4: Nonideal Transistor Theory 1

Junction Leakage

• Reverse-biased p-n junctions have some leakage– Ordinary diode leakage– Band-to-band tunneling (BTBT)– Gate-induced drain leakage (GIDL)

n well

n+n+ n+p+p+p+

p substrate

15: Nonideal Transistors Slide 2

Junction Leakage• Reverse-biased p-n junctions have some

leakage

• Is depends on doping levels– And area and perimeter of diffusion regions– Typically < 1 fA/m2

e 1D

T

V

vD SI I

n well

n+n+ n+p+p+p+

p substrate

pn Junction Reverse-Bias CurrentDrain and source to well junctions are typically reversebiased, causing pn junction leakage current. A reverse-biaspn junction leakage (I1) has two main components: one isminority carrier diffusion/drift near the edge of the depletion region; the other is due to electron-hole pair generationin the depletion region of the reverse-biased junction .

For an MOS transistor, additional leakage can occur betweenthe drain and well junction from gated diode device action(overlap of the gate to the drain-well pn junctions) or carriergeneration in drain to well depletion regions with influenceof the gate on these current components.

pn junction reverse-bias leakage (IREV) is a function of junction area anddoping concentration.