Punchthrough

)M9?r.HE4iA I"J0As to BJT,an emitter-to-collector breakdown which can occur in a junction transistor with very narrow base region at sufficiently high collector voltage when the space-charge layer extends completely across the base region.

2^;?pF"bqE0For MOS，the drain current of a MOS transistor will increase in some cases in which a parasitic current path exists between drain and source. This part of the drain current is poorly controlled by the gate contact since the current path is located deeper in the bulk, farther away from the gate. It adds to the subthreshold leakage current leading to an increased power consumption. Therefore, punchthrough should be avoided whenever possible.

Punch through in a MOSFET is an extreme case of channel length modulation where the depletion layers around the drain and source regions merge into a single depletion region. The field underneath the gate then becomes strongly dependent on the drain-source voltage, as is the drain current. Punch through causes a rapidly increasing current with increasing drain-source voltage. This effect is undesirable as it increases the output conductance and limits the maximum operating voltage of the deviceEDA中国门户网站@ _'G0A@#?vKx