large R value with polysilicon resistor

[taofeng]

polysilicon resistor contact contact resistance

hi,
Want to know which is a better way to implement a large value R (about 400K ohms) ? with one large size R or put a lot of small r in series ?

regards,

jeffrey

 

[JoannesPaulus]

It depends on the accuracy you need. It you have a lot of small resistors in series, the contact resistance might become a big contributor in the total resistance.

 

[malizevzek]

If you layout only one big resistor, the absolute error will be dominated from process variability. Of course, if you have a lot of smaller resistors in series, the contact resistances come into play as well. For high poly option is the contact resistance even higher.

 

[rillyxue]

i think , some r in series will be better, it is easy to layout.

 

[jecyhale]

hi,
Want to know which is a better way to implement a large value R (about 400K ohms) ? with one large size R or put a lot of small r in series ?

regards,

jeffrey

Ｉ　ｔｈｉｎｋ　ｉｔ　ｉｓ　ｂｅｔｔｅｒ　ｔｏ　ｐｕｔ　ｔｈｅｍ　ｉｎ　ｓｅｒｉｅｓ．

Ａｎｄ　ｕｓｕａｌｌｙ，　ｗｅ　ｌａｙｏｕｔ　ｔｈｅ　ｌａｒｇｅ　ｖａｌｕｅ　ｒｅｓｉｓｔｏｒ　ｔｏ　ａ　ｓｑｕａｒｅ．

 

[electronrancher]

You shouldn't use a very small resistor segment, but I expect your poly is about 2k per square. So make 20 resistors of 20k each. One example would be 40 micron length and 2 micron width if you want fairly accurate resistors. Or shrink it to the minimum width if you just want a divider and don't care about absolute value.

 

[ytliang]

Usually, resistors are laid out with segments of smaller resistors in series. I would think this gives a more accurate result

 

[mdcui]

poly resistors usually can not reach very big value, in our process, it is only ~20ohms/square, I am not sure what kind of process as electronrancher mentioned can achieve 2k/square poly resistance.
in our design, once we want big resistor, we use N-well resistor, not so accurate as poly resistor, but it has 1k~2kohm per square. check with your process information to see if you have that component available.

 

[ytliang]

poly resistors usually can not reach very big value, in our process, it is only ~20ohms/square, I am not sure what kind of process as electronrancher mentioned can achieve 2k/square poly resistance.

There are processes with high resistance poly resistors (2k/square, 1k/square). They are non-silicided, so they have higher resistance.