Micro-LED Display Semiconductors are miniaturized InGaP/GaN LEDs (1-100 µm pixel size) integrated with active-matrix CMOS backplanes, requiring mass-transfer technology and efficiency management for full-color high-brightness displays.

Micro-LED Device Physics:

• Pixel size: 1-100 µm individual dies (vs traditional mm-scale indicators)
• Epitaxy: GaN/InGaP on sapphire or Si wafer for mass production
• Efficiency droop: efficiency drops 20-40% at practical brightness levels
• Surface recombination: critical at small sizes (large surface-area-to-volume ratio)
• Thermal crosstalk: closely spaced emitters generate heat affecting neighbors

Epitaxy and Substrate Choices:

• GaN (blue/green): sapphire substrate traditional, Si substrate cost alternative
• InGaP (red): lattice-matched to GaAs but lower absolute efficiency
• Si substrate advantage: monolithic integration with CMOS backplane possible
• Sapphire advantage: higher thermal conductivity, established yield

Mass Transfer Process:

• Electrostatic/fluidic/stamp-based transfer: pick individual dies, place on target substrate
• Transfer speed: critical for yield (thousands of µLEDs per second)
• Bonding: flip-chip Au/Sn solder, direct bonding, or adhesive
• Yield challenge: repair of failed transfers/bonding

Active Matrix Backplane:

• CMOS pixel circuit: 1T1C (transistor + capacitor) per subpixel
• LTPS (low-temperature polysilicon): glass substrate option for flexible displays
• Oxide TFT: alternative to LTPS, lower process temperature
• Current source per pixel: constant-current drive for uniform brightness

Full-Color Implementation:

• RGB µLED: separate red/green/blue pixels (high cost per pixel)
• Color conversion: single-color µLED + phosphor layer (lower efficiency)
• Quantum dot conversion: narrower spectral lines

Repair and Yield:

• Repair rate: achieving <0.1% defects critical for large displays
• Laser repair, micro-bonding tools required post-transfer
• Apple Watch Series 8: first significant µLED adoption (~150 ppi)
• Samsung/Sony: continued development for premium displays

vs. OLED Comparison: Micro-LED advantages: higher efficiency at peak brightness, no burn-in, longer lifetime. Disadvantages: lower yield, higher transfer cost, color uniformity challenges. Combined with 6G deployment timeline and flexible electronics, µLED remains compelling multi-decade technology roadmap.