Flicker noise in PMOS VS NMOS

[ambreesh]

flicker noise nf

Why is the flicker noise in PMOS lesser than that in NMOS.
Is it for the reason that the holes in the PMOS move under a burried channel so they are farther from the oxide silicon junction. Or is their some other reason for it.

 

[bg21359]

nmos noise versus nmos noise

flicker noise mechanism is not understood well. The theory you mentioned is one possibility. This noise is very process dependent.

 

[ambreesh]

pmos nmos flicker noise

I read it in one of the books. It is also mentioned that flicker noise varies from technology to technology.
But is their a clear reason for NMOS to have worse flicker noise then PMOS.
I agree that flicker noise phenomenon is not well understood.
Correct me if i am wrong, to maintain the Vt we have channel implats so why should their be a difference in flicker noise of NMOS and PMOS

 

[vistapoint]

pmos vs nmos

Maybe just because PMOS has to be larger?

 

[hrkhari]

pmos flicker

Hi Guys:

I had done some simulations on the Noise Figure contribution of the circuitry due to flicker noise effect at around 100kHz, and there is a significant difference in the value of NF in comparison of utilizing PMOS and NMOS, where the value is lesser using PMOS architecture, but unable to figure out the reasons behind it. It is also quite evident that less current consumption results in better NF performance

Rgds

 

[ambreesh]

The NF values are going to be better for PMOS as the parameters we use have better value for PMOS compared to NMOS.

Tsividis in his book on MOS modelling has mentioned that MOS devices with same size, it is observed that PMOS has better performance compared to NMOS. So size could be counted out.
Also he mentions that for large Vgs PMOS and NMOS could have similar performance wrt flicker noise. Does the higher Vgs create more high-energy states in PMOS or is their something else to it.

What is the difference between normal P-Channel device and a Buried P-Channel device?

 

[bg21359]

I guess high Vgs causes high laternal electric field, which should helps electrons/holes travel along the channel with less possibility to be trapped.

I think a Buried P-Channel device has much deeper channel than does NMOS, which can smooth the flicker noise effect??

 

[ambreesh]

Dear bg21359,
A stronger VGS would imply by all means a stronger vertical feild.
And increase in VGS for PMOS deteriorates the noise performance.
I was tryoung to imply this in my previous responce.
Any idea what is the difference between simple and buried p channel transistors.
And presently industry uses simple pchannel or bried p-channel devices

 

[bg21359]

Yeah, you're right. The higher Vgs causes stronger vertical electric field. I read the paper by A. A. Abidi, it suggests that for PMOS, the flicker noise dependence on Vgs-Vth can apply to both surface-channel PMOS and buried-channel PMOS.
**broken link removed**

So it looks like no good theory to explain why high Vgs can cause larger flicker noise for surface-channel PMOS.

But for buried-channel PMOS, common theory is: because buried-channel is far away from Si-SiO2 surface, flicker noise is mainly due to mobility fluctuation(carrier interaction with lattice, I don't quite clear about this) which is kind of small; when Vgs becomes larger, it attracts lot of holes to the surfaces, which manifests the noise due to carrier-density fluctuation(carrier traped and released by the interface(Si-SiO2).

buried-channel PMOS is used to reduce Vth by adding a p-type implant to cancel the effect of ionized acceptor in substate.

 

[Karthikeya]

well,
the flicker noise in PMOS is less in comparison to NMOS bcoz of the mobility factor.....(µp < µn). Flicker noise is proportional to the mobility hence the diff. the expression is given in Tsividas and also i remember reading a similar thread in this forum sometime back so u can chk out there too...............

regards

 

[ambreesh]

Dear Karthikeya,
Both mobility and high energy state are contrbuting factor for flicker noise.
In nMOS mobility is not the factor contributing to flicker noise but the high energy states are. In PMOS case mobility is the major cause for fliker noise.
So how could we mix the two. And if one increases VGS why should the PMOS flicker noise behaviour nearly repilcate NMOS behaviour