[ask] Difference between standard MOSFET and RF MOSFET

[ktx2222]

Hi everyone,
I would like to ask a question about fabrication technique: what is the difference between standard MOSFET and RF MOSFET? I also looked at a thread in our forum:
https://www.edaboard.com/threads/59398/
However, I cannot fully understand. So I make new thread.

In 1st pdk which supports RF devices, RF MOS layout has body contacts surrounded the MOS (for both with/without deep N-well versions) and the layout clearly shows where is drain/source terminal. While the standard MOS does not. So I think it may have different doping technique between RF MOS and standard MOS?
And if those MOS are used the same doping technique, in 2nd pdk (which does not support RF devices), can I put body contacts surrounding standard MOS (very similar to layout of RF MOS in 1st pdk) for my RF circuit?
Please help me. Thank in advanced.

 

[erikl]

... if those MOS are used the same doping technique, in 2nd pdk (which does not support RF devices), can I put body contacts surrounding standard MOS (very similar to layout of RF MOS in 1st pdk) for my RF circuit?

A lot of body contacts surrounding standard MOS doesn't harm at all - in contrary: it's a good layout method. The only disadvantage is more area consumption, that's why most designers are content with body contacts close to or surrounding the source(s), which normally is sufficient, at least for low current MOSFETs.

 

[dick_freebird]

RF MOSFETs (integrated) tend to design / constrain the
gate width because Rg is a key term in fmax. You will see
short stubby fingers, heavier silicidation, maybe even a
"muffin top" gate structure.

The heavily contacted body ring is for noise control, to
keep busy body activity out of the substrate as far as
practical.

RF LDMOS, discretes, play games with field plates that
can be unlike power LDMOS. Tying the field plate between
gate and drain to the source, relieves the Miller capacitance
(D-G) trading it for less-frequency-limiting, but less-drain-
resistance-reducing gate field plate structure. Since the
usual system is 50 ohms, or maybe impedance transformed
down to single-digit ohms, DC Ron is not as big a deal for the
RF guys while ultimate frequency and efficiency @ operating
frequency, are.