TSMC - Photodiode - (in image sensor)

[e245]

Hello,

which cell I should use as a photodiode in a tsmc18rf Library?

all the TSMC diodes:
dio_dnwpsub, dio_pwdnw, dioden, dioden3v, diodenw, diodenw3v, diodep, diodep3v

I need to draw its layout too. I worry about LVS too. :sad: (application: Image Sensor)

Thank you,

Best Regards

 

[erikl]

As I don't know the junction depth of these diodes, I just can advice to don't take a deeply lying diode like, probably, dio_dnwpsub, if your photodiode should also detect blue light.

Drawing its correspondent layout shouldn't be too difficult, and if your extraction rule set is fine, also the LVS should run without problems, because you (hopefully) have all the views.

 

[e245]

thanks erikl.
the first and the 2nd one haven't layout counterpart in the library (only have schematic).
but the other-ones have both schematic and layout in the library.
I think it means that these two groups are not the same. this increase my doubt.
Could you give me any ideas?

 

[erikl]

Could you give me any ideas?

I think dio_dnwpsub, dio_pwdnw, and - guessing from their names - probably also diodenw, diodenw3v are parasitic diodes with deeply lying junctions, which you usually don't want to create intentionally. The others - dioden & diodep and their 3V counterparts probably are near-surface n⁺p (in substrate) or p⁺n (in n-well) diodes which are well appropriate for photo diodes. You can make a layout up to your required dimensions. Reading your PDK - and the DRC - will help you.

Which one you want to use depends on design considerations and voltage requirement. The n⁺p in substrate diode has its anode inevitably connected to GND, whereas the p⁺n in n-well diode is free for connection of both nodes, but involves a larger parasitic cap.

In any case I'd recommend the 3V version because of its wider depletion region, and hence better light efficiency (at least for fast light activity like movie application).

 

[e245]

I can not find good words to describe how your message help me from deep and dark worry.

Another expert, proposed me diodenw3V.

What do you think? which one I should choose and why? (diodenw3V or dioden3V)

I really thank you.

 

[erikl]

Another expert, proposed me diodenw3V.

What do you think? which one I should choose and why? (diodenw3V or dioden3V)

I really can't tell you, because I don't know their layouts. But if diodenw3V is a p⁺n 3V-diode in n-well, it surely would be a good choice.

Why? Both nodes are uncommitted, it's a near-surface diode with a 3V depletion region, hence good light absorption characteristic.

 

[e245]

I understood. Thank you erikl!