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Name: Raunak
Status: student
Grade: 9-12
Location: CA
Country: USA
Date: Summer 2012


Question:
How is it possible that we have made transistor gates that are so small that we cannot even see them? How did we make the machines that are capable of doing such tiny building?



Replies:
Hi Raunak,

There are many steps in the making of a transistor. Rather than me writing a long treatise on the subject, have a look at this site that allows you to see, one click at a time, each of the steps....

http://micro.magnet.fsu.edu/electromag/java/transistor/index.html

Note that the "mask" they refer to is created by a precision laser that allows such miniature features to be resolved.

Regards, Bob Wilson


The process for making these microscopic circuits is called "photolithography". Basically, it is like a projector you might see in a classroom, but instead of projecting large pictures on a wall, it uses a special kind of light and projects tiny pictures onto materials (the outlines of the transistors and other circuits being made). The process is very complicated, but it is all very well documented, and you can read about it online -- just look up "photolithography" (there are many hits). Although our eyes cannot see things that small, you can still see them using other tools (like an electron microscope).

Hope this helps, Burr Zimmerman


Most of the ideas that make this possible are probably familiar to you in other contexts: 1) When you take a photograph with a film camera, you get a tiny picture of something large. You can use the same idea to get an extremely tiny picture of something small. 2) The process of printing a picture - shining light through a negative onto light-sensitive paper - can be used for things other than making pictures to look at. The image you make can be functional as well. The light you shine through the negative could be used to alter the chemical properties of the thing you're illuminating. A photoresist is a substance that is changed by light so that it no longer can be dissolved as easily as unexposed resist. This allows you to make a tiny, detailed mask that in turn can be used to modify a semiconductor only in certain areas. 3) For very small features, the wavelength of light limits the resolution you can achieve, but you can use a shorter wavelength to get around this problem.

Tim Mooney


These are made by photolithographic process. one sees transistors with three legs or terminals. these transistors occupy much space. The interconnections in an array are done by photolithography and one transistor gets connected to another as you can see in

http://www.kip.uni-heidelberg.de/cms/vision/projects/recent_projects/evolvable_hardware/field_programmable_transistor_array/

The die is about 5mm*5mm and has an area of just 33 sq mm. there are many (256) transistors in this array. you might read this article to learn more.

V. Mani



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