Zhen Zhang's blog

A material less sticky than Teflon has been created by covering a surface with a "forest" of carbon nanotubes. Newscients.com has a very interesting report. Read more...

Electronic active device is built on the strained silicon-on-insulator (sSOI), e.g. strained Si layer on oxide, which in turn is bonded on bulk silicon wafer. Because no misfit dislocation can exist in strained silicon layer any more, will the dislocation be generated during later processing and operation? If there are still lots of dislocations in the strained silicon layer, where do they come from? Is there any experimental work to discover the dislocation nucleation sites? I guess they will nucleate from the triple junctions of gate-sSOI-cap, because the stress is singular in the triple junction. But I am not sure. So I want to know something about the experimental observations.

I use this blog entry to upload my research work, then I have links for my publications in my resume. Otherwise, I don't have any links for my preprints.

If people can upload any files without writing a blog entry, that will be great.

Zhen Zhang, Zhigang Suo, Jun He

Thermal strains and electromigration can cause voids to grow in conductor lines on semiconductor chips. This long-standing failure mode is exacerbated by the recent introduction of low-permittivity dielectrics. We describe a method to calculate the volume of a saturated void (VSV), attained in a steady state when each point in a conductor line is in a state of hydrostatic pressure, and the gradient of the pressure along the conductor line balances the electron wind. We show that the VSV will either increase or decrease when the coefficient of thermal expansion of the dielectric increases, and will increase when the elastic modulus of the dielectric decreases. The VSV will also increase when porous dielectrics and ultrathin liners are used. At operation conditions, both thermal strains and electromigration make significant contributions to the VSV. We discuss these results in the context of interconnect design.

This has been published and the related references are listed here:

• Z. Zhang, Z. Suo, and J. He, J. Appl. Physics, 98, 074501 (2005). link
  
• J. He, Z. Suo, T.N. Marieb, and J.A. Maiz, Appl. Phys. Lett. 85, 4639 (2004). link
  

Last year, I attended the course ES139/239 in Division of Engineering and Applied Sciences, Harvard University, the innovation in science and technology. The final project of my group was about carbon nanotube (CNT). In the stage of popping up ideas, we did not consider any feasibility issues, and just used our imagination to create fancy ideas. I was inspired by other guys a lot, felt too excited after the evening brainstorm session, and wrote down the ideas I coined up. Some of them are not nonsense, e.g. replacing Cu by CNT as conductor in integrated circuit (IC). Later on, I find a piece of news in nanotoday (Dec. 2005) that the company Arrowhead Research was to provide $680,000 over two years to Duke University to develop technology for IC based on CNTs. Of course, I am not the first one to come up with this idea. But this means the random imaginative idea is very helpful and sometimes feasible. Another point I learned from this course is to write down at least one idea per day. Keep doing this, then you have a large pool of ideas. One year later, you have 365 ideas. Don’t expect every idea to be useful. Even if just one or two of them are great, it is worthy doing. Imagine that if the future technology originated from one of your ideas, you will contribute the society and feel fullness of ecstasy. If you can realize your idea, you can be a millionaire or billionaire, and then lie on the beach of Caribbean to enjoy the sunshine.

Zhen Zhang and Zhigang Suo

For a crack impinging upon a bimaterial interface at an angle, the singular stress field is a linear superposition of two modes, usually of unequal exponents, either a pair of complex conjugates, or two unequal real numbers. In the latter case, a stronger and a weaker singularity coexist (known as split singularities). We define a dimensionless parameter, called the local mode mixity, to characterize the proportion of the two modes at the length scale where the processes of fracture occur. We show that the weaker singularity can readily affect whether the crack will penetrate, or debond, the interface.

Zhigang is really a master of good ideas. He learned the new technology from his son months ago, and then so many good ideas have been popping up in the mechanics community. Google group was the first trial, then google blog, wikepedia, etc. Now even fancier, iMech. I dreamed before, if I had money, I would buy a series of products by Apple. Now and in the future, I wish I can obtain iMech for free. I wish it has the quality as other products of i*** by Apple, but not as expensive as those. Good news is that the iMech is made by Zhigang, not Apple.