Thin film magnetic memory device including memory cells having a magnetic tunnel junction

Abstract

In the data read operation, a memory cell and a dummy memory cell are respectively coupled to two bit lines of a selected bit line pair, and a data read current is supplied thereto. In the selected memory cell column, a read gate drives the respective voltages on a read data bus pair, according to the respective voltages on the bit lines. A data read circuit amplifies the voltage difference between the read data buses so as to output read data. The use of the read gate enables the read data buses to be disconnected from a data read current path. As a result, respective voltage changes on the bit lines are rapidly produced, whereby the data read speed can be increased.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a thin film magnetic memory device. More particularly, the present invention relates to a random access memory (RAM) including memory cells having a magnetic tunnel junction (MTJ). [0003] 2. Description of the Background Art [0004] An MRAM (Magnetic Random Access Memory) device has attracted attention as a memory device capable of non-volatile data storage with low power consumption. The MRAM device is a memory device that stores data in a non-volatile manner using a plurality of thin film magnetic elements formed in a semiconductor integrated circuit and is capable of random access to each thin film magnetic element. [0005] In particular, recent announcement shows that significant progress in performance of the MRAM device is achieved by using thin film magnetic elements having a magnetic tunnel junction (MTJ) as memory cells. The MRAM device including memory cells having a magnetic...

AI Technical Summary

Benefits of technology

"The present invention relates to a thin film magnetic memory device with improved data write speed, reliability, and reduced power consumption. The invention includes a memory array with magnetic memory cells arranged in rows and columns, first and second bit lines, write word lines, and a coupling circuit. The invention also includes a normal operation mode and a test mode for compensating for manufacturing variation in magnetic characteristics. The invention further includes a memory array with a plurality of bit lines, write word lines, and a coupling circuit for reducing power consumption and improving operation reliability. The invention also includes a memory array with a plurality of sub write word lines for reducing data write current and magnetic field noise. Overall, the invention provides a thin film magnetic memory device with improved performance and reliability."

Problems solved by technology

This voltage change cannot be quickly produced with a large RC (resistance-capacitance) time constant of the sense current path, making it impossible to increase the data read operation speed.

As a result, the MTJ memory cell having such characteristics is extremely susceptible to the magnetic noise.

Electromigration may cause disconnection or short-circuit of the wirings, thereby possibly degrading the operation reliability of the MRAM device.

Moreover, an increased data write current may possibly produce a considerable amount of magnetic noise.

As described in connection with FIGS. 87 and 88, a large number of wirings are required to write and read the data to and from the MTJ memory cell, making it difficult to reduce the area of the memory array integrating the MTJ memory cells, and thus the chip area of the MRAM device.

This causes a voltage drop on these lines.

As a result, a current may unexpectedly flow through the MTJ memory cell, causing an erroneous data write operation.

Thus, the conventional MTJ memory cell using the access diode is advantageous in terms of improved integration, but is problematic in view of the stability of the data write operation.

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