NONVOLATILE SEMICONDUCTOR MEMORY

摘要

PURPOSE:To enable the memory of low writing voltage to be obtained by providing an impurity region of reverse conductivity type to that of a substrate under a floating gate. CONSTITUTION:An N<+> type source region 2 and an N<+> type drain region 3 are formed in the P type Si substrate 1. A selective gate electrode 7 is formed in a channel region 11 in contact with the region 2. The floating gate electrode 6 is formed above the region 3 and above the channel region 12 adjacent to the region 3 and electrically isolated by an oxide film 10. In this construction, an N type impurity region 14 is provided under the electrode 6. Providing this region 14 enables sufficient reduction in surface potential of the region 12 to the neighborhood of the potential of the region 3 even by an increase in impurity concentration of the substrate 1. Therefore, the variation of surface potential from the region 11 to the region 12 becomes very steep and comes close to the drain- source voltage. This intensifies the acceleration field and shortens the acceleration region; therefore, the write by a low drain voltage is enabled.