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Homemade Field Effect Transistor (FET)

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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 .
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