Weichung Ooi | Contrel: How do you fabricate monolithic CMOS-driven GaN MicroLEDs on a single silicon wafer without degrading the transistors?
08:00 - 10:55
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Summary of the clip:
How do you fabricate monolithic CMOS-driven GaN MicroLEDs on a single silicon wafer without degrading the transistors?
Monolithic integration of gallium nitride (GaN) LEDs onto silicon CMOS backplanes has historically struggled with thermal budget and material compatibility limitations. A breakthrough "double layer transfer" process addresses this by starting with a standard silicon-on-insulator (SOI) wafer. Crucially, the CMOS process is paused after the discrete transistors are formed but before they are interconnected. This partially processed device layer is bonded to a temporary handle wafer, and its original substrate is removed.
The flipped, ultra-thin silicon device layer is then bonded directly onto a high-quality GaN-on-silicon LED epi-wafer. This stack is processed in a standard silicon facility: windows are opened through the silicon layer to access the underlying GaN material, isolation structures are etched, and the wafer is planarized using chemical mechanical planarization (CMP) and trench-refill techniques.
Finally, standard CMOS back-end-of-line (BEOL) multi-level metallization is used to simultaneously wire up both the silicon transistors and the GaN LEDs. The resulting monolithic integrated circuit eliminates the traditional distinction between a backplane and an LED array, packing digital logic, drivers, and light emitters into a single co-designed chip.
In this short video, you can learn:
* The step-by-step process of double-layer transfer using SOI and handle wafers to flip and expose transistor layers.
* How sub-micron contact windows are opened through silicon to access underlying GaN epi-layers.
* Why utilizing standard CMOS back-end-of-line (BEOL) metallization eliminates the need for separate chip-to-chip packaging.
π **Clip Abstract** This clip describes a double-layer transfer process that monolithically integrates GaN LEDs and CMOS transistors on a single wafer using standard silicon processing. It details how paused CMOS device layers are bonded to GaN epi-wafers and interconnected using standard back-end-of-line metallization.
π Link in comments π
#DoubleLayerTransfer, #MonolithicIntegration, #GaNonSilicon, #BEOLMetallization, #MicroLEDDisplays, #ARLightEngines
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03:15 - 05:05
Why does traditional aligned bonding limit MicroLED microdisplay yields at commercial scale?
Why does traditional aligned bonding limit MicroLED microdisplay yields at commercial scale?
Microdisplay fabrication generally relies on two primary approaches to bring GaN light-emitting elements into the silicon world: aligned bonding and direct bonding. Aligned bonding, practiced by several industry pioneers, requires forming the LEDs and the silicon backplanes separately before bonding them with precise sub-micron alignment. However, this mechanical alignment step introduces significant defect rates, severely limiting overall manufacturing yields and preventing cost-effective commercial scaling.
Direct bonding techniques, such as blanket GaN transfer followed by post-bonding LED fabrication, eliminate the alignment challenge during bonding. Yet, standard direct bonding often requires proprietary tools and custom process lines, creating new hurdles in capital expenditure and manufacturing scalability.
To overcome these roadblocks, a novel approach integrates direct bonding seamlessly within a standard CMOS foundry flow. By forming GaN LEDs after wafer bonding and utilizing conventional multi-level metal interconnects, manufacturers can bypass dedicated packaging lines and leverage existing silicon infrastructure for high-yield, high-volume production.
In this short video, you can learn:
* The fundamental yield and alignment limits of traditional thermo-compression and molecular bonding.
* How direct bonding of blanket GaN films avoids sub-micron mechanical alignment issues.
* The manufacturing trade-offs between custom direct bonding process lines and standard CMOS-compatible integration.
π **Clip Abstract** This clip explains the critical differences between aligned and direct bonding for monolithic microdisplays, highlighting why mechanical alignment limits commercial yields. It outlines how integrating GaN processing directly into standard CMOS backplane fabrication solves these scalability challenges.
π Link in comments π
#DirectBonding, #MonolithicIntegration, #GaNOnSilicon, #ThermoCompressionBonding, #MicroLEDMicrodisplays, #ARMicrodisplays
12:25 - 13:55
Can microdisplay designers simulate and lay out GaN MicroLEDs using standard silicon EDA tools?
How can display manufacturers overcome the throughput and yield bottlenecks of micro LED mass production?
While non-contact laser-induced forward transfer (LIFT) methods drop unbonded dies onto a backplane by gravity, they require subsequent reflow steps and risk placement inaccuracies due to the gap. A compelling alternative is Laser-Induced Transfer Bonding (LITB). This approach combines a stamp head with localized laser heating under contact pressure, welding the micro LED directly to the backplane to form a robust intermetallic compound (IMC) without flux.
This contact-based LITB method achieves a placement accuracy of 1.5 microns, accommodating die sizes down to 5 x 10 microns and pitches of 10 microns. The resulting metallurgical bonds, verified via focused ion beam (FIB) cross-sections and push testing, exhibit strong dendrite structures. The process is highly versatile, compatible with passive and active matrix backplanes on PCB, glass, polyimide, and system-on-film (SOF) substrates, and can handle various incoming die configurations including COC1 and COC2.
To achieve the yields required for commercial viability, mass transfer must be paired with efficient mass repair. Traditional repair schemes rely on multiple customized COC2 templates mapped to specific defect zones. A more efficient approach utilizes a single stamp head to pick up a full array of replacement dies, repeatedly pressing and bonding them only onto the identified defective zones, which minimizes material waste and accelerates cycle times.
In this short video, you can learn:
* The mechanical and thermal differences between non-contact LIFT and contact-based LITB.
* How to achieve 99.99% transfer yields and sub-millisecond bonding times for micro LEDs.
* Advanced repair strategies for both defective dies and open/short TFT backplane traces.
π **Clip Abstract**
The speaker introduces Contrel's laser-based mass transfer and selective mass repair equipment designed for micro LED display manufacturing. He details their proprietary laser-induced transfer bonding (LITB) method, comparing its accuracy, yield, and bonding mechanism against alternative industry techniques.
π€ Speaker: Weichung Ooi
π’ Company: Contrel
π
Event: Mini- & Micro-LED Displays 2023: Markets, Manufacturing Innovations, Applications, Promising Start-ups
π Location: TechBlick Platform | Online
π Learn more at the next TechBlick event: https://www.techblick.com
#GaNMicroLEDs, #MicroLEDPDK, #MonolithicIntegration, #SiliconEDA, #ARMicrodisplays, #MicroLEDDisplays