Semiconductor storage device

Abstract

A level shift element adjusting a voltage level at the time of selection of a word line according to fluctuations in threshold voltage of a memory cell transistor is arranged for each word line. This level shift element lowers a driver power supply voltage, and transmits the level-shifted voltage onto a selected word line. The level shift element can be replaced with a pull-down element for pulling down the word line voltage according to the threshold voltage level of the memory cell transistor. In either case, the selected word line voltage level can be adjusted according to the fluctuations in threshold voltage of the memory cell transistor without using another power supply system. Thus, the power supply circuitry is not complicated, and it is possible to achieve a semiconductor memory device that can stably read and write data even with a low power supply voltage.

Description

technical field [0001] The present invention relates to a semiconductor memory device, and more particularly to a structure of a static semiconductor memory device capable of stably writing and reading data even under low-voltage operating conditions. Background technique [0002] With the advancement of miniaturization technology, after miniaturization of transistor elements, voltage scaling corresponding to miniaturization is required from the viewpoint of reliability of the elements and power consumption. However, with this miniaturization, the influence of manufacturing parameter fluctuations increases, and the threshold voltage variation of transistors (insulated gate field effect transistors: MOS transistors) constituting the memory cell increases, thereby reducing the operating margin. As a result, it is difficult to write and read data stably even at a low power supply voltage in a semiconductor memory device. [0003] Various proposals have been made for the purpos...

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Problems solved by technology

[0013] However, in the structure shown in this prior art document 1, the operating power supply voltage of the level conversion circuit is supplied from a system different from the power supply voltage of the memory cell, and the voltage level after the level shift is not affected by the threshold value of the memory cell. fixed voltage level of the voltage effect

Even in Patent Document 1, it is necessary to provide a power supply for level shifting in a system different from the memory cell power supply, and the configuration of the power supply system becomes complicated.

In addition, the potential of the selected word line is fixed, and it cannot flexibly cope with the dispersion of the threshold voltage of the memory cell transistor.

[0014] In addition, at the time of data writing, the selected word line is driven to a level higher than the potential of the memory cell power supply, and no consideration is given to the stability of the data of the non-selected memory cells connected to the selected row at the time of data writing.

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