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MOSFET IV Measuring Techniques

The metal oxide semiconductor field effect transistor (MOSFET) has been in existence since the early 1960s. Its use is popular in the semiconductor industry because it lends itself to being compacted with other MOSFETs more easily than other transistors. Packaged individually, MOSFETs are useful for creating low-power amplifiers. These transistors take on a variety of dimensions, so the IV characteristics change between designs, and there are some common methods already employed to measure these curves.

Prototyping Breadboard
- Since individual MOSFETs are mass produced there will likely be variations between each one with regard to IV characteristics. For some circuit designs, the variations may be noticeable between the theoretical and observed performance characteristics. To test each transistor before using it, the drain is connected to power and the source in connected to ground. The gate-to-source voltage is set to discrete values, while the drain voltage is varied. Measuring the current with each variation yields the data to construct a family of curves seen with many data sheets for MOSFETs.
Transistor Tester
- Due to the prohibitive cost, the typical hobbyist would not use a transistor tester with a graph display to determine the IV characteristics of a MOSFET. This is a piece of equipment more commonly seen in research and testing environments. By connecting leads to the source, gate, and drain, the transistor tester displays a family of IV measurement curves at appropriate intervals. Depending upon the model, the obtained data can also be recorded to a drive for later retrieval or transfer to a computer.
Probe and Test
- After a batch of MOSFETs are tested, the probe and test group at semiconductor device manufacturing facility tests each transistor to verify whether it is functioning. Probes are attached the the source, gate, and drain of each MOSFET. The IV characteristics can be learned about each one. Only the working transistors on a finished wafer will be cut out and packaged. Since the objective for this test is maximizing yield, each transistor is tested to be sure each one is within design specifications.
Design Software
- Much akin to designing buildings and various machines, special software is used to design MOSFETs. Besides the ability to lay out the mask layers necessary for the fabrication processes, this software is able to provide theoretical IV measurements. These results are based off of many factors that have been discovered through extensive research on MOSFETs. These factors include parasitic capacitances and internal impedances. With all of this information available, the IV characteristics of a MOSFET can be determined before it's fabricated.

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