Feb 6, 2018: Researchers from microelectronics research centre Leti have used proprietary micro tube hybridization technology to stack heterogeneous integration of self-aligned GaN/InGaN µLED arrays with a full-CMOS active matrix.
They explained how high-resolution 873 x 500 pixel GaN/InGaN µLED arrays can be connected to full-CMOS active-matrix bearing hard microtubes grown on top of its contact areas. These GaN/InGaN µLED arrays are designed at a 10µm pitch following a self-aligned process.
About 2.8µm high and 4µm in diameter and coated with a 240nm gold layer, the micro tubes can be grown using conventional IC process steps on top of fully functional CMOS circuits. Their proprietary composition was chosen to be relatively hard compared to Al-0.5Cu pads, so they can be pressed into softer contact pads to establish a reliable electromechanical contact.
After dicing the LED-arrays and the CMOS active matrix chips from their respective wafers, the researchers flipped the GaN chip over the silicon chip for a press-fit assembly (with an insertion force of about 0.1g per connection, or roughly 40kg for the insertion of 450 000 micro-tubes). The microdisplays can then be attached onto a daughter board and connected through wire-bonding.
Extending its expertise in high-brightness microdisplay technology for augmented-reality and other applications, Leti had demonstrated the world’s first wide video graphic array (WVGA) GaN microdisplay with 10-micron pixel pitch. The 10-micron pixel pitch technology will help address the growing demand for augmented-reality glasses for consumer and professional users, head-up displays for vehicle drivers and for pico projectors and other compact projectors. This prototype microdisplay, based on a self-emissive GaN-based technology, shows the highest resolution with smallest pixel pitch (10 µm) ever presented. Patterning high-density microLED arrays and hybridizing them on a CMOS circuit, using Leti’s micro-tube technology, enabled Leti to achieve this performance.