Mitsubishi Denki Kabushiki Kaisha

Kazuya Ikeda

Nobuyuki Kokubo

In a memory cell region, there are formed a pair of driver transistors and a pair of access transistors. On an insulating layer covering these transistors, there are formed a pair of high resistances. To cover the high resistances, there is formed an insulating layer. On the insulating layer, there is formed a word line. To cover the word line, there is formed an insulating layer and, on the insulating layer, there are formed a GND wiring and bit lines. Thereby, a semiconductor memory device capable of stabilized operation even when a lowered power source voltage is used can be obtained.

Semiconductor memory device

A memory cell region is provided with a pair of driver transistors as well as a pair of access transistors. Each of the access transistors is formed of a field effect transistor having a gate electrode layer. An insulating layer is formed over the driver transistors and access transistors, and is provided with contact holes located within the memory cell region and reaching the gate electrode layers. Conductive layers are formed on the insulating layer, and are in contact with the gate electrode layers through the contact holes. Thereby, a memory cell structure of an SRAM has a small planar layout area and thus is suitable to high integration.

SRAM with small planar layout

A power supply voltage level detecting circuit includes a reference voltage generating circuit for generating a constant reference voltage independent of a power supply voltage, a to-be-compared voltage generating circuit for generating a voltage to be compared changing dependent upon the power supply voltage, a current mirror type differentially amplifying circuit for amplifying differentially the reference voltage and the voltage to be compared, and a determining circuit for generating a level detecting signal indicating whether or not the power supply voltage has attained a predetermined level in accordance with an output of the differentially amplifying circuit. The to-be-compared voltage generating circuit generates the voltage to be compared by dropping the power supply voltage using the resistance division or the forward voltage drop of diode. Since a signal corresponding to the power supply voltage level is provided from the differentially amplifying circuit, it is possible to detect the power supply voltage level reliably without being affected by variation of an input logic threshold voltage of an inverter circuit due to the manufacturing process.

Growing community of inventors

Hyogo, Japan

Kazuya Ikeda