Semiconductor memory device

Abstract

A semiconductor memory device according to an aspect of the invention includes plural writing word lines; first and second writing bit lines that intersect with the writing word lines; and plural memory cells that are provided at portions in which the plural writing word lines and the first and second writing bit lines intersect with each other. In the semiconductor memory device, the memory cell includes a flip-flop circuit that includes first and second nodes of a complementary pair; a first transfer transistor that is connected between the first writing bit line and the first node, a gate of the first transfer transistor being connected to the writing word line; and a second transfer transistor that is connected between the second writing bit line and the second node, a gate of the second transfer transistor being connected to the writing word line. The first and second writing bit lines are in a floating state whenever data is not written in the memory cell.

1 . A semiconductor memory device comprising:
 a plurality of word lines each of which includes a writing word line and a reading word line;   a plurality of bit lines each of which includes first and second writing bit lines and first and second reading bit lines, the first and second writing bit lines and the first and second reading bit lines intersecting with the plurality of word lines; and   a plurality of memory cells that are provided at portions in which the plurality of word lines and the plurality of bit lines intersect with each other,   wherein the memory cell includes:   a flip-flop circuit in which inputs and outputs of a first inverter and a second inverter are mutually connected, the first inverter including a first transistor of the first conduction type and a second transistor of the second conduction type, the first inverter being connected between a power supply line and a ground line, the second inverter including a third transistor of the first conduction type and a fourth transistor of the second conduction type, the second inverter being connected between the power supply line and the ground line;   a fifth transistor of the second conduction type that is connected between the output of the first inverter and the first writing bit line, a gate of the fifth transistor being connected to the writing word line;   a sixth transistor of the second conduction type that is connected between the output of the second inverter and the second writing bit line, a gate of the sixth transistor being connected to the writing word line;   a seventh transistor of the second conduction type that is connected between the output of the first inverter and the first reading bit line, agate of the seventh transistor being connected to the reading word line; and   an eighth transistor of the second conduction type that is connected between the output of the second inverter and the second reading bit line, a gate of the eighth transistor being connected to the reading word line, and   the first and second writing bit lines are in a floating state whenever data is not written in the memory cell.   
     
     
         2 . The semiconductor memory device according to  claim 1 , wherein thresholds of the fifth and sixth transistors are lower than thresholds of the second and fourth transistors. 
     
     
         3 . The semiconductor memory device according to  claim 1 , wherein one of the first and second writing bit lines is a power supply potential and the other is a ground potential during data write. 
     
     
         4 . The semiconductor memory device according to  claim 1 , wherein the writing word line is divided into a plurality of unit writing word lines, and
 data is written in the predetermined memory cell connected to the selected unit writing word line during data write.