Download Mpps V12 Software 2015 21
Tensioner for Bodenwoogle BDM100 2015. blackhorseimpex. Related links .1. Field of the Invention
The present invention relates to a semiconductor memory device, and more particularly, to a static random access memory (hereinafter, referred to as an “SRAM”) which is suitably used for a cache memory of a computer system.
2. Description of the Background Art
In recent years, in the computer industry, an SRAM has been employed for a cache memory in order to improve a data access speed. Since the speed of the SRAM is not as high as that of a DRAM, the SRAM uses a high resistance layer, instead of a capacitor, as a storage node in which information is stored. However, in the high resistance layer, the amount of charges which are stored in the node is decreased depending upon the leak current. In this case, when the SRAM is activated, the level of the potential of the high resistance layer which is the storage node is decreased. That is, since the leakage current is increased, the information stored in the high resistance layer of the storage node is lost before the SRAM is accessed.
In order to solve such a problem, a technique is proposed in which a PN junction diode is formed in a vicinity of a high resistance node of an SRAM in Japanese Patent Application Laid-Open No. 2-147838. When this technique is used, it is possible to make the level of the potential of the storage node larger than that in the SRAM which does not employ the diode. In addition, since the charge stored in the storage node can be increased, the power source voltage can be decreased. However, the leakage current from the storage node to a bit line is increased by the forward voltage of the diode in this technique. That is, even if the leakage current from the storage node to the bit line is decreased, a large power loss is generated when the SRAM is accessed.
In order to decrease the power loss, it is also proposed in Japanese Patent Application Laid-Open No. 1-306920 to use a diode-connected transistor as the transistor of the SRAM. In this technique, since a channel region of the transistor is formed below a junction portion of a first electrode of the diode and a collector region, the leakage current is increased when an electric potential of a node is increased. That is, the leakage current is increased since