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

Organic Device Simulation Using Silvaco Softw are

Silvaco Taiwan September 2005

Organic Device Simulation Using Silvaco Software

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

• f 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

Density of States p-0.62

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. I.D. Parker J.Appl. Phys. 75(3),1 Feb 1994, p.1656

• Simulated

Measured

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

Transient Simulation of OLED Pixel

Organic Device Simulation Using Silvaco Software

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 RON, 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
• f 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