A Discussion of Interline Scheme CCD Image Sensor Combining Buried Photo-Diode and CCD Register Driven through a Barrier

Abstract

We propose a new interline CCD (IL-CCD) image sensor which combines buried photodiodes and CCD registers driven through a barrier (DTB-CGD). The performance of the image sensor was simulated by three-dimensional numerical analyses, emphasizing on dark current and charge capacity. It was clarified that highly biased electrodes of the DTE-CCD absorbed most of the generation-recombination (g-r) currents at Si-SiO2 interfaces beneath their electrodes and also the currents between electrodes with low biases and electrodes with high biases. The g-r currents were reduced by several orders at the interface under electodes with low biases, because holes were introduced under the interface. Most of the reduced g-r currents are also absorbed into their respective electrodes. However, a small part of the g-r currents generated at the above three interfaces flew into a channel, going over the potential barrier between the bottom of the SiO2 layer and channel, to become a dark current. When the barrier height was increased, dark currents were significantly reduced. Therefore, the IL-CCD image sensor enables a device with very few dark currents. When a 8.3 μm(H)×12 μm(V) pixel includes two photodiodes and four transfer electrodes was used, more than 4.5∼5.0×104 electrons were transferred from photodiodes to CCD registers by 0 V to 9.5 V and -5.8 to 0 V transfer pulses. Additionally, 4.0×104 electrons were transferred in the CCD by -5.8 V to 0 V amplitude using conventional 4-phase driving pulses.