impatt diode seminar

8/7/2019 Impatt Diode Seminar........

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IMPATT DiodeName:- Dheeraj D. Mor

Stream:- EIERoll: 10BEI0136


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IntroductionWhen the pn junction diode is reverse-biased, then current doesnot flow.However when the reverse voltage exceeds a certain value, the

junction breaks down and current flows with only slight increase of voltage. This breakdown is caused by avalanche multiplication of electrons and holes in the space charge region of the junction.The pn junction in the avalanche breakdown condition exhibitsnegative resistance characteristics in the microwave frequencyrange.Since the negative resistance is based upon avalanchemultiplication and transit-time effect of carriers, the device has beencalled the IMPATT (Impact Avalanche Transit-Time) Diode.


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Device StructureThe original suggestion for a microwave device employing

transit-time effect was made by W. T. Read andinvolved an n+-p-i-p+ structure such as that shown in

figure. This device operates by injecting carriers into thedrift region and is called an IMPATT diode.The device consists essentially of two regions:

1) the n+p region, at which avalanchemultiplication occurs, and

2) the i (essentially intrinsic) region, through whichgenerated holes must drift in moving to p+ contact.


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Principle of operation

| N D

- N A | 10 20

10 16

1012 x

E

x

realideal

Drift region

K A

~V(t)

p+ n +i n

Avalancheregion I(t)


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IMPATT diode

V(t)=V DC +v AC (t) E(t)=E DC + E AC (t) E DC E b

E(t) E AC (T/4)

x

E bn(x,t)

T=0

E(t)

x

E b E AC (T/2)=0

n(x,t)T=T/4

E(t)

x

E b

E AC (3T/4)n(x,t)

T=T/2

E(t)

x

E b

E AC (T)=0

n(x,t)T=3T/4

T =T/4


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IMPATT I-V Characteristics

0 T/2 T 3T/2 2T 5T/2Q inj

t 0 T/2 T 3T/2 2T 5T/2

I

t 0 T/2 T 3T/2 2T 5T/2

I DC

V DC

V

t

v AC

i AC

i AC ~-v AC r AC


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Classification Device structure is based on the doping profile. The three basic

types of Impatt diodes are:-1. Single drift region (SDR) - The SDR diode consists of a

single avalanche zone and a single drift zone with p+nn+ structure.2. Double drift region (DDR) A DDR diode has a p+pnn+structure that consist of two drift layers, one for electrons and other for holes on either side of the central avalanche zone.

3. Double avalanche region (DAR) The DAR diode has ap+nipn+ structure that consist of one drift zone sandwichedbetween two avalanche zones. The electrons and holes from thetwo junctions travel across the central i-region in oppositedirections and deliver power.


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ApplicationsThese diodes make excellent microwavegenerators for many applications like:-

1. Parametric amplifier,2. Parametric up converter,3. Parametric down converter,

4. Negative resistance parametricamplifier.


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SummarySummary

IMPATT stands for Impact Avalanche And TransitTime

Operates in reverse-breakdown (avalanche)

region Applied voltage causes momentary breakdown

once per cycle

This starts a pulse of current moving through thedevice Frequency depends on device thickness


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IMPact Ionization Transit Time IMPATT devices can be used for oscillator andamplifier applications

They can be fabricated with Si, GaAs, and InP

Can be used up 400 GHz. Noisy oscillator In general, IMPATTs have 10 dB higher AM

noise than that of Gunn diodes IMPATT diode is not suitable for use as a local

oscillator in a receiver.


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Thank YouThank You

impatt diode seminar

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