A DVGA Indirect Time-of-Flight Image Sensor With 3.5μm Pixel in 65nm/65nm Stacked BSI CMOS Technology

A double VGA ($960 \times 640$) resolution indirect time-of-flight (iToF) image sensor with a pixel pitch of $3.5 \mu \mathrm{~m}$ has been implemented in a $65 \mathrm{~nm} / 65 \mathrm{~nm}$ stacked BSI technology. It achieves a quantum efficiency (QE) of 40% at 940 nm wavelength and a demodulation efficiency (DME) of 86% at 100 MHz demodulation frequency. A special focus was laid on balancing the utilization of the sensor wafer with the bottom logic wafer to achieve the best pixel count to silicon area ratio. In order to guarantee system level performance, the major target use-cases like face authentication, room scanning, and computational photography have been analyzed and mapped on the sensor architecture. This enables the best compromise between depth performance, silicon cost and power consumption for the given target applications. The sensor consumes 180 mW at 30fps. A special low power always-on mode switches the sensor to full capture once an activity is detected. During this operation mode, the imager (including VCSEL) consumes less than 1 mW.