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 magnetic memory cells for retaining storage data written by an applied magnetic field; and
a dummy memory cell for generating a read reference voltage in data read operation, wherein
each of said magnetic memory cells and said dummy memory cell include
a magnetic storage portion having either a first electric resistance value or a second electric resistance value that is higher than said first electric resistance value depending on a level of said storage data, and
an access gate connected in series with said magnetic storage portion, and selectively turned ON, said thin film magnetic memory device further comprising:
a first data line that is electrically coupled to a magnetic memory cell selected from said plurality of magnetic memory cells in data read operation so that a data read current is supplied to said first data line;
a second data line that is electrically coupled to said dummy memory cell in data read operation so that a data read current equal to that of said first data line is supplied to said second data line;
a data read circuit for producing read data based on respective voltages on said first and second data lines; and
a resistance adding circuit for adding a third electric resistance in series with said first data line, said third electric resistance being smaller than a difference between said first and second electric resistance values, wherein
said magnetic storage portion in said dummy memory cell stores a data level corresponding to said second electric resistance value.
2. The thin film magnetic memory device according to claim 1 , wherein said resistance adding circuit includes a field effect transistor receiving a variable control voltage at its gate.