Impact of Spacers on the Uniformity of a Large-area Field Emission Display

Zheng Hu, Zhuoya Zhu*, Wei Lei, Xiaobing Zhang, Huan Feng, Yajun Sun, Linhu Zheng School of Electronic Science and Engineering, Southeast University, Nanjing, P R China 210096

Abstract: Spacers are very important in field emission displays (FEDs), which can separate the cathode and the anode panel. We have investigated the impact of spacers on the field emission properties of a large-area FED. Simulation results showed that spacers would change the electric potential distribution inside FEDs, and would further affect the display uniformity. In FEDs with spacers of a low relative dielectric constant, the enhanced display uniformity can be achieved.

Keywords: Field emission display; spacers; uniformity

Introduction FEDs boast the advantages of CRTs and flat panel displays, so they attract the attention of scientists all over the world. However, many studies are focusing on structure designs of displays and characteristics of emission materials, while the uniformity is also very important.

This article is focusing on the 25-inches FED screen under the research of our group, and the emission material is Zinc oxide (ZnO). A large amount of spacers are used to support the two substrates because of the large display-area, so the impact of spacers on uniformity can’t be ignored [1].

F-N Theory and Structure of FEDs CST Studio is a useful software which can be applied to stimulate the electric field and the electric potential distribution in the vicinity of the spacers inside FEDs. The software calculates the electric field through the Finite Integration method and the Fowler-Nordheim Equation of field emission is described as follows:

2 expb

J aEE

 

Here, a and b are related to the properties of Materials. The values of a and b can be calculated through two

points of the J-E curves of ZnO. In this work, a and b are determined to be 9.34 10-12A/V2 and 4.28 e7V/m, which have been used in our work [2].

Figure 1. Cross-section view of a pixel of FEDs

Figure 2. Top View of a pixel of FEDs

Fig.1 and Fig.2 show the structure of a FED. The parameters are set as follows: the thickness of emitters, cathode and anode is 8m, 10m and 10m respectively. Cylinder spacers were adopted, with the radius of 1.2mm and the height of 0.5mm. The anode voltage is 500V and the gate voltage is 250V.

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Simulation and Results

 

Figure 3. the Electric Potential Distribution of a pixel without spacers nearby

Figure 4. the Electric Potential Distribution of a pixel

with a Spacer (made of Barium Titanate Ceramics)

Figure 5. the Electric Potential Distribution of a pixel with a Spacer (Made of glass)

Fig.3. shows the electric potential distribution of a pixel without spacers nearby. However, considering the area around spacers, the uniformity of this distribution is much worse. Assuming spacers are made of Barium titanate ceramics, the simulation result is shown in Fig.4. It’s obvious that there is an electric potential distortion near the spacer, compared with that of Fig.3. Try to use spacers made of some other kinds of materials in order to reduce the distortion.

Fig.5 shows the electric potential distribution of a pixel with a glass-made spacer. The distribution is much more close to that shown in Fig.3, so the display effect would be much better.

The relative dielectric constant is very important to measuring the influence of mediums on the electric field outside. Barium titanate ceramics has a relative dielectric constant of 500 while the glass only has a 4.82 one. These figures above proved that FEDs with spacers made of low relative dielectric constant have a better display effect.

Conclusion The relative dielectric constant of spacers material is very important to the electric potential distribution, and it is closely associated with the uniformity of FEDs. We proved that spacers with a low relative dielectric constant had little impact on the display effect. It is essential to conduct further theory analysis and experiment for of FEDs.

Acknowledgements This work is supported by National High Technology R&D Program of China (2008AA03A314), National Natural Science Foundation Project (50872022, 60801002).

References 1. Chenggang Xie, Yi Wei. “Spacer Visibility

Problem in Field Emission Displays Due to Surface Contamination,” IEEE Transactions on Electron Devices, Vol, 50, No.12, December 2003.

2. Lei Wei, Xiaobing Zhang and Baoping Wang, “a Stable Field-Emission Light Source with ZnO Nanoemitters,” IEEE Electron Device Letters, Vol.29, No.5, MAY2008.

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