solid state devices

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Last Updated: Tuesday, 25 October 2022 22:34

Published: Thursday, 12 November 2020 20:02

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solid state devices:

Before we get into VLSI and running various tools, it's important to get basic idea of transistors on which all of VLSI material is based. Knowing about transistors is not really needed for doing VLSI work, but it will help you get a more wholesome picture of how things work.

Transistors is the basic fundamental element of making any circuit. We had Resistance, Capacitors and Inductors but they were all considered passive elements. When tarnsistors were invented, they solved the problem of making automatic switches - switches that you can turn on or off by applying different voltages to it. These were called active elements and brought a paradigm shift in making circuits.

Modern transistors are built in Silicon material, and have 2 flavors: NMOS and PMOS. This is called CMOS (or complimentary Metal Oxide) technology.

Transistor can be in off state or on state. In on state, there are 2 separate regions of operation identified:

1. linear region:

Linear current of a transistor is defined via following eqn:

I_ds(lin) = µ*C_ox*W/L*[(V_gs-V_TH)*V_ds - V_ds²/2]

2.saturation region:

Saturation current of a transistor is defined via following eqn:

I_ds(sat) = µ*C_ox*W/L*(V_gs-V_TH)² /2