A Fully-Integrated Micro-Display System With Hybrid Voltage Regulator

A fully-integrated active matrix light-emitting diode (AMLED) micro-display system is demonstrated in this paper. The system consists of a $36\times64$ AMLED array chip based on GaN-on-Silicon epilayers and a silicon driving chip integrating an on-chip hybrid voltage regulator, pixel drivers, and peripheral circuits. Then two chips are bonded with low-cost Au-free flip-chip bonding technology. As such, this system is able to directly operate with a battery without any external passive components. Multiple techniques were proposed to achieve the system integration: 1) A fully-integrated hybrid voltage regulator consisting of a step-up switched-capacitor (SC) converter cascaded by a step-down linear voltage regulator was fabricated in a $0.18 \mu \text{m}$ CMOS technology. It achieved only 1.38% output voltage ripple without external capacitors, and be able to deliver a maximum power of 216mW with peak efficiencies of 91% in the linear mode and 78% in the SC mode; 2) Micro-LEDs are fabricated on GaN-on-Silicon substrate that significantly suppresses the light crosstalk between pixels and reduces the cost; 3) An Au-free flip-chip bonding technique is developed to reduce the bonding cost and achieved reliable connections between AMLED array chip and silicon driving chip. The whole system achieved 635 pixel/in (PPI) pixel density. Images and videos with 4-bit grayscale could be rendered. This prototype achieved a high integration level and demonstrates the tremendous potential of the highly efficient, low cost fully integrated AMLED micro-display system.