Fundamentals of Modern VLSI Devices

The basic components of a bipolar transistor are described in Chapter 9. Both vertical bipolar transistors, including SiGe-base transistors, and symmetric lateral bipolar transistors on SOI are covered. The discussion focuses on the vertical n–p–n transistors, since they are the most commonly used. The difference between n–p–n vertical transistors and symmetric lateral n–p–n transistors are pointed out where appropriate. The basic operation of a bipolar transistor is described in terms of two p–n diodes connected back to back. The basic theory of a p–n diode is modified and applied to derive the current equations for a bipolar transistor. From these current equations, other important device parameters and phenomena, such as current gain, Early voltage, base widening, and diffusion capacitance, are examined. The basic equivalent-circuit models relating the device parameters to circuit parameters are developed. These equivalent-circuit models form the starting point for discussing the performance of a bipolar transistor in circuit applications.