Leakage current characteristics of offset-gate-structure polycrystalline-Silicon MOSFET's

Leakage current characteristics of offset-gate-structure polycrystalline-silicon (poly-Si) MOSFET's are studied as a function of dopant concentration N
off
in offset-gate regions. Leakage current markedly decreases from 1 × 10
^-9
to 2 × 10
^-11
A at V
D
= 10 V as N
off
is varied from 1 × 10
¹⁸
to 1 × 10
¹⁷
cm
^-3
. A maximum ON/OFF current ratio of 10
⁸
is obtained at 1 × 10
¹⁷
cm
^-3
. Calculations based on a quasi-two-dimensional model indicate that the reduction of leakage current is attributable to a decrease of the maximum lateral electric field strength in the drain depletion region. An analysis of the leakage current characteristics in terms of carrier emission from grain-boundary traps implies that thermonic emission accompanied by thermally assisted tunneling could be the dominant mechanism in determining leakage current.