Organic electronics : structural and electronic properties of OFETs /

Contents 7
Foreword 21
Acknowledgement 33
List of Contributors 35
Color Plates 47
PartI Industrial Applications 99
1 Organic Transistors as a Basis for Printed Electronics 101
1.1 Introduction 101
1.2 What is an Organic Transistor? 102
1.3 How Does an Organic Transistor Work and How Does it Distinguish Itself from a Conventional One? 103
1.4 Basic Logical Integrated Circuits: Ring Oscillators 104
1.5 Complex Organic Circuits: the 64-Bit RFID Tag 107
1.6 Organic CMOS Circuits 108
1.7 Printing Electronics 109
1.8 Application and Future Prospects 111
1.9 Summary and Prospects 112
Acknowledgements 112
References 112
2 Printable Electronics: Flexibility for the Future 115
2.1 Introduction 115
2.2 Printed Electronics Market Forecasts 115
2.3 New Products 116
2.3.1 Advantages of Printed Electronics 117
2.3.2 Passive Elements 118
2.3.3 TFT-Backplanes 119
2.3.4 RFID Tags 119
2.4 Printing Considerations 121
2.5 Materials 122
2.5.1 Conductors 123
2.5.2 Dielectrics 125
2.5.3 Semiconductors 126
2.5.3.1 Organic Semiconductors 127
2.5.3.2 Inorganic Semiconductors 128
2.6 Creavis Science-to-Business Approach 129
2.7 Conclusion 130
Acknowledgements 131
References 131
Part II Molecular Compounds 133
3 Fluorinated Phthalocyanines as Molecular Semiconductor Thin Films 135
3.1 Introduction 135
3.2 Experimental 137
3.2.1 Chemical Synthesis 137
3.2.1.1 Phthalocyaninato 137
3.2.1.2 2,29,20,2-Tetrafluorophthalocyaninato Zinc(II) (F(4)PcZn) 137
3.2.1.3 4,5-Difluorophthalonitrile 138
3.2.1.4 2,29,20,2-,3,39,30,3-Octafluorophthalo-cyaninato Zinc(II) (F(8)PcZn) 138
3.2.1.5 1,19,10,1-,2,29,20,2-,3,39,30,3-,4,49,40,4-Hexadecafluorophthalocyaninato Zinc(II) 138
3.2.2 Calculation of Energy Levels 138
3.2.3 Thin Film Preparation and Measurements 139
3.3 Results and Discussion 140
3.3.1 Synthesis and Molecular Characterisation 140
3.3.2 Thin Evaporated Films of Zinc(II) Phthalocyanines with a Different Degree of Fluorination 142
3.3.3 Growth of F(16)PcZn Thin Films 149
3.3.4 Response to Oxygen from Air 150
3.3.5 Measurements of the Field Effect 153
3.4 Conclusions 155
Acknowledgements 156
References 156
4 Novel Organic Semiconductors and Processing Techniques for Organic Field-Effect Transistors 159
4.1 Introduction 159
4.2 Molecular Alignment from Solution Through the Zone-Casting Technique 160
4.3 Solution Processed Donor\u2013Acceptor Copolymer Field-Effect Transistors 165
4.4 Processing of Giant Graphene Molecules by Soft-Landing Mass Spectrometry 167
4.5 Conclusion 170
Acknowledgements 170
References 170
5 Assembly, Structure, and Performance of an Ultra-Thin Film Organic Field-Effect Transistor (OFET) Based on Substituted Oligothiophenes 173
5.1 Introduction 173
5.2 Experimental 176
5.2.1 General Procedures 176
5.2.2 Sample Preparation 177
5.2.3 OFET Device Fabrication 178
5.3 Results and Discussion 179
5.3.1 Bulk Characterisation 179
5.3.2 Film Characterisation 183
5.3.3 OFET Performance Characteristics 187
5.4 Conclusion 190
Acknowledgements 191
References 191
6 Organic Transistors Utilising Highly Soluble Swivel-Cruciform Oligothiophenes 193
6.1 Introduction 193
6.2 Optical and Thermal Properties 195
6.2.1 Optical Properties 195
6.2.2 Thermal Properties 197
6.3 Morphology Studies on Layers of Substituted Xruciforms 197
6.3.1 XRD Studies 198
6.3.2 AFM Studies 200
6.4 OFET Studies 202
6.5 Mobilities from Radiation Induced Conductivity Measurements 205
6.6 Conclusions 207
6.7 Experimental Section 207
Acknowledgement 208
References 208
Part III Structural and Morphological Aspects 211
7 Chemical Approaches to the Deposition of Metal Electrodes onto Self-Assembled Monolayers \u2013 A Step Towards the Fabrication of SAM-Based Organic Field-Effect Transistors 213
7.1 Introduction 213
7.2 Results and Discussion 215
7.2.1 Nature of the SAM 215
7.2.2 Seeding Material 217
7.2.3 Stabilising Layer of the Nanoparticles 218
7.2.4 Amplification Method (CVD vs. ELD) 219
7.2.5 Composition of the ELD Bath 223
7.3 Conclusions 230
7.4 Experimental 231
7.4.1 Nanoparticles 231
7.4.2 Substrate Preparation 231
7.4.3 Plasma Cleaning [66] 231
7.4.4 Stamp Preparation 231
7.4.5 SAM Preparation 232
7.4.6 Ellipsometry 232
7.4.7 碌CP of Nanoparticles 232
7.4.8 Electroless Deposition of Gold 232
7.4.9 Chemical Vapour Deposition of Gold 232
7.4.10 AFM Measurements 233
Acknowledgements 233
References 233
8 Growth Morphologies and Charge Carrier Mobilities of Pentacene Organic Field Effect Transistors with RF Sputtered Aluminium Oxide Gate Insulators on ITO Glass 237
8.1 Introduction 237
8.2 Experimental 238
8.3 Results and Discussion 240
8.3.1 Structural and Morphological Properties of the Pc Films 240
8.3.1.1 X-Ray Diffraction 240
8.3.1.2 Scanning Force Microscopy 243
8.3.2 Analysis of the Electrical Characteristics 246
8.3.2.1 Overview of the ID\u2013VD Characteristics 246
8.3.2.2 Temperature Dependence of the Mo-bilities 249
8.3.2.3 Detailed Analysis of the Field Effect Mobilities as a Function of VD and VG 250
8.3.3 Discussion and Conclusions 255
8.3.3.1 Correlation of the Electrical Transport Properties and the Film Morphology 255
8.3.3.2 Origin of the Structural Defects and Conclusions 256
8.4 Summary 257
Acknowledgements 257
References 258
9 In Situ X-Ray Scattering Studies of OFET Interfaces 259
9.1 Introduction 259
9.2 X-Ray Scattering 261
9.3 Growth Physics 262
9.3.1 Monolayer Deposition 262
9.3.2 Thin Film Growth and Dynamic Scaling 263
9.3.3 Growth of Organic Molecular Materials 264
9.4 Organic Thin Films 265
9.4.1 Pentacene on Silicon Oxide 265
9.4.2 DIP on Silicon Oxide 267
9.4.3 PTCDA on Ag(111), Cu(111), and Au(111) 271
9.5 Organic Heterostructures 273
9.5.1 Metal Capping Layers 273
9.5.2 Insulating Capping Layers 274
9.5.2.1 Degradation of Devices 275
9.5.2.2 Encapsulation of Devices 275
9.5.2.3 Aluminium Oxide Capping Layers 276
9.5.2.4 Thermal Stability of Capped Organic Films 278
9.6 Conclusion 281
Acknowledgements 282
References 282
10 X-Ray Structural and Crystallinity Studies of Low and High Molecular Weight Poly(3-hexylthiophene) 287
10.1 Introduction 287
10.2 Sample Preparation 289
10.3 X-Ray Grazing-Incidence Diffraction Studies 289
10.4 Structure Determination for LMW Fraction 293
10.5 Temperature-Dependent Measurements 296
10.6 Discussion 300
Acknowledgements 302
References 302
11 Molecular Beam Deposition and Characterisation of Thin Organic Films on Metals for Applications in Organic Electronics 305
11.1 Introduction 305
11.2 Electronic Level Alignment at the Metal/Organics Interface 306
11.3 Structural Properties at the Metal/Organic Interface 309
11.4 General Principles Governing Organic Molecular Beam Deposition (OMBD) on Metal Substrates: Case Studies for Rubrene, Perylene and Pentacene 310
11.4.1 Rubrene Deposition on Au(111) 311
11.4.2 Adsorption-Induced Restructuring of Metal Substrates: Perylene on Cu(110) 312
11.4.3 Organic Molecular Beam Deposition of Pentacene on Clean Metal Surfaces 314
11.5 Organic Molecular Beam Deposition of Perylene 318
11.6 Growth of Other Molecules of Interest for Organic Electronics on Metal Substrates 321
11.7 Growth of Pentacene on Modified Gold Surfaces 322
11.8 Realisation of an \u201cIdeal\u201d Diode-like Organic Electronic Device 324
Acknowledgement 326
References 327
12 Fundamental Interface Properties in OFETs: Bonding, Structure and Function of Molecular Adsorbate Layers on Solid Surfaces 333
12.1 Introduction 333
12.2 Bonding 336
12.2.1 Bonding: What can be Learned for OFETs? 341
12.3 Structure 344
12.3.1 Structure: What can be Learned for OFETs? 350
12.4 Function 353
12.5 Conclusion 357
Acknowledgements 357
References 358
13 Metal/Organic Interface Formation Studied In Situ by Resonant Raman Spectroscopy 361
13.1 Introduction 361
13.2 Methods 361
13.2.1 Sample Preparation and Characterisation 361
13.2.2 Theoretical Methods 362
13.3 Results and Discussion 362
13.3.1 Chemistry of Metal/Organic Interfaces 362
13.3.2 Morphological Properties and Indiffusion of Metals at the Interfaces with Organic Semiconductors 368
13.3.3 Assignment of Raman Intensities with DFT Calculations 374
13.4 Conclusion 376
Acknowledgements 377
References 377
14 Development of Single-Crystal OFETs Prepared on Well-Ordered Sapphire Substrates 379
14.1 Introduction 379
14.1.1 The Present Micro-OFET Concept 380
14.2 Experimental 381
14.3 Results and Discussion 382
14.3.1 Realisation of the Micro-OFET Concept 382
14.3.1.1 Sapphire Substrate 382
14.3.1.2 Growth of DIP on Sapphire 384
14.3.1.3 Contacts \u2013 the Au/DIP Interface 387
14.3.1.4 Gate Electrode 392
14.3.1.5 In Situ Device Characterisation 393
14.4 Conclusions 394
Acknowledgements 395
References 395
Part IV Device Performance and Characterisation 397
15 Pentacene Devices: Molecular Structure, Charge Transport and Photo Response 399
15.1 Introduction 399
15.2 Pentacene Thin Films 399
15.2.1 Film Formation on Inert Surfaces 399
15.2.2 Film Formation on Metallic and Conductive Surfaces 403
15.2.3 Mixed Films 404
15.3 Pentacene OTFT Properties 405
15.3.1 Mobility and Charge Carrier Density 405
15.3.2 Influence of Trap States and Fixed Interface Charges 407
15.3.3 Injection 409
15.4 Photo Response 409
15.5 Outlook 410
Acknowledgements 411
References 412
16 Characteristics and Mechanisms of Hysteresis in Polymer Field-Effect Transistors 415
16.1 Introduction 415
16.2 Literature Survey 416
16.3 Experimental Results 418
16.3.1 Organic Field-Effect Transistors 418
16.3.1.1 Short Channel OFET Based on P3HT 418
16.3.1.2 OFET Based on a Modified PPV and with Silanised Gate Oxide 420
16.3.2 Organic MIS Capacitors 421
16.3.2.1 Quasi-Static CV Curves for a Capacitor with Arylamino-PPV 421
16.3.2.2 Dynamic CV Curves 423
16.4 Trap Recharging Mechanism 425
16.4.1 Simulations for the MIS Capacitor 425
16.4.2 Simulations for Thin-Layer OFETs and the Corresponding Capacitor 427
16.5 Equilibrium of Polarons With Doubly Charged States of the Polymer Chain 429
16.5.1 Polarons and Bipolarons or Polaron Pairs 430
16.5.1.1 Polarons and Bipolarons 430
16.5.1.2 Polarons and Polaron Pairs 431
16.5.2 Polarons, Bipolarons and Polaron Pairs 433
16.5.3 Polarons and General Dipolarons 435
16.6 Bipolaron Mechanism for Hysteresis 437
16.6.1 Formation and Dissociation of Bipolarons 437
16.6.1.1 Kinetics of Formation and Dissociation 437
16.6.1.2 The Bipolaron Mechanism 438
16.6.2 Formation of Complexes With Counter Ions 439
16.6.2.1 The Kirova\u2013Brazovskii Scenario of Complex Formation 439
16.6.2.2 Slow Ion Capture by an Overcharged Complex 440
16.7 Conclusion 441
Acknowledgements 442
References 442
17 Ambipolar Charge Carrier Transport in Organic Semiconductor Blends 445
17.1 Introduction 445
17.2 Materials, Device Preparation and Experimental Methods 446
17.3 Unipolar Field-Effect Transistors 450
17.4 Ambipolar Field-Effect Transistors 451
17.5 Charge Carrier Mobility and Threshold Voltage 452
17.6 Film Morphology and Structure 455
17.7 Electronic Structure 457
17.8 Charge Carrier Injection 460
17.9 Ambipolar and Complementary Inverter 463
17.10 Summary 467
Acknowledgements 467
References 468
18 Gate Dielectrics and Surface Passivation Layers for Organic Field Effect Transistors 471
18.1 Introduction 471
18.2 Experimental 472
18.2.1 Transistor Device 472
18.2.2 Inorganic Dielectrics 472
18.2.3 Polymer Dielectrics 473
18.3 Results and Discussion 474
18.3.1 Inorganic Gate Dielectric Layers 475
18.3.1.1 Thermally Grown Silicon Dioxide 476
18.3.1.2 TEOS Oxide 478
18.3.1.3 Silicon Nitride 480
18.3.1.4 Low-Temperature Oxide: LTO 481
18.3.1.5 PECVD 482
18.3.1.6 Ta(5)O(2) 483
18.3.1.7 Conclusion 484
18.3.2 Polymer Dielectrics 485
18.3.2.1 Bectron(庐) Varnish 487
18.3.2.2 High-k Resist 488
18.3.2.3 OFET on Foil Substrates 489
18.3.2.4 Conclusion 490
18.4 Degradation 491
18.5 Conclusion 496
Acknowledgements 497
References 497
19 Influence of Metal Diffusion on the Electronic Properties of Pentacene and Diindenoperylene Thin Films 499
19.1 Introduction 499
19.2 Experimental 500
19.2.1 Organic Semiconductors 500
19.2.2 Thin Film Deposition 501
19.2.3 Radiotracer Measurements 502
19.2.4 Serial Sectioning by Ion Beam Sputtering 503
19.2.5 Electrical Measurements 503
19.3 Results and Discussion 503
19.3.1 Radiotracer Measurements 503
19.3.2 Correlation Between Metal Diffusion and Device Properties of OFETs 514
19.3.3 Teflon-Based Electret Layers for Threshold Voltage Tuning 519
19.4 Conclusions 522
Acknowledgements 523
References 523
20 Potentiometry on Pentacene OFETs: Charge Carrier Mobilities and Injection Barriers in Bottom and Top Contact Configurations 525
20.1 Introduction 525
20.2 Device Geometries and Sample Preparation 527
20.3 Pentacene OFETs With Bottom Contacts 529
20.3.1 Potentiometry and Electrical Probes 529
20.3.2 Mobility Estimates 529
20.3.3 Two-Dimensional Device Simulation 531
20.3.4 Charge Transient Spectroscopy 534
20.4 Investigations of Top-Contacted Pentacene OFETs 536
20.4.1 Electrical Characterisation In Situ 536
20.4.2 Potentiometry Measurements Ex Situ 537
20.4.3 Charge Transient Spectroscopy 539
20.5 Conclusion 540
Acknowledgements 541
References 541
21 Microscopic and Spectroscopic Characterisation of Interfaces and Dielectric Layers for OFET Devices 543
21.1 Introduction 543
21.2 Experimental 545
21.2.1 Microscopic Methods 545
21.2.1.1 PEEM 545
21.2.1.2 SKPM 546
21.2.2 Ferroelectric Devices 546
21.2.2.1 Interface Characterisation 546
21.2.2.2 Electrical Characterisation (CV, IV) 547
21.3 Results and Discussion 548
21.3.1 Microscopic Methods 548
21.3.1.1 PEEM 548
21.3.1.2 SKPM 552
21.3.2 Ferroelectric Devices 554
21.3.2.1 Interface Characterisation 554
21.3.2.2 Electrical Characterisation of MFIS Capacitors (CV Measurements) 558
21.3.2.3 Ferroelectric OFET 560
21.4 Summary and Conclusions 563
Acknowledgements 565
References 565
22 Scaling Limits and MHz Operation in Thiophene-Based Field-Effect Transistors 567
22.1 Introduction 567
22.2 Device Preparation 569
22.2.1 Geometries 569
22.2.2 Sample Preparation 570
22.3 Thiophene-Based Semiconductors 571
22.3.1 Unsubstituted Oligothiophenes 571
22.3.2 Substituted Oligothiophenes 572
22.3.3 Polythiophenes 573
22.4 L Dependence of OFETs 574
22.4.1 Influence of the Electrode Material 574
22.4.2 Influence of the Insulator Thickness 576
22.5 Optimised Sub-micron OFETs 577
22.5.1 Semiconductor Related Performance 577
22.5.2 Tuning the Contact Resistance 579
22.6 Influence of the Semiconductor Thickness 581
22.6.1 Large Channels 582
22.6.2 Sub-micron Channels 583
22.7 Megahertz Operation 586
22.7.1 Theoretical Considerations 586
22.7.2 Experimental Results 589
22.8 Summary 592
Acknowledgements 593
References 593
23 Aluminium Oxide Film as Gate Dielectric for Organic FETs: Anodisation and Characterisation 597
23.1 Introduction 597
23.2 Experimental 598
23.2.1 Preparation 598
23.2.2 Characterisation 598
23.3 Results and Discussion 599
23.3.1 Influence of Formation Current Density 599
23.3.2 Influence of the Formation Voltage 602
23.3.3 Influence of Anodisation Time 604
23.3.4 Influence of Surface Roughness 606
23.3.5 Barrier Aluminium Oxide Films as Gate Dielectrics for Organic Transistors 607
23.4 Conclusion 608
Acknowledgements 609
References 609
24 Electronic States at the Dielectric/Semiconductor Interface in Organic Field-Effect Transistors 611
24.1 Introduction 611
24.2 Experimental 615
24.2.1 Device Structure 615
24.2.2 Device Measurement 616
24.3 Results and Discussion 617
24.4 Conclusion 633
Acknowledgements 635
References 635
25 Aspects of the Charge Carrier Transport in Highly-Ordered Crystals of Polyaromatic Molecules 637
25.1 Introduction 637
25.2 Experimental 639
25.2.1 Material Selection 639
25.2.2 Purification 639
25.2.2.1 Purification by Zone Refinement 640
25.2.2.2 Purification by Sublimation 641
25.2.2.3 Control of Chemical Purity 641
25.2.3 Crystal Growth 642
25.2.4 Field-Effect-Transistor Fabrication 644
25.2.4.1 Gate Insulator Thickness 645
25.3 Results and Discussion 646
25.3.1 Tetracene Crystals: Surface Versus Bulk Transport 646
25.3.2 Diindenoperylene Crystals: Structural Impact on Transport 652
25.4 Conclusion 659
Acknowledgements 660
References 660
Part V Novel Devices 663
26 Carbon Nanotube Transistors \u2013 Chemical Functionalisation and Device Characterisation 665
26.1 Introduction 665
26.2 Carbon Nanotubes \u2013 Fundamentals 666
26.2.1 Physical and Electronic Structure 666
26.2.2 Field-Effect Transistors Based on Single SWCNTs 667
26.2.3 CNT-FETs Based on Electrochemical Field-Effect 670
26.2.4 Role of Capacitances 671
26.3 Chemical Functionalisation 673
26.3.1 Motivation and Strategies 673
26.3.2 Chemically Modified Devices 674
26.3.3 Electrochemical Functionalisation 675
26.3.4 Selective Electrochemical Functionalisation 677
26.3.5 Chemical Doping 681
26.3.6 Sensors Based on Functionalised SWCNT-FETs 683
26.4 Device Characterisation of CNT-FETs 683
26.4.1 Back-Gated Devices 684
26.4.1.1 Saturation 684
26.4.1.2 Transconductance 684
26.4.1.3 Sub-Threshold Swing 684
26.4.1.4 Mobility 685
26.4.2 Electrochemically Gated Devices 685
26.4.3 Scanning Photocurrent Microscopy 685
26.5 Future Perspectives 687
26.6 Conclusion 688
Acknowledgements 688
References 688
27 Contact Effects in Cu(TCNQ) Memory Devices 693
27.1 Introduction 693
27.2 Experimental and Results 695
27.2.1 Device Preparation 695
27.2.2 Contact Size 696
27.2.3 Oxide Interlayer Between Top Contact and Cu(TCNQ) 697
27.2.4 Reversible Loss of Bistability in Oxygen-Free Ambience 698
27.2.5 Tip Contacts of Various Metals to Cu(TCNQ) 699
27.2.6 Planar Device Structure 702
27.2.7 Localisation of Switching Region 703
27.3 Discussion and Conclusion 707
Acknowledgements 710
References 710
28 Organic Field-Effect Transistors for Spin-Polarised Transport 711
28.1 Introduction 711
28.2 Concepts and Progress of Spintronics 712
28.3 Organic Semiconductors in Spintronics Applications 714
28.4 OFET Concept for Spin-Polarised Transport 715
28.5 Experimental Realisation 718
28.6 Results and Discussion 719
28.7 Conclusion 724
Acknowledgements 725
References 725
Index 727