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Name: Rita
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: Before 1993


Question:
Why is silicon used in making computer chips? Is it because of special chemical properties? Could other crystals be used equally well?



Replies:
Hi rita, great question! I have a few guesses in answer to this. One thing that makes silicon desirable for manufacturing purposes is that it is abundant (it is the second most abundant substance in the earth's crust) and therefore cheap. Another, more directly relevant reason, is that silicon is an "impurity semiconductor." What this means is that if you deliberately make a sample of silicon with certain impurities lodged in the crystal, you can control the conductivity of the sample by varying the concentration of impurities. What is more, you can do it over a range of conductivity values that correspond to small voltages. And best of all, you can either increase or decrease the conductivity, depending on what kind of impurity you introduce. Germanium (Ge) also has these properties, but is more expensive. These properties make form the basis for a wide variety of semiconductor devices. Also, I believe that silicon wafers can be etched by chemical process (involving fluorine, I think) to change the conductivity along well- defined channels in the wafer. This combination of properties makes silicon a uniquely good choice for making computer chips . . . it has special chemical AND physical properties. I just received this note from "Eric Peterson" who has agreed to let me post it in this space. - robert Great answer to the question on silicon use in chips. As an expansion, the use of Gallium Arsenide is becoming more popular as a base material for doping than silicon, or in conjunction with it. Gas chips are much faster because of two reasons. 1) Wafers can be sub-micron, and therefore quicker because of the less amount of circuitry involved, and 2) GAs substrate has a faster charge transfer rate than does Silicon. There are several good trade publications that delve into this subject at great length. One is called "surface Mount Technology" and another is a weekly tabloid called "Electronics Products News". Both are very good sources for those who are interested in keeping up with the latest new tech stuff in chip making.

Eric Peterson



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