One big problem with "zero-VT" MOSFETs is that they are
probably the most poorly controlled of any, in a given PDK.
They suffer the most influence from uncontrolled factors,
being the lightest-doped.
Another practical matter is, if you like to say that VT is
roughly where a one-square device runs 1uA IDsat, then
you have 1uA leakage through it with Vgs=0 - give or
take at least a decade, due to problem #1. If you are
trying to do a nanopower energy harvester (like RFID)
with micropower waste terms, go directly to FAIL, do not
pass Go, do not collect $200.
Zero-VT devices' light (or nil) channel doping fails to push
field back against the LDD effectively, so they break down
lower and leak more than the same-L VT-implanted FET.
They have worse lambda as well for the same reason.
The only reason you find them in PDKs is that you can
"run them hotter" for the same available gate drive, in
RF applications. 50-ohm guys don't care about microamps
of DC leakage (or DC attributes much, at all). But I don't
think this is your case.
And in my little, long-past RFID dabbling and later charge
pump designs, I found the best answer, for a compromise
between forward inefficiency and leak-back inefficiency,
was the "mid-VT" devices I had available, at 200-350mV
VT (between the "0" (that is, -150 - +150mV) and "regular"
(600-700mV) devices, which would lose everything they
gained, and gain nothing at low amplitudes respectively.
Q-boosting with a resonant tank is something you might
be able to take advantage of. But nonetheless, you need
the best balance of forward and slosh-back terms and I
have not seen the zero-VT FET be that.
Fewer technologies have the mid-VT device, or have it
in your sweet spot. But they're worth seeking out.