Design and fabrication of vertically-integrated CMOS image sensors

Area of Science:

• Integrated Circuit Design
• Microsystems Engineering
• Solid-State Electronics

Background:

• 3D integrated circuit (IC) fabrication enables vertical stacking of active components for heterogeneous microsystems.
• Vertically-integrated (VI) technologies offer significant advantages for electronic image sensors, including enhanced pixel-level data processing and device optimization.

Purpose of the Study:

• To present the design principles of vertically-integrated (VI) CMOS image sensors fabricated using flip-chip bonding.
• To detail a specific VI-CMOS image sensor prototype developed at the University of Alberta.

Main Methods:

• Utilized flip-chip bonding to integrate a CMOS die with active pixels and a photodetector die with metal-semiconductor-metal devices.
• Employed a commercial process for CMOS dies and a custom process with hydrogenated amorphous silicon for photodetector dies.
• Developed a digital camera system featuring an FPGA board for real-time data acquisition and a PC for processing and display via USB.

Main Results:

• The VI-CMOS image sensor prototype demonstrated a higher dynamic range compared to conventional sensors.
• The prototype exhibited a lower dark limit, indicating improved low-light performance.
• Experimental validation was conducted using a custom-built digital camera system.

Conclusions:

• Vertically-integrated CMOS image sensors represent a promising advancement in electronic imaging technology.
• The demonstrated prototype validates the potential of 3D IC fabrication for superior image sensor performance.
• Flip-chip bonding is an effective technique for realizing heterogeneous microsystems in image sensor applications.