Dual conversion gain pixel using Schottky and ohmic contacts to the floating diffusion region and methods of fabrication and operation

An imager pixel, comprising:

• a photosensor for accumulating charge;
• a diffusion region, connected to receive the charge from the photosensor, said diffusion region having an associated first conversion gain;
• and
• a Schottky diode for switchably connecting a capacitive element to said diffusion region to provide said diffusion region with a second associated conversion gain different from said associated first conversion gain.

An imager pixel, comprising:

• a photosensor for accumulating charge;
• a first transistor for resetting said pixel;
• a second transistor for transferring the charge from the photosensor;
• a diffusion region, for receiving the charge from said photosensor through said second transistor, said diffusion region having a first associated conversion gain;
• a capacitive element;
• and
• a Schottky contact coupled between said diffusion region and said capacitive element, said Schottky contact switchably controlling the connection of said capacitive element to said diffusion region such that said diffusion region obtains a second associated conversion gain when the capacitive element is connected to the diffusion region.

An imager, comprising:

• an array of pixel cells formed of a plurality of pixel cells, each pixel comprising:
• photosensor for accumulating charge;
• a first transistor for resetting said pixel;
• a second transistor for transferring the charge from the photosensor;
• a diffusion region, for receiving the charge from said photosensor through said second transistor, said diffusion region having a first associated conversion gain;
• a capacitive element;
• and
• a Schottky contact coupled between said diffusion region and said capacitive element, said Schottky contact switchably controlling the connection of said capacitive element to said diffusion region such that said diffusion region obtains a second conversion gain when the capacitive element is connected to the diffusion region.

An imager system, comprising:

• a processor;
• and
• an imaging device electrically coupled to said processor, said imaging device comprising a pixel array, at least one pixel of said array comprising:
• a photosensor for accumulating charge,
• a diffusion region, connected to receive the charge from the photosensor, said diffusion region having a first associated conversion gain, and
• a conversion gain altering circuit, including a contact, connected to said diffusion region, said conversion gain altering circuit changing the first associated conversion gain to a second associated conversion gain in response to the amount of charge in the diffusion region.

A method of operating an imager device, said method comprising the acts of:

• transferring photo-generated charge to a diffusion region;
• activating a Schottky diode to change a conversion gain of the diffusion region when the amount of transferred charge exceeds a threshold;
• and
• outputting a signal indicative of the charge in the floating diffusion region.

A method of operating an imager device, said method comprising:

• providing a photosensor;
• providing a diffusion region having a first charge storage capacitance;
• storing photo-generated charge from the photosensor in the diffusion region;
• and
• changing the storage capacitance of the diffusion region in response to the charge stored in said diffusion region reaching a predetermined value.

A method of fabricating a dual conversion gain pixel, said method comprising the steps of:

• fabricating a photosensitive region;
• forming a first transistor within the substrate for resetting the pixel;
• providing a diffusion region, the diffusion region having a first associated conversion gain;
• providing a second transistor between the photosensitive region and the floating diffusion region, the second transistor for transferring charge collected in the photosensitive region to the diffusion region;
• and
• forming a Schottky for switchably connecting said diffusion region with a capacitive element to provide said diffusion with a second associated conversion gain.