Last edited 09apr04 by ryhsiao@uiuc.edu
illiBJT: A Journey Deep into the Wonderful World of Semiconductors
By Roger Hsiao (ryhsiao)
Abstract
To create an RTICA that will demonstrate how a Bipolar Junction Transistor (BJT)
operates under normal biasing and how amplification of current is achieved.
The program will be an interactive program with the user being able to define
different doping concentrations for the base (n type semiconductor), in a p+ n p+
semiconductor. Also, the user will be able to define different forward and reverse
biases for the semiconductor, with each change instantly reflected in the behavior
of the RTICA BJT. The program will show the movement of holes and electrons within
the emitter(p+), base (n), and collector (p+). Also, as output, there will be
a display of the base current (input) and the resulting collector current
(amplified current) to help the user to get a quantitative feel of what his/her
changes actually did to the behavior of the transistor.
Checklist
NOTE: This list is by no means comprehensive...Just general major checkpoints
1. Create framework of transistor
a. Create outer shell of transistor (color coded wire shell for each region) COMPLETED
b. Create inner matrix of intrinsic holes in p type and electrons in n type semiconductors - COMPLETED
2. Create excess holes/electrons to demonstrate carrier movement
a. Create arrays to completely describe each particle to be moved with velocity, position, force, and color - COMPLETED
b. Create carrier particles to be able to pass from one region to another if correct conditions (create testing functions, etc) - (COMPLETED - April 26)
c. Write function to display approximate currents (input and output currents) - COMPLETED
3. Create user interactivity
a. Modify functions to allow for users to be able to adjust input current, etc - COMPLETED
4. Add extra features as I get more and more comfortable and as I'm working, I'm bound to think "Hmm....Itd be really cool if it could do this" - To be completed as ideas come to me
Instructions
- To increase the number of base electrons, press (D) until the Current Difference is positive. Hold Shift + (D) until the Current Difference is negative to decrease base electrons
- To switch views to see the effect of electric fields (potentials), hit (P). To switch back to the more accurate view without the potentials, hit (P) again.
- Enjoy!
Roger's Final Thoughts
The final RTICA that I was able to create was able to accomplish
my goal, in that I was able to create a program that demonstrates
the inner workings of a BJT transistor without bogging the user down
with unnecessary calculations or with too many objects on the screen.
Some young hotshot in a future Math 198 class might criticize some of
the methods which I chose to represent particle movement in that I didn't
display a steady stream of moving particles, but rather just show a group
of particles moving through the transistor. However, I did put some thought
into the method of display. The problem that I foresaw with a steady stream
of moving particles is that the user would not be able to easily count the
moving particles, essentially reducing the RTICA to something that is
slightly more fundamentally sound, but lacking in the teaching aspect that
I wanted to include. My main goal with illiBJT was to instill a passion for
transistors within the hearts of non-electrical engineering people, and while I did
want an accurate RTICA, my higher priority was to create something that a
layperson would be able to follow. With that, I move onto future improvements
on illiBJT.
Possible Advances in the design of future BJT RTICAs
- More efficient coding in terms of calculations or testing
- A higher limit in the number of base region particles (or no limit at all....ooh....aah)
- Shapes drawn slightly closer to actual scale(base region shorter than emitter and collector regions)
- Perhaps moving the BJT into the 4th dimension....I gave this some thought in thinking how it would
look and how it would act with particles travelling from one region to another, but it made my head hurt
And finally....
Here is a screenshot of the BJT RTICA at work.
Non-Electrical Engineering people all over 3rd Floor-Beckman Institute are now swooning over the immense beauty of transistors....