ECE445 Project Proposal

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					ECE445 Project Proposal                                          Spring 2006




                    Al-free Metallization for
                          AlGaN/GaN HEMTs




                                                            Hyung Joon Koo
                                                                TA: Ran Hu
                                Dept. of Electrical and Computer Engineering
                                  University of Illinois at Urbana-Champaign
                                                             Urbana, IL 61801
I. Introduction

   1. Title
       AlGaN/GaN high electron mobility transistors (HEMTs) are very attractive for
      high power and high frequency applications due to their high breakdown voltage
      and high saturation current. For these high performance devices, low-resistance
      ohmic contacts are very important. Therefore, I would like to conduct profound
      research on the ohmic contacts of GaN-based devices for my project.


   2. Objectives
       The conventional Ti/Al-based contacts for AlGaN/GaN HEMTs have shown
      poor reliability in short gate-length devices due to the formation of low-melting,
      viscous AlAu4 phase. Among a number of possible solutions, my goal is to
      investigate on the Al-free metallization approach.


       A. Benefits
          - Enhanced reliability
          - Enhanced reproducibility
          - Temporal and thermal stability
          - Higher device performance
          - Better understanding of contact formation of GaN materials
       B. Features
          - Ohmic contact
          - Low-resistance contact
          - Uniform metal-semiconductor interface
           -   Smooth surface morphology
           -   General design rule for optimization




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II. Design

   1. Block Diagram

                   Process Flow



                  Book Research:
      Principles of Ohmic Contact Formation
         and Characterization Techniques



             Ohmic Contact Processing



             Electrical Characterization



        Optimization of Contact Parameters



   2. Block Descriptions
      A. Book Research
           I will first study the principles of ohmic contact formation in order to
          develop a better understanding of the entire process and mechanism of
          contact formation on GaN-based materials. Then, I will also learn about
          ohmic contact characterization techniques, which will directly aid me in
         characterization and optimization of the contacts.
      B. Contact Processing
          This step will include all the fabrication steps before characterization. I will
         start from mesa lithography/etching and prepare materials for further
         processing. Then, I will fabricate the contact through TLM lithography and
         metal deposition using different parameters. This will prepare the actual
         samples for characterization.
      C. Characterization
           Characterization step will enable me to study the electrical properties, such
          as the I-V characteristics and resistance values, of the contact. Since the goal
          of the whole project is to fabricate low-resistance ohmic contact, this step




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          will be essential.
       D. Optimization
           In this step, I will be doing the overall analysis, accounting for all the
          different measures and parameters taken, and thus, optimizing the
          experiment parameters. Through this, I will be able to come up with a final
          design for the entire research of Al-free metallization.


   3. Performance Requirement
       Generally, the conventional Ti/Al-based contacts have shown contact resistance
      of RC < 0.3 Ω•mm and specific contact resistance of ρC < 10-5 Ω-cm2. Although I
      will be substituting other metals for Al, these values will be sought after for low-
      resistance contact.




III. Verification

   1. Testing Procedures
      - I-V characteristics: The conventional probes and ICS software will be used to
      observe the desired ohmic behavior.
      - Resistance: Both the contact resistance RC and the specific contact resistance
      ρC will be measured through the widely used transfer length method (TLM).
      Specifically, I will be using the linear TLM since the contacts will be prepared
      with the particular TLM structure.


   2. Tolerance Analysis
       Since the Al-free metallization approach has not been well researched yet, there
      aren’t any standard measures to compare the results. However, since I will have
      10 test structures on each sample, this will allow me to understand how each
      parameter variation may affect the contact formation process with a some degree
      of certainty.




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IV. Cost and Schedule

   1. Cost Analysis
         Labor : $50/hr x 2.5 x 12hr/wk x                      12wk     = $18,000
         Parts: $0 (covered by Professor Adesida)
         Grand Total: $15,000


   2. Schedule
                Week                                        Tasks
                 1/30              - Initial ideas/designs
                  2/6              - Get checked out on equipment
                                   - Get checked out on equipment
                 2/13
                                   - Book research
                                   - Book research/design review
                 2/20
                                   - Material preparations (mesas)
                 2/27              - TLM lithography & contact deposition (*)
                  3/6              - Electrical characterization of contact (**)
                                   - Contact fabrication and characterization
                 3/13
                                     (steps * & **)
                 3/20              - Spring break
                 3/27              - Repeat steps * & **
                  4/3              - Repeat steps * & **
                 4/10              - Optimization of contact parameters
                 4/17              - Final design of contact fabrication
                 4/24              - Demo and presentation
                  5/1              -Final paper

      -all tasks will be done on my own
      -Schedule may vary slightly due to equipment availability and sample quality




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