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How does these effect the performance of short channel and long channel?

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syeda amna

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hi
how these effect the performance of short channel and long channel?
body effect, velocity saturation channel length modulation, hot carrier, cmos latch up effect.
which effect is more prominent in short channel and why?
 

Braski

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Re: short channel effets

the channel length modulation, which is valid also for long channels, is very relevant in short channel MOSTs. In the simple parabolic equation, the lambda coefficient is inversely proportional to L, so for very short transistors the drain current increment with Vds is decisively relevant.
Body effect is not a phenomena involved only in short, but in all type of MOS.
Velocity saturation is off course another important effect, which decreases the effective mobility of the transistor. It depends on the technology, like the other effects. Hot carrier phenomena occur especially for high VDS, over 2 V.
There is another effect, namely DIBL (drain induced barrier lowering), which is not easy to take into account with simple modelling.

However, the channel length modulation is very relevant, and quite easy to take into account.
 

syeda amna

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Re: short channel effets

thanks for your reply. what will be the effect of these papmeters on device operation?
what is effect on switching?
where we prefer short channel devices and why?
on what factors Vt is dependant?
 

yadavvlsi

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Re: short channel effets

Hot carriers tunnels in gate oxide and cause degradation of device characteristics in long term usage. Hot carries increases gate leakage current. Hot carries caught in gate insulator can change threshold voltage also in long term.

Due to Channel Length Modulation drain current does not remains constant in saturation region. It increase linearly in saturation with change in Vds.

Carriers drift velocity increases with increase in applied voltage. Velocity saturation drift velocity increase no more with increase in applied voltage limiting device switching speed.

Latch up cause significant increase in power consumption , in worst case it can spoil devices also.

Speed of transistor depends on how fast it can switch ON/OFF. A transistor with shorter channel can switch ON fast because time requires to reach carriers from source to drain is less.

Threshold voltage depends upon:
1. Gate material
2. Gate insulator martial
3. Gate insulator thickness
4. Channel dopping
5. Impurities at Silicon-Insulator interface
6. Voltage between source and substrate
7. Temperature
 
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