Gallium Nitride (GaN) Based Transistors Jason Ross Physics Santa - - PowerPoint PPT Presentation

Jason Ross – Physics Santa Barbara City College Mentor: Nidhi Faculty Advisor: Umesh Mishra Department of Electrical and Computer Engineering UCSB Funded by:

Gallium Nitride (GaN) Based Transistors

The Transistor

e- flow Gate

Amplifier Switch

Why GaN?

• Forms 2D Electron Gas (2DEG)

making it a High Electron Mobility Transistor (HEMT)

• Tough
• High Thermal Conductivity
• High Breakdown Voltage

GaN AlGaN

Source Drain Gate

Mishra, U. Eastman, L. Toughest Transistor Yet, IEEE, Volume 39 May 2002

Why Do the Research?

They Are Everywhere:

Computers Stereos and TVs Wireless Internet Communication Infrastructure Hybrid Electric Cars The Electric Grid Defense Satellites and Radar

Research Goals

Characterize Transistors Bring Out GaN Advantages:

Handle High Voltages Perform at High Frequencies

Transistor Design (Fabrication) Examples

Self Aligned Gate Measure Electron Velocity Determine Electron Mobility

Gate e- flow

GaN

Drain/Sourc e

Material Deposition

The Fabrication Process

Photolithography Annealing

e- beam Gold Photoresist (PR) Mask UV Light PR Wafer

870oC

Plasma

Self Aligned Gate Design

Sapphire AlGaN

GaN

SiO2 Cr W Drain Source Gate n++ GaN

Advantages:

• Reduces distant between

source and drain resulting in a small, fast device (Great high frequency performance).

• Reduces contact resistance

with highly Silicon doped GaN terminals.

Transmission Line Measurement (TLM)

Purpose: Measure e- Velocity And Mobility

AlGaN GaN

V

w Analysis: Current = qnsv E = (V – IRc)/w

q = e- charge I = current ns = charge density v = e- velocity

Rc

TLM Results

0.0 3.0x10

4

6.0x10

4

9.0x10

4

0.0 2.5x10

6

5.0x10

6

7.5x10

6

1.0x10

7

Velocity (cm/s) Electric Field (V/cm)

3 micron 5 micron 8 micron 12 micron 20 micron

Spacing (w) 9.4x106 cm/s 1300 cm2/Vs

In Perspective

Velocity: 9.4x106 cm/s Mobility: 1300 cm2/Vs

Test: 3 micron Target: <100nm

Mishra, U. Eastman, L. Toughest Transistor Yet, IEEE, Volume 39 May 2002

Future Plans

• Improve regrowth process.
• Use Indium Nitride for the terminals.
• Develop methods for better measurement
• f sidewall thickness and quality.
• Compare results to Nitrogen faced design.

Sapphire AlGaN

GaN

SiO2 Cr W Drain Source Gate

Summary

Accomplishments:

• Learned and help perform fabrication processes in clean room.
• Gained knowledge of semiconductor device physics.
• Performed tests and collected valuable data on transistor

performance.

• Gained communication and technical skills.
• Learned what graduate research is like.

Nidhi Umesh Mishra INSET and CNSI Our Sponsors The Nanofab

Acknowledgements

Thank You!

Drain Source Gate Photoresist (PR) Chromium (Cr) SiO2 Chromium (Cr) Tungsten (W)

Self Aligned Gate Process

Cr SiO2 Cr W PR Mask SiNx n++ GaN

Goals:

• Reduce resistivity with

highly doped GaN terminals.

• Bring Source and Drain

close together resulting in a very fast device (great high frequency performance)

UV Light Sapphire AlGaN

GaN

Process:

Deposition Regrowth Etching Photolithography