Patent Application
20050196525
The present invention relates to the manufacture of framed donor sheets used for use in the manufacture of organic light-emitting diode (OLED) display devices.
OLED displays are one of the most recent flat panel display technologies and are predicted to overtake LCD display technology within the next decade. OLED displays offer brighter displays, significantly wider viewing angles, lower power requirements, and longer lifetimes than their LCD counterparts. OLED technology offers more display flexibility and alternatives to backlit LCD displays. For example, OLED displays can be made of thin, flexible materials that conform to any desired shape for specific applications. However, OLED displays and their components, known as OLED structures, which constitute subpixels of the display, are more difficult and costly to manufacture than LCD displays. It is a continuing focus of the industry to increase the throughput in an effort to lower the cost of OLED manufacturing.
Conventional OLED display devices are built on glass substrates in a manner such that a two-dimensional OLED array for image manifestation is formed. The basic OLED cell structure includes a stack of thin organic layers sandwiched between an array of anodes and a common metallic cathode. The organic layers comprise a hole transport layer (HTL), an emissive layer (EL), and an electron transport layer (ETL). When an appropriate voltage is applied to the cell, the injected holes and electrons recombine in the EL near the EL-HTL interface to produce light (electroluminescence).
The EL within a color OLED display device most commonly includes three different types of fluorescent molecules that are repeated through the EL. Red, green, and blue regions, or subpixels, are formed throughout the EL during the manufacturing process to provide a two-dimensional array of pixels. Each of the red, green, and blue subpixel sets undergoes a separate patterned deposition, for example, by evaporating a linear source through a shadow mask. Shadow masking is a well known technology, yet it is limited in the precision of its deposition pattern and in the pattern's fill factor or aperture ratio; thus, incorporating shadow masking into a manufacturing scheme limits the achievable sharpness and resolution of the resultant display. Laser thermal transfer promises a more precise deposition pattern and higher aperture ratio; however, it has proved challenging to adapt laser thermal transfer to a throughput manufacturing line, which is necessary to warrant its use in the manufacture of cost-effective OLED display devices.
During laser thermal transfer, a donor sheet having the desired organic material is placed into close proximity to the OLED substrate within a vacuum chamber. A laser impinges through a clear support that provides physical integrity to the donor sheet and is absorbed within a light-absorbing layer contained atop the support. The conversion of the laser's energy to heat sublimates the organic material that forms the top layer of the donor sheet and thereby transfers the organic material in a desired subpixel pattern to the OLED substrate. The donor sheets are ideally fed automatically into the process such that the stoppages between depositions can be minimized.
U.S. Pat. No. 6,485,884 provides a method for patterning oriented materials to make OLED display devices, and also provides donor sheets for use with the method, as well as methods for making the donor sheets. However, U.S. Pat. No. 6,485,884 fails to provide a continuous way to manufacture the donor sheets. Donor sheets must be cut from a sheet of fragile web prior to being coating with the organic material layer that is subsequently deposited on the OLED display via laser thermal transfer. To provide the ease of robotic handling necessary for a high throughput process, it is also desirable to provide a continuous way of mounting the donor sheets to frames.
It is an object of the present invention to provide an effective way of delivering cut donor sheets into a frame for use in OLED manufacturing.
It is therefore another object of the invention to provide a high-throughput method for the cutting and framing of donor sheets from a roll of web for use in the manufacture of OLED display devices.
The present invention is a high-throughput system for cutting and framing donor sheets from a roll of web for use in laser thermal transfer during the manufacture of OLED display devices.
This object is achieved by a method of delivering donor sheets to be subsequently processed in the process of making an organic light-emitting device, comprising:
The present invention provides an improved way of delivering cut donor sheets into frames for use in subsequent OLED manufacturing. A particular feature of the present invention is the use of cassettes for receiving frames each with a corresponding cut sheet. The cassette is then used in the OLED manufacturing process.
Donor sheet conversion apparatus 100 further includes a drive roller 122 that pays out donor web 112 over a guide shoe 118, a slack loop roller 120 that maintains an appropriate level of tension in donor web 112, and a pinch roller 124 that helps to drive the forward motion of donor web 112. Guide shoe 118 is a mechanical means of guiding donor web 112 such that donor web 112 does not run off its track while advancing. Donor sheet conversion apparatus 100 further includes a bed knife 128, against which translates a slitter knife 132 (shown in
Donor sheet conversion apparatus 100 can further include a hopper 136 that collects donor sheets 114 upon their singulation. Hopper 136 includes a lift plate 134 that is mounted on an elevator mechanism (not shown) for stacking singulated donor sheets 114.
Donor sheet conversion apparatus 100 is assumed to further include an appropriate level of machine control electronics and software.
In operation, donor sheet conversion apparatus 100 converts web roll 110 to a stack of singulated donor sheets 114. Motorized spindle 116 mounts web roll 110 and pays out donor web 112. Slack loop roller 120 is weighted and vertically positioned so as to provide an appropriate amount of tension in donor web 112, and so as to control the rotation of spindle 116 and the payout rate of donor web 112. Alternately, a vacuum box looper or vacuum drum can be substituted for slack loop roller 120 and would limit surface contact with precoated donor web 112. Drive roller 122, along with pinch roller 124, serve as a drive assembly that advances donor web 112 a predetermined distance and subsequently halts the translation of donor web 112 to await cutting. The predetermined distance for advancing donor web 112 before halting its translation for singulation into donor sheets 114 can be accomplished, for example, using rotary encoder counts of the rotation of drive roller 122 or direct sensor detection of the lead edge of donor web 112. Once the translation of donor web 112 is halted, clamping mechanism 126 secures donor web 112 while slitter knife cartridge 130 translates along a rail (not shown) that forms a line of contact between slitter knife 132 and bed knife 128. As rotating slitter knife 132 translates across bed knife 128, a cut is made on donor web 112 that forms donor sheet 114. Slitter knife 132 can be translated along bed knife 128 in a number of ways, including manually or with the use of a pneumatic cylinder or a motor-driven lead screw. Other cutting assemblies can be substituted for bed knife 128 and slitter knife 132, such as a point contact shear cutter (chopper) or a laser cutting assembly. Clamping mechanism 126 can be operated manually or by an actuator. As the cut is made, donor sheet 114 is formed. Donor sheet 114 is stacked atop previously formed donor sheets 114 in hopper 136 while lift plate 134 lowers an incremental vertical distance to accommodate the next donor sheet 114.
The next step in preparing uncoated donor sheets 114 for the subsequently deposited organic material layer is to mount donor sheets 114 to frames. Frames can be mounted to donor sheets 114 manually in a number of ways, such as by collecting a stack of donor sheets 114 in hopper 136, as previously described, and subsequently providing loaded hopper 136 to an operator at a work table, at which time the operator manually mounts each donor sheet 114 to a frame and forms a stack of mounted donor sheets 114 in a cassette 218.
In operation, and in reference to
In operation, a set of robotics automatically transfers frame 214 from dual-stack frame hopper 412 into indexing dial 410. Indexing dial 410 incrementally rotates, e.g., 90°, bringing frame 214 to a position at which a set of robotics automatically transfers donor sheet 114 from hopper 414 into indexing dial 410, and appropriately aligns donor sheet 114 atop frame 214 to form donor sheet with frame 416. Indexing dial 410 incrementally rotates again, bringing donor sheet with frame 416 to a position at which a set of robotics automatically mounts donor sheet 114 to frame 214, e.g. by clamping, to form frame-mounted donor sheet 418. Indexing dial 410 incrementally rotates again, transferring frame-mounted donor sheet 418 to a position at which a set of robotics automatically transfers frame-mounted donor sheet 418 from indexing dial 410 into cassette 218. During each incremental stop of indexing dial 410, a new frame 214 is robotically transferred from frame hopper 412 into indexing dial 410, a new donor sheet 114 is robotically transferred from hopper 414 into indexing dial 410 and onto frame 214, a new frame-mounted donor sheet 418 is formed from donor sheet with frame 416, and a new frame-mounted donor sheet 418 is robotically unloaded from indexing dial 410 into cassette 218. Once cassette 218 is filled with frame-mounted donor sheets 418, cassette 218 is undocked from frame-mounting apparatus 400, eventually to be pumped down to an appropriate level of vacuum and docked with a process chamber for organic material layer deposition. In an alternate embodiment, donor sheets 114 can be fed directly into indexing dial 410 from donor sheet conversion apparatus 100, as described with reference to
The operation of frame-mounting apparatus 500 is similar in all respects to the operation of frame-mounting apparatus 400 except that the lead edge of donor web 112 pays out directly into indexing dial 512, a cut is made along cut line 514, and donor sheet 114 is laid atop frame 214. Frame-mounted donor sheets 418 are formed from donor sheets 114 and frames 214 and are transferred into cassette 218 in a manner identical to that described in reference to frame-mounting apparatus 400.
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.
