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ECS Short Courses


Vancouver, Canada | Sunday, April 25, 2010

Short Course #6 (1/2 day Short Course)
Fundamentals of Modern Si- and SiGe-based Bipolar Transistors
Tak H. Ning, Instructor

This course is intended for physicists, chemists, materials scientists, and electrical engineers with an interest in understanding the basic physics governing the operation, design, design optimization, and scaling characteristics of the modern Si- and SiGe-based bipolar transistors. The attendee is assumed to have an introductory understanding of the transport of electrons and holes in a semiconductor. The course will start with a discussion of the basic properties of a p-n diode that are relevant to bipolar transistors. Through a systematic discussion of the emitter region, the base region, and the collector region of a bipolar transistor, the attendee will develop an understanding of the key device parameters and factors that govern the performance of a bipolar transistor. A portion of the course is devoted to the discussion of the heterojunction nature of a SiGe-based bipolar transistor and the design tradeoffs of the Ge profile in the SiGe base. The course concludes with a comparison of the fundamental differences between a SiGe-based bipolar transistor and a III-V compound semiconductor HBT, and a comparison of the scaling limits of the two transistors. The course outline and topics covered are as follows:

  • Key p-n diode properties relevant to understanding the operation and design of a bipolar transistor
    • energy band diagram for a p-n diode
    • quasi-Fermi potentials and their spatial variation across a p-n junction
    • current-voltage characteristics
    • time-dependent and switching characteristics
    • diffusion capacitance
  • n-p-n transistors
    • basic operation of a bipolar transistor
    • applying the simple diode theory to bipolar transistor
    • current-voltage characteristics of an ideal bipolar transistor; introduction of the concepts of base current, collector current, current gain, and early voltage
    • characteristics of a typical real transistor; real transistors have characteristics that deviate from those of the ideal transistor, and the main reasons are discussed
    • the basic device models for a bipolar transistor are introduced, including the basic dc model, the basic ac model, and the basic small-signal equivalent-circuit model; the role of the emitter diffusion capacitance in determining the speed of a bipolar transistor is discussed in some detail
    • the relationship between the design a bipolar transistor and its breakdown voltages
  • Bipolar device design
    • the design of the modern polysilicon-emitter bipolar transistor is discussed by considering the design emitter region, the base region, and the collector regions separately; the concepts of base transit time and base widening are introduced, and the subtle difference between the design of a small-dimension modern transistor and that of a larger-dimension transistor are explained
    • the design of the Ge profile in a SiGe-base transistor is discussed in some detail; the topics covered include the effect of Ge in the emitter region, the optimization of the Ge profile for performance, and the optimization of the Ge profile for minimizing device performance variations
    • a SiGe-base bipolar transistor is often called a heterojunction bipolar transistor (HBT); the heterojunction nature of a SiGe-base bipolar transistor is discussed in some detail, with a goal of helping the attendee understand the subtle but importance difference between a SiGe-base bipolar transistor and a III-V compound HBT; the key technology features of a modern bipolar transistor are discussed
  • Performance factors and scaling of a bipolar transistor
    • the commonly used figures of merit (fT, fmax, and ring-oscillator speed) are introduced
    • the optimization of a bipolar transistor is discussed; the optimization details depend on the application (digital versus analog and RF); the tradeoffs involved in the design optimization are discussed
    • the scaling of an optimized bipolar transistor to small dimension as well as the factors limiting scaling are discussed
    • the performance and scaling properties of a SiGe-base transistor and a III-V HBT are compared


About the Instructor

Tak H. Ning is an IBM Fellow at IBM Research. He consults on strategy, planning, and technical issues in IBM’s silicon technology area for high-end system applications. His research includes understanding the industry-wide silicon technology directions, and he guides research projects on device reliability, SOI devices, and system-on-chip technologies. He also has served, since 1997, as IBM’s representative to the Semiconductor Research Corporation (SRC) Executive Technical Advisory Board, with the responsibility of providing guidance to university research programs funded by SRC.

In 2007, Tak Ning was awarded the ECS Gordon E. Moore Medal. He is an IEEE Fellow and an APS Fellow, and a member of the U.S. National Academy of Engineering. Dr. Ning is the inventor or co-inventor of 37 U.S. patents, including the widely used DRAM cell and self-aligned bipolar transistor.

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