Layered memristive and memcapacitive switches for printable electronics

SUPPLEMENTARY INFORMATIONDOI: 10.1038/NMAT4135

NATURE MATERIALS | www.nature.com/naturematerials 1

1

Layered memristive and memcapacitive switches for printable electronics

Alexander A. Bessonov1, Marina N. Kirikova1, Dmitrii I. Petukhov1,2, Mark Allen3, Tapani Ryhänen3, Marc J.A. Bailey1

1 Nokia Labs Skolkovo, Nokia Technologies, Moscow region 143025, Russia 2 Department of Chemistry, Lomonosov Moscow State University, Moscow 119991, Russia 3 Sensor Systems, Nokia Technologies, Cambridge CB3 0FA, United Kingdom

Figure S1. Solution-processed MoOx/MoS2 memristors.

Figure S2. XPS analysis of MoOx/MoS2 heterostructures.

Figure S3. Photonic flash oxidation of transition metal dichalcohenides (TMDs).

Figure S4. I-V characteristics of layered switching devices.

Figure S5. Memristive and memcapacitive effects.

Figure S6. Multilevel operation and endurance test.

© 2014 Macmillan Publishers Limited. All rights reserved.

http://www.nature.com/doifinder/10.1038/nmat4135

2 NATURE MATERIALS | www.nature.com/naturematerials

SUPPLEMENTARY INFORMATION DOI: 10.1038/NMAT4135

2

Figure S1 | Solution-processed MoOx/MoS2 memristors. a, Top-view optical image of a cross-point

area (~130×170 m2) with inkjet printed bottom electrode (BE) and screen printed top electrode (TE).

b, Cross-section SEM image of the AgNW/MoOx/MoS2 switching device with both BE and TE

fabricated by screen printing; insets show a top-view image of the MoOx/MoS2 film on printed silver

(top) and a cross-section of the MoOx/MoS2 film conformally covering the Ag BE (bottom). c, UV-vis

transmittance spectra of MoOx/MoS2 and WOx/WS2 films on the 50 m thick PEN substrate. Thermal

oxidation is performed at 200°C for 3 h. The transmittance at 565 nm is 51% for MoS2 and 68% for

WS2.

400 500 600 700 800Wavelength (nm)

0

20

40

60

80

100

Tran

smitt

ance

(%)

MoOx/MoS2

WOx/WS2

1 m

500 nm

MoOx/MoS2

Ag BE

AgNW

PEN

1 m

b

Inkjet-printed silver BE

Screen-printed silver TE

100 m

MoOx/MoS2 filma

c

3

Figure S2 | XPS analysis of MoOx/MoS2 heterostructures. a, Evolution of Mo 3d core levels with

depth profiling for layered MoOx/MoS2 films obtained by 200°C / 3 h oxidation. The intensities are

normalized for visual clarity. The features at 228.8 and 231.9 eV are associated with Mo4+ 3d5/2 and

3d3/2 core levels in MoS2, respectively, while S 2s appears at 225.9 eV. The peak at 229.7 and

232.8 eV could be attributed to the Mo5+ 3d core level in MoOxSy. The features at 232.4 and 235.5 eV

indicate the presence of Mo6+ (MoO3) on the surface of the film. With oxidation progression the oxide

components are seen to increase in intensity. The MoOx thickness of < 3 nm is confirmed, which is

consistent with previous data1,2. In addition, we observe a shift of the Mo 3d peaks from the inner

disulfide to the top oxide layer towards the higher binding energy values that can be attributed to a

stronger n-doping process at the MoOx/MoS2 interface due to more electronegative oxygen, indicating

a relative shift of the Fermi level towards the conductive band edge3. However, it should be noted that

the interfacial MoOx layer is assumed to reveal p-type semiconductivity because of heavily

chemisorbed oxygen, as discussed in the main text of paper. b, Mo6+ and Mo5+ oxidation-state XPS

profiles of the MoOx/MoS2 sample oxidized at various conditions; the sputtering rate is approximately

0.1 nm/s. We note that the oxidation at 150°C for 3 h reveals a larger Mo5+/Mo6+ ratio and thus a more

pronounced MoOxSy content with depth showing a less distinct MoOx/MoS2 interface compared to

annealing at higher temperatures (180°C and 200°C for 3 h) and photonic flash oxidation for 600 s,

which is probably caused by a greater oxygen diffusion through the poorly oxidized top layers.

0 30 60 90 120 1500

20

40

Sputtering time (s)

Rel

ativ

e pe

ak a

rea

(%)

Mo5+ (MoOxSy)

10

20

30 150oC 180oC 200oC xenon flash lamp

Mo6+ (MoO3)

224226228230232234236238240242

Mo5+ 3d (MoOxSy)

S 2sMo6+ 3d (MoO3)

Mo4+ 3d3/2 (MoS2)

Mo4+ 3d5/2 (MoS2)

Nor

mal

ized

inte

nsity

10 nm depth

3 nm depth

surface

Binding energy (eV)

ba





2

Figure S1 | Solution-processed MoOx/MoS2 memristors. a, Top-view optical image of a cross-point

area (~130×170 m2) with inkjet printed bottom electrode (BE) and screen printed top electrode (TE).

b, Cross-section SEM image of the AgNW/MoOx/MoS2 switching device with both BE and TE

fabricated by screen printing; insets show a top-view image of the MoOx/MoS2 film on printed silver

(top) and a cross-section of the MoOx/MoS2 film conformally covering the Ag BE (bottom). c, UV-vis

transmittance spectra of MoOx/MoS2 and WOx/WS2 films on the 50 m thick PEN substrate. Thermal

oxidation is performed at 200°C for 3 h. The transmittance at 565 nm is 51% for MoS2 and 68% for

WS2.

400 500 600 700 800Wavelength (nm)

0

20

40

60

80

100

Tran

smitt

ance

(%)

MoOx/MoS2

WOx/WS2

1 m

500 nm

MoOx/MoS2

Ag BE

AgNW

PEN

1 m

b

Inkjet-printed silver BE

Screen-printed silver TE

100 m

MoOx/MoS2 filma

c

3

Figure S2 | XPS analysis of MoOx/MoS2 heterostructures. a, Evolution of Mo 3d core levels with

depth profiling for layered MoOx/MoS2 films obtained by 200°C / 3 h oxidation. The intensities are

normalized for visual clarity. The features at 228.8 and 231.9 eV are associated with Mo4+ 3d5/2 and

3d3/2 core levels in MoS2, respectively, while S 2s appears at 225.9 eV. The peak at 229.7 and

232.8 eV could be attributed to the Mo5+ 3d core level in MoOxSy. The features at 232.4 and 235.5 eV

indicate the presence of Mo6+ (MoO3) on the surface of the film. With oxidation progression the oxide

components are seen to increase in intensity. The MoOx thickness of < 3 nm is confirmed, which is

consistent with previous data1,2. In addition, we observe a shift of the Mo 3d peaks from the inner

disulfide to the top oxide layer towards the higher binding energy values that can be attributed to a

stronger n-doping process at the MoOx/MoS2 interface due to more electronegative oxygen, indicating

a relative shift of the Fermi level towards the conductive band edge3. However, it should be noted that

the interfacial MoOx layer is assumed to reveal p-type semiconductivity because of heavily

chemisorbed oxygen, as discussed in the main text of paper. b, Mo6+ and Mo5+ oxidation-state XPS

profiles of the MoOx/MoS2 sample oxidized at various conditions; the sputtering rate is approximately

0.1 nm/s. We note that the oxidation at 150°C for 3 h reveals a larger Mo5+/Mo6+ ratio and thus a more

pronounced MoOxSy content with depth showing a less distinct MoOx/MoS2 interface compared to

annealing at higher temperatures (180°C and 200°C for 3 h) and photonic flash oxidation for 600 s,

which is probably caused by a greater oxygen diffusion through the poorly oxidized top layers.

0 30 60 90 120 1500

20

40

Sputtering time (s)

Rel

ativ

e pe

ak a

rea

(%)

Mo5+ (MoOxSy)

10

20

30 150oC 180oC 200oC xenon flash lamp

Mo6+ (MoO3)

224226228230232234236238240242

Mo5+ 3d (MoOxSy)

S 2sMo6+ 3d (MoO3)

Mo4+ 3d3/2 (MoS2)

Mo4+ 3d5/2 (MoS2)

Nor

mal

ized

inte

nsity

10 nm depth

3 nm depth

surface

Binding energy (eV)

ba





4

Figure S3 | Photonic flash oxidation of transition metal dichalcohenides (TMDs). a, Schematics

of the oxidation of TMD film on PEN using a xenon flash lamp tool (UIS-100, Aeromed LLC). As a

result, an ultrathin transition metal oxide (TMO) layer forms on the top of TMD film. The technique is

fast and works at low bulk temperatures making it preferable in high-volume roll-to-roll

manufacturing4,5,6. The apparatus consists of a power supply, discharge unit, controller, and lamp

housing. A linear xenon flash lamp with an emission spectrum ranging from 200 to 900 nm is placed

in the elliptical reflector (reflectivity of > 98%). A forced air cooling of the lamp and the sample can be

applied in the case of high power operation. The reflector projects an image on the substrate with an

illumination area of 20 × 250 mm. An adjustable table for samples allows tuning the focus line width

and thus changing the light intensity. The setup has an average electric power consumption of

~1000 W with a pulsed peak power of approximately 2.2 MW. A pulse energy is adjustable in the

range of 12 – 108 J, a pulse frequency can be varied from 1 to 50 Hz, and a pulse duration is 50 s.

b, Few-layer MoS2 and WS2 materials absorb the light in the UV-visual range where the xenon flash

lamp emits. The photonic exposure in air causes a local heating of the TMD film facilitating rapid

oxidation of the topmost layers and finally resulting in TMO/TMD heterostructures.

200 400 600 800 1000

MoS2

WS2

Xenon flash lamp

Nor

mal

ized

abs

orba

nce/

emitt

ance

Wavelength (nm)

PEN

TMD

PEN

TMO

Xenon flash lamp

Elliptic reflector

Focus line

ba

5

Figure S4 | I-V characteristics of layered switching devices. a, b, The MoOx/MoS2 and WOx/WS2

heterostructures sandwiched between two screen-printed silver electrodes show a typical bipolar

resistive switching in contrast to a linear I-V curve of non-oxidized MoS2 device (in forward direction

the TE is negatively charged, the sweep rate is 16.5 mV/s, the compliance current is 1 mA). Being

structural analogues and having similar electronic properties, MoOx/MoS2 and WOx/WS2 exhibit an

almost identical I-V behavior. Thus, we show that few-layer TMD-based systems can be used as a

viable way for active materials to enable printable resistive switches. An observed rectifying I-V

orientation suggests an important role of a Schottky junction at the interface of TMO and Ag TE, which

blocks the current in the OFF state (IOFF). A compositional gradient (Mo6+ to Mo4+) built into the

switching layer supports a resistance memory effect via oxygen vacancy migration under applied

voltage, similar to that previously observed in WO3 devices7,8. Pre-electroforming is not required since

the insulating oxygen-saturated MoOx interfacial layer with the thickness of less than 3 nm is located

on the oxygen-deficient area with anion vacancies ready to move towards the negatively biased TE.

When a large fraction of applied voltage drops on the resistive Ag/MoOx interface, a virtual anode

naturally propagates towards the cathode along defects and structural imperfections supported by the

low-dimensional nature9. c, Temperature effect on the AgNW/MoOx/MoS2 resistive switching

performance. The activation energy (EA) of 0.36 ± 0.04 eV extracted from temperature-dependent

measurements of the reverse IOFF at -0.2 V appears to be slightly higher than EA = 0.30 ± 0.02 eV

obtained for MoOx/MoS2 memristors lacking an intermediate AgNW layer (Fig. 2e).

-0.2 -0.1 0.0 0.1 0.210-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

25oC 40oC 60oC 80oC

Cur

rent

(A)

Voltage (V)

32 34 36 38 40-28

-27

-26

-25

ln (I

R/T

2 )

1/kT (eV-1)

EA=0.36 eV

-0.1 0.1-0.2 0.0 0.210-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

Cur

rent

(A)

Voltage (V)

WOx/WS2

-0.2 -0.1 0.0 0.1 0.2

-1.0

-0.5

0.0

0.5

1.0

Reset

SetOFF

Cur

rent

(mA)

Voltage (V)

MoS2

MoOx/MoS2

WOx/WS2

ON

c

a b





6

Figure S5 | Memristive and memcapacitive effects. a, Resistive (RM) and capacitive (CM)

components of the MoOx/MoS2 as a function of AC 10 mV signal frequency in the ON (after +0.2 V

bias) and OFF (after -0.2 V bias) states. Inset shows the Nyquist plot in the OFF state. The equivalent

circuit is represented as a parallel combination of a resistor and a capacitor. b, AgNW/MoOx/MoS2

switches concurrently support memristive and memcapacitive behavior with the same state variables,

which is consistent with previous observations10. The CM-V and RM-V profiles are extracted from the

impedance measurements with 10 mV 0.5 kHz AC signal superimposed on a continuous DC bias

sweep. Capacitive and resistive switching ratios appear to be 103 and 106, respectively.

1 10 100 1k 10k 100k 1M

100

1k

10k

100k

1M

10M MoOx/MoS2

RM(ON)

Res

ista

nce

()

Frequency (Hz)

RM(OFF)

CM(OFF)

CM(ON)

1p

10p

100p

1n

10n

Cap

acita

nce

(F)

0 1 2 30

1

2

3-Z

" (M

)

Z' (M)

1p10p

100p1n

10n

-0.1 0.1-0.2 0.0 0.210

1k

100k

10M

dwewdweddeeedededdedede de xd

CM (F

)

AgNW/MoOx/MoS2

CM

RM

RM (

)

Voltage (V)

ba

7

Figure S6 | Multilevel operation and endurance test. a, Multiple states of the resistance recorded

after three pulses of 0.3 V for 10 s with varied compliance currents (IC). The read voltage is 0.01 V.

The resistance values are calculated by Ohm’s law at 1000 s. The AgNW/MoOx/MoS2 device under

investigation is obtained by heat-assisted oxidation at 200⁰C for 10 h. The range of possible resistance

states depends on the Schottky junction height; when the depletion width becomes narrow electron

tunneling occurs reducing the contact resistance. b, Cycling endurance of the AgNW/MoOx/MoS2

switch. ON/OFF switching is programmed by alternating pulses of +0.3 V for 0.6 s and -0.1 V for 1.8 s

(IC = 1 mA).

0 200 400 600 800 1000

10-9

10-8

10-5

10-4

10-3

Ic=10 mA

Ic=1 mA

Ic=100 A

Ic=10 A

Ic=5 A

Ic=1 A

Cur

rent

(A)

Time (s)

25.5

123

614

1.51 k

3.09 M

13.1 M

0 10000 20000 30000

10-11

10-9

10-7

10-5

10-3

10-1

OFF

ON

Cur

rent

(A)

Number of cycles

-0.1 V

+0.3 V

0

ba





6

Figure S5 | Memristive and memcapacitive effects. a, Resistive (RM) and capacitive (CM)

components of the MoOx/MoS2 as a function of AC 10 mV signal frequency in the ON (after +0.2 V

bias) and OFF (after -0.2 V bias) states. Inset shows the Nyquist plot in the OFF state. The equivalent

circuit is represented as a parallel combination of a resistor and a capacitor. b, AgNW/MoOx/MoS2

switches concurrently support memristive and memcapacitive behavior with the same state variables,

which is consistent with previous observations10. The CM-V and RM-V profiles are extracted from the

impedance measurements with 10 mV 0.5 kHz AC signal superimposed on a continuous DC bias

sweep. Capacitive and resistive switching ratios appear to be 103 and 106, respectively.

1 10 100 1k 10k 100k 1M

100

1k

10k

100k

1M

10M MoOx/MoS2

RM(ON)

Res

ista

nce

()

Frequency (Hz)

RM(OFF)

CM(OFF)

CM(ON)

1p

10p

100p

1n

10n

Cap

acita

nce

(F)

0 1 2 30

1

2

3

-Z" (

M

)

Z' (M)

1p10p

100p1n

10n

-0.1 0.1-0.2 0.0 0.210

1k

100k

10M

dwewdweddeeedededdedede de xd

CM (F

)

AgNW/MoOx/MoS2

CM

RM

RM (

)

Voltage (V)

ba

7

Figure S6 | Multilevel operation and endurance test. a, Multiple states of the resistance recorded

after three pulses of 0.3 V for 10 s with varied compliance currents (IC). The read voltage is 0.01 V.

The resistance values are calculated by Ohm’s law at 1000 s. The AgNW/MoOx/MoS2 device under

investigation is obtained by heat-assisted oxidation at 200⁰C for 10 h. The range of possible resistance

states depends on the Schottky junction height; when the depletion width becomes narrow electron

tunneling occurs reducing the contact resistance. b, Cycling endurance of the AgNW/MoOx/MoS2

switch. ON/OFF switching is programmed by alternating pulses of +0.3 V for 0.6 s and -0.1 V for 1.8 s

(IC = 1 mA).

0 200 400 600 800 1000

10-9

10-8

10-5

10-4

10-3

Ic=10 mA

Ic=1 mA

Ic=100 A

Ic=10 A

Ic=5 A

Ic=1 A

Cur

rent

(A)

Time (s)

25.5

123

614

1.51 k

3.09 M

13.1 M

0 10000 20000 30000

10-11

10-9

10-7

10-5

10-3

10-1

OFF

ON

Cur

rent

(A)

Number of cycles

-0.1 V

+0.3 V

0

ba





8

References

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2. Tagawa, M., Yokota, K., Matsumoto, K., Suzuki, M. & Teraoka, Y. Space environmental effects on MoS2 and diamond-like carbon lubricating films: Atomic oxygen-induced erosion and its effect on tribological properties. Surf. Coat. Technol. 202, 1003–1010 (2007).

3. Fang, H., et al. Degenerate n-doping of few-layer transition metal dichalcogenides by potassium. Nano Letters 13, 1991–1995 (2013).

4. Abbel, R., et al. Photonic flash sintering of silver nanoparticle inks: a fast and convenient method for the preparation of highly conductive structures on foil. MRS Communications 2, 145–150 (2012).

5. Niittynen, J., et al. Alternative sintering methods compared to conventional thermal sintering for inkjet printed silver nanoparticle ink. Thin Solid Films 556, 452–459 (2014).

6. Perelaer, J., et al. Roll-to-Roll compatible sintering of inkjet printed features by photonic and microwave exposure: from non-conductive ink to 40% bulk silver conductivity in less than 15 seconds. Adv. Mater. 24, 2620–2625 (2012).

7. Yang., R., et al. On-demand nanodevice with electrical and neuromorphic multifunction realized by local ion migration. ACS Nano 6, 9515–9521 (2012).

8. Guo, J., et al. Reconfigurable resistive switching devices based on individual tungsten trioxide nanowires. AIP Advances 3, 042137 (2013).

9. McDonnell, S., Addou, R., Buie, C., Wallace, R. M. & Hinkle, C. L. Defect-dominated doping and contact resistance in MoS2. ACS Nano 8, 2880–2888 (2014).

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Layered memristive and memcapacitive switches for printable electronics

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