Magneto-resistive memory with shared wordline and sense line

Details Magneto-resistive memory with shared wordline and sense line Magneto-resistive memory with shared wordline and sense line

2000-08-14

2002-03-26

Ho, Hoai V. (Department: 2818)

Static information storage and retrieval

Systems using particular element

Magnetoresistive

C365S171000

Reexamination Certificate

active

06363007

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to the field of magneto-resistive memory devices, and more particularly, to methods and apparatus for writing such magneto-resistive memory devices.
Digital memories of various kinds are used extensively in computer and computer system components, digital processing systems and the like. Such memories can be formed, to considerable advantage, based on the storage of digital bits as alternative states of magnetization of magnetic materials in each memory element, typically thin-film materials. These films may be thin magneto-resistive films having information stored therein based on the direction of the magnetization vector occurring in those films. The information is typically obtained either by inductive sensing to determine the magnetization state, or by magneto-resistive sensing of each state.
Such thin-film magneto-resistive memories may be conveniently provided on the surface of a monolithic integrated circuit to thereby provide easy electrical interconnection between the memory elements and the memory operating circuitry on the monolithic integrated circuit. When so provided, it is desirable to reduce the size and increase the packing density of the thin-film magneto-resistive memory elements to achieve a significant density of stored digital bits.
Many thin-film magneto-resistive memories include a number of parallel word lines intersected by a number of parallel digital lines. A thin magneto-resistive film or magneto-resistive bit is provided at the intersection of each word line and digital line. As such, the thin-film magneto-resistive memory elements are typically configured in an array configuration having a number of rows and a number of columns.
FIG. 1
is a schematic diagram illustrating a conventional thin-film Magnetic Random Access Memory (MRAM) architecture. Parallel word lines
12
,
14
, and
16
are provided in a vertical direction and parallel digital lines
18
a
-
18
h
are provided in a horizontal direction. Only a portion of the MRAM array is shown in
FIG. 1. A
thin-film magneto-resistive memory element or magneto-resistive bit is provided at the intersection of each word line and digital line. For example, and referring specifically to
FIG. 1
, thin-film magneto-resistive bits
28
a
,
28
b
, and
28
c
are provided at the intersection of digital line
18
a
and word lines
12
,
14
, and
16
, respectively.
The thin-film magneto-resistive bits in each row are typically connected in a string configuration to form a corresponding sense line. For example, thin-film magneto-resistive bits
28
a
,
28
b
, and
28
c
, which correspond to row
32
, are connected in a string configuration to form sense line
34
a
. Sense line
34
a
typically includes a umber of non-magnetic connectors, such as non-magnetic connector
36
, to connect each end of the thin-film magneto-resistive bits to the end of the adjacent thin-film magneto-resistive bits. The non-magnetic connectors are typically formed using a conventional metal interconnect layer. The sense lines are used to provide current to a particular row of thin-film magneto-resistive bits, and ultimately, to sense the resistance of a selected one of the bits.
To write a value (i.e., zero or one) to a selected magneto-resistive bit, a word line current is provided to the word line that passes adjacent to selected magneto-resistive bit. Likewise, a digital line current is provided to the digital line that passes adjacent to selected magneto-resistive bit. Depending on the selectivity of the memory, a sense line current may also be provided to the sense line that includes the selected magneto-resistive bit.
The polarity of the word line current typically determines the value that is written to the selected magneto-resistive bit. To illustrate this further, the magnetic fields produced by a word line current
40
, a digital line current
42
and a sense line current
44
at magneto-resistive bit
28
a
are shown in
FIG. 2
, assuming digital line
18
a
and word line
12
extend above magneto-resistive bit
28
a
. The polarity of the various currents would of course change if the corresponding word line or digital line extend below the magneto-resistive bit
28
a.
The magnetic field H
wl
48
produced by word line current
40
extends to the right along the major axis of the magneto-resistive bit
28
a
as shown. The magnetic field Hd
50
produced by digital line current
18
a
extends downward along the minor axis of the magneto-resistive bit
28
a
. Finally, the magnetic field H
sl
52
produced by sense line current
44
also extends downward along the minor axis of the magneto-resistive bit
28
a
.
The magnetic field H
wl
48
produced by word line current
40
provides the longitudinal force to switch the magnetization vector of the selected magneto-resistive bit from left to right, which in the example shown, corresponds to the desired value to be written to the magneto-resistive bit
28
a
. The magnetic field H
dl
50
produced by digital line current
42
provides the lateral torque that is necessary to initiate the switching of the magnetic vector of the selected magneto-resistive bit
28
a
. In some cases, the magnetic field H
sl
52
may also be provided to provide additional lateral torque.
For many applications, it is beneficial to write an entire word of data to selected magneto-resistive bits during a single write cycle. This can be accomplished by organizing the magneto-resistive bits into a number of words. For example, and referring back to
FIG. 1
, each word of data may correspond to a corresponding row of magneto-resistive bits, such as row
32
. One such word is shown at
60
. While word
60
is shown including all magneto-resistive bits
28
a
,
28
b
and
28
c
in row
32
, it is contemplated that word
60
may in some cases only include a subset of the magneto-resistive bits in row
32
, such as the first “n” magneto-resistive bits of row
32
.
In another configuration, each word of data may correspond to a column of magneto-resistive bits, such as column
70
. One such word is shown at
72
. Again, while word
72
is shown including all magneto-resistive bits
28
a
,
62
a
,
62
b
,
62
c
,
62
d
,
62
e
,
62
f
, and
62
g
in column
70
, it is contemplated that word
72
may in some cases only include a subset of the magneto-resistive bits in column
70
, such as the first “n” magneto-resistive bits of column
72
.
When each word of data corresponds to a row or portion of a row of magneto-resistive bits, the digital lines
18
a
-
18
h
and/or sense lines
34
a
-
34
h
can be used to select a particular word during a write operation. This is often accomplished by decoding a write address
80
via decoder and control block
82
, and passing a current down a selected digital line and/or sense line. For example, to select the magneto-resistive bits in row
32
, decoder and control block
82
may pass a current down digital line
18
a
and/or sense line
34
a
. The remaining digital lines
18
b
-
18
h
and/or sense lines
34
b
-
34
h
may remain deactivated to prevent the magneto-resistive bits in deselected rows from being written.
Once the appropriate digital line
18
a
and/or sense line
34
a
is activated, decode and control block
82
may provide a word line current to all of the word lines that are associated with the magneto-resistive bits of the selected word. In the example shown in
FIG. 1
, this includes word lines
12
,
14
and
16
. The polarity of the word line current for each word line typically depends on the data state to be written to the corresponding magneto-resistive bit. In one example, if the first five bits of word
60
are to be written to a zero state, the word line current provided to the first five word lines may be in a first direction. Likewise, if the last three bits of word
60
are to be written to a one state, the word line current provided to the last three word lines may be in the opposite direction. Once the word line currents are activated for a sufficient period of time to write the correspondin

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