Considering an NMOS transistor with separate body and source terminals, with the following voltages: Vd – 10V; Vg = Vs = 5V and Vb = 0V, why wouldn't it conduct?
Isn't the channel of electrons formed mainly because of the potential difference between the gate and the body?
Is the source voltage disturbing the channel?
Best Answer
The electrons come from the source, which is an N-doped region. This source quotes Chenming Hu's book "Modern Semiconductor Devices for Integrated Circuits":
I also ran across a (probably illegal) PDF copy of Ali Niknejad's book "Electromagnetics for High-Speed Analog and Digital Communication Circuits". I'm not going to link to it, but here's the relevant quotation from section 2.3 regarding MOS capacitors:
I redrew Figure 2.25 to illustrate what he's talking about. You can see how similar this is to a MOSFET:
In an NMOSFET, when \$V_S > V_B\$, you get a secondary effect called the body effect or the substrate bias effect. This effect acts to increase the threshold voltage. According to Wikipedia, the body is acting more like a second gate.