Image Sensor Contact Layout for Lower Leakage Current
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Solution Overview
Problem
Leakage current in imaging devices with charge accumulation regions in semiconductor substrates leads to image quality deterioration due to defects and increased depletion layer extension.
Innovation Solution
The imaging device design includes a semiconductor substrate with a first and second diffusion region of a specific conductivity type, where the second diffusion region has a larger contact area and a higher impurity concentration, reducing the depletion layer extension and leakage current by attenuating the electric field strength at the junction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If charge accumulation regions are provided in a semiconductor substrate, then image signals can be accumulated and read, but leakage current occurs leading to image quality deterioration
Solution Approach 1:
The patent applies local quality by creating a second diffusion region with higher impurity concentration specifically at the contact area where the second contact connects to the semiconductor substrate. This localized high-concentration region reduces the depletion layer extension and leakage current at the critical contact interface without affecting the overall charge accumulation function. The asymmetric doping strategy targets the specific problem area (contact region) while preserving the photoelectric conversion and charge accumulation capabilities in other regions.
Solution Approach 2:
The patent changes the impurity concentration parameter by introducing a second diffusion region with higher impurity concentration compared to the first diffusion region. This parameter change reduces the depletion layer width and contact resistance at the second contact interface, thereby suppressing leakage current. The conductivity type parameter is also utilized by making the second diffusion region have the same conductivity type as the semiconductor substrate, creating a low-resistance contact path that minimizes leakage.
2Reliability
If the contact area is increased to reduce contact resistance, then leakage current increases due to larger depletion layer extension
Solution Approach 1:
The patent resolves this contradiction by applying local quality through asymmetric contact design. The first contact has a smaller area with lower impurity concentration in its diffusion region, while the second contact has a larger area with higher impurity concentration in its diffusion region. This localized differentiation allows the second contact to achieve low contact resistance through higher doping without suffering from increased leakage current, as the high-concentration region confines the depletion layer and reduces leakage pathways.
Solution Approach 2:
The patent employs asymmetry by designing the second diffusion region with higher impurity concentration and larger contact area compared to the first diffusion region. This asymmetric configuration optimizes each contact for its specific function: the first contact for signal readout and the second contact for low-resistance connection with reduced leakage. The asymmetric doping profile creates different electrical characteristics at each contact interface, allowing simultaneous optimization of contact resistance and leakage suppression.
3Object-generated harmful factors
If the depletion layer extension is reduced to suppress leakage current, then the electric field strength must be attenuated
Solution Approach 1:
The patent changes the impurity concentration parameter in the second diffusion region to achieve the desired balance between depletion layer extension and electric field strength. By increasing the impurity concentration in the second diffusion region, the depletion layer width is reduced, which suppresses leakage current. The higher doping concentration also modifies the electric field distribution, attenuating the peak field strength at the contact interface while maintaining sufficient field for charge collection. This parameter optimization resolves the contradiction between reducing leakage and maintaining electric field effectiveness.
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 effectively suppresses leakage current and improves image quality by reducing the depletion layer extension and contact resistance, enhancing the overall performance of the imaging device.
Implementation Method 1
a photoelectric converter that converts light into a charge
Implementation Method 2
reducing the depletion layer extension and leakage current by attenuating the electric field strength at the junction
Data Source
AI summary
An imaging device includes: a photoelectric converter that converts light into a charge; a first diffusion region of a first conductivity type to which the charge is input; a second diffusion region of the first conductivity type; a first contact that is directly connected to the first diffusion region; a second contact that is directly connected to the second diffusion region; a first transistor that includes the first diffusion region as one of a source and a drain and that includes a first gate; and a second transistor that includes the second diffusion region as one of a source and a drain and that includes a second gate. A dimension of the second contact in a direction parallel to a width direction of the second gate is greater than a dimension of the first contact in a direction parallel to a width direction of the first gate.