48
W. C. Law and S. De W. Wong
Table 1 Overview of key performance indicators for existing stand-alone memory technologies.
Key strengths are shaded in green, while limiting factors are shaded in orange or red [10, 11, 12]
Types
Features
Mature Memory Technologies
Emerging Memory Technologies
SRAM DRAM
Flash
PCM
RRAM
FeRAM
MRAM
Non-volatile
No
No
Yes
Yes
Yes
Yes
Yes
Endurance
(# of cycles)
10
16
10
16
10
5
10
8
10
6
10
10 -10
14
>10
15
Read Speed
(ns)
1 - 100
30
50
20 – 50
10
20 - 80
2 - 20
Write Speed
(ns)
5 - 10
10
10
4
75
5 – 20
50
2 - 20
Write Power
Low
Low
Very
High
Medium
Low
Low
Low to
Medium
Cell Size (F
2 )
50 -
120
6 - 10
4
6 – 12
6 – 12
15 - 34
6 - 12
Scalability
Limited Limited
Yes
Yes
Yes
Under
Research
Yes
2 History
The emergence of modern spintronic devices originates from the independent
discovery of giant magnetoresistance (GMR) effect by Albert Fert and Peter Grünberg in 1988 [13, 14]. We will cover the magnetoresistance effect in greater detail in
Sect. 3.1. For now, one may simply consider that the directions of the magnetization
can result in a difference in spin-dependent scattering rate, thereby resulting in a
change of resistance states, which is defined as GMR =
R AP −R P
R P
, where R AP and R P
refers to the resistance of the GMR device when the two magnetization states are in
the antiparallel and parallel states, respectively.
The term GMR was coined due to enhanced effect as compared to anisotropic
magnetoresistance (AMR) and has been extensively employed in a various applications, such as magnetic field sensors and hard disk drive read heads in the form of
spin valve structures [15, 16, 17, 18, 19]. The spin valve stack is considered as the
early concept of MTJ, consisting of two magnetic layers sandwiching a metallic
layer (typically copper), in which an electron current can flow either along the
electrodes (Current In-Plane/CIP) or perpendicular through the electrodes (Current
Perpendicular to Plane/CPP).
Nonetheless, interest within the community was momentarily piqued, as the
concept was still plagued with numerous challenges such as achieving observable
effects at room temperature as well as low throughput since molecular beam epitaxy
is used in sample fabrication. In 1990, Parkin et al. were able to demonstrate large
GMR in sputtered multilayers, which greatly ease the manufacturing of GMR-based
read sensor [20]. As such, spin valves have begun to take over as read head sensors in
hard disk drive applications that require a low resistance-area (RA) product despite
W. C. Law and S. De W. Wong
Table 1 Overview of key performance indicators for existing stand-alone memory technologies.
Key strengths are shaded in green, while limiting factors are shaded in orange or red [10, 11, 12]
Types
Features
Mature Memory Technologies
Emerging Memory Technologies
SRAM DRAM
Flash
PCM
RRAM
FeRAM
MRAM
Non-volatile
No
No
Yes
Yes
Yes
Yes
Yes
Endurance
(# of cycles)
10
16
10
16
10
5
10
8
10
6
10
10 -10
14
>10
15
Read Speed
(ns)
1 - 100
30
50
20 – 50
10
20 - 80
2 - 20
Write Speed
(ns)
5 - 10
10
10
4
75
5 – 20
50
2 - 20
Write Power
Low
Low
Very
High
Medium
Low
Low
Low to
Medium
Cell Size (F
2 )
50 -
120
6 - 10
4
6 – 12
6 – 12
15 - 34
6 - 12
Scalability
Limited Limited
Yes
Yes
Yes
Under
Research
Yes
2 History
The emergence of modern spintronic devices originates from the independent
discovery of giant magnetoresistance (GMR) effect by Albert Fert and Peter Grünberg in 1988 [13, 14]. We will cover the magnetoresistance effect in greater detail in
Sect. 3.1. For now, one may simply consider that the directions of the magnetization
can result in a difference in spin-dependent scattering rate, thereby resulting in a
change of resistance states, which is defined as GMR =
R AP −R P
R P
, where R AP and R P
refers to the resistance of the GMR device when the two magnetization states are in
the antiparallel and parallel states, respectively.
The term GMR was coined due to enhanced effect as compared to anisotropic
magnetoresistance (AMR) and has been extensively employed in a various applications, such as magnetic field sensors and hard disk drive read heads in the form of
spin valve structures [15, 16, 17, 18, 19]. The spin valve stack is considered as the
early concept of MTJ, consisting of two magnetic layers sandwiching a metallic
layer (typically copper), in which an electron current can flow either along the
electrodes (Current In-Plane/CIP) or perpendicular through the electrodes (Current
Perpendicular to Plane/CPP).
Nonetheless, interest within the community was momentarily piqued, as the
concept was still plagued with numerous challenges such as achieving observable
effects at room temperature as well as low throughput since molecular beam epitaxy
is used in sample fabrication. In 1990, Parkin et al. were able to demonstrate large
GMR in sputtered multilayers, which greatly ease the manufacturing of GMR-based
read sensor [20]. As such, spin valves have begun to take over as read head sensors in
hard disk drive applications that require a low resistance-area (RA) product despite