Stacked Photodiode Readout With One Vertical Transistor
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Solution Overview
Problem
Conventional image sensors face sensitivity issues due to the miniaturization of pixels, which leads to a decrease in signal charge capacity and the need for multiple vertical transistors to read signal charges from stacked photodiodes, making the process complex and difficult to implement.
Innovation Solution
A solid-state imaging element with multiple photodiodes stacked in a semiconductor substrate, where a single vertical transistor with a gate electrode embedded in the substrate reads signal charges by controlling the voltage applied to the gate electrode, allowing individual reading of charges from each photodiode without the need for multiple transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple vertical transistors are formed to read signal charges from stacked photodiodes, then individual reading capability is achieved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent merges the function of multiple vertical transistors into a single vertical transistor by stacking photodiodes in the thickness direction. This single transistor can individually read signal charges from multiple photodiodes through selective voltage application, eliminating the need for multiple transistors while maintaining individual reading capability.
Solution Approach 2:
The patent transitions from a planar arrangement of photodiodes and transistors to a three-dimensional stacked structure. By stacking photodiodes in the thickness direction and embedding the transistor gate electrode within the substrate, the system achieves individual reading capability without increasing the number of transistors, effectively using the vertical dimension to resolve the contradiction.
2Area of moving object
If pixel region is decreased for miniaturization, then pixel density increases, but signal charge capacity decreases
Solution Approach 1:
The patent addresses the signal charge capacity reduction caused by pixel miniaturization by stacking multiple photodiodes in the thickness direction. This vertical stacking increases the total photoelectric conversion volume within the same pixel footprint, thereby maintaining or enhancing signal charge capacity despite reduced planar pixel area.
Solution Approach 2:
The patent creates a composite photoelectric conversion structure by stacking multiple photodiodes with different light absorption characteristics at different depths. This composite structure enables efficient utilization of the limited pixel volume while maintaining adequate signal charge capacity through the combined contribution of multiple photodiodes.
3Reliability
If stacked photodiode structure is implemented, then sensitivity improves, but manufacturing process complexity increases
Solution Approach 1:
The patent segments the photoelectric conversion function into multiple stacked photodiodes, each optimized for different light wavelengths or depths. This segmentation improves sensitivity by capturing light more efficiently at different penetration depths while using a single shared transistor for readout, simplifying the overall manufacturing compared to forming multiple complete transistor-photodiode units.
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 improves sensitivity by allowing individual reading of signal charges from multiple photodiodes with a single transistor, enhancing signal charge capacity and simplifying the manufacturing process, even in miniaturized pixel structures.
Implementation Method 1
a photodiode for obtaining a signal charge corresponding to blue light, a photodiode for obtaining a signal charge corresponding to green light, and a photodiode for obtaining a signal charge corresponding to red light are stacked
Data Source
AI summary
The present technology relates to a solid-state imaging element, a method of manufacturing the same, and an electronic device capable of implementing a stacked structure of a plurality of photodiodes, thereby improving sensitivity. A solid-state imaging element according to the present technology includes a plurality of photodiodes stacked in a semiconductor substrate in a thickness direction of the semiconductor substrate, and a transistor including a gate electrode at least a part of which is embedded in the semiconductor substrate, the transistor that individually reads a signal charge accumulated in each of the plurality of photodiodes according to a voltage applied to the gate electrode. The present technology is applicable to, for example, an imaging device.