Nanoscale resistive switchingdevices based on metal oxides
Jacopo FrascaroliSupervisor Prof. Alberto PulliaCo-Supervisor Dr. Sabina Spiga
Jacopo Frascaroli Milano, October 15th 2013
Outline
Resistive switching:
phenomenology and applications
Device characterization
Nano devices using block copolymers
Pt
TiN
ALD - HfO2
5 - 6 nm
40 μm
40 μm
Jacopo Frascaroli Milano, October 15th 2013
Resistive switching in MIM structures
AMetal
Metal
Insulator
Capacitor-like structure with electrically alterable resistivity
A large variety of insulating materials shows resistive switching properties:
Transition metal oxides (TMO) metal doped perovskites Polymers ...
Jacopo Frascaroli Milano, October 15th 2013
Switching behavior
Applying a proper potential difference at the two electrodes, the device resistance changes
Reset
Set
Jacopo Frascaroli Milano, October 15th 2013
Resistive switching mechanism in TMO
The anion motion leads to a valence change of the metal sublattice (cations) R change
Filamentary type
R. Waser, Adv. Mater. 2009 and ref. therein; A. Sawa, Materials Today 2008
Mobile species:Oxygen ions – oxygen vacancies
Initial state Forming
Reset Set
Jacopo Frascaroli Milano, October 15th 2013
Very simple structure Highly scalable CMOS process compatibility Low switching time Low power consumption
Crossbar array
Resistive switching applications
Memory
Need for a lithographictechnology to enable cell scaling
Si nanocrystal
NAND-Flash (FG)
Techn.node F [nm]
Cell size[F2]
10
20
30
40
180 130 90 65 5x 3x
NOR-Flash (FG/NROM)
MRAM
FeRAM
PCM
ReRAM ?3D stack
2x4x 1x
niche and niche and
embedded embedded
applicationsapplications
codecode
datadata
evolutionaryevolutionary
disruptivedisruptive
3D-SONOS
Spintronics
NAND-Flash (FG)
Techn.node F [nm]
Cell size[F2]
10
20
30
40
180 130 90 65 5x 3x
NOR-Flash (FG/NROM)
MRAM
FeRAM
PCM
ReRAM ?3D stack
2x4x 1x
niche and niche and
embedded embedded
applicationsapplications
codecode
datadata
evolutionaryevolutionary
disruptivedisruptive
3D-SONOS
Spintronics
MRAM-spin torque
Jacopo Frascaroli Milano, October 15th 2013
Resistive switching applicationsLogic Artificial neural
networks
Yang, J. Joshua, Dmitri B. Strukov, and Duncan R. Stewart. "Memristive devices for computing" Nature nanotechnology 8.1 (2012)
Jacopo Frascaroli Milano, October 15th 2013
Experimental results
Up to 2000 reproducible switching cycles demonstrated
Pt
TiN
ALD - HfO2
5 - 6 nm
40 μm
40 μm
Microscopic device characterization
-2 -1 0 1 2
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
C
urr
ent
(mA
)
Voltage (V)
Reset
Set
Jacopo Frascaroli Milano, October 15th 2013
Possible to tune the low resistance varying the maximum allowed current
during set (current compliance)
0.1 110
2
103
104
RLO
W (
)
Set max current (mA)
Experimental resultsElectrical characterization
-1.5 -1.0 -0.5 0.0
-5
-4
-3
-2
-1
0
Curr
ent
(mA
)
Voltage (V)
Jacopo Frascaroli Milano, October 15th 2013
1.0 1.5 2.0 2.5 3.0104
105
RH
IGH
(
)
Reset voltage (V)
Possible to tune the high resistance varying the maximum reset voltage
0 1 2 3
0.0
0.2
0.4
0.6
0.8
1.0
Curr
ent
(mA
)
Voltage (V)
Experimental resultsElectrical characterization
Jacopo Frascaroli Milano, October 15th 2013
• Two different retention behaviors
• Arrhenius dependence of the retention time on temperature
100
101
102
103
104
105
106
101
102
103
104
105
106
Low resistance stateR (
)
t (s)
TiN/HfO2/Pt 150°C
Failure bit
Typical bits
High resistance state
2.2 2.3 2.4 2.5 2.6 2.7 2.8
1000/T (K-1)
Ea
HR = 1.5 +/- 0.1 eV
180 160 140 120 100 80
T (°C)
100
101
102
103
104
105
106
(
s)
Experimental resultsRetention behavior
Retention behavior at 150°C
Jacopo Frascaroli Milano, October 15th 2013
Slow retention loss• Modification of the residual
filament• The TiOxNy /HfO2 interface
may play a role
Fast retention loss• Very narrow gap.
Diffusion of a few vacancies can reconstruct the conductive channel
100
101
102
103
104
105
106
101
102
103
104
105
106
Low resistance stateR (
)
t (s)
TiN/HfO2/Pt 150°C
Failure bit
Typical bits
High resistance state
Experimental resultsRetention modeling
Pt
TiN
HfO
x
Oxigen speciesOxigen vacancies
Forming
-V
Pt
TiN
HfO
x
Oxigen speciesOxigen vacancies
Reset
+V
Set Reset
J. Frascaroli et al., in preparation
Jacopo Frascaroli Milano, October 15th 2013
Slow retention loss• Modification of the residual
filament• The TiOxNy /HfO2 interface
may play a role
Fast retention loss• Very narrow gap.
Diffusion of a few vacancies can reconstruct the conductive channel
100
101
102
103
104
105
106
101
102
103
104
105
106
Low resistance stateR (
)
t (s)
TiN/HfO2/Pt 150°C
Failure bit
Typical bits
High resistance state
Experimental resultsRetention modeling
Pt
TiN
HfO
x
Oxigen speciesOxigen vacancies
Forming
-V
Pt
TiN
HfO
x
Oxigen speciesOxigen vacancies
Reset
+V
Set Reset
J. Frascaroli et al., in preparation
Jacopo Frascaroli Milano, October 15th 2013
10-5
10-4
10-3
102
103
104
105
RHI
RLOW
R (
)
Area (cm2)
Filamentary conduction
High scalability potential
Experimental results
No area dependence of the resistance
Device area dependence
Jacopo Frascaroli Milano, October 15th 2013
Previous works
ReRAM nanoscaling
Top-down
B. Govoreanu et al. IEEE Electron DevicesMeeting (2011)
Anodized-Aluminium Oxide templates
Bottom-up
D. Perego et al. Nanotechnology 24
(2013)
Electron beam lithography
• Slow and serial lithographic technique• Limited number of devices • Not compatible with actual
technology
Jacopo Frascaroli Milano, October 15th 2013
Block Copolymers
Hexagonal cylinders template
Experimental result: block copolymers self assembling of hafnium dioxide
Jacopo Frascaroli Milano, October 15th 2013
GraphoepitaxyM. Perego et al. Nanotechnology 24, 8 (2013)
Pre-patterned structures can be used to drive the self assembly of block copolymers Courtesy of F. Ferrarese Lupi, MDM IMM-CNR
Jacopo Frascaroli Milano, October 15th 2013
Top electrode nano patterning
Electrical measurements with c-AFM
Combining directed self-assembling with electron beam lithography
Lift-off process
Jacopo Frascaroli Milano, October 15th 2013
Substrate: ALD – HfO2
MetalPhysical
depositionThickness
Tungsten (W) sputtering 5 nm
Platinum (Pt)
sputtering 5 nm
ebeam 5 nm
Lift-off process study
Experimental result
Jacopo Frascaroli Milano, October 15th 2013
200 nm
We demonstrated the possibility to obtain nano scaled top Pt electrodes over
large areas of HfO2
Experimental result
Jacopo Frascaroli Milano, October 15th 2013
Current activity
Device characterization andstudy of the retention behavior
Implementing the block copolymer self-assembling on HfO2
Study of the lift-off process for top electrodes nano patterning
Jacopo Frascaroli Milano, October 15th 2013
Future outlook
Electrical characterization of the nano devices using C-AFM to inspect the physical properties at the nano scale
Find alternative strategies for the fabrication of resistive switching devices using block copolymers self-assembly
Jacopo Frascaroli Milano, October 15th 2013
Jacopo Frascaroli Milano, October 15th 2013
Initial state
Fresh cell
Resistive switching mechanismH. Akinaga and H. Shima, Proceedings of the IEEE 2010
Jacopo Frascaroli Milano, October 15th 2013
Soft breakdown
Initial state
GND
SET (forming)
On state(Low resistance)
Fresh cell Forming
V+
Resistive switching mechanism
Jacopo Frascaroli Milano, October 15th 2013
V-
GND
Off state(High resistance)
RESET
Fresh cell Forming Reset
On state(Low resistance)
Resistive switching mechanism
Jacopo Frascaroli Milano, October 15th 2013
GND
Off state(High resistance)
SET (forming)
On state(Low resistance)
Fresh cell Forming Reset Set
V+
Resistive switching mechanism
Jacopo Frascaroli Milano, October 15th 2013
V-
GND
GND
Off state(High resistance)
SET (forming)
On state(Low resistance)
RESET
Fresh cell Forming Reset Set Many cycles
V+
Resistive switching mechanism
Jacopo Frascaroli Milano, October 15th 2013
X-ray photoemission spectroscopy• TiO2/TiOxNy in serie with the HfO2 film• Significant percentage of non-lattice oxide
542 540 538 536 534 532 530 528 526 524
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
Data
sum
peak1 (O1s)
peak2
background
Co
un
ts
BE (eV)
O1s
Non-lattice oxide
475 470 465 460 455 4500
2000
4000
6000
8000
10000
12000
14000
Data
Sum
Peak1
Peak2
Peak3
Background
Counts
BE (eV)
Ti2p
TiO2
TiOxNy
HfO2 filmTiN film
Experimental resultsMetal/Oxide interface
Jacopo Frascaroli Milano, October 15th 2013
ITRS 2012 UPDATE - Winter Presentations
Jacopo Frascaroli Milano, October 15th 2013
Conduction in metal oxides
J. Joshua Yang et al., "Memristive devices for computing" Nature nanotechnology 8.1 (2012)