substrate or well contact

[p_shinde]

hi,
the substrate or well contact which is put in the transistor, ( p + is put for n transistor ....) now where is this p+ connected to ? to n diffusion or gate?

please let me know whats done in industry as till now in my diploma we used to connect this well contact to the gate.

waiting for reply.
Prasad

 

[truebs]

Usually substrate connection is connected to power supply, although this can vary , as this depends mainly on the circuit and its designer.
As far as i think it should not be connected to gate, i've not come across such a condition so far.
although you can connect it to source diffusion area...its also a common practice.

 

[pandit_vlsi]

yes truebs is correct.
i also used connect well or substrate to source&i never connected substrate to gate.
pandit

 

[jackson_peng]

substrate are negative biased in Digital and most Analog Circuit, which meas the p-substrate is connected to VSS, and n-substrate is connected to VDD.

however, this would could cause body effect when source are not connect to ground or supply.

 

[singu31]

You should not connect the substrate to gate. That is a bad idea. Usually they are connected to VDD or GND. But by varying the VSB( Source to body voltage) we can change the Threshold voltage of the device becos of the dependence of Vt on body effect. If VSB is not equal to zero there is a drop in the threshold voltage's nominal value becos of body effect.

 

[semi_jl]

I think there may be something wrong with the connection.

 

[ananish]

substrate connection should be connected to source not to the gate. this is done to reduce the body effect.

 

[Ikon]

Hi,

In CMOS we come across "LATCH-UP" . If this occurs then our ckt /transistor fails.
In order to avoid this latch up, the layout engineers use Substarte and well contacts.