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Giant Magneto-Resistive Switches & Spin Torque Transfer Switches
friendly critic analysis
ERD "Beyond CMOS" Technology Maturity Evaluation Workshop
San Francisco, CaliforniaJuly 12, 2008
Eli YablonovitchUC Berkeley
Electrical Engineering & Computer Sciences Dept.
Si (001) Substrate
Ta 5nm
Ru 50nm
Ta 5nm
NiFe 5nm
Antiferromagnetic MnIr 8nm
CoFe 2nm
Ru 0.8nm
Ferromagnetic CoFeB 3nm
MgO 1.5nm Tunnel Barrier
Ferromagnetic CoFeB 3nm
Ta 5nm
Transpinnor Structure:
Ru 15nm
6:1 Resistance Change inTunnel Magnetoresistive (TMR)
stack[1]
Current Gate
Isignal
Magnetization
Drain
Source
InsulatorCurrent Gate
Drain
Source
Isignal
[1] Ikeda et. al., Japanese Journal of Applied Physics, Vol. 44, No 48, pp. L1442-L1445
BField
BField
Device Area 1μm2
Gate
5μA output5μA input
Complementary Transpinnor Logic
500Ωor
2.275kΩ
2.275kΩor
500Ω
+V +3mV
-V -3mV
Output Power = 1.6*10-8 WTotal Power = 2.5*10-8 W
Efficiency=65%
80
Efficiency for Complementary Transpinnor Circuit
100
90
70
60
50
40
30
20
10
010 100 1000 100001
On/Off Ratio
Efficiency (%)
Best On/Off ratio today, 4.5:1
NAND Gate:
input A
+
output
input B
Transpinnor Logic Example
-
NOR Gate:
+
input A
input Boutput
Transpinnor Logic Example
-
Si (001) Substrate
Ta 5nm
Ru 50nm
Ta 5nm
NiFe 5nm
Antiferromagnetic MnIr 8nm
CoFe 2nm
Ru 0.8nm
Ferromagnetic CoFeB 3nm
MgO 1.5nm Tunnel Barrier
Ferromagnetic CoFeB 3nm
Ta 5nm
Transpinnor Structure:
Ru 15nm
6:1 Resistance Change inTunnel Magnetoresistive (TMR)
stack[1]
Current Gate
Isignal
Magnetization
Drain
Source
InsulatorCurrent Gate
Drain
Source
Isignal
[1] Ikeda et. al., Japanese Journal of Applied Physics, Vol. 44, No 48, pp. L1442-L1445
BField
BField
Device Area 1μm2
Gate
Isignal
InsulatorCurrent Gate
BField
BField
What is the minimum current required for switching?
10nm=10-8m
Ampere's Law: H = J 2r H = I
H needs to be at least H=1 Oersted to switch a GMR deviceequivalent to B=10-4Tesla
(private communication from Stuart Parkin of IBM)(This is equivalent to saying the best relative magnetic permeability is =104
to generate and effective B=1Tesla)
I =2r H = 2r (B/o) = 2r 10-4/(4 10-7) and take r=10nm
I = 10-8 10-4/(2 10-7) Amps
I = 5 Amps are required for switching!This is really pretty good, but required very optimistic assumptions!
l
Repeater Repeater Repeaterl l
a
RC time = (clock period) /2
2R,Resistance
a
l
lorCe,Capacitanc
2
2
2
RC timeRC
a
l
a
loror
cm102F/cm102
sec10
2
periodclock612
10
o
ra
l
4800
a
laspect ratio
of wire
Physics of Wires:
<V2> = 4kT R f
Vsignal = 0.56 milli-Volts
200045
1024800
4800R,Resistance
6
2
nm
cm
aa
l
aa
l
a
lal rr ooCe,Capacitanc
4800
a
laspect ratio
of wire
<I2> = 4(kT/R) f
Isignal = 0.25 Amps
C = r o a 4800
C 7 femto-Farads
Isignal
InsulatorCurrent Gate
BField
BField
What is the minimum current required for switching?
10nm=10-8m
I = 5Amps are required for switching!This is really pretty good, but required very optimistic assumptions!
According to the previous slide, operation at 1micro-Amp implies a good noise margin ~ 48kT.
Operation at 5Amps implies 1200kT per bit function, which is at least 100 better than today's technology,
and might be worth pursuing, but it still falls 25 short
of the practical engineering limit of 48kT.
That was the Giant Magneto-Resistive Effect. What about the Spin Torque effect?
Si (001) Substrate
Ta 5nm
Ru 50nm
Ta 5nm
NiFe 5nm
Antiferromagnetic MnIr 8nm
CoFe 2nm
Ru 0.8nm
Ferromagnetic CoFeB 3nm
MgO 1.5nm Tunnel Barrier
Ferromagnetic CoFeB 3nm Magnetization
Drain
Si (001) Substrate
Ta 5nm
Ru 50nm
Ta 5nm
NiFe 5nm
Antiferromagnetic MnIr 8nm
CoFe 2nm
Ru 0.8nm
Ferromagnetic CoFeB 3nm
MgO 1.5nm Tunnel Barrier
Ferromagnetic CoFeB 3nm
Drain
Ta 5nm
Ru 15nm
Source
Magnetization is changed by literally transferring the electrons!
Take for a minimum domain size, that 1000 electrons have to be transferred.
Current I=1000e- 1.610-19Coul/10-10seconds
I=1.610-6Amps = 1.6 Amps
Slightly better than the GMR case, but not quite to the theoretical goal<1A.
But 1000e- for switching is very optimistic.Further improvements require going slow to keep the current down. Might be interesting at a clock speed <100MHz
Magnetization
Summary:
1. Giant Magneto-Resistive Effect Switch:Better than today's technology, but not quite to the level of theoretical goal.
2. Spin-Torque Switch:Slightly better than GMR Switch, and capable of achieving theoretical goal at slow clock speeds, <100MHz.
Backup Slides:
nano-transformerh
~1eV
A low-voltage technology, or an impedance matching device,needs to be invented/discovered at the Nano-scale:
transistor amplifier with steeper sub-threshold slope
photo-diode
+ ++
-
+VG
MEM's switch
Cryo-ElectronicskT/q~q/C
Cu
Cu
solid electrolyte
Electro-Chemical Switch
giant magneto-resistancespintronics
+
giant magneto-resistance
"spintronics"
These switches are made of metallic components and are of inherently low impedance
+
10μm
1μm
100nm
10nm
Moore's Law
1960 1980 2000
Crit
ical
D
imen
sion
2020 2040 2060Year
Te
chn
olo
gy G
apG
ates only
Gates including w
ires
107
105
102
1
0.1
104
106
10
108
103
Ene
rgy
per
Bit
func
tion
(kT
)
The other , for energy per bit function
Shoorideh and Yablonovitch, UCLA 2006
Transistor Measurements by Robert Chau, Intel
Recommendations:
1. Milli-Volt powering should be regarded as a Goal for future electronic switching devices.
2. There would be both an immediate power benefit, as well as a benefit at the end of the roadmap.
3. Band edge steepness is poorly known, and should be investigated for a number of semiconductors and semi-metals.
4. The full range of technology options should be included.
Moore
You?
!
Transistor
Nano-transformers
High Impedance Magnetically Loaded Transmission Line
C
q
q
kTV
C
kTV
RCRkTV
fRkTV
noise
noise
noise
noise
4
4
14
4
2
2
2
2
What about very short wires?
Johnson Noise:
,4
C
q
q
kTIf
then the signals could be large enough to be efficiently amplified.
kT
qC
2
If The Coulomb Blockade Capacitance.
For wires less than 1m, a conventional transistor amplifier configuration may be adequate.
10 atto-Farads,
mVolt1V
CqqkT4V
C
q
q
kT4V
C
1kT4V
RC
1RkT4V
fRkT4V
Volts10mVolts100
noise
2noise
2noise
2noise
2noise
//
The natural voltage range for wired communication is rather low:
The thermally activated device wants at least one electron at ~1Volt.
The wire wants1000 electrons at 1mVolt each.
(to fulfill the signal-to-noise requirement >1eV of energy)
Voltage Matching Crisis at the nano-scale!
If you ignore it the penalty will be (1Volt/1mVolt)2 = 106
The natural voltage range for a thermally activated switch like transistors is >>kT/q, eg. ~ 40kT/q
or about ~1Volt
In the future, Vdd in digital circuits will drop to 1 milli-Volt,
for communication wires.