Imaging Device Global Shutter via Photoelectric Conversion Layer
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Solution Overview
Problem
CMOS image sensors operating in rolling shutter mode face issues with image distortion and brightness variations when capturing fast-moving subjects or using flash, as exposure timing differs across pixel rows, necessitating a global shutter function that synchronizes exposure across all pixels.
Innovation Solution
An imaging device with a simple pixel circuit structure, featuring a photoelectric conversion unit with a first and second electrode, a photoelectric conversion layer, and a hole-blocking or electron-blocking layer, allowing for voltage application that maintains equal current density with and without light, enabling global shutter functionality without a transfer transistor or charge accumulation unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a global shutter function is implemented using conventional CMOS image sensor structures, then exposure timing is synchronized across all pixels, but the pixel circuit structure becomes complex requiring transfer transistors and charge accumulation units
Solution Approach 1:
The invention extracts and removes the transfer transistor and charge accumulation unit from the pixel circuit structure. By using a photodiode with a cathode connected to a floating diffusion region and an anode connected to a readout circuit, the patent achieves global shutter functionality without these additional components, thereby simplifying the pixel circuit while maintaining synchronized exposure timing across all pixels
Solution Approach 2:
The photodiode structure is designed to perform multiple functions: it serves as both the photoelectric conversion element and the charge storage element during the exposure period. The floating diffusion region acts as both a charge collection node and a signal amplification node, eliminating the need for separate charge accumulation units and transfer transistors
2Device complexity
If rolling shutter mode is used to simplify the pixel circuit structure, then the device complexity is reduced, but image distortion and brightness variations occur when capturing fast-moving subjects
Solution Approach 1:
By removing the transfer transistor and charge accumulation unit, the patent simplifies the pixel circuit to essentially a photodiode connected to a readout circuit. This simplified structure still enables global shutter operation through synchronized exposure timing, thereby eliminating rolling shutter distortion while maintaining device simplicity
Solution Approach 2:
The patent changes the operational parameters of the photodiode by applying a reverse bias voltage that can be dynamically adjusted. During the exposure period, a specific voltage is applied to accumulate charges, and during readout, the voltage is changed to facilitate charge transfer and signal readout, enabling global shutter functionality without complex circuitry
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 imaging device achieves a global shutter function with a wide dynamic range and increased charge extraction efficiency, reducing rolling distortion and enhancing sensitivity, particularly suitable for capturing fast-moving subjects and varying light conditions.
Implementation Method 1
a photoelectric conversion unit including a first electrode including a first conducting material, a second electrode facing the first electrode, a photoelectric conversion layer between the first and second electrodes
Data Source
AI summary
An imaging device having pixels, each pixel including: a photoelectric conversion unit including a first electrode, a second electrode, a photoelectric conversion layer between the first and second electrodes, and a hole-blocking layer between the first electrode and the photoelectric conversion layer. The photoelectric conversion unit is applied with a voltage between the first electrode and the second electrode. The photoelectric conversion unit has a characteristic, responsive to the voltage within a range from a first voltage to a second voltage, showing that a density of current passing between the first electrode and the second electrode when light is incident on the photoelectric conversion layer becomes substantially equal to that when no light is incident on the photoelectric conversion layer. The range from the first voltage to the second voltage includes 0V, and a difference between the first voltage and the second voltage is 0.5 V or more.