Solid-state image sensor, control method for the same, and electronic device

1. A solid-state image sensor comprising:

a plurality of unit pixels each including

a photoelectric transducer which generates a charge corresponding to an amount of incident light and accumulates the charge therein,

a first transfer gate which transfers the charge accumulated in the photoelectric transducer,

a charge holding region in which the charge transferred from the photoelectric transducer by the first transfer gate is held,

a second transfer gate which transfers the charge held in the charge holding region,

a floating diffusion region in which the charge transferred from the charge holding region by the second transfer gate is held to be read out as a signal,

a charge discharging gate which transfers the charge received from the photoelectric transducer, to a charge discharging part, and

a structure including an overflow path formed in a boundary portion between the photoelectric transducer and the charge holding region, the overflow path being formed at a potential for determining a predetermined charge amount and transferring a charge exceeding the predetermined charge amount as a signal charge from the photoelectric transducer to the charge holding region,

wherein as a channel electric-potential of the charge discharging gate, an electric-potential lower than an electric-potential of the overflow path is set, or an electric-potential higher than the electric-potential of the overflow path and lower than an electric-potential causing the photoelectric transducer to be completely depleted is set.

2. The solid-state image sensor according to claim 1 ,

wherein when an intermediate electric-potential is applied to the charge discharging gate as a gate electric-potential, the channel electric-potential is set at a predetermined electric-potential.

3. The solid-state image sensor according to claim 1 ,

wherein when an electric-potential of a drain of the charge discharging part is driven, the channel electric-potential is set at a predetermined electric-potential.

4. The solid-state image sensor according to claim 3 ,

wherein a channel of the charge discharging gate is formed in a region deeper in a direction to a substrate than a silicon surface.

5. The solid-state image sensor according to claim 1 ,

wherein an off-state voltage of each of the charge discharging gate, the first transfer gate, and the second transfer gate is a negative voltage.

6. A control method for a solid-state image sensor, the solid-state image sensor including

a plurality of unit pixels each including

a photoelectric transducer which generates a charge corresponding to an amount of incident light and accumulates the charge therein,

a first transfer gate which transfers the charge accumulated in the photoelectric transducer,

a charge holding region in which the charge transferred from the photoelectric transducer by the first transfer gate is held,

a second transfer gate which transfers the charge held in the charge holding region,

a floating diffusion region in which the charge transferred from the charge holding region by the second transfer gate is held to be read out as a signal,

a charge discharging gate which transfers the charge received from the photoelectric transducer, to a charge discharging part, and

a structure including an overflow path formed in a boundary portion between the photoelectric transducer and the charge holding region, the overflow path being formed at a potential for determining a predetermined charge amount and transferring a charge exceeding the predetermined charge amount as a signal charge from the photoelectric transducer to the charge holding region,

the method comprising:

as a channel electric-potential of the charge discharging gate, setting an electric-potential lower than an electric-potential of the overflow path, or setting an electric-potential higher than the electric-potential of the overflow path and lower than an electric-potential causing the photoelectric transducer to be completely depleted.

7. An electronic device having a solid-state image sensor mounted thereon, the solid-state image sensor including

a plurality of unit pixels each including

a photoelectric transducer which generates a charge corresponding to an amount of incident light and accumulates the charge therein,

a first transfer gate which transfers the charge accumulated in the photoelectric transducer,

a charge holding region in which the charge transferred from the photoelectric transducer by the first transfer gate is held,

a second transfer gate which transfers the charge held in the charge holding region,

a floating diffusion region in which the charge transferred from the charge holding region by the second transfer gate is held to be read out as a signal,

a charge discharging gate which transfers the charge received from the photoelectric transducer, to a charge discharging part, and

a structure including an overflow path formed in a boundary portion between the photoelectric transducer and the charge holding region, the overflow path being formed at a potential for determining a predetermined charge amount and transferring a charge exceeding the predetermined charge amount as a signal charge from the photoelectric transducer to the charge holding region,

wherein as a channel electric-potential of the charge discharging gate, an electric-potential lower than an electric-potential of the overflow path is set, or an electric-potential higher than the electric-potential of the overflow path and lower than an electric-potential causing the photoelectric transducer to be completely depleted is set.