Transistor history and types

KRCT

What is a Transistor?Semiconductors: ability to

change from conductor to insulator

Can either allow current or prohibit current to flow

Useful as a switch, but also as an amplifier

Essential part of many technological advances

THREE TERMINALS

EMITTERBASECOLLECTOR

The Transistor is BornBell Labs (1947):

Bardeen, Brattain, and Shockley

Originally made of germanium

Current transistors made of doped silicon

Nobel prizeWilliam Shockley ,Walter Brattain ,John Bardeen

How Transistors WorkDoping: adding small amounts of

other elements to create additional protons or electrons

P-Type: dopants lack a fourth valence electron (Boron, Aluminum)

N-Type: dopants have an additional (5th) valence electron (Phosphorus, Arsenic)

Importance: Current only flows from P to N

DOPINGThe addition of a small

amount of a different substance to a pure semiconductor crystal.

The impurities give an excess of conducting electrons or an excess of conducting holes which is crucial for making a working transistor.

TYPES OF TRANSISTORBipolar Junction Transistor (BJT)

Field-Effect Transistor (FET)

Junction Field Effect Transistor (JFET)

Metal Oxide Semiconductor Field Effect Transistor (MOSFET)

Junction Field Effect Transistor (JFET) The field-effect

transistor (FET) controls the current between two points but does so differently than the bipolar transistor. 

The FET operates by the effects of an electric field.

This is why the FET is sometimes called a unipolar transistor.

JFET Properties Cut-off voltage is varying

for each JFET0.3V – 10V

N-Channel – Negative VGS P-Channel – Positive VGS

Internal Capacitance Do not Forward Bias

JFET – burn out

Metal oxide semiconductor field effect transistor(MOSFET)

The most common field effect transistor in both digital and analog circuits.Uses channel of n or p-type semiconductor, named NMOSFET and PMOSFET, respectively.

SILICON ON INSULATOR (SOI)For high-frequency

circuits (about 5 GHz) capacitive coupling to the Si substrate limits the switching frequency.

These problems are being avoided by making circuits on insulating substrates that have a thin, approximately 100 nm layer of crystalline silicon

APPLICATIONIn integrated circuits, the desirable

properties of MOSFETs allowed them to capture nearly all market share for digital circuits.

Discrete MOSFETs can be applied in transistor applications, including analog circuit.

MEDICAL APPLICATIONThere is great interest in

constructing nano electronic devices that could detect the concentrations of bio molecules

A parallel line of research seeks to create nano electronic devices which could interact with single cells for use in basic biological research.

These devices are called nano sensors.

NANO MEDICINE

USING IN COMPUTER

Transistors have continued to get smaller and smaller.

For instance, each memory location in a computer has a pair of transistors, and there are 16 of them for each byte of memory.

COMPUTER MEMORYNormally, a junction transistor is "off" when

there is no base current and switches to "on" when the base current flows. That means it takes an electric current to switch the transistor on or off.This kind of arrangement is known as a

flip-flop

ADVANTAGE & LIMITATIONADVANTAGE;Lower power dissipation and generally

greater energy efficiency.Low operating voltages compatible with

batteries of only a few cells

LIMITATION;Silicon transistors can age and failSensitivity to radiation and cosmic rays