Introducing the RoVaCBE Flagship project: Roll-to-roll Vacuum-processed Carbon Based Electronics. Dr Hazel Assender, University of Oxford

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1 Introducing the RoVaCBE Flagship project: Roll-to-roll Vacuum-processed Carbon Based Electronics Dr Hazel Assender, University of Oxford DALMATIAN TECHNOLOGY 21 st Sept

2 Organic electronics Opportunity for large-area roll-to-roll processing Mechanical flexibility Low density Low environmental impact Low cost, simple devices 21 st Sept

3 Roll-to-roll processing Camvac Oxford vacuum web coating 21 st Sept

4 Roll-to-roll processing: easy? All materials need to be cheap and available No high temperature processes Rough surfaces Polymers often stretch during winding Polymers outgas Brittle layers may crack or be abraded during winding Effect of deposition on underlying layers 21 st Sept

5 Solvent vs. Vacuum Solvent No pumping Patterning relatively easy Less water-loss from substrate Most UK development recently Vacuum No solvent/low energy Metallisation/ceramic layers PVD rapid Multilayers easier 21 st Sept

6 Example application Tagging devices on packaging Anti-counterfeiting Brand protection Product tracking Sensors Displays 21 st Sept

7 Manufacturing capability Source and Drain (Metal) SEMICONDUCTOR EVAPORATION L Org. Semiconductor Gate Substrate (e.g. PET) W Possible interlayer Insulator (e.g. acrylic dielectric) Possible surface modification 21 st Sept

8 Materials Organic semiconductor Molecular materials can have higher mobility than polymers (e.g. 5 cm 2 /(Vs)) Without requirement for solubility, can design for high stability product Donor R1 R1 Si R1 Acceptor R2 R2 R1 R1 Si R1 Organic dielectric Flash evaporation High speed process Already used for capacitor technology Free of pin-holes over large area Explore modification to curing process and monomers R1, R2, R3 alkyl 21 st Sept

9 Circuit design Model circuits based on measured device performances Design circuits around transistor performance and patterning capability Minimise number of transistors Circuit design defines manufacturing priorities 21 st Sept

10 Patterning Circuit lay-out based on MD stripes with ±100 m registration 2D patterning Decrease feature size Select and apply existing technologies Flexoprinting/oil patterning Ink jet printing Evaporation jets Contact masks Laser ablation 21 st Sept

11 Technology hurdles Optimisation of process conditions for deposition of organic and inorganic thin film multilayer structures Patterning and registration of the organic layers Reproducibility and reliability in manufacture of arrays of transistors 21 st Sept

12 Getting the manufacture right: pentacene deposition Self-assembling molecules -orbital overlap gives good carrier mobility. C C p z orbital overlap: bond plane of sp 2 bonding (rings) Mobility Mobility Mobility ~10-8 cm 2 V -1 s -1 ~10-6 cm 2 V -1 s -1 ~10 0 cm 2 V -1 s -1 Ordered organic material has higher charge transport mobility IBM J. RES. & DEV. VOL. 45 NO st Sept

13 Intensity (counts/s) Intensity Intensity (arb. unit) Effect of Background Gases 1154 cm cm cm (deg.) N 2 Vacuum Ar (deg.) N 2 Vacuum Ar Raman shift (cm -1 ) Pentacene grown in N 2 ambience has the best quality of crystalline material as compared to those grown at Ar or higher vacuum. 21 st Sept

14 Absorbance Absorbance Absorbance Getting the manufacture right: dielectric layer Smooth, pin-hole free layer High degree of cure Optical Profilometry acrylate_run1 Well-cured acrylate_run3 Well-cured acrylate_run4 Incompletely cured acrylate_run1 acrylate_run3 acrylate_run High quality PEN Wavenumber (cm -1 ) Wavenumber (cm -1 ) 0.00 acrylate_run1 acrylate_run3 acrylate_run Wavenumber (cm -1 ) FTIR can determine the degree of cure Acrylic smoothing layer 21 st Sept

15 I D (A) I D (A) I D (A) I D (A) -2.0x10-9 Improving device performance V s-d (V) V S-D (V) x x x x x V s-d =-40V I on /I off =1.3x x x x (I D ) 1/2 (A) 1/ Increase cure current -1.0x x x x10-6 Thermal anneal 0V -10V -20V -30V -40V -10V -20V -30V -40V V G (V) V s-d (V) 21 st Sept

16 Summary Can make transistors in a R2R environment High yield (>90%) Using solventless, high-speed processes Close interface between circuit design, choice of materials and manufacture Additionally need to develop tailored patterning methods and assess circuit mechanical/thermal properties. 21 st Sept