Passive matrix OLED displays

On the basis of these initial results passive matrix OLED displays were realized in a German government funded project, headed by AIXTRON, to investigate the potential of OVPD for display applications. Figure 9.17 shows low information-content displays produced on passive matrix substrates and large-area OLEDs. 

Although there have been several examples of flexible OLED displays on plastics, including passive-matrix OLED displays on poly(ethylene terephthalate) (PET) substrates from Pioneer and Universal Display Corporation [26, 27], and a-Si H TFT-driven monochrome active-matrix OLED displays on poly(ethylene naphthalate) (PEN) from Honeywell [28], there have been no demonstrations of organic TFT-... 

Several typical properties of PEDT PSS polymers that depend on the PEDT PSS ratio are summarized in Table 10.1. To meet requirements for conductivity, antistatic grades of PEDT PSS have relatively low PSS-contents, and therefore higher conductivity values. In contrast, PEDT PSS grades designed for hole-injection in polymer OLEDs have larger PSS contents, smaller particles (Figure 10.6), and lower conductivities. Specifically, PEDT PSS grades useful for passive matrix OLED displays have the lowest... 

FIGURE 6.4.17 (a) Passive matrix and (b) active matrix OLED display pixels. 

Displays based on OLEDs may be addressed either passively or actively [124], and the drive requirements are quite different in each case. In passive-matrix addressing, the display is addressed one line at a time, so if a display has 480 lines then a pixel can only be emitting for... 

OLEDs grown and encapsulated using these techniques are beginning to show significant promise. Recently, Chwang et al. demonstrated the effects of flexing a 64x64 (180 dpi) passive-matrix flexible OLED (FOLED) display fabricated on a PET substrate with thin film encapsulation [166], In addition, lifetimes of thin-film-encapsulated OLED test pixels on flexible substrates have now been demonstrated to be thousands of hours [162,167],... 

Kodak is commercialising its low molecular weight OLEDs for use in both passive and active matrix display architectures. It has also licensed its technology to Pioneer Corp who have commercialised passive matrix displays for car radios and cellular phone displays. TDK has displays for cellular phones, personal digital assistants and car instrumentation clusters. Perhaps the most significant collaboration to date has been with Sanyo. Sanyo s capabilities in low-temperature polycrystalline silicon have been married with Kodak s low MW materials to produce a full colour, 5 inch active matrix display, commercialisation of which was expected in 2001. 

Fig. 9.17. Passive matrix display and large-area OLED logos showing RGB and AIXTRON obtained by OVPD at TU Braunschweig.

The advantage of AMOLED over PMOLED displays arises because emission in a passive matrix occurs one line at a time, so each OLED element operates at high peak currents and low duty-cycle. The duty-cycle in a PMOLED display is approximately equal to the inverse of the number of rows. For example, in an SXGA (1280 X 1024) display, the duty cycle is approximately 0.1%. The peak current of an OLED pixel may be 1 mA or more. High OLED currents lead to reduced power efficiency and operational lifetime and also place greater demands on the current capacity of the row driver circuits, which may have to handle currents of hundreds of miUiamperes on each output (although not simultaneously). 

Screen printing allows relatively thick films to be patterned, but lacks the lateral resolution of the other techniques presented. It seems likely that low-resolution OLED [24] and electrochromic matrix displays will be produced with this technique. It may also be used to apply protective (passivation) films to seal devices in order to prevent oxygen and water from reaching the sensitive electroactive films (see Section 4.6). 

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