Solid-state Image Pickup Device Charge Transfer Path
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Solution Overview
Problem
In solid-state image pickup devices, a high drive voltage is required to transfer charges from the charge holding portion to the floating diffusion due to the expansion of the depletion layer and narrowing of the transfer path caused by the positional relationship between the high-concentration P-type layer and the charge transfer path.
Innovation Solution
A configuration where a second-conductivity-type semiconductor region with a higher impurity concentration is disposed under the first semiconductor region to form a PN junction, reducing the depletion layer expansion and maintaining a wider transfer path, allowing charge transfer at a lower voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a high-concentration P-type layer is disposed under the charge holding portion via the P-type well, then noise is reduced by suppressing inflow of charges, but a high drive voltage is required to transfer charges due to depletion layer expansion
Solution Approach 1:
The patent applies local quality by creating a P-type layer with non-uniform impurity concentration distribution. The high-concentration P-type layer is positioned specifically under the charge holding portion to suppress charge inflow and reduce noise, while the impurity concentration gradually decreases toward the transfer path region. This localized variation in material properties allows noise reduction without requiring high drive voltage for charge transfer.
2Object-affected harmful factors
If a high-concentration P-type layer is disposed under the charge holding portion, then charge inflow is suppressed, but the transfer path narrows and transfer efficiency decreases
Solution Approach 1:
The patent implements local quality by spatially varying the impurity concentration of the P-type layer. The high-concentration region is localized under the charge holding portion to block charge inflow, while the concentration decreases toward the transfer path, maintaining an open transfer channel. This localized differentiation allows simultaneous achievement of charge inflow suppression and high transfer efficiency.
Solution Approach 2:
The patent resolves the contradiction by introducing a depth dimension to the impurity concentration distribution. Instead of a uniform lateral distribution, the impurity concentration varies with depth, being highest under the charge holding portion and decreasing toward the transfer path. This three-dimensional concentration gradient allows the P-type layer to perform multiple functions at different spatial locations without conflict.
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 configuration enables charge transfer at a low voltage while suppressing depletion layer expansion and transfer path narrowing, enhancing the efficiency of charge transfer in solid-state image pickup devices.
Implementation Method 1
A second-conductivity-type second semiconductor region is disposed under the first semiconductor region so as to form a PN junction together with the first semiconductor region
Implementation Method 2
a photoelectric conversion portion configured to generate charges in accordance with incident light
Data Source
AI summary
A photoelectric conversion portion, a charge holding portion, a transfer portion, and a sense node are formed in a P-type well. The charge holding portion is configured to include an N-type semiconductor region, which is a first semiconductor region holding charges in a portion different from the photoelectric conversion portion. A P-type semiconductor region having a higher concentration than the P-type well is disposed under the N-type semiconductor region.