Hamamatsu Proposes ToF Sensor with Potential Adjusting Nodes
Hamamatsu patent application US20140071429 "Range sensor and range image sensor" by Mitsuhito Mase and Takashi Suzuki proposes to use circular transfer gates 5 and potential adjusting gates 6 to maximize a fill factor of ToF sensor. Basically, the whole area outside of transfer gate 5 generates photoelectrons:
