Fig. 1. (Color online) (a) The schematic 3-D views and (b) optical image of the circular a-IGZO TFTs.

Fig. 2. (Color online) The typical measurement results of (a) transfer (I_DS–V_GS) and (b) output (I_DS–V_DS) characteristics of the circular a-IGZO TFTs with inner electrode as source and outer electrode as drain (inset is the typical output characteristics of a rectangular TFT).

Fig. 3. The (a) schematic and (b) timing diagram of the proposed active image sensor.

Fig. 4. (Color online) (a) Equivalent circuit, (b) output and gain of the proposed active image sensor pixel with circular a-IGZO TFT.