Thin film magnetic memory device provided with a dummy cell for data read reference

A thin film magnetic memory device comprising:

• a plurality of memory cells each being configured to exhibit an electric resistance corresponding to a magnetization direction, and being magnetized in a direction corresponding to storage data;
• a dummy cell having a structure and a form similar to those of said memory cell, and being magnetized in advance in a direction corresponding to a predetermined level of said storage data;
• a first voltage line provided for said plurality of memory cells for transmitting a first predetermined voltage;
• a second voltage line provided corresponding to said dummy cell for transmitting a second predetermined voltage different from said first predetermined voltage;
• first and second data lines being electrically coupled to said first and second voltage lines via the selected memory cell among said plurality of memory cells and said dummy cell in a data read operation, respectively;
• and
• a data reading portion for performing data reading in accordance with a difference between passing currents of said first and second data lines, wherein
• said first and second predetermined voltages are determined such that the passing current of said dummy cell attains a level intermediate between two kinds of passing currents corresponding to respective levels of said storage data in said selected memory cell.

A thin film magnetic memory device comprising:

• a plurality of memory cells each having a magneto-resistance element configured to be magnetized in a direction corresponding to a level of storage data, and to have either a first or second electric resistance in accordance with the magnetization direction, and an access transistor connected in series to said magneto-resistance element and being selectively turned on in a data read operation;
• a dummy cell for comparing a passing current with that of the selected memory cell selected as an access target among said plurality of memory cells in said data read operation;
• first and second data lines electrically coupled to a fixed voltage via said selected memory cell and said dummy cell in the data read operation, respectively;
• and
• a data reading portion for performing data reading in accordance with a difference between passing currents of said first and second data lines, wherein
• said dummy cell includes:
• a dummy magneto-resistance element having a structure and a form similar to those of said magneto-resistance element, and being magnetized in advance to have a smaller one between said first and second electric resistances,
• a dummy access transistor connected in series to said dummy magneto-resistance element, being selectively turned on in the data read operation and being designed similarly to said access transistor, and
• a dummy resistance adding portion connected in series to said dummy magneto-resistance element, and having an electric resistance smaller than a difference between said first and second electric resistances;
• and
• said dummy resistance adding portion has at least one transistor designed similarly to said access transistor and having a gate supplied with an adjustable control voltage.