A Time-of-Flight 3-D Image Sensor With Concentric-Photogates Demodulation Pixels

In this paper, we develop pixels with concentric-photogates for applications in time-of-flight 3-D image sensors with single-tap architecture. The pixel uses a buried-channel device and features a reduced effective electron transit length, for the rapid transfer of a signal electron. A reduction in the interpixel irregularity of signal levels and a consequent increase in the demodulation signal amplitude are observed in the single-tap operation mode as opposed to the multitap operation mode. Specifically, we are able to achieve a demodulation contrast higher than 50% from 20 MHz modulation of an 850 nm light-emitting diode illumination. Finally, we construct a sensor composed of 198 x 108 concentric photogate pixels, each with a pitch of 28 mu m, and use it to generate a 3-D image conveying gross distance information and detailed object features with a distance error of less than 1% over a range of 1 to 7 m.