US 5,703,642 A · Full depletion mode clocking of solid-state image sensors for improved MTF performance

Abstract

The present invention teaches how to maintain temporally the increased collection region (depletion depth) of detectors within a solid-state image sensor. A novel clocking method is used to control charge transfer within charge coupled devices to reduce cross talk with a resulting improvement in the MTF and quantum efficiency. Specifically, the present invention employs a pulsing type of clocking technique wherein the duty cycle is adjusted to maximize the depletion region. These pulses are spaced equally from phase to phase within the multiphase clocking scheme. The present invention is specifically designed for high speed CCD devices in which improvements in the MTF and QE are desired. Time Delay Integration (TDI) image sensors are such devices that have high speed characteristics as a common requirement and the application of the present invention to these devices is discussed. Additionally, the application of the present invention to certain full frame and frame transfer devices having requirements for high speed characteristics will benefit from the teachings of the present invention.

Claims19

Dependent claims

A method of imaging with charge coupled devices (CCD) to reduce lateral diffusion of charge carriers within the CCD by increasing depletion depth comprising the steps of:

employing with an image sensing system having a CCD with clock means for capability of transferring charge under control of a multiphase clock having at least two phases, said clock means having barrier means for separating of charger representative of individual pixels;
capturing image data to be stored and transferred by the CCD via image sensing means by allowing photons to become incident upon photosensors contained on the CCD;
applying to the charge coupled device the multiphase clock having n phases, each phase having a substantially larger duty cycle in a first logic state that increases depletion depth within the CCD as compared to a second logic state that does not increase depletion within the CCD as much as the first logic state;
and
arranging each phase of the multiphase clock such that all phases of the multiphase clock exist at the first logic state during integration periods for the CCD.

2 more elements

An image sensing system comprising:

a charged coupled device (CCD) having image sensing means for allowing photons from an image to be stored in cells within the CCD;
clock input means for allowing a multiphase clock to transfer stored charges within the CCD in a manner determined by CCD architecture from one cell to an adjacent cell;
a clock generator that can generate multiphase clocks, having a first potential that creates a deep depletion region within the CCD and a second potential that does not create as deep a depletion region within the CCD;
timing means for applying the clock generator such that the first potential of each phase is active during integration periods of the CCD and for creating at least one pulse of the second potential within each phase during readout periods;
and
barrier means for separation of stored charges between each pixel.

3 more elements

A method of reducing lateral diffusion within an image sensor comprising the steps of:

employing an image sensor having a photosensor array formed by a charged coupled device having cells constructed with a substrate doped of a first conductivity type, a buried channel doped of a second conductivity type having opposite polarity from the first conductivity type adjacent the substrate, and electrode means for allowing application of a clocking potential to transfer charge from one cell to another, the electrode means having barrier means for assisting pixel separation under full depletion mode conditions;
capturing image data within the image sensor by allowing photons to become incident upon photosensors contained on the charge coupled device;
applying a multiphase clock to the electrode means, such that sequential phases of the clock are applied to adjacent electrodes, each phase of the multiphase clock having a first state with a potential to create a large depletion region within the substrate;
and
holding each phase of the multiphase clock in the first state for integration periods, thereby, creating an increase depletion region under all phases within the substrate.