EEL 6398

Semiconductor Device Theory II

 

Instructor:   J. G. Fossum

 

Credits:   3

 

Prerequisite:   EEL 6397

 

Textbooks: ULSI Devices

C. Y. Chang and S. M. Sze (Eds.)

 

Key References: Those listed for EEL 6397, and the following:

Device Electronics for Integrated Circuits, 3rd Ed.

R. S. Muller and T. I. Kamins

Modeling the Bipolar Transistor

I. E. Getreu

Silicon Integrated Circuits, Part A

D. Kahng (Ed.)

Operation and Modeling of the MOS Transistor

Y. P. Tsividis

Fundamentals of Modern VSLI Devices

Y. Taur and T. H. Ning

 

Content:   This course teaches the principles of semiconductor device operation by applying the basic physics treated in EEL 6397. Contemporary aspects of scaled (submicron) integrated-circuit devices are emphasized.

The bipolar junction transistor (BJT) is analyzed first, clearly separating out its current components to define its characteristic gains for low, intermediate, and high current levels. Emitter efficiency is discussed with reference to heavy-doping effects in silicon and polysilicon contacts. Base transport is described in the Moll-Ross formalism, extended to account for bandgap narrowing (in scaled BJTs). Discussion of heterojunction bipolar transistors (e.g., SiGe-base HBTs) is included. High-current effects in the (epitaxial) collector (i.e., quasi-saturation) are described, as well as base-width modulation and collector-emitter breakdown. Large-signal modeling is studied with emphasis on charge control and the quasi-static approximation. The Gummel-Poon model is overviewed and a new physical charge-based model is introduced. Non-quasi-static modeling of BJTs is discussed. Small-signal modeling based on linearization is demonstrated, and frequency limits of the BJT are outlined.

Next, the MOS capacitor is analyzed in detail as a basis for the MOSFET analysis, which is emphasized. The topics covered include the basic field effect (Gauss's law with Poisson's equation) leading to accumulation, inversion, and depletion, oxide and interface charges, flatband and threshold voltages, and capacitance-voltage-frequency characteristics. The MOSFET is treated in depth, beginning with strong-inversion theory but including analyses of weak and moderate inversion. Further, the effects of small geometry on the current-voltage characteristics (short-channel effects, quantization, polysilicon-gate depletion, velocity overshoot, ballistic transport) are overviewed, and hot-carrier effects are discussed. MOSFET modeling is addressed; the superiority of charge-based modeling over the conventional capacitance-based (equivalent-circuit) characterization is stressed. Some discussion of thin-film SOI and DG (double-gate) MOSFETs is included.

Time permitting, metal-semiconductor contacts are analyzed. Ohmic contacts are contrasted with Schottky-barrier contacts, noting the significance of interface states as well as the work-function difference.

Syllabus