MEASUREMENTS AND MODELING OF MOSFET-IV CHARACTERISTICS WITH POLYSILICON DEPLETION EFFECT

We present the degradation of MOSFET current-voltage (I-V) characteris tics as a function of polysilicon gate concentration (N-p), oxide thic kness (t(ox)) and substrate impurity concentration (N-D) using measure d and modeled results. Experimentally it is found that for MOSFET's wi th thin gate oxide (t(ox) approximate to 70 Angstrom) and high substra te concentration (N-D approximate to 1.6 x 10(17) cm(-3)) the reductio n in the drain current I-DS can be as large as 10% to 20% for devices with insufficiently doped polysilicon gate (5 x 10(18) less than or eq ual to N-p less than or equal to 1.6 X 10(19) cm(-3)). Theoretically i t is shown that the drain current degradation becomes more pronounced as N-p decreases, or t(ox) decreases, or N-D increases. A modified Pao -Sah model that takes into account the polysilicon depletion effect an d an accurate gate field dependent mobility model is used to compute I -V characteristics for various values of N-p, t(ox), and N-D. Good agr eement between experimental and modeled results is observed over a wid e range of devices.