Solid-State Image Sensor Stacked Photodiodes Charge Capacity
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Solution Overview
Problem
The challenge in solid-state image sensors is the decrease in pixel size leading to reduced saturated charge capacity, coupled with complex manufacturing processes that make process control difficult.
Innovation Solution
A solid-state image sensor design featuring a semiconductor substrate with a first conductivity type region and a second conductivity type charge accumulation region, where the second region is divided into portions along the substrate surface, forming a potential barrier and depletion regions to increase charge saturation, with a lens for light condensation and reverse bias voltage application to enhance depletion and charge accumulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of pixels is increased, then the pixel size becomes small, but the saturated number of charges decreases
Solution Approach 1:
The patent transitions from a two-dimensional planar structure to a three-dimensional stacked structure by arranging multiple photodiodes vertically in the depth direction. This dimensional change allows each pixel to accumulate charges in three dimensions, significantly increasing the saturated charge capacity while maintaining small pixel dimensions on the surface.
Solution Approach 2:
The patent implements a nested structure where multiple photodiodes are stacked within a single pixel footprint. The photodiodes are arranged in layers at different depths, with each photodiode nested within the vertical space of the pixel, allowing maximum charge accumulation within the constrained lateral dimensions.
2Quantity of substance
If multiple photodiodes and vertical transistor are formed in semiconductor substrate, then the saturated quantity of charges is increased, but the structure becomes complex and manufacturing process control becomes difficult
Solution Approach 1:
The patent segments the charge accumulation function into multiple independent photodiodes stacked vertically. Each photodiode operates as a separate charge accumulation unit, allowing the system to achieve high saturated charge capacity through modular stacking rather than requiring a single complex large-volume structure.
Solution Approach 2:
The patent uses a shared readout circuit structure that can read out charges from multiple stacked photodiodes. This multi-functional readout mechanism eliminates the need for separate readout circuits for each photodiode, reducing overall device complexity while maintaining the ability to utilize charges from all stacked photodiodes.
3Quantity of substance
If multiple photodiodes and vertical transistor are formed in semiconductor substrate, then the saturated quantity of charges is increased, but the manufacturing steps increase and process control becomes difficult
Solution Approach 1:
The patent merges the formation processes of multiple stacked photodiodes into a single integrated manufacturing sequence. By combining the diffusion or implantation steps for multiple photodiodes into one coordinated process, the patent reduces the total number of manufacturing steps compared to forming each photodiode separately, thereby improving ease of manufacture.
4Productivity
If the pixel size is reduced, then the number of pixels increases, but the dynamic range is limited due to reduced charge capacity
Solution Approach 1:
The patent extends charge accumulation into the depth dimension by stacking photodiodes vertically. This allows each pixel to maintain a large effective charge accumulation volume despite small lateral dimensions, thereby preserving wide dynamic range capability while enabling high pixel density.
Solution Approach 2:
The patent changes the geometric parameters of charge accumulation by transitioning from lateral expansion to vertical stacking. By increasing the depth parameter and utilizing the third dimension, the patent maintains large charge capacity in small pixels, enabling both high pixel count and wide dynamic range.
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 design simplifies manufacturing, increases saturated charge capacity, and lowers depletion voltage, enabling a wider dynamic range and improved sensitivity while maintaining process control and sensitivity.
Implementation Method 1
a lens for condensing light to the second semiconductor region
Implementation Method 2
a second semiconductor region of a second conductivity type constituting a charge accumulation region
Implementation Method 3
by applying a reverse bias voltage, having a predetermined magnitude, between the first semiconductor region and the second semiconductor region, a depletion region expands from the first semiconductor region toward the second semiconductor region
Data Source
AI summary
An image sensor including a first semiconductor region of a first conductivity type that is arranged in a substrate, a second semiconductor region of a second conductivity type that is arranged in the first semiconductor region to form a charge accumulation region. The second semiconductor region includes a plurality of portions arranged in a direction along a surface of the substrate. A potential barrier is formed between the plurality of portions. The second semiconductor region is wholly depleted by expansion of a depletion region from the first semiconductor region to the second semiconductor region. A finally-depleted portion to be finally depleted, of the second semiconductor region, is depleted by the expansion of the depletion region from a portion of the first semiconductor region, located in a lateral direction of the finally-depleted portion.