Engineers at the University of Wisconsin-Madison have isolated a single-crystal film of semiconductor from the substrate on which it is built. Then they transferred this very thin film -- 200 nanometers thick -- on plastic. Both sides of the film can host active components and several layers can be stacked, opening the way to very powerful 3-D flexible computer chips. Besides computer chips, this technique could be used for solar cells, smart cards, RFID tags or active-matrix flat panel displays. But will the semiconductor industry adopt this technique? Read more...
Here is a short description of this technique picked from a University of Wisconsin-Madison news release.
A team led by electrical and computer engineer Zhenqiang (Jack) Ma and materials scientist Max Lagally have developed a process to remove a single-crystal film of semiconductor from the substrate on which it is built. This thin layer (only a couple of hundred nanometers thick) can be transferred to glass, plastic or other flexible materials, opening a wide range of possibilities for flexible electronics.
In addition, the semiconductor film can be flipped as it is transferred to its new substrate, making its other side available for more components. This doubles the possible number of devices that can be placed on the film. By repeating the process, layers of double-sided, thin-film semiconductors can be stacked together, creating powerful, low-power, three-dimensional electronic devices.
Below is a picture of graduate student Hao-Chih Yuan holding a sample of a semiconductor film on plastic (Credit: University of Wisconsin-Madison).
This research work has been published in the latest issue of the Journal of Applied Physics under the title "High-speed strained-single-crystal-silicon thin-film transistors on flexible polymers" (Volume 100, Issue 1, Article 013708, July 1, 2006). Here is a link to the abstract.
Here is a comment about one researcher about the performance that could be reached by using such a manufacturing process..
"It's important to note that these are single-crystal films of strained silicon or silicon germanium," says Ma. "Strain is introduced in the way we form the membrane. Introducing strain changes the arrangement of atoms in the crystal such that we can achieve much faster device speed while consuming less power."
And Lagally goes further.
"This is potentially a paradigm shift," says Lagally. "The ability to create fast, low-power, multilayer electronics has many exciting applications. Silicon germanium membranes are particularly interesting. Germanium has a much higher adsorption for light than silicon. By including the germanium without destroying the quality of the material, we can achieve devices with two to three orders of magnitude more sensitivity."
It's probably premature to call this technique "a paradigm shift." The semiconductor industry has invested billions of dollars in its current factories and it will take time for this new process to be used.
Sources: University of Wisconsin-Madison news release, July 18, 2006; and various web sites
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