Gate-current injection and surface impact ionization in MOSFET's with a gate induced virtual drain

In this paper, gate current injection into the gate oxide of MOSFET's with a split-gate (virtual drain) structure is examined. The split-gate structure is commonly employed in flash EEPROM and CCD's. An important parameter characterizing the gate current injection is the ratio phi b/ phi i (where phi b is the effective energy barrier for electron injection into gate oxide, and phi i is the impact ionization energy). We present new experimental data of the ratio phi b/ phi i measured at relatively constant vertical and lateral electric fields. Using a novel triple-gate MOSFET, the vertical field, the lateral field, and the drain current of the MOSFET can be independently controlled using proper biases. The measured phi b/ phi i ranged from 2.6 to 3.2 depending on gate and drain biases, and gate geometry.