埋め込み塾高速電荷転送フォトダイオードを用いたTOF距離画像センサの試作

摘要

本稿では，埋め込み塾高速電荷転送フォトダイオードを用いたTime-of-Flight（TOF）距離画像センサの駆動方法，画素構造及び試作について述べる．提案する駆動方法は、デューティー比が小さくパルス幅の短いLEDパルス光を対象物に照射し，その反射光をTOF距離画像センサで受光する．受光素子から電荷蓄稽部までの高速電荷転送はTOF距離画像センサ等に必須の技術である．フォトダイオード内に一定の転送方向の電界を発生させることで高速電荷転送が可能となり，完仝空乏化電位とフォトダイオードの幅の関係に従いフォトダイオードの形状を決めることで高速電荷転送を埋め込みフォトダイオードで実現できる．埋め込み塾高速電荷転送フォトダイオードを用いたTOF距離画像センサの試作を行い，画素における信号パルスと信号出力との関係を測定した．%This paper presents a new structure and method of range calculation for CMOS time-of-flight (TOF) range image sensors using pinned photodiodes. In the proposed method, a LED light with short pulse width and small duty ratio irradiates the objects and a back-reflected light is received by the TOF range imager. In TOF range image sensors, high speed charge transfer from the light receiving part to a charge accumulator is essential. It was found that the fastest charge transfer can be realized when the lateral electric field along the axis of charge transfer is constant and this condition is met when the shape of the diode exactly follows the relationship between the fully-depleted potential and the photodiode width. A TOF range imager prototype is designed and implemented with 0.18um CMOS image sensor technology for pinned photodiode 4T pixels. In the prototype, the response of the pixel output as a function of the light pulse delay has been measured.