MOS Capacitor, MOSFET and BJT

Syllabus: BJT, MOS capacitor, MOSFET.

8 hand-picked visual resources on this topic — under each card, look for See it. Every link is checked against the live site before it ships.

MOS capacitor regimes

Sweeping the gate takes a p-type MOS capacitor through accumulation, depletion and inversion. Once in strong inversion the depletion width stops growing and extra gate charge goes into the inversion layer.

$\Delta Q_{inv}=C_{ox}\Delta V_G$
in strong inversion; surface potential is pinned
$C_{ox}=\frac{\varepsilon_{ox}}{t_{ox}}$
$W_{dep}\ \text{saturates at }V_G>V_T$

See it

MOSFET regions

Below threshold the device is off; above it, whether it is linear or saturated depends on $V_{DS}$ against the overdrive.

$V_{DS}<V_{GS}-V_T:\ I_D=\mu C_{ox}\frac{W}{L}\left[(V_{GS}-V_T)V_{DS}-\frac{V_{DS}^{2}}{2}\right]$

BJT in forward active

Emitter is the most heavily doped region, base the most lightly doped and physically thin — that is what makes $\beta$ large. The Early effect gives the finite output slope.

$I_C=\beta I_B,\qquad I_E=(\beta+1)I_B$

← P-N Junction and Diodes

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