CMOS Global Shutter Pixel Charge Distribution
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Solution Overview
Problem
Conventional CMOS-type solid-state imaging devices face challenges in downsizing due to the need for a large charge accumulation region with stepwise potential to prevent residual charge and ensure complete charge transfer, leading to increased device size and potential distortion in output images.
Innovation Solution
The implementation of a solid-state imaging device with a photoelectric conversion unit, a generated charge retaining unit, and an output charge retaining unit, where the generated charge is transferred and uniformly distributed between these units to achieve equal potential, allowing for a global shutter function while reducing device size through optimized impurity concentration and potential control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a charge accumulation unit is included in each pixel with stepwise potential to prevent residual charge, then charge transfer completeness is improved, but device size increases
Solution Approach 1:
The pixel structure is segmented into distinct functional regions: a photoelectric conversion unit, a generated charge retaining unit, and a floating diffusion region. This segmentation allows each region to be optimized independently, with the charge retaining unit having a specific impurity concentration range that is different from other regions, thereby achieving complete charge transfer without requiring excessive device size.
Solution Approach 2:
Different regions within the pixel are assigned different impurity concentrations to achieve their specific functions. The generated charge retaining unit has an impurity concentration between 1×10^17 and 1×10^19 atoms/cm³, which is higher than the photoelectric conversion unit but lower than the floating diffusion. This local quality differentiation ensures complete charge transfer while minimizing overall device size.
2Device complexity
If exposure is started immediately after signal reading in conventional CMOS imaging devices, then device complexity is reduced, but image distortion occurs due to shifted exposure timings
Solution Approach 1:
The generated charge retaining unit is prepared in advance during the signal reading period, maintaining charge retention capability while allowing immediate restart of exposure. The unit holds generated charge from the photoelectric conversion unit without requiring complex additional structures, enabling continuous exposure operation while maintaining image accuracy through proper charge retention and transfer timing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables the downsizing of imaging devices with a global shutter function by ensuring uniform charge distribution and potential equality, thereby reducing noise and improving image accuracy without increasing device size.
Implementation Method 1
the photoelectric conversion unit is a semiconductor element which performs photoelectric conversion for generating charge corresponding to the amount of incident light
Implementation Method 2
a retained charge distributing unit for rendering the generated charge retaining unit and the output charge retaining unit conductive therebetween to uniformly distribute the charge retained in the generated charge retaining unit
Data Source
AI summary
An imaging device of a CMOS type having a global shutter function is downsized.In the imaging device, a photoelectric conversion unit generates charge corresponding to an exposure amount in a predetermined exposure period. A generated charge retaining unit is formed to have a predetermined impurity concentration in a semiconductor substrate and retains the charge. A generated charge transferring unit renders the photoelectric conversion unit and the generated charge retaining unit conductive therebetween after the exposure period has elapsed and transfers the charge from the photoelectric conversion unit to the generated charge retaining unit. An output charge retaining unit is formed to have substantially the same impurity concentration as that of the generated charge retaining unit and retains charge. A retained charge distributing unit renders the generated charge retaining unit and the output charge retaining unit conductive therebetween and uniformly distributes the charge retained in the generated charge retaining unit to the generated charge retaining unit and the output charge retaining unit. A signal generating unit generates a signal corresponding to the charge retained in the output charge retaining unit as an image signal after the distribution in the retained charge distributing unit.