**5.4 True colors**

The purer red provided by Ag appeared owing to Ag's suitable optical parameters. However, the simulated and experimental data were not close to target red identified in Figure 13. Other metals such Au and Cu were examined to see how they provide interfered colors. Figure 41 is the simulations done with Au and Cu electrodes. As indicated by its color purity deviation (*CPD*), the red color by Au and green color by Cu provided smallest values. However, these values were not small enough to be true colors. Thus true colors of red and green require either new electrode materials or a multiple layer which serves as a single electrode layer to perform color interference. Other popular metals such as chrome (Cr) and cobalt (Co) were exempt from the simulation database because of their poor color and transmittance performance during simulation.

Possibilities for Flexible MEMS:Take Display Systems as Examples 411

Spacer height (nm)

685

Blue 680 600 515 Table 9. Color behavior under OFF states with uneven spacer heights

system require neither solid substrate nor photolithography process.

which is a must for commercialization and safety concern.

related works were partially supported by the following projects: National Science Council (NSC) of Taiwan (Republic of China)

technique for flexible applications.

production fields.

**7. Acknowledgment** 

Green 600 520 445 (0.30, 0.24)

Recent research and development in the printed electronics field indicated usable Ag nano particle ink, which can be a good candidate for printed electrode. But designer also has to consider the influence of high resistivity of this ink because even though the resistivity does not influence the electrostatic behavior, the device requires a high electrical yield for connection lines. After these discussion focused on specific issues from process, material, and operation point of view with possible solutions, one can further expect a perfect final display device which is controlled by MEMS and manufactured by printing processes with

The flexible MEMS by roll-to-roll printing system is an epoch-making concept that the

A complex model which is a superposition of a single-end fixed cantilever and a parallel plate was proposed and proved by simulation and experiments. The model clearly indicated key parameters which play crucial roles on operation voltage which is also a key for portable, light weight, low cost, and maybe disaposable appliation. The Fabry-Perot color interferometer concept was taken as a demonstrator which was controlled by the MEMS. With this complex model, similar MEMS device can easily achieve low operation voltage

The roll-to-roll process system showed a budget-friendly, high-efficiency, and large area supportive production and suggested high potential on replacing current photolithography

With the successful electrical, mechanical, and optical demonstration, the large area flexible MEMS as well as the roll-to-roll printing process system opened great applications on portable and disposable electronic devices thus provided significant values in design and

The author wants to thank Prof. Dr. Hiroyuki Fujita and Prof. Dr. Hiroshi Toshiyoshi (both are with the University of Tokyo, Japan) for their advisory helps. The author also wants to thank Kuan-Hsun Liao, Sheng-An Kuo, and Chung-Yuan Yang for their lab works. The

Spacer

Red 765

**5.6 Processes** 

flexibility.

**6. Summary** 

height (nm)

CIE coordinate when OFF

(0.25, 0.26)

Solution 1 Solution 2 Solution 3

CIE coordinate when OFF

(0.22, 0.26)

Spacer height (nm)

600

CIE coordinate when OFF

Fig. 41. Simulated best design with Au electrodes.

#### **5.5 Structures**

Even though the combinational full color display is not a must of the goal for decoration applications, this study implied a full color possibility by combining all three primary colors. However, the original design, which used a unified spacer thickness of 600nm, showed different combinational layer thickness. When combine the structures in Figure 11, a total thickness difference will appear since the isolation (Intermediate 5) thicknesses are different. This means that when using a unified lower substrate, the upper substrate will not be flat as shown in Figure 42. The uneven layer will not only cause process difficulties but will also result in reliability concerns. To overcome this, a structure with unified upper layer which requires different spacer heights and different isolation thickness for different colors should be designed. Some candidate solutions suggested in Table 9 provide uniform OFF state colors (same CIE coordinate). The process detail will be complicated but by doing this, the process issue disappears and the spacer heights can be controlled by gravure printing's cylinder and ink engineering discussed in section 3.4.

Fig. 42. Unified spacer height will leave an uneven upper layer.


Table 9. Color behavior under OFF states with uneven spacer heights
