Nonvolatile semiconductor memory and its drive method

Abstract

The invention provides a NOR-type nonvolatile semiconductor memory that can inject electric charge into a charge accumulation layer through the use of an FN tunnel current without compromising an increase in the packing density of memory cells. The above problem is solved by a nonvolatile semiconductor memory in which nonvolatile semiconductor memory cells are arranged in a matrix, each nonvolatile semiconductor memory cell having an island semiconductor layer in which a drain diffusion layer formed in the upper part of the island semiconductor layer, a source diffusion layer formed in the lower part of the island semiconductor layer, a charge accumulation layer formed on a channel region of the side wall sandwiched between the drain diffusion layer and the source diffusion layer via a gate insulation film, and a control gate formed on the charge accumulation layer are formed. Further, bit lines connected to the drain diffusion layer are laid out in a column direction, control gate lines are laid out in a row direction, and source lines connected to the source diffusion layer are laid out in the column direction.

Description

technical field [0001] The invention relates to a nonvolatile semiconductor memory and a driving method thereof. Background technique [0002] In a NOR flash memory cell (memory cell) having a control gate and a charge storage layer, a MOS transistor structure is known in which hot electrons are used to inject charges into the charge storage layer (see, for example, Non-Patent Document 1). The difference in threshold voltage due to the difference in the charge storage state of the charge storage layer is stored as data "0" and "1". For example, in the case of an N-channel memory cell using a floating gate in the charge storage layer, charges are injected into the floating gate, a high voltage is applied to the control gate and the drain diffusion layer, and the source diffusion layer and semiconductor substrate ground. At this time, the energy of the electrons in the semiconductor substrate is increased by the voltage between the source and the drain, so that they overcome...

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Problems solved by technology

[0007] However, using figure 1 As shown in the equivalent circuit of the conventional NOR flash memory, it is difficult to use the FN tunneling current to inject charge into the charge storage layer of a selected memory cell.

This is because when a high voltage is applied to the control gate line, all the memory cells connected to the control gate line are turned on, and the source line is connected to all the memory cells connected to the control gate line, so all the bit lines are shorted

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