Impatt Diode

IMPATT DIODE

“Be A Diode To Remove Negative Thinking”

GROUP MEMBERS

SALEEM SHAHID FA07-BET-143

MUHAMMAD MAJID FA07-BET-098

MUHAMMAD RIZWAN FA07-BET-104

OVERVIEW

PHYSICAL STRUCTURE

PRINCIPLE OF OPERATION

APPLICATIONS

PERFORMANCE

DIFFERENCE BETWEEN IMPATT AND ORDINARY DIODE

IMPATTThe word IMPATT stands for IMPact Avalanche Transit Time

The IMPATT diode is an RF semiconductor device that is used for generating microwave radio frequency signals

Mostly used in high-frequency electronics and microwave devices

Form of high power diode

PHYSICAL STRUCTUREp+nin structure

a) Avalanche Region or injection region

b) Drift Region

PHYSICAL STRUCTUREN-type layer is around one or two microns thick.

The intrinsic layer between 3 and 20 microns.

At High frequencies intrinsic will be more thinner.

For Fabrication we use silicon, gallium arsenide, germanium and indium phosphide.

Mounted in microwave packets to ensure that performance is not impaired by substandard packages.

CLASSIFICATIONTypes of Impatt diodes are:-

1. Single drift region (SDR)

2. Double drift region (DDR)

3. Double avalanche region (DAR)

Intentionally Left Blank

PRINCIPLE OF OPERATIONImpact ionization of atoms

Avalanche multiplication of electrons

Transit time effect

PRINCIPLE OF OPERATIONThe Avalanche or Injection RegionRegion with relatively high doping and high field, Avalanche multiplication occurs here

Drift RegionRegion with essentially intrinsic doping and constant field where the carriers move across the diode taking a certain amount of time dependent upon its thickness

PRINCIPLE OF OPERATIONThe IMPATT diode is operated under reverse bias conditions (No current flows ideally)

Current flows due to breakdown caused by avalanche multiplication of electrons

The electric field at the p-n junction is very high because the voltage appears across a very narrow gap creating a high potential gradient

PRINCIPLE OF OPERATIONAn AC voltage superimposed on the dc is applied

If sufficient then free electron liberate an electron from the covalent bond this process can cascade (avalanche) very quickly into chain reaction producing a number of electrons

Impact avalanche

PRINCIPLE OF OPERATIONAvalanche region introduces a 90o phase shift between the ac signal and the electron concentration in this region

Length of the drift region equal to the wavelength of the signal then additional phase shift of 90o between the ac voltage and the diode current

ADVANTAGE

High Power Capability

Negative Resistance

DISADVANTAGEHigh input voltageHigh level of phase noiseLess efficiency (40%)

Noise - Microwave Devices

0.05.0

10.015.0

20.025.030.035.0

Bip

ola

r

ME

SF

ET

TU

NN

EL

TE

D I

nP

TE

D

Ga

As

BA

RIT

T

IMP

AT

T

Devices

Noise Figurein dB

Intentionally Left Blank

IMPATT I-V Characteristics

0 T/2 T 3T/2 2T 5T/2 Iinj

t0 T/2 T 3T/2 2T 5T/2

VDC

V

t

vAC

rAC<0

PAC=IV

COMPARISONImpatt is designed for high power applications whereas, a diode burns (heat-up) at high power

Impatt is operated at reverse bias whereas a diode is normally operated at forward bias because at reverse bias there is high voltage drop

APPLICATIONSIMPATT diodes are ideal where small cost effective microwave radio sources are needed

The main application for IMPATT diodes is in microwave generators

Used in high-frequency electronics and microwave devices

APPLICATIONSBest performance at frequencies extending into the mm-wave range

The negative resistance property of IMPATT diode can be used in oscillator

The stable region of operation can be used to amplify the RF signals

IMPATT diodes give more output power

APPLICATIONSLow power RADAR transmitters may use an IMPATT diode as a power source

They can be fabricated with Si, GaAs, and InP

Used in a variety of applications from low power radar systems to alarms, radios

APPLICATIONSIt is also used in applications where phase noise performance is unlikely to be of importance

THANK YOU FOR YOUR PATIENCE!!