**3. Fabrication based on printing techniques**

As introduced before, a novel process should be used for the special requirement on not only the structure's flexibility but also on the dot spacer layer design. Several promising solutions were examined in section 1.3 and with the structure set up before; material, process, and concerns will be discussed layer by layer here.

#### **3.1 Material selection and system setup**

#### **3.1.1 Substrate**

According to Figure 11, the whole structure will be made and the device will be operated in atmospheric ambient. Besides the Intermediate 1 in Figure 11, the multilayer structure contains six layers. The substrate material plays a crucial role for flexibility since it is the thickest part of the structure. When its thickness is below 500m, it is with sufficient flexibility for display applications. However, when a large curvature is expected, only thinner substrates can satisfy this requirement. The latest glass manufacturing techniques support 30m thick commercial products for large scale (300×400mm). Even though thin glass substrates provide very promising options for curved or flexible applications with large curvature, its fragility still limits its realization on flexible electronic devices especially for portable products. The potential safety and reliability concerns also put a barrier between its benefit and realization. In contrary to the fragile glass, elastic polymer material (plastic) is a very good option for the substrate. Because the plastic substrate will be used for the flexible display system, some special requirements including:


are primary material selection principles. Within polymer materials, one can screen out polyvinyl chloride (PVC), polycarbonate (PC), polyethylene (PE), and polyimide (PI) from stability, reliability, deformation, and transparency point of view, respectively. With these concerns, polyethylene teraphthalate (PET) and polyethylene naphthalate (PEN) are relatively suitable for this flexible MEMS design. PET is also famous for its low cost and high transmittance in visible region while PEN is famous for its high temperature stability and sharp cutoff performance for UV light. According to these characteristics, PEN was chosen as the substrate material.
