Last Wednesday (Jan 11) Patently Apple posted a report titled "Apple is reportedly planning to start using its own Custom micro-LED Displays for Apple Watch and iPhones in the next few years." Today the US Patent & Trademark Office published a highly technical patent application from Apple that relates to methods of fabricating microLED displays. Apple's patent stays focused on the technology while staying clear of market applications or target devices.

MicroLED based Display Panel

Apple's highly technical patent describes light emitting structures and methods of forming light emitting structures. In an embodiment, a method of forming a light emitting structure includes forming one or more pluralities of LED coupons on one or more corresponding temporary substrates, transferring the one or more pluralities of LED coupons to a carrier substrate, patterning the one or more pluralities of LED coupons into LED mesa structures, and transferring the LED mesa structures to a display substrate.

In some embodiments, well structures may also be formed around the LED mesa structures prior to transferring to the display substrate. Additionally, hybrid bonding may be utilized for bonding to the display substrate. The processing sequences in accordance with embodiments may be used to form both monochromatic and full color displays.

In an embodiment, a light emitting structure includes an LED bonded to an electrode pad of a substrate, such as a complementary metal-oxide-semiconductor (CMOS) substrate. The LED may include an inorganic semiconductor-based p-n diode, and a metallic bottom contact bonded to the electrode pad. An insulating fill layer may additionally be located laterally around the LED and the metallic bottom contact.

In an embodiment, a planar bottom surface of the metallic bottom contact is bonded to a planar top surface of the electrode pad with a metal-metal bond, and a planar bottom surface of the insulating fill layer is bonded to a planar top surface of the substrate with an oxide-oxide bond. Additionally, the LED may be mounted within a well structure embedded within the insulating fill layer.

In an embodiment, a light emitting structure includes a first inorganic semiconductor-based p-n diode designed to emit a first color emission, and a first metallic bottom contact bonded to a first electrode pad. The light emitting structure may additionally include a second LED (as well as more) including a second inorganic semiconductor-based p-n diode designed to emit a second color emission different from the first color emission, and a second metallic bottom contact bonded to a second electrode pad.

In some embodiments, the first metallic bottom contact is thicker than the second metallic bottom contact, and the second inorganic semiconductor-based p-n diode is thicker than the first inorganic semiconductor-based p-n diode.

In some embodiments, the bottom surfaces of the first and second metallic bottom contacts are co-planar. In addition, the first metallic bottom contact may be thicker than the second metallic bottom contact by a first thickness, and the second inorganic semiconductor-based p-n diode may be thicker than the first inorganic semiconductor-based p-n diode by approximately the first thickness. Additionally, the LEDs may be mounted within corresponding well structures embedded within the insulating fill layer.

In accordance with some embodiments, the processing sequence may facilitate the integration scaling of the LEDs to small micro dimensions, and integration of optical structures around and over the LEDs with mitigated alignment challenges. Additionally, the integration of reflective well structures, and micro-optic elements may additionally bolster on-axis light extraction efficiency.

Apple's patent FIG. 1A below includes a process flow and corresponding cross-sectional side view illustrations of a method of forming a light emitting structure; FIG. 1B includes a process flow of a method of forming a monochromatic light emitting structure; FIG. 7 is a schematic cross-sectional side view illustration of a pair of LEDs mounted within reflective well structures on a display substrate.

Apple's patent FIG. 3A below includes a process flow and corresponding cross-sectional side view illustrations of a method of patterning a pair of LED mesa structures from an LED coupon on a carrier substrate; FIG. 3B includes a process flow and corresponding cross-sectional side view illustrations of a method of integrating a pair of LED mesa structures on a display substrate.

Apple's patent FIG. 12A above is a schematic cross-sectional side view illustration of a transparent half-ball high-index lens over an LED; FIG. 12B is a schematic cross-sectional side view illustration of a transparent cone-shaped high-index lens over an LED.

For more details, review Apple's patent application number # US 20230018406 A1. For those interested in Apple's microLED technology, Patently Apple covered another microLED patent in March 2022 in a report titled "An Apple micro-LED Display patent describes integrating features such as Fingerprint & Health Sensing, Water Tolerant Touch & more."

A Few of Apple's Inventors

• Dmitry Sizov: Senior Hardware Engineer
• John T. Leonard, Ph.D.: Senior Machine Learning Engineer
• Xiaobin Xin: Technologist
• Ranojoy Bose: Display Engineering
• Jonathan Steckel: Lead Technologist (now with STMicroelectronics)
• Ion Bita: Former Sr. Hardware Development Manager (now with Google)