why we need dummy resistors

[jaylin]

Hi guys,

Can anybody tell me why we need dummy resistors?

If I want to well-match R0 R1, and R0, R1 should be some matched to R3. Which way is better:
(a) dummy R3 R0 R1 dummy
(b) R3 dummy R0 R1 dummy


Regards

 

[pph_cq]

I will choose a.
It isn't necessary to put dummy between R3 and R0. R3 is the dummy for R0 and R1.

 

[yorande]

Dummies are to provide similar operating enviroment for devices.
In the manufacture process, there are some variations of mask and echings.
Then the length or width u draw for a resistor or so may varies, even for the same one.
I guess it could be called of some kind of internal mismatch of devices.

 

[flatulent]

30 years ago it was standard practice to put dummy resistors at the outside of resistor networks. These were there to produce the doping gas turbulence before it reached the real resistors.

 

[vbhupendra]

dummy are used to not to allow overetching and give sam environmental condition.

 

[vijay.kumarreddy]

Mainly dummies are placed to create same environment and to prtect the main resistor devices from the u nder and over etching processes in the manufacturing steps.The dummy should of the same width of the original devise and spacing also should be same as that of the internal strip spacing.

Example:

If u have res of W=3um and Number of strips =4 strips, spacing =0.3um.Then u need to place a single strip dummy resistor of 3 um width on the both sides .otherwise u can place a ring type dummy called etch guard(follow the same spacing and width). Dont forgot to connect it to ground in both the cases.
Better use first option as u specified.

regards
vijay