Thanks to the tiny hardware system, less post-processing computational requirement and lower cost, Time-of-Flight (ToF) technique is considered as one of the promising approaches for three-dimensional imaging in various application scenarios such as virtual/augmented reality, autonomous driving, machine vision for smart manufacture, and gesture control interface for human-machine interaction. The most widely used device in the state-of-art ToF image sensor is the current-assisted photonic demodulator (CAPD), which can achieve high modulation ability. However, the huge DC leakage current between two guide electrodes from the majority carriers makes this device suffer from serious power consumption problem.

In this work, different approaches to pursue a photonic demodulator with low powe...[ Read more ]

Thanks to the tiny hardware system, less post-processing computational requirement and lower cost, Time-of-Flight (ToF) technique is considered as one of the promising approaches for three-dimensional imaging in various application scenarios such as virtual/augmented reality, autonomous driving, machine vision for smart manufacture, and gesture control interface for human-machine interaction. The most widely used device in the state-of-art ToF image sensor is the current-assisted photonic demodulator (CAPD), which can achieve high modulation ability. However, the huge DC leakage current between two guide electrodes from the majority carriers makes this device suffer from serious power consumption problem.

In this work, different approaches to pursue a photonic demodulator with low power consumption have been studied. Firstly, Due to the rectify nature of p/n junction, a junction assisted photonic demodulator (JAPD) is proposed and experimentally demonstrated in a standard CMOS foundry process to achieve a low power consumption of 29 fW per pixel and a high modulation contrast of 98%. Then, to make the junction based photonic demodulator be friendly to large optical window application, a photonic demodulator with multiple junctions in the optical sensing region is proposed. The influence of the n- and p- regions has been studied through theoretical calculation and TCAD simulation. Furthermore, since the junction method cannot fully eliminate the leakage current, an alternative approach, gate based photonic demodulator, has been studied. To improve the sensitivity and modulation ability, multiple gate photonic demodulator and embedded guide gate photonic modulator (EGPD) has been proposed. In the end, a four-tap ToF pixel based on the gate based photonic demodulator has been designed and implemented into a ToF ranging camera. The functionality of the ToF camera system has been demonstrated by successfully capturing a set of three-dimensional images.