Solid-State Image Pickup Device Global Shutter Charge Transfer

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Solution Overview

Problem

CMOS image sensors face challenges in achieving global electronic shutter functionality while maintaining high sensitivity and low dark current, as they typically operate with rolling shutters, leading to residual charges in photodiodes and increased circuit complexity due to high power supply voltages and blooming effects.

Innovation Solution

A solid-state image pickup device with a pixel array and control circuit that utilizes multiple charge transfer paths with shutter switches and storage diodes to enable multiplexed global shutter operations, allowing for simultaneous charge transfer and accumulation, thereby reducing residual charges and improving sensitivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If high power supply voltage is used to enhance charge storage capacity in the storage diode, then the electronic shutter function is improved, but residual charges remain in the photodiode which lowers sensitivity

Engineering Contradiction:

Improveelectronic shutter functionVSAvoidsensitivity

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The pixel is divided into two independent charge storage regions: a photodiode for photoelectric conversion and a storage diode for charge holding. By segmenting the charge transfer function, the patent enables complete charge migration to the storage diode while maintaining photodiode sensitivity, resolving the contradiction between shutter function and sensitivity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A transfer gate is introduced as an intermediary component between the photodiode and storage diode. This transfer gate controls the complete migration of charges from the photodiode to the storage diode, ensuring that residual charges in the photodiode are minimized while achieving effective electronic shuttering through the storage diode.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If multiple charges are accumulated in a single potential well, then the dynamic range is extended, but the complexity of charge transfer control increases

Engineering Contradiction:

Improvedynamic rangeVSAvoidcharge transfer control

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent segments the charge accumulation function into multiple independent potential wells (photodiode and storage diode). Each well can independently accumulate charges, allowing the system to achieve extended dynamic range through multiple exposure levels while keeping the control logic for each well relatively simple and modular.

Inventive Principle:

Principle #1Segmentation

3Device complexity

If embedded storage diode is used instead of CCD structure, then the device complexity is reduced, but the global electronic shutter function becomes difficult to achieve

Engineering Contradiction:

ImprovestructureVSAvoidglobal electronic shutter function

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent merges the photodiode and storage diode within the same pixel structure, combining the photoelectric conversion function and charge storage function in a unified CMOS-based architecture. This integration achieves global electronic shutter functionality without requiring complex CCD structures, maintaining simplicity while enabling simultaneous charge transfer across all pixels.

Inventive Principle:

Principle #5Merging (Combining)

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 enables wide dynamic range imaging with high shutter efficiency and low noise, allowing for multiplexed global shutter operations that enhance image quality and reduce dark current, while maintaining low power consumption.

Implementation Method 1

a photoelectric transducer (11a) for generating an electric signal from light received thereby

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentEP2541896B1Solid-state image pickup device, method of reading pixel signal, and pixel

Publication Date: 2019.06.12 NAT UNIV CORP SHIZUOKA UNIV

Figure 1
Figure 2
Figure 3(a)~3(b)

AI summary

In a pixel (11), a floating semiconductor region (FD) accumulates electrical charges from a photoelectric transducer (PD). A first charge transferring path (CTP1) extends from the photoelectric transducer (PD) to the floating semiconductor region (FD) via a storage diode (SD). A second charge transferring path (CTP2) extends from the photoelectric transducer (PD) to the floating semiconductor region. An output portion (AMP) provides signals according to the potential at the floating semiconductor region (FD). The first charge transferring path (CTP) includes a first shutter switch (TR(GS1)) that controls transferring of the electrical charges from the photoelectric transducer (PD), the storage diode (SD) that accumulates the electrical charges from the photoelectric transducer (PD), and a transferring switch (TR(TF1)) that controls transferring of the electrical charges from the storage diode (SD) to the floating semiconductor region (PD). The second charge transferring path (CTP) includes a shutter switch (TR(GS2)) that controls transferring of the electrical charges from the photoelectric transducer (PD).