Image sensor with a reset transistor having spontaneous polarization characteristcs and method for operating the same

An image sensor, comprising:

• a photoelectric conversion element suitable for generating photocharges corresponding to incident light;
• a transfer transistor suitable for transferring the generated photocharges to a floating diffusion node based on a transfer signal;
• and
• a reset transistor suitable for resetting the floating diffusion node based on a reset signal activated to a first level,
• wherein the reset transistor includes a gate dielectric layer having spontaneous polarization characteristics, where a direction of spontaneous polarization of the gate dielectric layer is changed based on the reset signal,
• wherein the reset transistor is kept in the turn-on state during a predetermined operation section following the resetting of the floating diffusion node even though the activated reset signal is not applied,
• wherein the reset transistor is turned-off in response to a reset signal activated to a second level opposite to the first level.

A method for operating an image sensor that includes a photoelectric conversion element suitable for generating photocharges corresponding to incident light, a transfer transistor suitable for transferring the photocharges to a floating diffusion node, a reset transistor suitable for resetting the floating diffusion node, and including a memory gate, comprising:

• turning on the reset transistor by applying a first reset pulse to the memory gate in a first section;
• allowing the incident light to impact the photoelectric conversion element during a second section following the first section, and turning off the reset transistor by applying a second reset pulse to the memory gate at an ending period of the second section;
• and
• turning on the transfer transistor by applying a transfer signal to a gate of the transfer transistor in a third section following the second section,
• wherein the reset transistor is kept in the turn-on state during the second section even though the first reset pulse is not applied,
• wherein the reset transistor is turned-off in response to the second reset pulse
• wherein the first reset pulse and the second reset pulse have different signal polarities.