This could be the reason why Apple gave Corning $200m for advanced manufacturing.
[0048] Display substrate 202 can be formed from a variety of materials including glass, amorphous silicon, polysilicon, single crystal silicon, metal foil, metal foil covered with dielectric, or a polymer such as poly(methyl methacrylate) (PMMA), polyethylene terephthalate (PET), polyethelyne naphthalate (PEN), polycarbonate (PC), polyethersulphone (PES), aromatic fluorine-containing polyarylates (PAR), polycyclic olefin (PCO), and polyimide (PI). In an embodiment, display substrate includes a polymer-silicon stack. In an embodiment, display substrate 202 is a flexible glass substrate. For example, display substrate 202 may be a flexible boro-silicate glass substrate. One exemplary flexible glass substrate is manufactured under the tradename WILLOW.TM. glass by Corning Incorporated located in Corning, N.Y.
Micro-LED is a vital part of the patent.
[0050] A wiring layer 212 may also be located on the top surface 203 of display substrate 202 in electrical contact with the plurality of through vias 204. Wiring layers 212, 210A, 210B and vias 204, 206 may be formed of any suitable electrically conductive material used in packaging applications including metals films, conductive polymers, conductive oxides, etc. Referring now to FIG. 3, in accordance with an embodiment of the invention and array of LED devices 214 and optionally micro chips 216 may be transferred and bonded to the display substrate 202. For example, the array of LED devices 214 and micro chips 216 may be in electrical connection with the plurality of through vias 204.
[0051] In accordance with embodiments of the invention, the LED devices 214 are semiconductor-based LED devices including one or more active layers (e.g. quantum well layers) between two doped semiconductor cladding layers. In the particular embodiments illustrated, the LED devices 214 are vertical LED devices in which the layers are horizontal, and the layers are stacked vertically. Top and bottom conductive contacts are formed on the vertical LED devices in order to make electrical contact with the top contact layers 220 described in further detail with regard to FIG. 4 below and wiring layer 212, respectively. In another embodiment, the LED devices 214 are horizontal LED devices in which the contacts to the doped cladding layers are both formed on the bottom surface of an LED device in order to make electrical contact with wiring layer 212.
[0052] In accordance with embodiments of the invention, the micro chips 216 replace the TFT layer of a conventional active matrix display to switch and drive one or more LED devices 214. In one embodiment, each micro chip 216 couples with one or more red, green, and blue led devices 214 that emit different colors of light. In such an exemplary red-green-blue (RGB) sub-pixel arrangement, each pixel includes three sub-pixels that emit red, green, and blue light. The RGB arrangement is exemplary and embodiments are not so limited. For example, alternative sub-pixel arrangements include red-green-blue-yellow (RGBY), red-green-blue-yellow-cyan (RBGYC), red-green-blue-white (RGBW), or other sub-pixel matrix schemes where the pixels have a different number of sub-pixels, such as displays manufactured under the trademark name PenTile.RTM.. In the exemplary embodiments illustrated in the following description, a single micro chip 216 is illustrated as controlling two pixels. It is to be appreciated that this configuration is likewise exemplary and embodiments are not so limited. For example, each micro chip 216 can switch and drive one or more LED devices 214 arranged in series, in parallel, or a combination of the two, such that multiple LED devices are driven from the same control signal. A variety of alternative configurations are contemplated in accordance with embodiments of the invention. In other embodiments, sensors such as touch sensors or light sensors can also be located on the front surface of the display substrate within the display area similarly as the micro chips.
[0053] In one aspect, embodiments of the invention describe display panels and display module packaging configurations in which micro LED devices and/or micro chips are transferred and bonded to a wiring 212 using an electrostatic transfer head assembly. In accordance with embodiments of the present invention, a pull-in voltage is applied to an electrostatic transfer head in order to generate a grip pressure on a micro LED device or micro chip. It has been observed that it can be difficult to impossible to generate sufficient grip pressure to pick up micro devices with vacuum chucking equipment when micro device sizes are reduced below a specific critical dimension of the vacuum chucking equipment, such as approximately 300 .mu.m or less, or more specifically approximately 100 .mu.m or less. Furthermore, electrostatic transfer heads in accordance with embodiments of the invention can be used to create grip pressures much larger than the 1 atm of pressure associated with vacuum chucking equipment. For example, grip pressures of 2 atm or greater, or even 20 atm or greater may be used in accordance with embodiments of the invention. Accordingly, in one aspect, embodiments of the invention provide the ability to transfer and integrate micro LED devices and micro chips into applications in which integration is not possible with current vacuum chucking equipment. In some embodiments, the term "micro" chip, "micro" LED device, or other "micro" structure may refer to the descriptive size, e.g. length or width, of certain devices or structures. In some embodiments, "micro" chips or "micro" LED devices may be on the scale of 1 .mu.m to approximately 300 .mu.m or less, or 100 .mu.m or less in many applications. However, embodiments of the present invention are not necessarily so limited, and certain aspects of the embodiments may be applicable to larger micro devices or structures, and possibly smaller size scales.
