| 摘要 |
PURPOSE:To obtain a DRAM to show the constant life of a TDDB without depending on a process variation by a method wherein the operating point of a reference voltage generating circuit is set in such a way that a variation in a reference voltage to a variation in the gate oxide film thickness of a MOS transistor satisfies a specified relation. CONSTITUTION:In this DRAM, the operating point of a reference voltage generating circuit 1 is set in such a way that a variation Vref in a reference voltage Vref to a variation Tox in a gate oxide film thickness Tox of a MOS transistor satisfies the formula. Accordingly, a word line drive voltage VWL obtainable by multiplying a constant amplification factor to the voltage Vref is also proportional to the film thickness Tox. According to such a way, when the film thickness Tox is varied by a process variation, the voltage VWL is also varied in proportion to the variation. After all, an electric field which is applied to a gate oxide film is always kept constant without depending on the variation in the film thickness Tox. Accordingly, there is not the deterioration of a TDDB due to irregularity in the gate oxide film thickness. Moreover, a temperature variation can be also eliminated by specified conditions. |
