Handed out on Thursday, August 27
Physical properties of gates
Over the next 1–2 lectures, we will discuss some of the physical characteristics of integrated circuits. It reviews and
expands on material covered in Elec 220 and introduces concepts from ELEC 261/305 as well. We will
review the structure of MOS transistors,
develop a very simple structural model for gates that demonstrates how they work,
introduce some special types of gates, including transmission, tri-state, and open collector gates,
discuss some of the differenced between real and ideal gates,
discuss some of the physical properties of gates,
understand how timing, voltage, and current properties of real gates are described,
look at analysis and synthesis of gate networks, and
conclude with an introduction to Verilog and its use in specifying gate network behavior.
Use this list as a starting point to explore chapters 2, 3, and 4 in the textbook.
Metal-oxide-semiconductor field effect transistors (MOSFETs) are the transistors most widely used in integrated cir-
cuits today. The name is due to:
the device structure – a sandwich of a metal conductor, an oxide insulator, and a semiconductor substrate and
the way it works – an electric field controls the flow of current through the device.
Although early MOSFET transistors used metal for the first layer, current ones use a polysilicon material (a conductor
with somewhat more resistance than a conductor), which is easier to fabricate
n-Channel MOSFET transistors
With no voltage between the gate terminal and the substrate, there are two junctions between the two n regions
and the p region.
This acts like two oppositely connected diodes, and no current can flow between the source and the drain.
Application of a positive voltage between the gate terminal and the substrate creates an electric field that drives
holes out of the region under the gate, creating a channel of n-type material that connects the source and drain