Homemade Field Effect Transistor (FET)

By Matt Barnekow Sam North Devin Vagt

Chris Dickason

ENGR45, SRJC 2012

History

In late 1947 the point contact transistor was invented by John Bardeen and Walter Brattain.

Early 1948 Russell Ohl came up with the concept for a p-n junction resistor.

One month later John Shive created such a transistor using germanium. In 1950 Bell labs created the n-p-n transistors Since then they have been getting progressively smaller and more

powerful.

What is a Field Effect Transistor(FET)

In a FET, the width of the conducting channel in a semiconductor and its current carrying capability is varied by the application of an electric field.

Metal Oxide Semiconductor FET (MOSFET) Junction FET (JFET) Most commonly used is MOSFET which is manufactured as an

enhancement or depletion type.

Consists of a source, a gate and a drain.

How does a FET work?

Valve Metaphor The more voltage added the more current is produced Enhancement vs Depletion MOSFET An enhancement MOSFET is a voltage control switch, a small voltage is applied

which causes a large current to be activated.

The depletion MOSFET is almost the same although a negative charge is applied to the substrate to turn off the large current.

How we created our FET

http://www.youtube.com/watch?v=w_znRopGtbE Jeri Ellsworths Video

Using nothing but easy to obtain items from the store and internet we were able to recreate a FET similar to the one created in the video by Jeri Ellsworth.

http://www.youtube.com/watch?v=w_znRopGtbE

How we created our FET

First the silicon wafer had to be broken down into small squares.

How we created our FET

An oxide layer needed to be formed We tried with electrolysis using a piece of copper in some salt water attached to

the wafer.

We made orange juice

How we created our FET

Grew oxide layer, by baking the wafers at 1000C. T Thickness of layer shown by color.

http://www.htelabs.com/appnotes/sio2_color_chart_thermal_silicon_dioxide.htm

http://www.htelabs.com/appnotes/sio2_color_chart_thermal_silicon_dioxide.htm

How we created our FET

Etched the active layer with hydrofluoric acid using electrical tape as a template.

Complete etch leaves water beads on hydrophobic silicon. Doped in Phosphoric Acid spun on fan to achieve a thin even layer. Placed back in furnace at 1000C to create a high concentration on top of the

wafer.

How we created our FET

Etched in hydrofluoric acid to remove film (containing contaminants) Furnace creates an oxide layer over the P driving it into the wafer. Finally using a conductive epoxy we made our points of contact.

What we learned

Teflon coated steel is Flammable! While attempting to create an oxide layer by introducing water into th furnace envionment we burned a teflon coated steel dish. Glass Film on wafers proves troublesome for making a MOSFET We were able to etch some glass off with acid Picture shows ground down glass layer

What we learned

Ceramics are great insulators! If heated gradually. We placed the ceramic crucible in the oven making it heat rapidly from 50 degrees to over 1832 degress in a matter of second, causing it to shatter.

What we learned

Contaminates prove annoying After burning the teflon, we noticed these chunks growing on our wafers.

What we learned

Oxide on silicon looks interesting under the microscope. This gives us a better idea of how the silicon is oxidizing.

Results

By process of the hot lead test we determined that we did make several JFETs. The hot lead test is when a source of thermal energy is added, in this case on the

side of the transistor, and then checking to see if there is any kind of current change.

Results Here you can see the separate leads

hooked up to our JFET.

Results The average saturation for a JFET of our

caliber is about 10V, however we didn't hit a

saturation point until almost 17V.

On the left is a graph showing the voltage capacity of a standard JFET with

saturation.

The right is a graph created from our voltage reading passing though the JFET

Links

http://www-ferp.ucsd.edu/najmabadi/CLASS/ECE60L/02-S/NOTES/FET.pdf http://www.pbs.org/transistor/science/info/transmodern.html http://www.engr.sjsu.edu/kghadiri/EE221/Class_Notes/EE_221_L13_Solid%20state%20Diffus

ion%20of%20impurities%20in%20Silicon.pdf

http://www.computerhistory.org/semiconductor/timeline/1957-Zone.html http://www.htelabs.com/appnotes/sio2_color_chart_thermal_silicon_dioxide.htm http://www.dauniv.ac.in/downloads/Electronic%20Devices/12EDCMOSFETLesson12.pdf

http://www-ferp.ucsd.edu/najmabadi/CLASS/ECE60L/02-S/NOTES/FET.pdfhttp://www.pbs.org/transistor/science/info/transmodern.htmlhttp://www.engr.sjsu.edu/kghadiri/EE221/Class_Notes/EE_221_L13_Solid state Diffusion of impurities in Silicon.pdfhttp://www.engr.sjsu.edu/kghadiri/EE221/Class_Notes/EE_221_L13_Solid state Diffusion of impurities in Silicon.pdfhttp://www.computerhistory.org/semiconductor/timeline/1957-Zone.htmlhttp://www.htelabs.com/appnotes/sio2_color_chart_thermal_silicon_dioxide.htmhttp://www.dauniv.ac.in/downloads/Electronic Devices/12EDCMOSFETLesson12.pdf

Homemade Field Effect Transistor(FET)HistoryWhat is a Field Effect Transistor(FET)How does a FET work?How we created our FETHow we created our FETHow we created our FETHow we created our FETHow we created our FETHow we created our FETWhat we learnedWhat we learnedWhat we learnedWhat we learnedResultsResultsResultsLinks