Organic Device Simulation Using Silvaco Softw are Silvaco Taiwan - PowerPoint PPT Presentation

Organic Device Simulation Using Silvaco Softw are Silvaco Taiwan September 2005

Organic Devices Simulation: Contents � � Introduction – Silvaco TCAD Simulator � � Theory – Models � � OTFT Simulation v.s Measurement � � OLED Simulation v.s Measurement � � Bilayer TPD/Alq3 OLED Example � � Transient Simulation of OLED Pixel � � Summary ����� � Organic Device Simulation Using Silvaco Software

Organic Devices Simulation: Silvaco’s TCAD Software � � ATHENA - 2D Process Simulator � � ATLAS – Device Simulator � � SPisces – Silicon material Drift-Diffusion Simulator � � Blaze – Hetero-interfaces (Compound Semiconductor) Materials Simulator � � TFT – a-Si/poly-Si TFT Device Simulator � � OTFT – Organic TFT Simulator � � OLED – Organic Light Emitting Diode Simulator ����� � Organic Device Simulation Using Silvaco Software

Organic Devices Simulation: Transport Mechanisms � � Metal & Semiconductors: charge transport is limited by scattering of the carriers, mainly due to thermally induced phonons and lattice deformations. Transport is limited by phonon scattering. Charge mobility decreases with temperature � � Organic materials: transport occurs by phonon assisted hopping of charges between localized states. Charge mobility increases with temperature � � General mobility model of organic material : � � Poole-Frenkel field-dependent mobility ����� � Organic Device Simulation Using Silvaco Software

Organic Devices Simulation: Organic Transport TheoryFor Simulation � � Charge Injection (metal contact) � � Ohmic (Dirichlet boundary condition) � � Schottky contact (injection limited current) : � � thermionic emission model - tunneling � � interface barrier lowering � � Transport model(bulk) � � Band-like transport model (organic molecular crystals: pentacene, tetracene) at low T. � � Space-Charge-Limited Current(SCLC): Poisson + Current continuity equations � � Hopping transport in disordered organic semiconductor � � Density of States � � Poole-Frenkel Mobility ����� � Organic Device Simulation Using Silvaco Software

Organic Devices Simulation: Classical Theory Of Charge Transport – Drift Diffusion Model � � Poisson Equation � � Current Continuity Equations � � Drift Diffusion Equations ����� � Organic Device Simulation Using Silvaco Software

Organic Devices Simulation: Density Of State & Trapped Charge – Organic Defects � � Density Of States (DOS) � � Trapped Charge ����� � Organic Device Simulation Using Silvaco Software

Organic Devices Simulation: Organic Defects � � Probability of Occupation � � Steady State: Recombination/Generation (SRH) ����� � Organic Device Simulation Using Silvaco Software

Organic Devices Simulation: Poole-Frenkel Mobility Models ����� � Organic Device Simulation Using Silvaco Software

Organic Devices Simulation: Langevin Recombination Rate & Exciton Rate Equations � � Langevin Radiative Rate � � Singlet Exciton ������ � Organic Device Simulation Using Silvaco Software

Organic Devices Simulation: Langevin Recombination Rate & Exciton Rate Equations (con’t) � � Triplet Exciton where ������ � Organic Device Simulation Using Silvaco Software

ATLAS – Organic Device Simulation: Mobility Simulation � � Time-of-flight(TOF) method � � SCLC method � � Field Effect Transistor(FET) method ������ � Organic Device Simulation Using Silvaco Software

ATLAS – Organic Device Simulation Measurement vs. Simulation � p -0.62 Density of States ������ � Organic Device Simulation Using Silvaco Software

ATLAS – Organic TFT Device Simulation Transfer curve: linear & sqrt(Ids) ������ � Organic Device Simulation Using Silvaco Software

ATLAS – Organic LED Device Simulation: OLED Example � � Metal/Organic Interface injection I.D. Parker J.Appl. Phys. 75(3),1 Feb 1994, p.1656 � ������ � Organic Device Simulation Using Silvaco Software

ATLAS – Organic LED Device Simulation Injection - Calcium Ca(2.9eV) is better than other cathode metal. Simulated Measured I.D. Parker J.Appl. Phys. 75(3),1 Feb 1994, p.1656 � ������ � Organic Device Simulation Using Silvaco Software

ATLAS – Organic LED Device Simulation: High- Efficient Amorphous OLED Fraction of injected charge that form excitons ������ � Organic Device Simulation Using Silvaco Software

ATLAS – Organic LED Device Simulation: Bilayer TPD/ Alq3 OLED Example: Singlet Exciton Density Profile � � Exciton Profile ������ � Organic Device Simulation Using Silvaco Software

ATLAS – Organic LED Devices Simulation: Bilayer TPD/Alq3 OLED Example: IL & Internal Efficiency IL curve Internal Efficiency ������ � Organic Device Simulation Using Silvaco Software

ATLAS – Organic LED Device Simulation: Bilayer TPD/Alq3 OLED Example: Optical Output Coupling n=1.5 n=1.9 n=1.8 ������ � Organic Device Simulation Using Silvaco Software

Organic Device Simulation Transient Simulation of OLED Pixel

Organic Devices Simulation: Basic OLED Equivalent Circuit � � A p-type poly-Si TFT AM-OLED pixel is shown � � The cathode and anode electrodes of the OLED form an intrinsic capacitance C and the resulting equivalent circuit is shown � � When it is connected to a poly- Si TFT with an on resistance R ON , it forms a circuit with its speed limited by the RC time constant ������ � Organic Device Simulation Using Silvaco Software

Organic Devices Simulation: Corresponding OLED Pixel Structure � � The device simulation structure of a p-type Poly-Si TFT AM-OLED pixel is shown here � � The structure is set up for device simulation and does not represent actual process steps � � More complicated OLED pixels can be simulated using Atlas MIXEDMODE ������ � Organic Device Simulation Using Silvaco Software

Organic Devices Simulation: OLED Pixel Simulation � � Curve 1: Transient current simulation results of the PPV OLED only (in blue) � � Curve 2: The combined poly-Si TFT/OLED pixel (in black) – note the effect of TFT on current level � � The rise/fall (ON/OFF) signal is coupled through the poly-Si TFT and is converted as a current spike in the OLED as shown � ������ � Organic Device Simulation Using Silvaco Software

Organic Devices Simulation: OLED Experiment � � The transient OLED current density response due to a 600ns square data voltage pulse of the experimental and simulation curves are characterized by: � � A sharp charging spike due to the capacitance of the device followed by a quasi-steady state � � At turn-off there is a sharp discharging spike followed by some decay * Pinner et al, J Appl Phys 86 (9) 5116 ������ � Organic Device Simulation Using Silvaco Software

Organic Devices Simulation: Exciton Simulation � � A simulated transient result of the exciton density is shown � � The exciton density assumes a Langevin recombination process and takes into account singlet excitons, inclusive of diffusive and decay terms ������ � Organic Device Simulation Using Silvaco Software

Organic Devices Simulation: Experimental EL Curve* � � One can observe the fast initial EL rise followed by a slower rise, fast modulation in the turn-off, and a decaying exponential tail � � Assuming the exciton density is proportional to EL, note the similar shape of the previous exciton density simulation with the EL curve * Pinner et al, J Appl Phys 86 (9) 5116 ������ � Organic Device Simulation Using Silvaco Software

Organic Devices Simulation: OLED Langevin Recombination Zone (2D plot) ������ � Organic Device Simulation Using Silvaco Software

Organic Devices Simulation: Langevin Recombination and Exciton Density � � Calculation of transient OLED Langevin recombination and exciton density based on 3 pulses ������ � Organic Device Simulation Using Silvaco Software

Organic Devices Simulation: PPV OLED Exciton Density (2D plot) ������ � Organic Device Simulation Using Silvaco Software

Organic Devices Simulation: Extraction of OLED Internal Efficiency IV-Curve Internal Efficiency Curve ������ � Organic Device Simulation Using Silvaco Software

Summary � � Organic Materials: � � Default Bandgap parameters. Others are defined by user-defined � � Density-Of-States(DOS) � � Transport: Drift-Diffusion/Poole-Frenkel mobility model � � Bimolecular Langevin Recombination � � Excition Rate Equation: singlet/triplet exciton profiles � � Radiative rate for luminescence or phosphorescence � � Reverse Ray-Tracing: external efficiency (refractive index step) � � Angular power plot/optical output coupling coefficient/near&far field distribution ������ � Organic Device Simulation Using Silvaco Software