ESD resistor question

esd resistor

Hi all,

I have a question about resistor for ESD.

when MOSFET gate is directly connected to PAD,
I can use resistor between PAD & gate for protect ESD damage.

and then, what kind of resistor is suitable for that case??
poly resistor or diffusion resistor?

someone says poly resistor is better because poly layer is higher than other layer,
And others says diffusion resistor is better.......

Anyone tell me clearly please.

Thanks in advance.

Regards.

esd protection resistor

I have saw a layout with ESD resistor of diffusion.
But I do not know why.


Best regards.

esd resistors

diffusion is better, if you use poly ,layout it as dogbone.

resistor esd

No one resistor never protect your circuit against ESD. To protect your circuit dedicated device with snapback action or circuit (e.g. rail based ESD protection with central RC-timed clamp).
Resistors in ESD protection usually used for ballast purpose to sustain excess voltage. In this case diff. resistor have better current capability than poly resitor, but sometimes it's hard to use it.

ggnmos + esd + resistor

Thanks all!

According to your answers, Diff. resistor looks better. thanks for your answer.

But, why diff. resistor is better????
anyone tell me why more cleary please?

and, DenisMark, of course I used npn type & scr type ESD protection circuit at all pins. I want to use resistor for excess voltage & current as you says.

Thanks, Regards.

resistor question

From Alan Hastings "Art of analog layout":

"...Diffused resistors are more robust than poly resistors because they dissipate a portion of their energy through a distributed avalanche mechanism, so many authors suggest using them instead of poly resistors..."

how soft connecting resistor to gate helps in esd

Of course diff. resitors can dissipate more that poly. resistors and so more current capable. Another property of diff. resistor is nonlinear behavour of resistance at high electric field across one. Due to velocity saturation current becomes independent from voltage (resistance increased) up to thermal breakdown. This is current limit function, limititing current depends from impurity concentration and width of resistor.
This property often is used to improve properties of ESD protection, e.g. to move Vt2 point higher than Vt1 if initially it lower.

how soft connecting resistor helps in esd

For protecting a CMOS gate, the resistor could be either diffusion or poly, but if you use poly it's recommended to make them at least 8 to 10um wide and they also should have at least 6 to 8 contacts at each end in order to prevent excessive local heating. Also, you must avoid have any bends.

resistor esd

Thanks a lot All!!!!

Regards.

resistor esd rating

bluesmaster said:

diffusion is better, if you use poly ,layout it as dogbone.

Click to expand...

agree this.
both resisters can, layout must be carefully.

esd and resistors

The purpose of using a resistor between PAD and gate of the mosfet is to introduce a “soft-ground” and allow for RC-coupling of the physical element associated with the resistor, the mosfet drain to gate capacitance (e.g. overlap capacitance). So, I think both diff. res. or poly res. or N-well res. are all right, but one thing is important, you should estimate the value of the parasitic capacitance and then determine the value of the resistor.

Added after 2 minutes:

And can you tell me how to determine your resistor value and have you solved the problem?

poly resistor for esd purpose

I think the resistor is limiting the current, so , it dosen't matter to use any type of resistor. But diff resistor can dissipate some ESD energy.

proper resistance for esd protection

I think there is no difference between them. because its purpose is to provide a Voltage when there a current flow through it. I use the poly resistor but you should pay attention the width of it. because there will be a very current about 1A.
So the width of it should more than 10um usually.

the value of it can be set between 100Ω to 300Ω.

poly resistor and diffusion resistor in esd

jecyhale said:

I think there is no difference between them. because its purpose is to provide a Voltage when there a current flow through it. I use the poly resistor but you should pay attention the width of it. because there will be a very current about 1A.
So the width of it should more than 10um usually.

the value of it can be set between 100Ω to 300Ω.

Click to expand...

i don't think there is lots of current flowing through the resistor contacted between the GND and the gate of GGNMOS (as ESD protection device)

dog bone resistor picture

i think there's no difference. i have seen plenty of designs using poly res. poly res are easier to fab.

series resistors esd

Thanks for the answer of jecyhale.
you said width of poly res. is more than 10um..

But I had been used poly res. of 3um (0.5um process) & it can sustain over 1500V at measurement.

Am I missing something??

Regards.

resistorquestion

prcken said:

jecyhale said:

I think there is no difference between them. because its purpose is to provide a Voltage when there a current flow through it. I use the poly resistor but you should pay attention the width of it. because there will be a very current about 1A.
So the width of it should more than 10um usually.

the value of it can be set between 100Ω to 300Ω.

Click to expand...

i don't think there is lots of current flowing through the resistor contacted between the GND and the gate of GGNMOS (as ESD protection device)

Click to expand...

Hi, Prcken

Is there a Resistor connected between the GND and the gate of GGNMOS for ESD application?
I haven't used this structure. Usually, I only use the GGNMOS connected to GND and the resistor just connect the pad and the gate of input MOS.

resistor esd damage

how much current does the secondary ESD device have to carry?
1 mA, 10 mA, 100 mA , or even more?
Anybody knows?

resistor for esd

Hi wjmqyyzj

The secondary protection robustness level is not fixed. You will have to define the right current capability together with the value of the resistance and the primary ESD approach.

I guess your design team will provide a maximum value for the resistance in order to reduce the influence on the normal operation. Most foundries recommend a 100-200 ohm resistance. I like to think of the secondary protection as a way to increase the maximum voltage at the pad during ESD such that there is more voltage margin for the primary ESD concept. This way the primary concept is depending less on the amount of bus resistance, diode size and trigger voltage.

Conclusion: It is up to you to you to determine the amount of current flows through the secondary stage within constraints provided by the design (max R) and the voltage drop over the primary path.

Regarding the discussion between 'jecyhale' and 'prcken' it seems there is a misunderstanding:
- prcken is talking about a resistance between gate and source that designers typically use to reduce the Vt1 trigger voltage of a ggNMOS ESD protection.
- The rest of the discussion is related to a resistance placed between gate and IO pad.
--> see picture to clearly see the difference between both.
Of course you can use both together!

ES

Re: resistorquestion

jecyhale said:

prcken said:

jecyhale said:

I think there is no difference between them. because its purpose is to provide a Voltage when there a current flow through it. I use the poly resistor but you should pay attention the width of it. because there will be a very current about 1A.
So the width of it should more than 10um usually.

the value of it can be set between 100Ω to 300Ω.

Click to expand...

i don't think there is lots of current flowing through the resistor contacted between the GND and the gate of GGNMOS (as ESD protection device)

Click to expand...

Hi, Prcken

Is there a Resistor connected between the GND and the gate of GGNMOS for ESD application?
I haven't used this structure. Usually, I only use the GGNMOS connected to GND and the resistor just connect the pad and the gate of input MOS.

Click to expand...

hey, sorry for the late response.
i forgot why i talked about the resistor between the gate and source
anyway, ES has clarified everything