Regarding Low Vth transistors in 180nm CMOS Technology

[cs.gautam]

I am designing RFID tags. I want to use low Vth MOS transistors in my design.
I need 50mV Vth. Which Technology is suitable for my design.
What do you think about Zero Vt transistor in UMC 180nm CMOS technology.

With Regards,

CS Gautam

 

[erikl]

What do you think about Zero Vt transistor in UMC 180nm CMOS technology.

The pb. is you either need

• another std. Vth series transistor, or
• a small negative bias (a few 100mV)

... to actually cut it off (if this is required). Using the RF energy you should be able to additionally create such a small neg. bias. In this case, the usage of zero Vt ("native") transistors is perfect.

 

[cs.gautam]

Dear erikil,

Thanks for your reply. But i am not getting your point.
Could you explain in more detail?
There are many options in order to select technology (like TSMC, UMC, XFAB, AMS).
I have selected UMC 180nm RF CMOS. Is it ok. my application needs communication distance more than 10m.

 

[erikl]

... i am not getting your point.

You asked

What do you think about Zero Vt transistor ...?

... and I told you what I think about them.

Could you explain in more detail?

Sure, if you ask a detailed question!

 

[dick_freebird]

Zero-VT (low-VT) devices are fine for anything that doesn't
need to turn off. Like RF amps. Point is that your circuit has
to work at negligible standby power so you also need the
high (normal) VT devices. Generally the 0-VT device is just
an add-on (or "don't forbid") option to a regular CMOS flow.

Low-VT devices tend to be poorer for high drain voltage
as they exhibit more DIBL and GIDL (leakage goes up the
more you drive the gate below VT, after a point). And as
they are poorly controlled and application-interest-limited,
their DC modeling can be given less than complete attention
by the foundry and have some detail surprises left.

 

[ic98]

be aware that in a standard/twin-well process you can change the threshold voltage of the MOS devices according to bulk-source voltage (especially in short-channel devices).