does the SKY130 process support depletion-mode fet...
# sky130p
proppy
02/14/2022, 1:35 AMdoes the SKY130 process support depletion-mode fet?
h
Harald Pretl
02/14/2022, 11:08 AMThere is an NMOS NVT available which has a Vth ~ 0V (not exactly what you are looking for but close). There is no MOS-FET available with a negative Vth (NMOS) and positive Vth (PMOS), respectively.
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proppy
02/14/2022, 11:40 AMneat, is that
sky130_fd_pr__nfet_05v0_nvtproppy
02/14/2022, 11:42 AMI didn't realize there was something between the enhanced and depleted variant.
proppy
02/14/2022, 11:51 AMthe cross section doesn't look that different from a regular FET
proppy
02/14/2022, 11:51 AMis the only difference in the size?
proppy
02/14/2022, 11:52 AMoh it doesn't have that
Vt adjust implantsproppy
02/14/2022, 11:53 AMthat makes sense if the only difference is the Vt 🙂
proppy
02/14/2022, 11:53 AMimage.png
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Harald Pretl
02/14/2022, 12:07 PMExactly, the difference is the channel implant (under the gate). This influences the Vth. The “natural Vth” (NVT) sit without additional implant in the well/substrate.
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proppy
02/14/2022, 12:24 PMDoes it trigger on Vg >= Vs or 0 <= Vg <= Vs ?
proppy
02/14/2022, 12:24 PM(I assumed the former, but I wasn't 100% clear after reading https://en.wikipedia.org/wiki/Native_transistor)
proppy
02/14/2022, 12:30 PMactually https://en.wikipedia.org/wiki/Threshold_voltage#Basic_principles makes it all clear 🙂
h
Harald Pretl
02/14/2022, 1:03 PMThanks for Wiki link on the native MOS-FET, didn’t know that one exists 🙂
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proppy
02/14/2022, 1:10 PMthose wikipedia pages are suprisingly good (and accessible!)
proppy
02/14/2022, 1:11 PMI tried to simulate the native fet in an inverter circuit https://gist.github.com/proppy/dd2352e210b58e6c4b0c9deb84aef579 but it looks a bit weird (i.e the voltage doesn't go back to 0)
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