Solid-State Image Sensor Floating Diffusion Capacitance
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Solution Overview
Problem
Solid-state image capturing devices face challenges in reducing the capacitance of the floating diffusion layer, which can lead to a decrease in the maximum storage charge amount of the photodiode, affecting the dynamic range and sensitivity.
Innovation Solution
The device incorporates a first-conductivity-type well with a second-conductivity-type diffusion layer having a higher impurity concentration than the first diffusion layer, and a first-conductivity-type diffusion layer with a lower impurity concentration than the well, allowing for increased depletion layer width and reduced capacitance of the floating diffusion layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the width of the depletion layer in the p-n junction is increased to reduce the capacitance of the floating diffusion layer, then the charge detection sensitivity is improved, but the maximum storage charge amount of the photodiode decreases
Solution Approach 1:
The patent applies local quality by creating a p-type impurity layer with locally varied impurity concentration - the concentration is lower in the region adjacent to the photodiode (to maintain wide depletion layer and low capacitance) and higher in other regions (to prevent maximum storage charge amount decrease). This spatial variation in impurity concentration allows simultaneous optimization of both sensitivity and storage capacity
Solution Approach 2:
The patent changes the impurity concentration parameter of the p-type impurity layer to resolve the contradiction. By adjusting the impurity concentration distribution - specifically making it lower near the photodiode interface - the depletion layer width increases and capacitance decreases, improving sensitivity while the overall charge storage capacity is preserved through controlled concentration gradients
2Measurement precision
If a p−-type impurity layer with low impurity concentration is provided to increase depletion layer width and reduce floating diffusion layer capacitance, then charge detection sensitivity is increased, but the maximum storage charge amount of the photodiode may decrease
Solution Approach 1:
The patent implements local quality by providing the p-type impurity layer with non-uniform impurity concentration distribution. The impurity concentration is specifically lowered in the region adjacent to the photodiode to increase depletion layer width and reduce capacitance, while maintaining higher concentration in other regions to preserve the maximum storage charge amount
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 enhances charge detection sensitivity and prevents a decrease in the maximum storage charge amount, while also reducing manufacturing steps and the number of capacitance.
Implementation Method 1
a first second-conductivity-type diffusion layer that is provided in the first-conductivity-type well and generates carriers upon being irradiated with light
Implementation Method 2
the width of a depletion layer in a p-n junction is increased and the capacitance of a floating diffusion layer is reduced
Data Source
AI summary
A solid-state image capturing device according to the present invention includes: a first-conductivity-type well; a first second-conductivity-type diffusion layer that is provided in the first-conductivity-type well and generates carriers upon being irradiated with light; a second second-conductivity-type diffusion layer that is provided in the first-conductivity-type well and stores carriers that are generated in the first second-conductivity-type diffusion layer and are transmitted thereto; and a first first-conductivity-type diffusion layer provided below the second second-conductivity-type diffusion layer, wherein an impurity concentration of the second second-conductivity-type diffusion layer is higher than an impurity concentration of the first second-conductivity-type diffusion layer, and an impurity concentration of the first first-conductivity-type diffusion layer is lower than an impurity concentration of the first-conductivity-type well.