Semiconductor structure and operating method for improving charge transfer of image sensor device

An image sensor device, comprising:

• a semiconductor substrate;
• a plurality of unit pixels;
• a floating diffusion region disposed at a center of the plurality of unit pixels;
• and
• a reset transistor adjacent to the plurality of unit pixels and configured to reset the floating diffusion region;,
• wherein each of the plurality of unit pixels comprises:
• a first photodiode disposed in the semiconductor substrate and configured to generate first charges in response to radiation;
• a second photodiode configured to generate second charges in response to the radiation;
• a first transistor disposed over the first photodiode;
• and
• a second transistor disposed over the first photodiode, wherein the second transistor is also disposed between the reset transistor and the floating diffusion region, the first transistor and the second transistor being configured to generate an electric field moving the first charges generated by the first photodiode to the floating diffusion,
• wherein the floating diffusion region is configured to store the first and second charges generated by the plurality of unit pixels, and wherein the first transistor and the second transistor are enabled by a first pulse and a second pulse, respectively, during a shutter operation, wherein the first pulse and the second pulse have a same polarity, wherein the first transistor and the second transistor are further enabled by a third pulse and a fourth pulse, respectively, during a readout operation for providing a voltage in response to a potential at the floating diffusion region, wherein the third pulse and the fourth pulse have opposite polarities.

A method of operating an image sensor device, the method comprising:

• configuring a photodiode to generate charges in response to radiation;
• biasing a first transistor by a first pulse to generate a first electric field that transfers a first portion of the charges from the photodiode to a floating diffusion region in a first period during a shutter operation;
• and
• biasing a second transistor by a second pulse to generate a second electric field that transfers a second portion of the charges from the photodiode to a source or a drain region of the second transistor during the shutter operation, wherein the second transistor and the floating diffusion region are disposed on opposite sides of the photodiode, and the second transistor is disposed over the first photodiode and also is disposed between the reset transistor and the floating diffusion region,
• wherein the first pulse and the second pulse have a same polarity,
• wherein the first transistor and the second transistor are further enabled by a third pulse and a fourth pulse, respectively, during a readout operation for providing a voltage in response to a potential at the floating diffusion region, and the third pulse and the fourth pulse have opposite polarities.