual compressive stresses are often induced in the surface layers because of the mismatch in the thermal expansion coefficients. Under such compressive residual stresses, the surface thin film is susceptible to buckling-driven delamination. Various shapes of buckled region are observed, including long straight-sided blisters, circular and the ‘telephone cord’ blister.

Each student completes a term paper of selected topics that (a) addresses a phenomenon in thin film materials, and (b) involves analyses using mechanics. The project contributes 25% of the grade, distributed as follows:

• 5%: November 30 (Thursday). Post your title and abstract in iMechanica, formated as below

1. Title (EM 397 Term Paper: e.g., Dislocations in Epitaxial Thin Films).
2. Tags (EM 397, Fall 2006, University of Texas at Austin, thin films, term paper)
3. Body: (i) Describe the phenomenon. (ii) Explain how mechanics is relevant. (iii) Cite at least 1 journal article.

• 10%: December 12 Tuesday (2:00-4:00 pm). 30 minute presentation. Use power point slides.
• 10%: December 18 Monday.
  

Starting from January 2006, my group has been posting in Modeling Place as a blogspot to share research experience and ideas. We will gradually migrate to iMechanica for better publicity and more web functions.