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 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 • 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%20Diffusion%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