Organic Thin film transistors
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Organic transistors were first developed in 1986 and use organic molecules rather than silicon as the active material. They have advantages over traditional silicon transistors such as being lightweight, flexible, cheap to produce, and compatible with solution processing and plastic substrates. Key parameters for organic transistors include mobility, on-off ratio, and threshold voltage. Device design can be top contact or bottom contact, with top contact having superior performance. Pentacene-based organic transistors currently have the best field effect mobility. Improving the dielectric, electrodes, and reducing contact resistance and leakage current can further increase performance. Organic transistors have applications in flexible displays, memory, sensors, and more.
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Organic Thin film transistors
- 2. Outline 1. Motivation and introduction 2. Types and mechanism 3. Different advancement 4. Vacuum and solution based processes 5. Applications
- 3. What and why an organic transistor? • First Organic Transistor - 1986 • Using organic molecules (Polymers) rather than silicon for their active material. • Semiconductor • Advantages 1. Light weight, 2. flexible, 3. Cheap 4. Solution Processing Photolithographic patterning 5. lower temperature manufacturing (60-120° C) 6. Print-able Organic Transistors 7. compatibility with plastic substances 8. foldable & light weight (Tsumura et al. 1986. B. kumar et al. 2014.
- 4. Device Structure • Important parameters Key Parameters – Mobility (µ ≈ 1-10 cm2/vs) – On-Off Ratio • Suitable (106) – Threshold voltage – Colin Rees et al. 2005
- 5. Device design • Top contact • Bottom contact Top contact devices have superior performance sue to low contact resistance between the source and active layer. Roichman et al. 2004
- 6. Comparison of different OTFTs Comparative plot of the OTFTs which are based on different materials is shown. Different materials have been assed to improve the device performance. Among all the materials pentacene based organic thin film transistors or electronic devices have best field effect mobility. Feng et al. 2015, B. kumar et al 2014
- 7. Interlayer between electrode and insulator Capacitance and leakage current of the device is reduced. J. Yoon et al. 2013 C. Chu et al.2005
- 8. High Performance OTFT with a metal/metal oxide bilayer electrode • TMO helps in controlling work function and charge injection properties • Reduces contact barrier and prevents the diffusion *Chih-Wei Chu, Sheng-Han Li, Chieh-Wei Chen, Vishal Shrotriya, and Yang Yang, High-performance organic thin-film transistors with metal oxide/metal bilayer electrode, Applied Physics Letters 87, 193508 (2005);
- 9. Other key factors to improve Field Effect Mobility • Higher the dielectric constant of insulator higher will be the field effect mobility • k↑ → Polarization↑ → Carrier Density↑ → Mobility↑ • Dielectric roughness also effect the field effect mobility • Roughness↓ → Mobility↑ • Higher the contact resistance of the insulator with the electrodes will lower the field effect mobility. Penetration of the electrode into the dielectric also effect the mobility, higher the penetration lower will be the mobility • Au coated (PEDOT/PSS) Charge Injection↑ → Contact Resistance↓ → mobility↑ • H. H. Lee et al. Appl. Phys. Lett. (2005) • 18- R. Schroeder et al, Appl. Phys. Letts (2005)
- 10. Vacuum Processes Solution Processes PECVD , PVD, LPCV, OVPD Conventional Process Provides advantage of Deposition Rate Monitoring Controlled Costly Colin et al. 2011. Coating by Spray, spin Electrodeposition Electroless deposition Also includes printing processes Very lost Cost Flexible Can be used for large area applications Efficiency few orders
- 12. Any Question?