Thin film magnetic memory device having dummy cell

A thin film magnetic memory device, comprising:

• a plurality of memory cells arranged in rows and columns, each memory cell holding magnetically-written stored data;
• a plurality of read word lines provided corresponding to respective rows of said plurality of memory cells and selectively activated on data reading;
• and
• a plurality of first data lines provided corresponding to respective columns of said plurality of memory cells, each of said first data lines being selectively connected to a selected memory cell among said plurality of memory cells and receiving data read current on data reading;
• wherein each said memory cell includes
• a magneto-resistance element having one of a first electric resistance and a second electric resistance larger than said first electric resistance corresponding to said stored data, and
• an access element connected with said magneto-resistance element in series between corresponding first data line and a prescribed voltage, and turned on in response to activation of corresponding read word line, wherein
• each of said first and second electric resistances has a characteristic which changes corresponding to a voltage applied to opposite ends of said magneto-resistance element;
• said thin film magnetic memory device further comprising:
• a dummy cell designed to have an intermediate electric resistance between said first and second electric resistances;
• a second data line connected to said dummy cell to allow said data read current to pass therethrough on data reading;
• and
• a data read circuit generating read data based on a difference in passing currents between one of said plurality of first data lines and said second data line;
• wherein
• each said dummy cell includes a prescribed number of dummy cell units among a plurality of dummy cell units divided into a plurality of groups arranged along a column direction so as to share a memory cell row with said plurality of memory cells,
• each said dummy cell unit is arranged corresponding to a memory cell row so as to share said second data line,
• each said dummy cell unit has
• a first dummy magneto-resistance element connected between said second data line and an inner node, and
• a dummy access element turned on in response to activation of corresponding read word line and electrically couples said prescribed voltage and said first dummy magneto-resistance element, and
• said inner node is electrically coupled to each said inner node within another dummy cell unit belonging to the same group among said plurality of groups.