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Kenneth Patterson Gwinnett School of Math Science and Technology Georgia Tech STEP-UP Summer 2018 Faculty Advisor: Doug Yoder

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Page 1: Kenneth Patterson Gwinnett School of Math Science and ...Gunn Diode fits into, that produce oscillations. LC Circuit Capacitor starts fully charged, energy stored in electric field

Kenneth Patterson

Gwinnett School of Math Science and Technology

Georgia Tech STEP-UP Summer 2018

Faculty Advisor: Doug Yoder

Page 2: Kenneth Patterson Gwinnett School of Math Science and ...Gunn Diode fits into, that produce oscillations. LC Circuit Capacitor starts fully charged, energy stored in electric field

¡ Electronics oscillate at low frequencies, photonics at high frequencies

¡ Very few technologies reliably produce EM radiation in 300 GHz - 10THz range

¡ Between microwaves and infrared¡ Applications include: Radar, high-speed

data transmission, astronomy, medical imaging “Mr. President, we must not

allow a Tera-Hertz gap!”

Image source: https://media.nature.com/m685/nature-assets/nature/journal/v417/n6885/images/417132b-f1.2.jpg

Page 3: Kenneth Patterson Gwinnett School of Math Science and ...Gunn Diode fits into, that produce oscillations. LC Circuit Capacitor starts fully charged, energy stored in electric field

§ Group is working on a semiconductor devicecalled a Gunn Diode

§ Should oscillate at a frequencyabove 1 THz

§ This project’s goal is to simulate a circuit that the Gunn Diode fits into, that produce oscillations

Page 4: Kenneth Patterson Gwinnett School of Math Science and ...Gunn Diode fits into, that produce oscillations. LC Circuit Capacitor starts fully charged, energy stored in electric field

LC Circuit

Capacitor starts fully charged, energy stored in electric field

Page 5: Kenneth Patterson Gwinnett School of Math Science and ...Gunn Diode fits into, that produce oscillations. LC Circuit Capacitor starts fully charged, energy stored in electric field

Capacitor discharges, and current creates magnetic field in Inductor

Page 6: Kenneth Patterson Gwinnett School of Math Science and ...Gunn Diode fits into, that produce oscillations. LC Circuit Capacitor starts fully charged, energy stored in electric field
Page 7: Kenneth Patterson Gwinnett School of Math Science and ...Gunn Diode fits into, that produce oscillations. LC Circuit Capacitor starts fully charged, energy stored in electric field

Inductor keeps current going, and re-charges capacitor in opposite direction

Page 8: Kenneth Patterson Gwinnett School of Math Science and ...Gunn Diode fits into, that produce oscillations. LC Circuit Capacitor starts fully charged, energy stored in electric field

Capacitor discharges again in opposite direction, and cycle repeats!

Page 9: Kenneth Patterson Gwinnett School of Math Science and ...Gunn Diode fits into, that produce oscillations. LC Circuit Capacitor starts fully charged, energy stored in electric field

Frequency of oscillation:

Of course, real physical elements have nonzero resistance, meaning loss of energy over time

Page 10: Kenneth Patterson Gwinnett School of Math Science and ...Gunn Diode fits into, that produce oscillations. LC Circuit Capacitor starts fully charged, energy stored in electric field

¡ An oscillator requirestwo things:§ Amplification§ Feedback

Desired frequency L C

100 Hz 1.0 H 3.0 uF

99.7 MHz 1.5 nH 1.75 nF

2.4 GHz 2.8 nH 1.5 pF

1.0 THz 0.01 nH 0.001 pF

LC circuit is called a“tank circuit”

Page 11: Kenneth Patterson Gwinnett School of Math Science and ...Gunn Diode fits into, that produce oscillations. LC Circuit Capacitor starts fully charged, energy stored in electric field

¡ Exhibits “negative resistance” over a certain voltage range

¡ Acts as its own source of amplification and feedback!

Page 12: Kenneth Patterson Gwinnett School of Math Science and ...Gunn Diode fits into, that produce oscillations. LC Circuit Capacitor starts fully charged, energy stored in electric field

¡ James Gunn in 1964 observedoscillations in current in aGaAs semiconductor device

¡ Later researchers discovered it to be explained by NDR ¡ GaAs Gunn Diodes are commercially available in waveguides

up to ~200GHz¡ Used in microwave devices like radar guns

Page 13: Kenneth Patterson Gwinnett School of Math Science and ...Gunn Diode fits into, that produce oscillations. LC Circuit Capacitor starts fully charged, energy stored in electric field

¡ GaN has been investigated and simulated as a potential NDR semiconductor material since year 2000

¡ Group has a design for fabricating such a device, but needs the resonant circuit to plug it into!

¡ Goal is to design andsimulate a resonantcircuit with Gunn-likeNDR device

Source: E. Alekseev, A. Eisenbach, D. Pavlidis, S. M. Hubbard, and W. Sutton, “GaN-based NDR Devices for THz Generation,” p. 10, 2000.

Page 14: Kenneth Patterson Gwinnett School of Math Science and ...Gunn Diode fits into, that produce oscillations. LC Circuit Capacitor starts fully charged, energy stored in electric field

¡ Circuit simulator: PSPICE¡ Schematic CAD software: Cadence OrCAD

¡ Two goals to accomplish:§ “Gunn Diode” is not a device in SPICE, so needed

an equivalent subcircuit that exhibits the NDR V-I curve

§ Place that subcircuit into a simple resonant circuit and demonstrate oscillations

Page 15: Kenneth Patterson Gwinnett School of Math Science and ...Gunn Diode fits into, that produce oscillations. LC Circuit Capacitor starts fully charged, energy stored in electric field

¡ Subcircuit uses an opamp to produce “-R”

¡ In practice, this subcircuit only lowered resistance of the total circuitrather than show NDR

Source: http://adamsiembida.com/negative-resistor-tutorial/

Page 16: Kenneth Patterson Gwinnett School of Math Science and ...Gunn Diode fits into, that produce oscillations. LC Circuit Capacitor starts fully charged, energy stored in electric field

Source: http://www.intusoft.com/nlhtm/nl52.htm

NDR at last!

Page 17: Kenneth Patterson Gwinnett School of Math Science and ...Gunn Diode fits into, that produce oscillations. LC Circuit Capacitor starts fully charged, energy stored in electric field
Page 18: Kenneth Patterson Gwinnett School of Math Science and ...Gunn Diode fits into, that produce oscillations. LC Circuit Capacitor starts fully charged, energy stored in electric field
Page 19: Kenneth Patterson Gwinnett School of Math Science and ...Gunn Diode fits into, that produce oscillations. LC Circuit Capacitor starts fully charged, energy stored in electric field

¡ 50.75 GHz

Page 20: Kenneth Patterson Gwinnett School of Math Science and ...Gunn Diode fits into, that produce oscillations. LC Circuit Capacitor starts fully charged, energy stored in electric field

¡ Proof of concept, success!¡ Simplest possible resonant circuit, too simple

for real-world fabrication

¡ Handed off three things to group:§ Simple SPICE NDR circuit design§ Primary Gunn diode circuit designs I found in

literature§ ALL sources I used this summer

Page 21: Kenneth Patterson Gwinnett School of Math Science and ...Gunn Diode fits into, that produce oscillations. LC Circuit Capacitor starts fully charged, energy stored in electric field

¡ This twin JFET subcircuit probably won’t truly behave like a GaN device

¡ Realistically building this circuit will require more details than simply R, L, and C

¡ Most likely final circuit will need filters or transmission lines of some type, will need a lot of refining

Page 22: Kenneth Patterson Gwinnett School of Math Science and ...Gunn Diode fits into, that produce oscillations. LC Circuit Capacitor starts fully charged, energy stored in electric field

1. Learned a ton about AC Circuits!

2. Lesson Plan: Introduction to inductors and capacitors at intro-physics level

3. Research and literature review methods ( using software like EndNote or Zotero to create citations)

4. Possible usage of SPICE in the classroom▪ Most likely not PSPICE, but online browser

versions are also available

Page 23: Kenneth Patterson Gwinnett School of Math Science and ...Gunn Diode fits into, that produce oscillations. LC Circuit Capacitor starts fully charged, energy stored in electric field

¡ A HUGE thanks to Jonathan Sculley¡ Dr. Doug Yoder¡ Bette Finn, ECE Research Librarian¡ NSF ¡ Dr. Leyla Conrad