Bipolar Junction Transistors

The NPN BJTs are tested in the lab using ICS, an automated testing program. For more information, see Testing.

Theory

The theory and operation of bipolar junction transistors (BJTs) is described in the Britanica Online entry available to subscribers. Students are also referred to their ECE 440 texts to review.

Mask Layout

13 Vertical BJTs are included in each device cell. (Don't be superstitious!)

• The array of 8 transistors on the left half use contacts to the substrate lying just below the horizontal centerline as their collectors.
• The base contacts are along the top and bottom for the two rows of devices. The various shapes and sizes of the emitter and base diffusions allow students to explore the dependencies of performance values on the area, perimeter and sharp corners.
• Contacts are implemented as small squares so that the contact resistances can be measured. The lower right transistor in the left half array is an exception - it has much better contacts and minimal metal over the emitter diffusion, making it very photosensitive.

In the right half of the array are:

• Two coplanar waveguide probable BJTs at the top
• a tiny BJT in the middle
• a powerful BJT with good contacts (Collector diffusion surrounding base) in the lower left
• the most powerful BJT in the lower right (maximum emitter periphery).

The FETs elsewhere on the mask can be operated as lateral (horizontal) BJTs although their performance will be poor. Keep this in mind in case your vertical BJTs fail.

References

For Additional Information Consult:

• Dieter K. Schroder, Semiconductor Material and Device Characterization, (John Wiley & Sons, New York, 1990).
• Ben G. Streetman, Solid State Electronic Devices, (Prentice-Hall, Englewood Cliffs, NJ, 1980).
• J. M. Early, "Effects of Space Charge Layer Widening in Junction Transistors," Proc. IRE 42, 1761-1772 (1954).