organic memory tutorial vs2 - university of exeter...

The Microelectronics Training Center, IMEC v.z.w.www.imec.be/mtc

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MTC 2008 : Polymer/Organic memoriesIMEC© 2008

Paul Heremans

Paul Heremans© imec restricted 2008 1

Polymer/Organic memories

Paul Heremans

IMEC Research FellowIMEC – Kapeldreef 75 – B3001 Leuven


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Paul Heremans


Some words about plastic electronics

foildielectric: sputtered oxideor solution-processed polymer

gate: metal

sourcedrain: metal via

patterned organic semiconductor e.g. pentacene

100fA

1pA

10pA

100pA

1nA

10nA

100nA

1µA

10µA

100µA

1mA

I DS

[A]

-10 -5 0 5 10

VG [V]

0.030

0.025

0.020

0.015

0.010

0.005

0.000

SQ

RT(ID

S) [A

1/2]

run PLTL10D4w/l = 5000/10 μ = 6.26e-01 cm2 / Vs VT0 = 2.2 VVon = 7.2 VSSub = 0.51 V/decIon/Ioff = 1.51e+09

interconnect


Applications of plastic electronics

• Display backplanes– Electronic paper

– Electrophoretic displays

– LCD

– Future: OLED

• Small circuits (on foil)– RFID tags: transponder circuit + HF front-end

– Such applications requireembedded memory!

• Disposable / Distributed sensor arrays


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Paul Heremans


Inventory of reprogrammable memories

• I: Charge-storage– In the gate dielectric of an organic TFT

• II: Polarization switching– Capacitor

– Transistor gate dielectric

– Diode

• III: Resistive switching– Cross-bar architecture

++

↑↓

MIS


Type I: charge storage

foilDouble-layer dielectric

gate: metal

source drain: metal

organic semiconductor e.g. pentacene

PolymerOxide

Gate-source field drives carriers into dielectricThis shifts the threshold voltage


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Paul Heremans


Example

Baeg et al., Adv. Mater. 18, 3179 (2006)

FIG. 2: Shifts in transfer curves at Vds = –10 V for an OFET memory device. For programming and erasing Vgs= 60 V and Vgs = –50 V were respectively applied for 1 ms.


Charge trapping in both directions

GSiO2

PαMS

pentaceneS D


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Paul Heremans


Charge as function of gate voltage

GSiO2

PαMS

pentaceneS D

~1 MV/cm


Charge as function of time

GSiO2

PαMS

pentaceneS D


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Paul Heremans


Retention

GSiO2

PαMS

pentaceneS D


Proposed mechanism


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Paul Heremans


Summary of charge-storage memory

• Transistor configuration lends itself to integration with circuitry

• Scaling of voltages is reasonable (Eprog ~ 1.5 MV/cm)with 1…10 ms programming time

• Further investigations:– Where exactly is charge trapped?

– Retention not studied in detail?

– Fatigue?


Inventory


• II: Polarization switchingof ferro-electric polymer– Capacitor


– Diode


++

↑↓

MIS


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Paul Heremans


μeffδ−

δ+δ+

δ−

p(VDF)

H

H F

F

n

CC

H H

F F

=C

C

H H

F F

Type II: Ferro-electric polymer

• poly(vinylidene fluoride) PVDF polymer is ferro-electric in β-phase:– Effective dipole moment (μeff= 7x10-30 Cm) perpendicular to polymer chain

• poly(vinylidene fluoride / trifluoroethylene) P(VDF-TrFE) co-polymer is spontaneously ferro-electric – Due to steric hindrance of F atoms :

SOLVAY

e.g. Katz et al., J. Appl. Phys. 91, 1572 (2002)


Properties of P(VDF-TrFE)

• Operating temperature

Best VDF content


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Paul Heremans


Polarization switching of P(VDF-TrFE) capa

• Very square loops: large Remanent Polarization (Pr~80 mC/m2)• Relatively large Coercitive Field (Ec~ 0.5 MV/cm)• True (large bandgap) insulator

0 20 40 60 80 100 120 140 160 180 200 220

0

20

40

60

80

100

P r [m

C/m

2 ]

Field [MV/m]



• Switching time τs depends on applied field E– Consistent with “nucleation and growth”

– 1-10 Micro-second range in reach with E ~ 3-4 Ec (1.5 – 2 MV/cm)

Eswατ exp∝

Naber et al., Appl. Phys. Lett., Vol. 85, No. 11, 2004


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Paul Heremans



• Data retention: excellent stability

0

20

40

60

80

100

0 10 20 30 40 50 60

Time [Hours]

P r [m

C/m

2 ]

Philips


P(VDF-TrFE) ferro-electric capacitor array

• Passive array• Destructive read-out• External reader• Fully printed on plastic foil

• Application examples:– Game cards

• Player level programmedon card

– Brand protection

Thin-Film ASA http://www.thinfilm.se


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Paul Heremans


Inventory




– Diode


++

↑↓

MIS


Ferro-electric organic memory transistors

FIG. 1b. Schematic diagrams of FETs with oriented dipoles embedded in the gate dielectric and influencing the effective voltage at the dielectric-semiconductor interface.

FIG. 3. Hysteretic drain current as a function of gate voltage for polymer FeFETs (Au / P(VDF/TrFE) / MEHPPV). The ferroelectric layer thickness is 0.85 μm. The arrows show the clockwise hysteresis of the drain current consistent with accumulation and depletion of p-type charge carriers. The FeFETs had previously been brought into the off-state.

Naber et al., Nat. Mat. 4, 243 (2005)


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Paul Heremans


Switching with 85 V / 850 nm gate pulses




retention fatigue



Switching with 77.5 V / 850 nm gate voltage sweep


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Paul Heremans




~ 1E13 q/cm2


Summary FE capa and TFT

• Scaling of thickness to ~ 60 nm has been done• Scaling of voltages is reasonable:

Ec ~ 0.5 MV/cmEprog ~ 2X … 3X Ec

• Large remanent polarization Pr~80 mC/m2 Large accumulation charge switching in TFT

• Programming time can scale to the range 1…10 μs (for Eprog ~ 3X … 4X Ec)

• Fatigue may be an issue (beyond 1000 cycles)• Operation temperature limited by TCurie ~ 140 ºC• Preliminary data show excellent retention


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Paul Heremans


Inventory




– Diode


++

↑↓

MIS


Ferro-electric memory diode

• Context: 1D-1R cell in cross-bar architecture with non-volatile switcheable resistors.

• Diode with switcheable characteristics

0 V 10 V

0 V

10 V

selected cell

Diode

Switcheable resistor

bit l

ine

word line

1D-1R crossbarRequired element


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Paul Heremans


How we can make a Diode using OSC

• Schottky diode between Ohmic and Rectifying contacts

S. Steudel et al., Nat. Mat., Vol 4, p. 597, 2005

Al

Organic semiconductor

Au

substrate

A

C

E


Polymer Ferro-Electric Diode

K. Asadi et al., Nat. Mat., Vol 7, p. 547, 2008

P3HT

P(VDF-TrFE)


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Paul Heremans


• 140-250 nm thickness

• Ag electrodes• Poled at +20V/-20V• Areas =

0.3×0.3mm2 to 4×4mm2







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Paul Heremans


Inventory

• Charge-storage– In the gate dielectric of an organic TFT

• Polarization switching– Capacitor


– Diode

• Resistive switching– Cross-bar architecture

++

↑↓

MIS


Resistive switching

• Cross-bar architecture• Non-volatile• Non-destructive read• Re-writeable• Materials:

– Charge transfer complexes

– Metal-nanoparticles

– Polymers


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Paul Heremans


Materials 1: charge transfer complexes

• Charge-Transfer complexes:• CuTCNQ and AgTCNQ

R.S. Potember et al., Appl. Phys. Lett. 34 (1979) 405Z. Fan et al., IEEE-NANO, (2003) 588-591

• Bengal Rose, Phloxine, …A. Bandyopadhyay et al., Appl. Phys. Lett. 82 (2003) 1215-1217

• PCBM/TTFC.-W. Chu et al., Adv. Mat. 17 (2005) 1440-1443

CC-

N

NN

NCu

+

I

I

Cl

Cl Cl

I

Cl COONa

O

I

ONaO

CuTCNQ

Bengal Rose

+

+

+

-

-

-

Partially neutral: high σ

+

+

+

+

+ +

- -

- -

- -

Ionized: low σ

Originally proposed mechanism:


Characteristics of M/CuTCNQ/Al cross-bars

• CuTCNQ (Potember 1979)• Metal: Cu, Ag• Polynitrile π-acceptors: TCNQ (+ derivatives), DDQ,

DCNQI, TCNE, …• Bipolar resistive electrical switching (in air)

Measurement setup Typical log|I|-V curve

10-9

10-8

10-7

10-6

10-5

10-4

Cur

rent

(A)

86420-2-4-6

Voltage Memory (V)

1

3 4

6

Start

25

Typical I-V curve

-300

-200

-100

0

100

Cur

rent

(µA

)

86420-2-4-6

Voltage Memory (V)

32

1 6

54

Start


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Paul Heremans


Materials 2: nanoparticles

• Metallic nanoparticles in organic semiconductor:• Organic/metal-nanocluster/organic system

L. Ma et al., Appl. Phys. Lett. 82 (2003) 1419-1421L. Bozano, Adv. Funct. Mat. 15 (2005) 1933

• Polyaniline nanofiber / Au nanoparticleR.J. Tseng et al., Nano Lett. 5, 2005, 1077-1080

Originally proposed mechanism:

+


Materials 3: polymers

• Polymers:• Polythiophene derivative

H.S. Majumdar et al., Synth. Met. 140 (2004) 203-206

• Alq3, superyellow PPV, OC1C10, polyspirofluoreneM. Cölle et al., Organic Electronics, 7, 305, 2006

• Isolators such as polystyreneM. Cölle et al., Organic Electronics, 7, 305, 2006

•Polymer blends:• P3HT+EC / PEDOT:PSS+LiCF3SO3+EC

J.H.A. Smits et al., Adv. Mat. 17 (2005) 1169-1173

R1

R2

polymers

Al = Electrode 2


Or

polymer

Electrode 1

substrate


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Paul Heremans


Typical curves for Polymers & NP

Typical characteristics for Metal/Polymer/Metal systems

• UNIPOLAR switching: ON and OFF can be achieved with same voltage polarity• Often possible in two directions

L. Bozano, Adv. Funct. Mat. 15 (2005) 1933


Characteristics

M. Coelle et al., Organic Electronics 7 (2006) 305–312

Al = Electrode 2


Polymer

Electrode 1

substrate


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Paul Heremans


Mechanism

• Filamentary conduction in “on” state• For many of the devices proposed, interfacial

(native) AlOx contains the current switches

M. Coelle et al. / Organic Electronics 7 (2006) 305–312

These devices are kin to Oxide RRAM!Review by Waser and Aono, Nat. Mat. Vol 6, p. 833, 2007

Similar to “Oxide”, also for “Organic” RRAMunipolar and bipolar switching has been shown

oxide

organic

e.g. “polymer” and NPe.g. CuTCNQ


Similarity with “nanoelectromechanical” switch ?

L. Bozano, Adv. Funct. Mat. 15 (2005) 1933

nature materials VOL 7 DECEMBER 2008

Y. Li, Nature Materials 7 (2008) 966

Electronic two-terminal bistable graphitic memories


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Paul Heremans



• CuTCNQ (Potember 1979)• Metal: Cu, Ag• Polynitrile π-acceptors: TCNQ (+ derivatives), DDQ,

DCNQI, TCNE, …• Bipolar resistive electrical switching (in air)

Measurement setup Typical log|I|-V curve

10-9

10-8

10-7

10-6

10-5

10-4

Cur

rent

(A)

86420-2-4-6

Voltage Memory (V)

1

3 4

6

Start

25

Typical I-V curve

-300

-200

-100

0

100

Cur

rent

(µA

)

86420-2-4-6

Voltage Memory (V)

32

1 6

54

Start



• Endurance of 104 write/erase cycles

4

68

1µA

2

4

68

10µA

2

4

Cur

rent

1000080006000400020000Cycle number

ON OFF

VM = -1 V

40003000200010000Counts

4

68

1µA

2

4

68

10µA

2

4

Cur

rent

ON OFF

VM = -1 V

Cycles (cross-bar memory):Au\CuTCNQ\Al: 0.04 mm2

Müller et al., Mater. Res. Soc. Symp. Proc., 997 (2007) I01-10

Pulsed measurements (capacitor):Al\CuTCNQ\Al: 0.005625 mm2

Kever et al., Thin Solid Films, 515 (2006) 1893

• Retention time up to 60h• Operational up to about 80°C

Müller et al., Mater. Res. Soc. Symp. Proc., 997 (2007) I01-10


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Paul Heremans



Müller et al., Appl. Phys Lett., 89 (2006) 223501

Cu SiO2 SiC TaN + Ta SiSiN CuTCNQ

10-11

10-10

10-9

10-8

10-7

10-6

Cur

rent

(A)

6420-2-4Voltage Memory (V)

1

2

3

4

OFF → ON ON → OFF

Mushroom like CuTCNQ growth in 250 nm vias

Single crystal CuTCNQ growth in 100 nm vias


Phase transition (II→I)(If not consequence of CuTCNQ roughness)Heintz et al. (1999)

Bulk phenomena(phase transition?)Potember et al. (1979)

Switching with c-STM tip → bulk effect (?)Matsumoto et al. (1991)

Bulk phenomena

Investigation of switching in CuTCNQ memory

Cu\CuTCNQ\Al: increase of resistance after air exposureHoagland et al. (1993)

Impedance spectroscopy →highly resistive CuTCNQ\Al interfaceKever et al. (2007)

Reproducible switching for ITO\Al (Al2O3)\CuTCNQ\AlOyamada et al. (2003)

Interfacial effect

Impedance & capacitance measurements →CuTCNQ\Al interface effectSato et al. (1990)

Raman signal of TCNQ during OFF→ON switchingKamitsos et al. (1982) Switching with probe

needles or oxide layersHefczyc et al. (2008)

Apparent contradiction? Two different switching mechanisms?

[Cu+(TCNQ-)]n Cu0x + (TCNQ0)x + [Cu+(TCNQ-)]n-x

high impedance

"OFF state"

low impedance

"ON state"

voltage

R. Mueller et al., proceedings of MRS 2008


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Paul Heremans


Role of interface native oxide in CuTCNQ devices

Further proofs:Yb top contact (same procedure)Encapsulated devices (Miplaza, Eindhoven (NL)) with Al : no switching

Billen et al., Appl. Phys. Lett., 91 (2007) 263507

Cu\CuTCNQ\Al crossbar: 0.04 mm2

10-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

Cur

rent

(A)

1050-5Voltage Memory (V)

N2 glovebox (prior to air exposure)

12 4

3

10-11

10-10

10-9

10-8

10-7

10-6

10-5

10-4

10-3

Cur

rent

(A)

1050-5Voltage Memory (V)

N2 glovebox (prior to air exposure) Cycle 1 (after air exposure) Cycle 2 (after air exposure) Cycle 3 (after air exposure) Cycle 4 (after air exposure)

1

2

4

3

air

N2

HV


Role of interface native oxide in CuTCNQ devices

A. Hefczyc et al., Phys. Stat. Solidi A, 205 (2008) 647

Status of device I is independent of device II

Always same status for devices I and II

15 mμ5 mμ

Al AlAuCuTCNQ

15 mμ5 mμ

Au AuAl

CuTCNQ

II

→ Localized switching at the CuTCNQ\Al interface (no bulk effect)

I

I II


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Paul Heremans


Filamentary conduction in CuTCNQ devices

Heat sensitive infrared camera


I-t measurement

-220

-200

-180

-160

-140

-120

-100

-80

I (µA

)

0.1 1 10 100t (s)

Al\CuTCNQ\Al crossbar: 0.04 mm2

switched to the ON state


Comparison with other types of memories

•Programmable Metallization Cell (PMC)Ag-Ge-S, Cu-Ge-S (Cu and Ag cations, Kozicki et al. NVMWS 2005)Bipolar switching, electrochemical reaction

Ag2STerabe et al., RIKEN Rev., 37 (2001) 7

gap

•Sulfide based memoriesAg2S, Cu2S (Ag+ and Cu+ cations)Solid-state ionic conductor (κ: 1-4 S.cm-1 for silver chalcogenides)bipolar switching, electrochemical reaction, metallic filament

Cu2S, NanoBridge® Technology (NEC)Kaeriyama et al., IEEE J Solid-State Circ., 40 (2005) 168

•CuTCNQCu+ cations (Ag+ cations for AgTCNQ)κ: 0.25 S.cm-1 (phase I, Heintz et al., Inorg. Chem., 38 (1999) 144)Similar switching mechanism?


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Paul Heremans


Proposed model for M1/CuTCNQ/SL/M2

OFF state to ON state:

Cu Cu+

e-

(i)

Cu2+Cu+

e-

(ii)TCNQ- TCNQ

e-(iii)

Cu+

Cu-e

Cu, Au,Pt, ...

Al, Yb,Ti, ...

+ -

porous layer or

gap

easy oxidizable

metal

“noble”metal solid ionic conductor

(Cu+TCNQ-)

growth of Cu

filament

Cu+

Cu+

Cu+Cu+

≈ 20 nm → several μm few nm

reductionoxidation

Rfilament (Rfilament Rgap)RON RCuTCNQ RgapROFF = +



Proposed model for M1/CuTCNQ/SL/M2

ON state to OFF state:

Cu Cu+

e-(i)

Cu2+Cu+

e-

(ii)TCNQ- TCNQ

e-

(iii)

Cu+

Cu-e

Cu, Au,Pt, ...

Al, Yb,Ti, ...

-

porous layer or

gap

easy oxidizable

metal

“noble”metal solid ionic conductor

(Cu+TCNQ-)

dissolution of Cu

filament

Cu+

Cu+

Cu+Cu

+


oxidation

Rfilament (Rfilament Rgap)RON RCuTCNQ= +

+reduction

RgapROFF



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Paul Heremans


Recapituation on switching experiments

Bulk phenomena Interfacial effect

Interfacial effect (oxide layer or nanometer-size gap)

Phase transition (II→I)(If not consequence of CuTCNQ roughness)Heintz et al. (1999)

Bulk phenomena(phase transition?)Potember et al. (1979)

Switching with c-STM tip → bulk effect (?)Matsumoto et al. (1991)

Cu\CuTCNQ\Al: increase of resistance after air exposureHoagland et al. (1993)

Impedance spectroscopy →highly resistive CuTCNQ\Al interfaceKever et al. (2007)

Reproducible switching for ITO\Al (Al2O3)\CuTCNQ\AlOyamada et al. (2003)

Impedance & capacitance measurements →CuTCNQ\Al interface effectSato et al. (1990)

Raman signal of TCNQ during OFF→ON switchingKamitsos et al. (1982) Switching with probe

needles or oxide layersHefczyc et al. (2008)


Generalisation of the model

• Examples:• CuTNAP, AgTNAP (TNAP = 1 1,11,12,12-tetracyano-2,6-napthoquinodimethane )

Potember et al., J. Am. Chem. Soc., 102 (1980) 3659• CuDDQ (DDQ =2,3-dichloro-5,6-dicyano-p-benzoquinone)

Weitz et al., Nano Lett., 6 (2006) 2810

M M+

e-

(i)

Mn+M+

(n-1)e-

(ii)A- A

e-(iii)

M+

M-e

M, Au,Pt, ...

Al, Yb,Ti, ...

+ -growth of

M filament

M+

M +

M +M +


reductionoxidation

solid ionic conductor(M+A-)

porous layer or

gap

Switchinglayer

SIC

R. Mueller et al., MRS spring meeting 2008


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Paul Heremans


Summary CuTCNQ crossbar

• Model proposed in which conduction is controlled by metal filaments in a “switching layer” (gap, spacer), formed and dissolved by electrochemistry from ions provided through/from Solid Ionic Conductor

• Improved switching layers are being explored (EMMA)

• Fatigue gradually improves (1E4 cycles)• Temperature limited (T < 80ºC)• Retention unknown• Can be scaled to < 100 nm


Summary

• Capacitor type:– Ferro-electric capa

• Transistor-types:– Charge storage in dual-layer gate dielectric

– Ferro-electric gate dielectric

• Switching diodes:– Mix of semiconducting polymer and ferro-electric insulator between electrodes

• Switching resistors: – Unipolar and bipolar have been shown in literature

– In the case of the charge-transfer complex M-TCNQ (and similar molecules), the bipolar switching mechanism is traced back to metal filaments in gap layer, and the role of the M-TCNQ is a Solid Ionic Conductor

• Types of Reprogrammable Non-volatile “Organic” memories:


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Paul Heremans


Summary

• Plastic electronic circuits will require one or several forms of electrically reprogrammable non-volatile memory

• For integration in CMOS:– The CuTCNQ cross-bar has been shown to scale to the dimensions of via holes

– The temperature stability of the organic compounds is an issue

• Use of these memories:

• Excellent progress has been done in the understanding of the physics and switching mechanisms, which will allow to further optimize the characteristics


Acknowledgements

• IMEC research teams– Robert Mueller, Jan Genoe, Maarten Debucquoy, Joris Billen,…

– Dirk Wouters, Ludovic Goux,

• IMEC research partners– Philips, TNO (Gerwin Gelinck, Paul Blom), RWTH, IM2NP, IUNET,

NUMONYX, MDM

• Financial support– Nosce Memorias, FP6 project

– EMMA, FP7 project


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organic memory tutorial vs2 - university of exeter...

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