Magnetic random access memory

A magnetic random access memory comprising:

• memory cells which are connected to each other in parallel and store therein data by utilizing the magneto resistive effect;
• a bit line which is connected to one end of said memory cells and extends in a first direction;
• and
• a read circuit connected to said bit line,
• wherein resistance values of said memory cells are different from each other even if magnetizing states of said memory cells are the same, and each of said memory cells has MTJ layers including anti-ferromagnetic layers, ferromagnetic layers and cap insulator layers, and a number of said MTJ layers is different in accordance with said each memory cell.

A magnetic random access memory comprising:

• memory cells which are connected to each other in parallel and store therein data by utilizing the magneto resistive effect;
• a bit line which is connected to one end of said memory cells and extends in a first direction;
• and
• a read circuit connected to said bit line,
• wherein resistance values of said memory cells are different from each other even if magnetizing states of said memory cells are the same, and each of said memory cells includes anti-ferromagnetic layers, ferromagnetic layers, non-magnetic metal layers and cap insulator layers, and a number of said non-magnetic metal layers or said cap insulator layers is different in accordance with said each memory cell.

A magnetic random access memory comprising:

• memory cells which are connected to each other in series and store therein data by utilizing the magneto resistive effect;
• a bit line which is connected to one end of said memory cells and extends in a first direction;
• and
• a read circuit connected to said bit line,
• wherein each of said memory cells has cap insulator layers whose number is different in accordance with said each memory cell.

A magnetic random access memory comprising:

• memory cells which are connected to each other in parallel and store therein data by utilizing the magneto resistive effect;
• a bit line which is connected to one end of said memory cells and extends in a first direction;
• and
• a read circuit connected to said bit line,
• wherein each of said memory cells has cap insulator layers whose number is different in accordance with said each memory cell.

A read method of a magnetic random access memory, said magnetic random access memory having memory cells which store therein data by utilizing the magneto resistive effect, resistance values of said memory cells being different from each other, said read method comprising:

• passing a read current to said memory cells in the state that said memory cells are connected to each other in series;
• subjecting said read current or a read potential generated from said read current to analog/digital conversion;
• and
• judging data values of said memory cells based on data obtained from said analog/digital conversion.

A read method of a magnetic random access memory, said magnetic random access memory having memory cells which store therein data by utilizing the magneto resistive effect, resistance values of said memory cells being different from each other, said read method comprising:

• passing a read current to said memory cells in the state that said memory cells are connected to each other in parallel;
• subjecting said read current or a read potential generated from said read current to analog/digital conversion;
• and
• judging data values of said memory cells based on data obtained by said analog/digital conversion.

A read circuit of a magnetic random access 4 memory, said magnetic random access memory having memory cells which store therein data by utilizing the magneto resistive effect and are connected to each other in series, said read circuit comprising:

• a current source which supplies a read current to said memory cells;
• an analog/digital converter which compares said read current and reference currents or a read current generated from said read current with reference potentials;
• and
• a logic circuit which judges data values of said memory cells based on an output signal from said analog/digital converter.

A read circuit of a magnetic random access memory, said magnetic random access memory having memory cells which store therein data by utilizing the magneto resistive effect and are connected to each other in parallel, said read circuit comprising:

• a current source which supplies a read current to said memory cells;
• an analog/digital converter which compares said read current and reference currents or a read potential generated from said read current with reference potentials;
• and
• a logic circuit which judges data values of said memory cells based on an output signal from said analog/digital converter.

A manufacturing method of a magnetic random access memory comprising:

• forming a read selection switch in a surface area of a semiconductor substrate;
• forming a first write word line extending in a first direction on said read selection switch;
• forming a first MTJ element directly above said first write word line;
• forming a first write bit line extending in a second direction crossing said first direction directly above said first MTJ element;
• forming a second MTJ element directly above said first MTJ element;
• forming a second write word line extending in said first direction directly above said second MTJ element;
• forming a third MTJ element directly above said second MTJ element;
• forming a second write bit line extending in said second direction directly above said third MTJ element;
• forming a fourth MTJ element directly above said third MTJ element;
• forming a third write word line extending in said first direction directly above said fourth MTJ element;
• and
• forming a read bit line extending in said second direction above said fourth MTJ element.

A manufacturing method of a magnetic random ° access memory comprising:

• forming a read selection switch in a surface area of a semiconductor substrate;
• forming N (N is a plural number) write word lines extending in a first direction on said read selection switch;
• forming a lower electrode directly above said N write word lines;
• forming N MTJ elements which contact said lower electrode directly above said N write word lines;
• and
• forming a read bit line which contacts said N MTJ elements and extends in a second direction crossing said first direction,
• wherein said MTJ elements include a step of forming a non-magnetic metal layer and a step of selectively oxidizing said non-magnetic metal layer and determining an oxidized part as a cap insulator layer.