Homemade Field Effect Transistor (FET)

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Homemade Field Effect Transistor. (FET). By Matt Barnekow. Sam North. Devin Vagt. Chris Dickason. ENGR45,. SRJC. 2012 ...
Homemade Field Effect Transistor (FET) ENGR45, SRJC 2012

By Matt Barnekow Sam North Devin Vagt Chris Dickason

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 it’s 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 Ellsworth’s 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.

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 1000°C. T Thickness of layer shown by color. 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 1000°C 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 • On the left is a graph showing the

• The average saturation for a JFET of our

voltage capacity of a standard JFET with

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

saturation.

saturation point until almost 17V.

• 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