Image sensor and method of operating the same

A method of operating an image sensor including a dual conversion gain transistor provided between and connected to a first charge detection node and a second charge detection node, and a reset transistor provided between and connected to the second charge detection node and a pixel power voltage, the method comprising:

• performing a first reset operation to reset the first charge detection node and the second charge detection node;
• turning off the dual conversion gain transistor and reading out a first reset signal from the first charge detection node;
• transferring an electric charge accumulated in a photoelectric conversion device, to the first charge detection node and reading out a first pixel signal from the first charge detection node;
• turning on the dual conversion gain transistor and reading out a second pixel signal from the first charge detection node;
• performing a second reset operation to reset the first charge detection node and the second charge detection node;
• and
• reading out a second reset signal from the first charge detection node,
• wherein the reset transistor is configured to have a potential gradient increasing in a direction from a channel region of the reset transistor to the pixel power voltage.

An image sensor, comprising:

• a semiconductor substrate of a first conductivity type;
• a pixel isolation structure provided in the semiconductor substrate to form a first pixel region and a second pixel region;
• a photoelectric conversion region provided in each of the first pixel region and a second pixel region in the semiconductor substrate, and is doped to have a second conductivity type;
• a floating diffusion region provided in each of the first pixel region and the second pixel region in the semiconductor substrate, and is spaced apart from the photoelectric conversion region;
• a transfer gate electrode provided between the photoelectric conversion region and the floating diffusion region, and provided in each of the first pixel region and the second pixel region;
• a reset gate electrode disposed on the semiconductor substrate in the first pixel region;
• a first source region provided in the semiconductor substrate in the first pixel region and at a side of the reset gate electrode;
• a first drain region provided in the semiconductor substrate in the first pixel region and at an opposite side of the reset gate electrode;
• a first gate insulating layer provided between the reset gate electrode and the semiconductor substrate;
• a dual conversion gain gate electrode disposed on the semiconductor substrate of the second pixel region;
• a second source region provided in the semiconductor substrate in the second pixel region and at a side of the dual conversion gain gate electrode;
• a second drain region provided in the semiconductor substrate in the second pixel region and at an opposite side of the dual conversion gain gate electrode;
• and
• a second gate insulating layer provided between the dual conversion gain gate electrode and the semiconductor substrate,
• wherein the first gate insulating layer comprises a first portion adjacent to the first source region and a second portion adjacent to the first drain region,
• wherein the first portion has a first thickness, and the second portion has a second thickness that is larger than the first thickness.