Manufacturing method for variable resistive element
View Patent ↗In the case where a variable resistive element, which is made of a variable resistor provided between a first and second electrodes, and of which the electrical resistance varies by applying a voltage pulse between the two electrodes, is applied to a resistance nonvolatile memory, there is a range of the resistance value of the variable resistive element in a low resistance state where the nonvolatile memory can operate normally. In the conventional manufacturing method the resistance value of the variable resistive element is too low, therefore, it can not be controlled within a desired range of the resistance value. A step of carrying out of a reduction process is provided at any point after the step of forming a variable resistor material as a film, it has thereby become possible to increase the resistance value of the variable resistive element, which is too low in the conventional method.
1. A manufacturing method for a variable resistive element comprising a variable resistor comprising a variable resistor material provided between a first electrode comprising a first electrode material and a second electrode comprising a second electrode material, the electrical resistance of the variable resistor being variable between a low resistance value and a high resistance value by applying a voltage pulse between the first electrode and the second electrode, said method comprising:
carrying out a reduction process on the variable resistor so that the electrical resistance of the variable resistor is increased; wherein
carrying out the reduction process comprises carrying out a heat treatment at low temperatures never exceeding 350° C. in a reduction atmosphere including hydrogen, and
carrying out the heat treatment comprises providing a material operating as a hydrogen catalyst, and
the variable resistor comprises an oxide having a perovskite structure which is represented by any one of the following general formulas:
Pr 1-X Ca X [Mn 1-Z M Z ]O 3 , wherein M is any element selected from Ta, Ti, Cu, Cr, Co, Fe, Ni and Ga,
La 1-X AE X MnO 3 , wherein AE is any bivalent alkaline earth metal selected from Ca, Sr, Pb and Ba,
RE 1-X Sr X MnO 3 , wherein RE is any trivalent rare earth element selected from Sm, La, Pr, Nd, Gd and Dy,
La 1-X Co X [Mn 1-Z Co Z ]O 3 ,
Gd 1-X Ca X MnO 3 , and
Nd 1-X Gd X MnO 3 , wherein 0<X<1, 0≦Z<1.
2. The manufacturing method according to claim 1 , wherein a reduction reaction is induced using hydrogen in atom form in carrying out the reduction process on the variable resistor.
3. The manufacturing method according to claim 1 , wherein at least either the first electrode or the second electrode comprises the material operating as a hydrogen catalyst.
4. The manufacturing method according to claim 1 including simultaneously carrying out heat treatment on a first semiconductor substrate having at least the variable resistor and a second semiconductor substrate having a material operating as the hydrogen catalyst on its surface in the reduction atmosphere including hydrogen.
5. The manufacturing method according to claim 1 , wherein the material operating as a hydrogen catalyst includes at least one metal atom selected from Ru, Rh, Pd, Ag, Os, Ir, Pt, Au, Mg, Ni, Cr, W and Ta.
6. The manufacturing method according to claim 1 , wherein the variable resistor comprises an oxide having a perovskite structure which includes at least one element selected from Pr, Ca, La, Sr, Gd, Nd, Bi, Ba, Y, Ce, Pb, Sm and Dy, and at least one type of element selected from Ta, Ti, Cu, Mn, Cr, Co, Fe, Ni and Ga.
7. The manufacturing method according to claim 1 , wherein the second electrode includes at least one material from single precious metals in the platinum group metals, alloys of which the base is a precious metal in the platinum group metals, oxide conductors comprising a metal selected from Ir, Ru, Re and Os, and oxide conductors selected from strontium ruthenium oxide (SRO), lanthanum strontium cobalt oxide (LSCO) and yttrium barium copper oxide (YBCO).
8. The manufacturing method according to claim 1 , wherein the first electrode includes at least one material from precious metals in the platinum group metals, single metals selected from Ag, Al, Cu, Ni, Ti and Ta or alloys of these, oxide conductors comprising a metal selected from Ir, Ru, Re and Os, and oxide conductors selected from strontium ruthenium oxide (SRO), lanthanum strontium cobalt oxide (LSCO) and yttrium barium copper oxide (YBCO).
9. The manufacturing method according to claim 1 including controlling a resistance value at low resistance state of the electrical resistance between the first electrode and the second electrode by adjusting at least one of temperature, hydrogen concentration, and processing time in the heat treatment carried out in the reduction atmosphere including hydrogen.
10. The manufacturing method according to claim 1 , wherein the heat treatment is carried out for about 1 min.
11. The manufacturing method according to claim 1 , wherein the method includes:
(1) forming a film from said second electrode material, (2) forming a film from said variable resistor material, and (3) forming a film from said first electrode material, in the order of (1), (2) and (3);
etching the film formed from the first electrode material to form the first electrode, etching the film formed from the variable resistor material to form the variable resistor; and then
carrying out the reduction process; and
etching the film formed from the second electrode material to form the second electrode.