Analysis of Thermal Variation of DRAM Retention Time

Abstract

Variation of DRAM retention time induced by thermal stress was investigated. Thermal activation energies (Ea) of sub-threshold leakage, junction leakage and GIDL (Gate Induced Drain Leakage) current of a DRAM cell were measured using the test vehicles. The values were compared with E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> of 1/tREF for the DRAM cell of which the retention time had been varied after a thermal stress. E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> of 1/tREF for the thermally degraded DRAM cell was in the range of that for GIDL current, while Ea for the normal DRAM cells with high retention time was in the range of E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> for junction leakage. It is insisted that the thermal degradation of retention time is induced by increase in GIDL current. The contributions of gate oxide/substrate interface states to the GIDL current are discussed