Demonstration of a novel drift field pixel structure for the demodulation of modulated light waves with application in three-dimensional image capture

A new pixel structure for the demodulation of intensity modulated light waves is presented. The integration of such pixels in line and area array sensors finds application in time-of-flight three-dimensional imaging. In 3D range imaging an illumination module sends a modulated optical signal to a target, where it is reflected back to the sensor. The phase shift of the reflected signal compared to the emitted signal is proportional to the distance to one point of the target. The detection and demodulation of the signal is performed by a new pixel structure named drift field pixel. The sampling process is based on the fast separation of photogenerated charge due to lateral electrical fields below a high-resistive transparent poly-Si photogate. The dominant charge transfer phenomenon of drift, instead of diffusion as in conventional CCD pixels, allows much higher modulation frequencies of up to 1 GHz and a much higher ultimate distance accuracy as a consequence. First measurements performed with a prototype pixel array of 3x3 pixels in a 0.8 micron technology confirm the suitability of the pixels for applications in the field of 3D-imaging. Depth accuracies in the sub centimeter range have already been achieved.