Magnetic random access memory

Details Magnetic random access memory Magnetic random access memory

2001-01-04

2002-09-03

Nguyen, Viet Q. (Department: 2818)

Static information storage and retrieval

Systems using particular element

Magnetic thin film

C365S173000, C365S225500, C365S232000, C365S097000, C365S099000

Reexamination Certificate

active

06445613

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic random access memory for magnetically storing information by utilizing a magnetic storage element. More specifically, the present invention relates to a structure of the magnetic random access memory, a method of accessing the magnetic random access memory and a method of manufacturing the magnetic random access memory.
2. Description of the Related Art
In recent years, a magnetic random access memory (MRAM) has vigorously been studied. The magnetic random access memory implies a nonvolatile memory for recording data by utilizing the magnetism of a magnetic storage element.
FIG. 1A
is a diagram of a memory cell
150
of the magnetic random access memory. The memory cell
150
is constituted by one magnetic storage element
151
and a metal oxide film semiconductor field effect transistor (MOSFET)
152
. A writing word line
154
for writing information to the magnetic storage element
151
is provided in the vicinity of the magnetic storage element
151
. The transistor
152
has a first electrode
152
-
1
connected to a reading word line
155
for reading information from the magnetic storage element
151
and has a second electrode
152
-
2
connected to the magnetic storage element
151
. A third electrode
152
-
3
of transistor
152
is grounded. Moreover, a bit line
153
is connected to the magnetic storage element
151
. The bit line
153
is utilized for writing information to the magnetic storage element
151
and reading the information from the magnetic storage element
151
. According to the above description, apparently, the memory cell
150
has such a structure that one magnetic storage element
151
is present for one reading word line
155
and one transistor
152
.
FIG. 1B
is a sectional view of the memory cell
150
. As shown, the magnetic storage element
151
, the bit line
153
and the writing word line
154
are stacked on the reading word line
155
or the transistor
152
. The magnetic storage element
151
is smaller than the transistor
152
. Therefore, the size of the memory cell
150
is determined by the size of the transistor
152
. Accordingly, if the size of the transistor
152
is reduced, a cell area is decreased correspondingly so that the degree of integration can be enhanced.
However, an enhancement in the degree of integration based on a reduction in the size of the transistor
152
also has limitations. In more detail, it is necessary to determine the resistance of the transistor
152
corresponding to the characteristic of a film depending on a GMR element or a TMR element to be used as the magnetic storage element
151
. However, the resistance of the transistor
152
also depends on a dimension thereof (condition 1). Furthermore, one transistor
152
is always present in one memory cell
150
(condition 2). Accordingly, the size and number of the transistors
152
which can be integrated into a chip having a constant area are considerably restricted according to the conditions 1 and 2. Therefore, it is impossible to obtain a memory having a small area, the small number of elements and a large capacity.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a magnetic random access memory in which the degree of integration of a memory is enhanced and the number of necessary components is small through the provision of a plurality of magnetic storage elements on a single transistor.
It is another object of the present invention to provide a method of writing information to the magnetic random access memory and a method of manufacturing the magnetic random access memory.
The present invention provides a magnetic random access memory comprising a plurality of magnetic storage elements for magnetically storing information, respectively, a plurality of bit lines connected to the magnetic storage elements, respectively, a plurality of writing word lines provided corresponding to the vicinity of the magnetic storage elements and utilized for applying magnetic field to write the information, respectively, and a switch including a first terminal and a second terminal, the first terminal being connected to a single reading word line to be utilized for determining whether current is caused to flow to the second terminal and the second terminal being connected to each of the magnetic storage elements. Consequently, the above-mentioned object can be achieved.
Preferably, the switch further include a third terminal which is different from both the first terminal and the second terminal and to which a predetermined voltage is applied, current flowing to the second terminal through the third terminal based on the voltage applied to the first terminal.
Preferably, the magnetic storage elements are laminated in a vertical direction to the switch.
Preferably, the writing word line is orthogonal to the bit line and the magnetic storage element is positioned between the writing word line and the bit line.
The present invention provides a method of writing information to a magnetic random access memory, comprising the steps of causing bit line writing current to flow to an object bit line corresponding to an object magnetic storage element, causing word line writing current to flow to an object writing word line corresponding to the object magnetic storage element, and changing a direction of magnetization of the object magnetic storage element into a direction corresponding to the information through the magnetic field generated by the bit line writing current and the word line writing current. Consequently, the above-mentioned object can be achieved.
Preferably, the method of writing information further comprises the step of causing current to flow to at least one bit line other than the object bit line.
Preferably, the current to flow to the at least one bit line has a smaller magnitude than that of the bit line writing current.
Preferably, at the step of causing current to flow to the at least one bit line, a direction of current flow is changed corresponding to a positional relationship between the at least one bit line and the object bit line.
Preferably, at the step of causing current to flow to the at least one bit line, the current is caused to flow in the same direction as the object bit line if the at least one bit line is positioned above the object bit line, and the current is caused to flow in a reverse direction to the object bit line if the at least one bit line is positioned below the object bit line.
Preferably, the information is recorded to represent an N-digit binary number by using the N magnetic storage elements.
The present invention provides a method of reading information from an object magnetic storage element, comprising the steps of applying a reading word line voltage to a single reading word line, causing bit line reading current to flow to an object bit line corresponding to the object magnetic storage element, detecting a terminal voltage of the object magnetic storage element, and deciding contents of the stored information based on the terminal voltage. Consequently, the above-mentioned object can be achieved.
Preferably, the method of reading information from the magnetic random access memory further comprises the steps of causing reference current to flow to a reference bit line different from the object bit line, detecting a reference terminal voltage of the magnetic storage element connected to the reference bit line, and deciding contents of the stored information based on the reference terminal voltage and the terminal voltage.
The present invention provides a method of manufacturing a magnetic random access memory, comprising the steps of (a) providing a substrate, (b) forming a single transistor including a first electrode, a second electrode and a third electrode on the substrate, the second electrode being conducted to the third electrode corresponding to a voltage to be applied to the first electrode, (c) forming a writing word line insulated from the single transistor, (d) forming a magn

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