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Abstract

Hardware based neuromorphic computing, which requires a synaptic memory capable of retaining a multitude of addressable conductance states, opens a possibility to bypass the von-Neumann bottleneck [1]. Ferroelectric field effect transistors (FeFETs) based on doped hafnium oxide have been demonstrated as viable candidates for neuromorphic synapses [2]. Here, the multitude of remnant polarization levels can be used to modulate the drain current. By utilizing any of three distinct types of signal sequences, the different levels can be addressed. Those sequences are described by a varying number of pulses, pulse width, or pulse height, respectively [3]. The resulting conductance response (CR) of the synapse can be described by a set of parameters: Abruptness, conductance variation and conductance dynamic range [4]. Here, we present the CR modulation capability of HfO2 based FeFETs. On the one hand, influences from the signal sequence and read gate voltage were investigated. In case of the former, the pulse width and amplitude were varied, whereas latter is demonstrated to vary the abruptness of depression and potentiation in opposed directions. On the other hand, influences resulting from the dopant, interface layer, and other device integration related quantities were investigated. Furthermore, endurance was investigated in regard to neuromorphic application. Additionally, it was demonstrated, that a CR with a nonlinearity coefficient smaller than 0.1 can be achieved for read voltages as low as 0.3V. [1] Indiveri, G. et al.; Proc. IEEE, 1379-1397, 2015 [2] Jerry, M. et al.; IEDM, 6.2.1-6.2.4, 2017 [3] Oh, S. et al.; IEEE Electron Device Lett. 38 (6), 732-735, 2017 [4] Gi, S.-G. et al.; IEEE Trans. Electron Devices 65 (9), 3996-4003, 2018
© Fraunhofer IPMS
Tuneable linearity in HfO2based multilevel
FeFETs for neuromorphic computing
M. Lederer, T. Kämpfe, T. Ali, K. Seidel
EMRS Fall 2019
© Fraunhofer IPMS
M. Lederer I18.09.2019 I slide 2
Ferroelectric Fieldeffect Transistor (FeFET)
Gate-First
ΔVT= 1-1.2 V
±5V, < 100 ns
104endurance
10y retention
28nm Proof of Concept
J. Müller et al., VLSI (2012)
SiO2
Si
S D
TiN
a-Si
HSO
SiO2
FeFET Gate Stack
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2
0.00
0.25
0.50
0.75
1.00
ID [µA]
VG [V]
Pr
Pr
Orthorhombic (Pca21)
Ferroelectricity in HfO2
Stabilized by Dopants, Stress, …
-3 -2 -1 0123
-40
-30
-20
-10
0
10
20
30
40
Polarization [µC/cm²]
E [MV/cm]
HSO 10nm
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M. Lederer I18.09.2019 I slide 3
Neuromorphic Computing
Conductance of crossbar array represent weight matrix
Level-based representation
Most efficient for fully connected layers
Dot-product engine
X1
X2
X3
X4
Xn
A1
A2
A3
An
Weight
matrix
Pre-
neuron
layer
Post-
neuron
layer
V1
V3
V4
Vn
I1I2I3In
Multilevel
memory
© Fraunhofer IPMS
M. Lederer I18.09.2019 I slide 4
Non-Linearity Coefficient
Switching
polarization of
grains/domains
Shifting the
threshold voltage
Seq. 1 Seq. 3
Seq. 2
Signal Shape
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2
0.00
0.25
0.50
0.75
1.00
ID [µA]
VG [V]
Potentation
(LTP):
Seq. 3: 150ns W: 50 µm, L: 25 µm
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2
0.00
0.25
0.50
0.75
1.00
I
D
[µA]
VG [V]
2.5V -3V
4V -4.5V
Depression
(LTD):
Transmission EBSD:
© Fraunhofer IPMS
M. Lederer I18.09.2019 I slide 5
Non-Linearity Coefficient
Extracted current at a certain read voltage
resembles the individual states (weight)
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2
0.00
0.25
0.50
0.75
1.00
ID [µA]
VG [V]
Potentation
(LTP):
Seq. 3: 150ns W: 50 µm, L: 25 µm
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2
0.00
0.25
0.50
0.75
1.00
ID [µA]
VG [V]
2.5V -3V
4V -4.5V
Depression
(LTD):
Seq. 3
M. Jerry et al., IEDM (2017)
,=1.726
+ 0.162
Ip,d= B 1 exp PD
A+ C
2. Nonlin. Coefficient:
P := Pulse Number
D := Start Pulse Number
1. Nonlinearity Fit:
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M. Lederer I18.09.2019 I slide 6
Non-Linearity Coefficient
Comparison of different non-linearities
0.21
0.12
0.00 (1.02*10^-7)
© Fraunhofer IPMS
M. Lederer I18.09.2019 I slide 7
0 5 10 15 20 25 30
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Current [µΑ]
Pulse Number
V
G
[V]:
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
0 5 10 15 20 25 30
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Current [µΑ]
Pulse Number
V
G
[V]:
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2
0.0
0.1
0.2
0.3
0.4
0.5
Nonlinearity Coefficient
Gate Voltage [V]
Potentiation
Depression
Influence of the Gate Voltage
Nonlinearity is
strongly
dependent on
gate voltage
LTP LTD
Seq. 3: 150ns W: 50 µm, L: 25 µm
© Fraunhofer IPMS
M. Lederer I18.09.2019 I slide 8
Influence of the Gate Voltage
Dynamic range strongly dependent on gate
voltage
Relative and absolute range show
maximum at different gate voltages
-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
-6x10-7
-4x10-7
-2x10-7
0
2x10-7
4x10-7
6x10-7
150ns Pot.
150ns Dep.
VG [V]
Iend - Istart [A]
10-4
10-3
10-2
10-1
100
101
102
103
104
150ns Pot.
150ns Dep.
Iend / Istart
0 5 10 15 20 25 30
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Current [µΑ]
Pulse Number
V
G
[V]:
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
 
0 5 10 15 20 25 30
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Current [µΑ]
Pulse Number
V
G
[V]:
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
 
LTD
LTP
Seq. 3: 150ns W: 50 µm, L: 25 µm
© Fraunhofer IPMS
M. Lederer I18.09.2019 I slide 9
Area scaling
Increase of nonlinearity with decreasing area
More deviation for smaller devices? Influence of width/length?
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M. Lederer I18.09.2019 I slide 10
Influence of the device layout
Seq2 W01 Potentation
Seq2 W01 Depression
VG= 0.2V VG= 0.8V VG= 1.5V
VG= 0.2V VG= 0.8V VG= 1.5V
Seq. 2
LTP
Seq. 2
LTD
© Fraunhofer IPMS
M. Lederer I18.09.2019 I slide 11
Sequence 1 3: Nonlinearity
Sequence 3 shows lowest nonlinearity
Seq. 1
Seq. 3
Seq. 2
0246810 12 14 16 18 20 22 24 26 28 30 32
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
0.22
Current [µA]
Pulse Number
Depression
Seq. 1
Seq. 2
Seq. 3
-0.2 0.0 0.2 0.4 0.6 0.8 1.0
0.00
0.25
0.50
0.75
1.00
1.25
Nonlinearity Coefficient
Gate Voltage [V]
LTP: Seq. 1
Seq. 2
Seq. 3
LTD: Seq. 1
Seq. 2
Seq. 3
W: 25 µm,
L: 25 µm
VG= 0.8V
W: 25 µm, L: 25 µm
© Fraunhofer IPMS
M. Lederer I18.09.2019 I slide 12
Sequence 1 3: Dynamic range (Ion/Ioff)
Seq. 2 & 3 less asymmetric
Higher variance for Seq. 2 & 3
Dynamic range can be improved by
using more pulses (Seq. 3)
0246810 12 14 16 18 20 22 24 26 28 30 32
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
0.22
Current [µA]
Pulse Number
Depression
Seq. 1
Seq. 2
Seq. 3
Seq. 1
Seq. 3
Seq. 2
-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
-1x10-6
-5x10-7
0
5x10-7
1x10-6 LTP: Seq. 1
Seq. 2
Seq. 3
LTD: Seq. 1
Seq. 2
Seq. 3
V
G
[V]
I
end
- I
start
[A]
-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
10
-4
10
-3
10
-2
10
-1
10
0
10
1
10
2
10
3
10
4
LTP: Seq. 1
Seq. 2
Seq. 3
LTD: Seq. 1
Seq. 2
Seq. 3
I
end
/ I
start
V
G
[V]
W: 25 µm,
L: 25 µm
VG= 0.8V
W: 25 µm,
L: 25 µm
© Fraunhofer IPMS
M. Lederer I18.09.2019 I slide 13
Sequence 1 3: Area Scaling
Seq. 1 shows a very rapid increase in nonlinearity with area scaling
Seq. 2 and 3 show slower increase, could be used for smaller devices
Origin lies in domain structure and nucleation limited switching
Seq. 1 Seq. 3
Seq. 2
Signal Shape
100 1000
0.00
0.05
0.10
0.15
0.20
0.25
Seq. 2 LTD
Seq. 3 LTD
Nonlinearity Coefficient
Area [µm²]
100 1000
10
-2
10
-1
10
0
Area [µm²]
Seq. 1 LTD
Seq. 2 LTD
Seq. 3 LTD
I
end
/ I
start
0200 400 600 800 1000 1200 1400
0
1
2
3
4 Seq. 1 LTD
Seq. 2 LTD
Seq. 3 LTD
Nonlinearity Coefficient
Area [µm²]
© Fraunhofer IPMS
M. Lederer I18.09.2019 I slide 14
Sequence 1 3: Area Scaling
Seq. 3 shows the same trend as
seq. 2
Much lower nonlinearity for seq. 3
even for the smaller devices
VG= 0.2V VG= 0.8V VG= 1.5V
VG= 0.2V VG= 0.8V VG= 1.5V
Seq. 3
LTD
Seq. 2
LTD
© Fraunhofer IPMS
M. Lederer I18.09.2019 I slide 15
Sequence 1 3: Possible Adjustments for Area Scaling
Adjusting signal shape for smaller devices improves nonlinearity
Seq. 1 Seq. 3
Seq. 2
100 1000
0.0
0.1
0.2
0.3
0.4
0.5
0.6 3/-3.5 LTD
3.5/-4 LTD
Nonlinearity Coefficient
Area [µm²]
100 1000
0
2
4
6
8
10
12 3.5/-4.5 V
50ns LTD
100ns LTD
150ns LTD
3/-4 V
100ns LTD
Nonlinearity Coefficient
Area [µm²]
100 1000
0.00
0.05
0.10
0.15
0.20
0.25
0.30 50ns Dep.
100ns Dep.
150ns Dep.
Nonlinearity Coefficient
Area [µm²]
© Fraunhofer IPMS
M. Lederer I18.09.2019 I slide 16
Endurance of Intermediate States
Sequence 3 shows slight degradation during 600 pulses (20 cycles)
Increasing asymmetry between LTP and LTD
Nonlinearity does not deviate strongly during 100 cycles
© Fraunhofer IPMS
M. Lederer I18.09.2019 I slide 17
Endurance of Intermediate States
Sequence 2 shows slight degradation during 4000 pulses (100 cycles)
Nonlinearity does not deviate strongly during 100 cycles
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M. Lederer I18.09.2019 I slide 18
Retention of Intermediate States
No retention loss for a readout time up to 1 h
0 400 800 1200 1600 2000 2400 2800 3200 3600
10
-10
10
-9
10
-8
10
-7
log(ID)
Readout Time [s]
0 400 800 1200 1600 2000 2400 2800 3200 3600
10
-10
10
-9
10
-8
10
-7
log(I
D
)
Readout Time [s]
© Fraunhofer IPMS
M. Lederer I18.09.2019 I slide 19
Conclusion & Outlook
Nonlinearity and dynamic range can be tuned
by signal shape and gate voltage
Scaling of area without strong increase in
nonlinearity possible for sequence 2 and 3
Device layout influences nonlinearity
Good retention during 1h measurement
Slight degradation during 4000 pulses for
sequence 2
FeFETs can be tuned for certain applications
SiO2
Si
S D
TiN
a-Si
HSO
SiO
2
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2
0.00
0.25
0.50
0.75
1.00
I
D
[µA]
VG [V]
VG= 0.2V VG= 0.8V VG= 1.5V
© Fraunhofer IPMS
M. Lederer I18.09.2019 I slide 20
Acknowledgements
We received funding within the ECSEL Joint Undertaking project TEMPO in collaboration with the European Union's H2020
Framework Program (H2020/2014-2020) and National Authorities, under grant agreement number 783176.
© Fraunhofer IPMS
M. Lederer I18.09.2019 I slide 21
FeFET SiO2 vs SiON
SiON: Lower voltages necessary to switch fully Increase in nonlinearity
SiO2
Si
S D
TiN
a-Si
HSO
SiO2
SiO2
Si
S D
TiN
a-Si
HSO
SiO
N
0-1 -2 -3 -4 -5 -6 -7 -8
0.1
0.3
0.5
0.7
0.9
1.1
1.3
Lower
ER
SiON
SiO
2
VT (V)
Erase Pulse Amplitude (V)
PG State Low (V
T
)
High (V
T
)
ER State
No FE
Switching
Low Voltage FE Switching
T. Ali et al., TED (2018)
Seq. 2
0.0 0.2 0.4 0.6 0.8
-1x10
-6
-8x10
-7
-6x10
-7
-4x10
-7
-2x10
-7
0
2x10
-7
4x10
-7
6x10
-7
8x10
-7
1x10
-6
SiO
2
: LTP
LTD
SiON:
LPT
LTD
SiO
2
: LTP
LTD
SiON:
LPT
LTD
V
G
[V]
I
end
- I
start
[A]
10
-4
10
-3
10
-2
10
-1
10
0
10
1
10
2
10
3
I
end
/ I
start
0.0 0.2 0.4 0.6 0.8 1.0 1.2
0.0
0.5
1.0
1.5
2.0
Nonlinearity Coefficient
VG [V]
10nm:
300 µm
2
LTP
300 µm
2
LTD
5nm: 300 µm
2
LTP
300 µm
2
LTD
W: 20 µm, L: 10 µm
© Fraunhofer IPMS
M. Lederer I18.09.2019 I slide 22
FeFET HSO vs HZO
Lower Variance due to larger MW (FeFET Comparison) not reaching
saturation current
More Subloop Behaviour Lower nonlinearity coefficient
SiO2
Si
S D
TiN
a-Si
HSO
SiO
N
SiO2
Si
S D
TiN
a-Si
HZO
SiO
N
-3 -2 -1 0123
-40
-30
-20
-10
0
10
20
30
40
Polarization [µC/cm²]
E [MV/cm]
HZO 10nm
HSO 10nm
Seq. 2
-0.2 0.0 0.2 0.4 0.6 0.8
0.0
0.5
1.0
1.5
2.0
2.5
Nonlinearity Coefficient
V
G
[V]
HZO:
300 µm
2
LTP
300 µm
2
LTD
HSO:
300 µm
2
LTP
300 µm
2
LTD
0.0 0.2 0.4 0.6 0.8
-1x10
-6
-5x10
-7
0
5x10
-7
1x10
-6
HSO: LTP
LTD
HZO: LPT
LTD
HSO: LTP
LTD
HZO: LPT
LTD
V
G
[V]
I
end
- I
start
[A]
10
-3
10
-2
10
-1
10
0
10
1
10
2
10
3
I
end
/ I
start
W: 20 µm, L: 10 µm
© Fraunhofer IPMS
M. Lederer I18.09.2019 I slide 24
FeFET thickness influence
Thinner film results in an increased electrical field Compressed /
steeper behaviour with VG
SiO2
Si
S D
TiN
a-Si
HZO
SiO
N
SiO2
Si
S D
TiN
a-Si
HZO
SiO
N
Seq. 2
0.2 0.4 0.6 0.8 1.0 1.2
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
I
D
[µA]
V
G
[V]
10 nm
5 nm
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2
-6x10-7
-4x10-7
-2x10-7
0
2x10-7
4x10-7
6x10-7 10 nm: 5 nm:
LTP LPT
LTD LTD
10 nm:
LTP
LTD
5 nm:
LPT
LTD
V
G
[V]
I
end
- I
start
[A]
10-3
10-2
10-1
100
101
102
103
I
end
/ I
start
0.0 0.2 0.4 0.6 0.8 1.0 1.2
0.0
0.5
1.0
1.5
2.0
Nonlinearity Coefficient
VG [V]
10nm:
300 µm2 LTP
300 µm2 LTD
5nm: 300 µm2 LTP
300 µm2 LTD
W: 20 µm, L: 10 µm
W: 20 µm, L: 10 µm
W: 20 µm,
L: 10 µm
© Fraunhofer IPMS
M. Lederer I18.09.2019 I slide 25
Sequence 1: Pulse Amplitude
Amplitude reduction:
Decrease of nonlinearity in potentation
Reduced assymetry of the variance
Decrease in absolute variance
Seq. 1
Amplitude Variation (100ns)
0.0 0.5 1.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Nonlinearity Coefficient
V
G
[V]
3.5V/-4.5V:
100ns LTP
100ns LTD
3V/-4V:
100ns LTP
100ns LTD
-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
-5x10
-7
-4x10
-7
-3x10
-7
-2x10
-7
-1x10
-7
0
1x10
-7
2x10
-7
3x10
-7
4x10
-7
5x10
-7
LTP: 3.5V
3V
LTD: -4.5V
-4V
LTP: 3.5V
3V
LTD: -3.5V
-4V
V
G
[V]
I
end
- I
start
[A]
10
-2
10
-1
10
0
10
1
10
2
I
end
/ I
start
© Fraunhofer IPMS
M. Lederer I18.09.2019 I slide 26
Sequence 1: Pulse Width
Strong effect on depression
Moving to lower VG
Converging at ~0.5
No clear/strong influence on
potentation
Seq. 1
Width Variation (3.5V/-4.5V)
0.0 0.5 1.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Nonlinearity Coefficient
V
G
[V]
3.5V/-4.5V:
LTP: 50ns
100ns
150ns
LTD: 50ns
100ns
150ns
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2
-5x10-7
-4x10-7
-3x10-7
-2x10-7
-1x10-7
0
1x10-7
2x10-7
3x10-7
4x10-7
5x10-7 LTP: 50ns
100ns
150ns
LTD: 50ns
100ns
150ns
V
G
[V]
I
end
- I
start
[A]
10-2
10-1
100
101
102
LTP: 50ns
100ns
150ns
LTD: 50ns
100ns
150ns
I
end
/ I
start
© Fraunhofer IPMS
M. Lederer I18.09.2019 I slide 27
Sequence 2: Pulse Amplitude
Trade-off between nonlinearity and variance
Seq. 2
0.0 0.5 1.0
0.00
0.25
0.50
0.75
1.00
Nonlinearity Coefficient
VG [V]
Potentation:
3V
3.5V
Depression:
3.5V
4V
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2
-1x10
-6
-5x10
-7
0
5x10
-7
1x10
-6
LTP: 3V
3.5V
LTD: -3.5V
-4V
LTP: 3V
3.5V
LTD: -3.5V
-4V
V
G
[V]
I
end
- I
start
[A]
10
-4
10
-3
10
-2
10
-1
10
0
10
1
10
2
10
3
I
end
/ I
start
© Fraunhofer IPMS
M. Lederer I18.09.2019 I slide 28
Sequence 3: Pulse Width
Longer pulses increase slope of
nonlinearity
Absolute variance reaches
maximum for 100ns
Variance improvements with
higher number of pulses
Seq. 3
0.0 0.5 1.0
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
Nonlinearity Coefficient
V
G
[V]
Potentation:
50ns
100ns
150ns
Depression:
50ns
100ns
150ns
-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2
-4x10
-7
-3x10
-7
-2x10
-7
-1x10
-7
0
1x10
-7
2x10
-7
3x10
-7
4x10
-7 LTP: 50ns
100ns
150ns
LTD 50ns
100ns
150ns
V
G
[V]
I
end
- I
start
[A]
10
-3
10
-2
10
-1
10
0
10
1
10
2
10
3
LTP: 50ns
100ns
150ns
LTD: 50ns
100ns
150ns
I
end
/ I
start
ResearchGate has not been able to resolve any citations for this publication.
  • S Oh
Oh, S. et al.; IEEE Electron Device Lett. 38 (6), 732-735, 2017
  • S.-G Gi
Gi, S.-G. et al.; IEEE Trans. Electron Devices 65 (9), 3996-4003, 2018