Pinned Photodiode Gate-Controlled SCR Switch Dark Current Prevention
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Solution Overview
Problem
Existing pinned photodiode sensors in active pixel sensors suffer from dark current leakage due to interface traps between the oxide layer and the substrate, which are not completely prevented by the depletion regions, leading to noise during image capture.
Innovation Solution
A gate-controlled SCR transfer switch with different doped regions, including a P+ and N+ doped region under the gate, and opposite types of electrical conductive materials, is implemented to prevent dark current leakage by forming a hole channel that does not allow the depletion region to reach the interface between the oxide layer and the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a depletion region is formed between the P-type substrate and N- doped region to prevent dark current leakage, then the depletion region can reach the interfaces to block interface traps, but the depletion region still allows electrons or holes to be released or captured by interface traps, resulting in dark current leakage
Solution Approach 1:
The patent changes the doping concentration parameter by introducing a heavily doped P+ region with doping concentration greater than 1×10^19 atoms/cm³, which is higher than the P-type substrate (1×10^16 to 1×10^18 atoms/cm³). This parameter change creates a more effective barrier that prevents interface traps from releasing or capturing carriers, thereby reducing dark current leakage while maintaining the depletion region's blocking function.
Solution Approach 2:
The patent creates a composite doped region structure combining P-type substrate, P+ heavily doped region, and N- doped region. This composite structure with varying doping concentrations forms a multi-layered barrier system that more effectively prevents dark current leakage compared to a single uniform doped region, as each layer contributes to blocking interface traps at different levels.
2Reliability
If the oxide layer contacts the P+ doped region or N- doped region to provide electrons or holes and prevent depletion region from touching interface traps, then some dark current is reduced, but dark current leakage cannot be completely prevented during operation
Solution Approach 1:
The patent applies local quality by creating a P+ doped region with specifically high doping concentration (greater than 1×10^19 atoms/cm³) at the critical interface area between the oxide layer and substrate. This localized high-doping region provides excess carriers that effectively saturate interface traps in that specific area, preventing dark current leakage where it occurs most during operation.
Solution Approach 2:
The P+ doped region is formed in advance during the manufacturing process, creating a reservoir of excess carriers before the device operates. This preliminary action ensures that interface traps are pre-saturated with carriers, so when the device operates and depletion regions form, the interface traps cannot release or capture additional carriers that would cause dark current leakage.
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
The solution effectively prevents dark current leakage during image capture by forming a hole channel that isolates the depletion region from the interface traps, reducing noise and improving image quality.
Implementation Method 1
the gate 18 is connected to a high voltage so as to generate a depletion region 13 (between dotted line 5 and dotted line 7) between the P-type substrate 10 and the N− doped region 14
Implementation Method 2
the P-type substrate 10, or the N− doped region 14, the region contacting the oxide layer 17 can provide electrons or holes to prevent a depletion region from touching interface traps
Implementation Method 3
there are plenty of interface traps between the oxide layer 17 and the substrate 10, such interface traps release or capture electrons or holes with changes of temperature or electric field intensity, resulting in dark current leakage
Data Source
AI summary
A pinned photodiode sensor with gate-controlled SCR switch includes a pinned photodiode and a gate-controlled SCR switch. The SCR switch includes a P-type substrate, an N− doped region, and an N+ doped region formed on the substrate; a P+ doped region formed on the N− doped region; an oxide layer formed on the P substrate, the N− doped region, the N+ doped region, and the P+ doped region; and a gate formed above the P substrate and the N− doped region. The gate includes a P+ doped region and an N+ doped region. During an exposure procedure, a depletion region will not reach the interface between the oxide layer and the substrate, thereby preventing dark current leakage.