Patent Application
20070131944
The present invention pertains to organic electroluminescent display devices. Particularly, the present invention relates to organic light emitting diode (OLED) display devices and the methods of protecting dual screen OLED display devices from harmful gaseous elements in the surrounding environment.
Organic light emitting diode (OLED) display devices, including both polymer and small-molecule OLEDs, can be used for a great variety of displays, such as those used on lap-top computers, televisions, digital watches, telephones, pagers, cellular phones, calculators and the like. Generally, OLEDs have simple structures and they are relatively easy and inexpensive to fabricate. A basic OLED display unit includes a flat, transparent substrate, and a display area fabricated on the substrate.
For some applications, such as flip-style mobile phones, it is desirable to have more than one display screen. For example, a larger-size main display shows receiving and transmitting functions or images when the handset is in use, while a smaller-size secondary display shows status information in a stand-by mode and shows information of an incoming call before the user answers. In a flip-style phone, for example, the two displays can be arranged back-to-back on the flip cover. For this kind of application, it is highly desirable that the total thickness of the two displays is minimized. Preferably, the two displays form a single module so that they can be easily assembled into the phone unit.
Certain OLED structure components, such as reactive metal cathode layer and organic light emitting materials, are susceptible to oxygen and moisture, which exist in the ambient atmosphere. Oxygen and moisture can produce deleterious effects that severely limit the lifetime of the display device. In order to maintain a satisfactory performance over an extended period of time, the active structure of an OLED display area must be protected to prevent water vapor and oxygen from penetrating the structure. It is known in the art to use organic or inorganic materials to form a protective layer surrounding the active OLED layers, for protection against those harmful gaseous elements. Examples of such protective layers can be found in Affinito (U.S. Pat. No. 6,268,695) and Graff et al. (U.S. Pat. No. 6,570,325). These protective layers are usually only a few hundred nanometers thick. They offer a moderate degree of protection.
For an improved protection, an OLED display area may be encapsulated between two solid plates. One of the plates may be the substrate itself and another may be a plate of an organic or inorganic material that is sealed onto the display area by an adhesive.
Brown et al. (U.S. Pat. No. 6,835,950) discloses some examples of the encapsulated OLED display area. In some of embodiments as disclosed in Brown et al., an adhesive layer is disposed directly on the OLED layer. In other embodiments, a protective layer made of organometallic materials, silicon compounds, or metal oxides is disposed between the adhesive layer and the OLED layer. Brown et al. also discloses the use of a getter material in the OLED display. The getter material is a material that reacts readily with active gases including water vapor and oxygen, forming stable low-vapor-pressure chemical compounds so as to remove the active gases from the gas phase. Preferred getter materials include Group IIA metals and metal oxides, such as calcium (Ca), barium (Ba), calcium oxide (CaO), and barium oxide (BaO). However, Brown et al., Affinito , and Graff et al only disclose a display module having a single OLED display.
A dual display module has two OLED displays, each of which is fabricated on a different substrate. In general, the displays are not encapsulated individually. Rather, a dual-display module is made by arranging the two display modules back-to-back such that the display areas are encapsulated between the two substrates. An adhesive material is used to provide a hermetic seal along the edges of the substrates. A simplified structure of a hermetically sealed dual-type display unit is shown in
During the encapsulating process, some air and moisture may become trapped inside the dual display unit. A trace amount of moisture and air may also infiltrate through the sealing material to reach the display areas over time. In order to reduce the amount of water vapor and oxygen within the encapsulated module, a getter material is also included inside the sealed area.
Kim et al. (U.S. Patent Application Publication No. 2004/0119740 A1) discloses a number of dual-type OLED devices that include a water-absorbing material. In one of the embodiments, as shown in
The present invention provides a dual OLED display unit comprising two OLED displays separately fabricated on two substrates. Each of the substrates has a peripheral area surrounding the OLED display. A sealing material is used to form a hermetic seal around the OLED displays. A getter material is provided on one or both substrates for absorbing harmful gaseous elements. The getter material is disposed on the peripheral areas at least between the displays and the sealing material. The getter material may also be disposed between the OLED displays. Because the getter material may expand as it absorbs water vapor, the OLED displays may experience a surface pressure due to the expanding getter material. Thus, a gap is provided between the two displays to allow for the expansion of the getter material over time.
The above and other objects, features and advantages of the present invention will become apparent from a consideration of the subsequent detailed description presented in connection with accompanying drawings, in which:
a is a cross sectional view of a prior art dual panel display device;
b is a plan view of one of the display areas of
a-4c are cross sectional views of the dual panel display devices according to the first embodiment of the present invention;
d is a plan view of a display area of
a is a detailed cross sectional view of the circled area in
The dual display panel of the present invention comprises a first display area on a first substrate and a second display area on a second substrate. A sealing material is disposed between the two substrates to provide a hermetic seal and a getter material is used to absorb water vapor and oxygen within the sealed area.
The present invention can be achieved in numerous ways, especially through the following exemplary embodiments.
The first embodiment of the present invention is depicted in
Preferred getter materials include Group IA metals, Group IIA metals and metal oxides, such as calcium (Ca), barium (Ba), calcium oxide (CaO), and barium oxide (BaO). Preferably, the getter band is coated on one or both of the substrates 110 and 130 using a predetermined mask to form a pattern as desired. It can be formed entirely on the substrate of one of the displays (as shown in
A schematic plan view of a display area with the getter band disposed in its peripheral area around the display area is shown in
Referring now to
The layers in the stack are preferably deposited by using chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), or physical vapor deposition (PVD). Techniques for deposition of materials are known to persons skilled in the art, and the scope of the present invention is not intended to be limited to any particular type or kind thereof.
The sealing member 150 is arranged such that when the display unit is hermetically sealed, an air gap between the top layer of the first display area and the top layer of the second display area exists to prevent these two displays from contacting each other, even after the thickness of the getter layer has changed as the result of absorbing water and/or oxygen.
It is to be understood that the above-described arrangements are only illustrative of the principles of the present invention. Although the present invention has been described and illustrated with respect to exemplary embodiments thereof, the foregoing and various other additions and omissions may be made therein without departing from the spirit and scope of the present invention.
