ORGANIC THIN FILM TRANSISTORS

Chemical Processes For Display Devices Professor Heeyeop Chae

Presented by Hussain FiazStudent ID 2016711218

Outline1. Motivation and introduction2. Types and mechanism3. Different advancement4. Vacuum and solution based processes5. Applications

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. Cheap4. Solution Processing Photolithographic patterning5. lower temperature manufacturing (60-120° C) 6. Print-able Organic Transistors7. compatibility with plastic substances 8. foldable & light weight

(Tsumura et al. 1986.B. kumar et al. 2014.

Device Structure

• Important parameters Key Parameters

– Mobility (µ ≈ 1-10 cm2/vs)

– On-Off Ratio• Suitable (106)

– Threshold voltage

– Colin Rees et al. 2005

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

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

Interlayer between electrode and insulator

Capacitance and leakage current of the device is reduced.

J. Yoon et al. 2013 C. Chu et al.2005

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);

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)

Vacuum Processes Solution Processes

PECVD , PVD, LPCV, OVPD

Conventional ProcessProvides advantage of Deposition Rate MonitoringControlledCostly

Colin et al. 2011.

Coating by Spray, spinElectrodepositionElectroless depositionAlso includes printing processes

Very lost CostFlexibleCan be used for large area applicationsEfficiency few orders

FlexibleOLED

FlexibleLCD

OrganicMemory

ImageSensor

BioSensor

OrganicLaser

Smart CardRFID Tag

E-paper

OTFT

ICTechnology

OpticalTechnology

BioTechnologyApparel

Technology

SensorTechnology

Memory device

Technology

LCDTechnology

OLEDTechnology

E-PaperTechnology

Smart Textile

Application of Organic TFT

Any Question?