薄膜封装对OLED寿命和性能的影响--悉尼Essay代写范文

悉尼Essay代写范文:“薄膜封装对OLED寿命和性能的影响”，这篇论文主要描述的是采用薄膜封装的工艺技术能够大大提高对于TFE期间的性能保护，建立起一个薄膜叠层，将封装后的温度控制在OLED适应的范围内，这样能够很好的保证OLED的性能没有收到损坏，当然薄膜封装也存在着一定的缺陷，就是粒子方面也有着不足之处，但这与其优点相比较，并不影响薄膜封装的广泛利用。

摘要 Abstract

We present our work on the optimization of our thin film encapsulation process. Except for particle related defects,encapsulation lifetimes of over 500 hours at 60 rH.

have been reached over a complete 20first direct comparison of the luminescence decay of our TFE devices and identical glass-desiccant encapsulated devices clearly

shows that lifetime of these PLED devices is no longer limited by the encapsulation method, but by the intrinsic quality of the light emitting polymers.   

简介 1. Introduction

Cathode materials and polymers used in organic light emitting displays (OLEDs) show a limited lifetime when exposed to oxygen or water.

Conventional methods to protect OLED devices from these elements during their lifetime are based on applying a metal or glass cap, filled with inert atmosphere and a desiccant.

Many different TFE stack designs have been proposed and investigated [1,2,3]. However, all TFE stacks struggle with two common problems. First, it is not trivial to create a hermetic barrier layer at the low temperatures that are acceptable to the OLED. Second, the processes and material sets should be chosen such that the performance of the resulting device is not adversely affected by the encapsulation.

In this paper we will address each of these problems and present an optimized stack of thin films that provides good shelf life performance while maintaining the brightness and color saturation of passive matrix full color OLED displays.

直插式制造工艺 2. Inline manufacturing process

At OTB, an inline tool was developed to perform all necessary processes to turn a structured substrate (including metal tracks, ITO pixel pads, printing banks and cathode separators) into an encapsulated PLED device. This tool uses square plates with a 20  encapsulation. The processes include plasma pretreatment,PEDOT printing, RGB LEP printing, cathode deposition and deposition of an encapsulating multilayer stack of inorganic andorganic thin films. The resulting stack [4] is shown in figure 1.

The thin film encapsulation consists of in total six alternating silicon nitride and organic polymer layers. The silicon nitride is deposited through a remote inductively coupled plasma source.The polymers are inkjet printed. The different polymer layers have layer thicknesses varying between 0.3 and 12 um.

Glass

ITO

LEP

PEDOT

Cathode

Cathode

separator

Anti-scratch

coating

Thin Film

Encapsulation

OTB process:

Substrate:

Figure 1: Schematic overvieride (SiN) layers can only be processed at a temperature of around 100

polymers, even though the minimum required temperature is 350present in the SiN layers, where the size and the frequency can be influenced by the process settings. These pinholes will allow moisture and air to penetrate the encapsulation and destroy the device. Therefore, multiple layers of SiN are used to create a labyrinth with very long effective diffusion paths.

To create this labyrinth each of the three SiN layers is covered with an organic polymer layer. These polymer layers function as seed layers for the next SiN layer. Without these seed layers the new SiN layer would mimic the pinhole pattern of the preceding SiN layer, and pinholes would grow uninterrupted from the bottom to the top. Next to this, the polymer layers are also used to planarize the vertical structures on the displays.

3. Creating a hermetic barrier layer

The plasma used to deposit the SiN barrier layers is a remote inductively coupled plasma (ICP). The NH3 gas is injected through a showerhead directly into the plasma volume. The resulting radicals diffuse to the substrate and react with the SiH4 gas that is injected right in front of the substrate, thus forming a SiN layer on the substrate.

Layer properties and their 20different gas flows, plasma power, pumping speed and surface temperature. Typical deposition rates reached with this plasma

source range from 1 to 10 nm/s.

Several layer properties are important for an optimum encapsulation performance. Therefore, a correct morphology of the layers is important. By varying the process settings both column structures and dense structures can be obtained. Column structures can be grown very quickly and with wide process windows, but they are fairly open structures (figure 2 left).

Figure 2: SEM pictures of PLED devices: (left) column structures due to wrong process conditions;(right) dense layers grown under the right process conditions.

However, to get layers with less pinholes it is crucial that a more dense amorphous layer is grown (figure 2 right).

After the right morphology is achieved, the number of pinholes has to be minimized further. One way to do this is looking at the density of the SiN layer. Figure 3 shows the film density and the hydrogen content as a function of the partial ammonia flow R, for both a display in the center of the substrate and the corner of the substrate. After optimization, the highest density of 2.6 g/cm3 is obtained around R=0.65 for both the center and corner sample.

This peak in density coincides exactly with the lowest value for the hydrogen content. From analysis of FTIR spectra, along with plasma physics it will be explained how these settings lead to the highest density, lowest hydrogen content, and the lowest number if defects.

确保OLED性能 4. Ensuring OLED performance

The polymer layers of the encapsulation stack have a large impact on the performance of the resulting OLED device. First, the solvents should be chosen such that they do not react with the light emitting polymers to degrade them. Second, the polymer interlayer should not be a source for water or oxygen after the encapsulation, as this would accelerate rather than slow down the degradation of the light emitting polymers and the cathode.

Therefore, a material set has been developed that can be inkjet printed and UV cured through a free radical polymerization process in an inert atmosphere to avoid oxygen and water inclusion.

4.1 Lifetime performance and failure mechanisms After optimization of the different layers, the complete encapsulation stack was applied on 20  containing 90 RGB printed PM OLED devices. Each device consists of 96 x 3 x 64 pixels.

Different lifetime tests were performed on these devices. A first set of samples was put in a climate chamber for storage at 60 and 90% relative humidity (%rH). Figure 4 shows the preliminary results for a device at the center of the substrate and one at the edge of the substrate, both directly after processing and after 504 hours in the climate chamber.

0.3 0.4 0.5 0.6 0.7 0.8 0.9

0.5

1.0

1.5

2.0

2.5 Corner

Center

 (g/cm3)

R = NH3/SiH4+NH3

0.3 0.4 0.5 0.6 0.7 0.8 0.9

0.20

0.24

0.26

0.28

0.30

Center

Corner

H%

R = NH3/SiH4+NH3

Figure 3: Film density (left) and hydrogen content (right) versus the partial ammonia flow.

1572 ? SID 06 DIGEST

Central display: fresh and after 504 hrs @ 60 ! %rH Edge display: fresh and after 504 hrs @ 60 ! %rH

Figure 4 Two 1

After 504 hours, both cells show short black stripes that are caused by dust particles that penetrate the encapsulation stack. Once the TFE stack is breached, oxygen and/or water can migrate from pixel to pixel in the line direction. Besides these black stripes, the encapsulation does not seem to suffer from the climate chamber test at all.

Results of failure analysis will be presented, indicating the source and solutions for these pinholes, and the reason for the directionality of the growth. Moreover, displays will be presented in which the pinholes have been eliminated.

To prove that the encapsulation stack does not affect the OLED device performance, a second set of 18 devices was tested for luminescence decay over time. This test was performed at room temperature and ambient humidity. The devices were continuously operated under the following driving conditions: MUX64, AllOn (6 devices for each color @ 15-20 Cd/m2). Figure 5 shows the first published experiments where the luminescence decay over time of these thin film encapsulated devices is compared to identical devices with a traditional glass/desiccant encapsulation. For each color and each encapsulation method, 6 devices were used. So in total, this graph represents 36 devices.

The initial rise in light output of red during the first 24 hours of operation is not uncommon for the material set used in these experiments and can be attributed to process settings not related to the encapsulation.

After 504 hours of active operation, the decay of the light output of all three polymers does not show any dependency on the encapsulation method. For red and blue, the TFE samples even outperform the glass-capped samples. Further experiments are planned to confirm these trends.

These results indisputably show that the TFE processes have done no harm to the sensitive polymers, and are therefore compatible with the PLED production process.

Additional data showing absolute values for the luminescence,excellent overlap of white points, and the stability over time of these important device properties, will be presented as well.

结论 5. Conclusions

We optimized the silicon nitride layer properties to have layers with an optimal Si/N ratio, a high density of more than 2.4 g/cm3, and low hydrogen content. Climate storage tests during 504 hours stack is uniform over the  particle related defects.

The first direct comparison between glass/desiccant capped devices and thin film encapsulated devices clearly shows that the luminescence lifetime of the TFE devices is identical to that of glass/desiccant capped devices. The observed decay of the luminescence is only caused by the intrinsic lifetime of the used light emitting polymers.

The combination of these two results hails an important step towards the viability of TFE as an industrial solution for OLED device manufacturing.

0%

20%

40%

60%

80%

100%

120%

140%

00 72 144 216 288 360 432 504

Time (hrs)

Relative luminescence

Red

Green

Blue

Figure 5: Relative luminescence decay of red, green, and blue over time of operated (MUX64, AllOn) TFE devices normalized to identical glass-capped devices (all at room temperature and ambient humidity)

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