**4.3 Electrical performance**

402 Microelectromechanical Systems and Devices

Rather, the increment decreased along the increasing pixel size. A special saturation behavior of the Newton's ring's size appeared in Figure 32(a). This means that the increased pixel size will only make the display aperture looks larger instead of reduce the Newton's ring. This conclusion strongly supports the necessity of a revolutionary structure change. With different spacer coverage designs – 100% (no air channel), 90%, 80%, and 60% – the experimental data showed great amount of improvement. The width of Newton's ring reduced with all the

Figure 33 is the picture which explains why saturation took place even with air channel design and why larger air channel did not yield in smaller Newton's ring: When the air channel is spacious enough, high applied voltage will let the lower layer attract the upper layer in the air channel area. Since the upper layer was put on the spacer and both sides (pixel area and air channel area) were competing each other, a see-saw performance showed – The more the air channel area in contact, the less the pixel area in contact. Thus a proper instead of a wide air channel is preferred. In this experiment a 90% coverage showed the smallest Newton's ring. This behavior was also obvious during simulation in Figure 20 and Figure 21: The display area tended to expand to the central part of air channel when the channel was wide enough but the display area tended to expand to the four corners when the channel with the same coverage was divided into two parts and were put aside. A combination of the experimental and simulation data suggested narrow and separate air channels are better. However, consider the resolution of printing process and the function of spacer layer for lamination, a single and large air channel was decided for the final

Fig. 33. Contact areas protruded into spacer areas when design was not optimized.

Fig. 32. Different spacer coverage alleviated the operation voltage.

coverage designs in Figure 32(b).

structure.
