Lec 56: Angular color shift and power consumption of RGB micro-LED displays Part A

This lecture addresses the critical issue of angular color shift in RGB micro-LED displays. It begins by defining angular color shift and its importance for color accuracy from varying viewing angles. The root causes are identified: negligible cavity effect in micro-LEDs, and mismatched angular intensity distributions of red versus blue/green subpixels due to different epitaxial materials (AlGaInP for red, InGaN for blue/green). The red emission follows a Lambertian pattern, while blue and green exhibit batwing patterns due to strong sidewall emission. The physics of sidewall emission is explained using a point-source model, showing that sidewall emission is significant for InGaN chips because of weak absorption in the multiple quantum wells, whereas AlGaInP absorbs strongly, limiting sidewall emission. Calculations show that for a 35×60 µm chip, sidewall emission is only 5.6% for red but over 50% for green and blue, causing a 10x mismatch. Quantification using 10 reference colors shows that at 60° viewing angle, average color shift (Δu’v’) is 0.013, with magenta worst at 0.081, exceeding the just-noticeable difference of 0.02. A black matrix solution that absorbs sidewall emissions from blue and green is proposed, reducing the worst-case shift to 0.014 (5.8x improvement) and passing the MacBeth color checker test. Alternatives include metallic sidewall coatings, asymmetric subpixel arrangement, and scattering films. Finally, the tolerance analysis indicates that blue/green angular distributions can deviate significantly from red’s pattern within a 3.5 JNCD limit, offering design flexibility. The lecture concludes that black matrix is an effective solution despite a ~2x efficiency penalty, and that surface texturing or microstructures can further improve performance.