semiconductors

Topics: Semiconductor, P-n junction, Bipolar junction transistor Pages: 55 (9889 words) Published: October 15, 2014


EE2 Semiconductor Devices

Switching of bipolar devices

10 lectures – 5 classes
Dr. K. Fobelets
k.fobelets@imperial.ac.uk

Taken from www.necel.com/process/en/ux6b_90nm_bicmos.html

The course aims:

(1) To review the operation of diodes and bipolar junction transistors. (2) To extend knowledge on bipolar devices to include the influence of recombination. (3) To investigate the physical mechanisms underlying the delays and speed limitations of the devices. (4) To extract equivalent circuit models for the devices.

Objectives:

Students should be able to
(1) Explain qualitatively the mechanisms of electronic conduction in bipolar devices, and calculate relevant quantities from given data. (2) Calculate and explain DC current-voltage behaviour of diodes and BJTs, given their geometry and material properties. (3) Explain the influence of excess minority carrier recombination of the performance of the devices. (4) Explain the large signal behaviour of the devices from the internal storage of charge.

Recommended textbooks

EE1 background knowledge on semiconductors and semiconductor devices is required. The EE1 course notes can be found on blackboard. It is strongly recommended that you read these notes in order to understand the basic principles of semiconductor devices.

“Solid State Electronic Devices”, B.G. Streetman & S. K. Banerjee, Prentice Hall International Editions, 6th ed. This is a more expensive book but the course is based on this book. It contains a lot more than what is taught in the 1st and 2nd year.

“Microelectronic Devices”, K.D. Leaver, IC Press, 2nd ed. This is a compact and relatively inexpensive book which covers all the essentials.

Note that in popular books such as “Microelectronics circuits” by Sedra & Smith some very brief descriptions of semiconductor device operation can be found. Whilst previous two books are very physics oriented, this book is more oriented towards the circuit engineer and thus might give additional insight.

There are plenty of copies available of all these books in the Central Library.

An interesting on-line text books can be found on:
http://ecee.colorado.edu/~bart/book/book/contents.htm
http://www.ecse.rpi.edu/~schubert/Course-ECSE-2210-Microelectronics-Technology-2010/

Course synopsis

1. Revision on semiconductor devices
Last year you studied the DC behaviour of metal-semiconductor, metal-oxide-semiconductor and semiconductor-semiconductor junctions. We looked at the simplified version of three devices: the pn junction, the MOSFET and the BJT. We will start the course with reviewing the basic device DC operation concepts of the pn diode and the BJT because this year we will focus on bipolar devices. For more extensive information on MOSFETs please see the 3rd year Advanced Electronics Devices course1.

2. Long pn diode
In contrast to the “short” devices we’ve studied in the first year, this year we will introduce recombination processes and check how they influence device behaviour. These devices will be referred to as “long” devices. Although an important characteristic of semiconductor devices is their fast response time, some delays do occur. We will investigate the physics behind the delays and investigate the resulting switching characteristics. The concept of a fast switching majority carrier device and a “slowly” switching minority carrier device will be made clear.

3. The BJT
An npn or pnp junction is the basis for the bipolar junction transistor (BJT). Based on our knowledge of pn junctions, the DC functioning of a BJT will be described. As in pn junctions, minority carriers will play an important role in the conduction mechanism of the BJT. We will look explicitly at the short BJT and discover that calculating the currents in this particular configuration is very straightforward. The BJT in which recombination is taken into account offers some challenging...
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