Homework #4

Homework due next monday is at a reduced level. It will just be out of Streetman, Ch. 5 #2. It is a diffusion problem that is graphic intensive. Please use proper engineering graph paper or a good graphics program to represent the solution in semi-log format.

Exam #1

The next exam will cover up to and including diffusion. Since we have not had ample time for you to digest the diffusion material, I have delayed the next exam till monday October 16th.

More about the exam format in wednesday's class.

Computer Problem

Here is the first, and perhap's only, computer problem of the quarter. Remember, this is 10% of your grade, so I would like a report that is clear and effective. Again, use good graphing techniques as in above.

"*Using the handouts given in today's class, design an npn double-diffused bipolar transistor that is required to have a 0.5 micron base width. For design reasons, it is desirable to have the base-collector junction 1.0 micron below the surface. Devise a suitable process recipe for the diffusions using boron and phosphorus. Any effects due to intermediate oxidations may be ignored*."

Please note, that when the emitter diffusion takes place, the base diffusion will be altered. Thus an iterative solution is needed.

Solution due in 3 weeks on October 30th in class. Note, this is one week later than the earlier email I sent.

Computer Problem Addendum (10/20/00)

It is not necessary for you to establish precise doping levels in the computer problem. In other words, you can guess whatever doping level you need as long as the BJT emitter has more doping than the BJT base, and that the BJT base has more doping than the BJT collector.

However, for more realistic numbers, you should strive for a collector doping of about 1E15 /cm^{3}, base about 1E16 /cm^{3}, and emitter 5E18 /cm^{3}. Of course, the doping across the base and emitter varies as a function of position, but I mean around the maximum concentration.