Thin film magnetic memory device capable of conducting stable data read and write operations
View Patent ↗A tunnel magnetic resistive element forming a magnetic memory cell includes a fixed magnetic layer having a fixed magnetic field of a fixed direction, a free magnetic layer magnetized by an applied magnetic field, and a tunnel barrier that is an insulator film provided between the fixed and free magnetic layers in a tunnel junction region. In the free magnetic layer, a region corresponding to an easy axis region having characteristics desirable as a memory cell is used as the tunnel junction region. A hard axis region having characteristics undesirable as a memory cell is not used as a portion of the tunnel magnetic resistive element.
1. A thin film magnetic memory device, comprising:
a plurality of memory cells for storing data, wherein
each of said memory cells includes
an access gate selectively turned ON in data read operation, and
a magnetic storage portion connected in series with said access gate, and having either a first electric resistance or a second electric resistance higher than said first electric resistance depending on the stored data, and
said thin film magnetic memory device further comprising:
a data line that is electrically coupled to a selected memory cell through a turned-ON access gate of said selected memory cell in said data read operation, said selected memory cell being a memory cell selected from said plurality of memory cells for said data read operation;
a reference data line for transmitting in said data read operation a read reference voltage for comparison with a voltage on said data line; and
a plurality of dummy memory cells for producing said read reference voltage, wherein
each of said dummy memory cells includes
a dummy access gate selectively turned ON in said data read operation,
a plurality of dummy magnetic storage portions that are electrically coupled to said reference data line in response to turning-ON of said dummy access gate, and
a dummy resistance gate made of a field effect transistor, and wherein an electric resistance of said plurality of dummy magnetic storage portions is equal to said first electric resistance, and said dummy access gate in an ON state has an electric resistance that is equal to that of said access gate in an ON state, and said dummy resistance gate has a third electric resistance, said third electric resistance being smaller than a difference between said first and second electric resistance.
2. The thin film magnetic memory device according to claim 1 , wherein said field effect transistor has a gate receiving an adjustable control voltage.
3. The thin film magnetic memory device according to claim 1 , wherein, in normal data write operation, data is written to at least one of said dummy magnetic storage portions in parallel with said magnetic storage portion in a memory cell selected from said plurality of memory cells for said data write operation.
4. The thin film magnetic memory device according to claim 1 , further comprising a test mode for writing prescribed data to each of said dummy memory cells, said test mode being conducted independently of normal operation, wherein data is written to at least one of said dummy magnetic storage portions in said test mode.