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P+ poly resistor layout, current density and max current applied

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AfiqahRS

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Hi guys,

I have a circuit with maximum current of 20mA. I am using a p+ poly resistor to the circuit with estimated layout size 1.5umx12um with sheet resistance 400ohm/sq.

From one of the book it is written that
p+ poly resistor 150ohm/mm2, max current 0.65mA/mm2.


How can I relate the maximum current applied to the circuit, current density and layout size of this p+ poly resistor? Will the layout of the p+ poly resistor able to sustained the max current of 20mA?

Thanks
 

Those "book's" units look wrong to me. Ohms per square
sheet resistance is dimensionless. Current should be per
micron of width and there should also be an areal power
density (W/mm2, W/um2, W/mil2) for reliable not-fusing
(heavily margined up) and reliable will-fuse (if you are
allowed to use poly fuses).

I don't know what relation the "book" has to your foundry
and their reliability position on such things - which is who
you want to listen to.
 

AfiqahRS said:
I have a circuit with maximum current of 20mA. I am using a p+ poly resistor to the circuit with estimated layout size 1.5umx12um with sheet resistance 400ohm/sq.
Click to expand...

So your poly resistor is 12µm/1.5µm = 8 squares long. R = 400Ω/sq.*8sq. = 3.2kΩ . V = 20mA * 3.2kΩ = 64V .
Resistor area related power P = I2*R/(W*L) = 1.28W/18µm2 = 71 mW/µm2 .

Width related current density = 20mA/1.5µm = 13mA/µm (max. recommended = 1mA/µm) .

If polysilicon thickness is e.g. 0.2µm (0.18µm process), then the (area related) current density is J = I/A = 20mA/(1.5µm*0.2µm) = 6.7·104 A/m2 , which is many (more than 7) decades below the polysilicon (fast) fuse blow limit (1012 A/m2).
 

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