Dynamic Electrical Biasing for Image Sensor Dark Current Reduction
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Solution Overview
Problem
Current image sensors face challenges in reducing dark current and improving signal-to-noise ratios, particularly in low-light conditions, due to limitations in quantum efficiency and optical crosstalk among adjacent pixels.
Innovation Solution
The implementation of dynamic electrical biasing techniques, including varying bias voltages during integration and readout phases, and the use of floating photodetectors to suppress dark current and enhance light sensitivity, utilizing optically sensitive materials like nanocrystals to improve pixel performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If dynamic electrical biasing is applied to reduce dark current, then dark current is reduced, but device complexity increases
Solution Approach 1:
The patent implements dynamic electrical biasing where the bias voltage applied to the photodetector is varied over time between different levels (first bias level during integration, second bias level during readout). This dynamic adjustment of electrical parameters reduces dark current while managing device complexity through controlled voltage switching rather than complex structural modifications
Solution Approach 2:
The patent changes the electrical bias parameter from a static single level to a dynamic multi-level system. By switching between a first bias level (higher voltage) during the integration period and a second bias level (lower voltage) during the readout period, the system optimizes both dark current reduction and signal readout capability without requiring fundamental redesign of the device architecture
2Reliability
If floating photodetectors are used to suppress dark current, then light sensitivity is enhanced, but manufacturing complexity increases
Solution Approach 1:
The patent divides the photodetector structure into electrically isolated regions using floating diffusion nodes. The photodetector is segmented into a photosensitive region that accumulates charge during integration and a readout region that reads the signal, with electrical isolation between them. This segmentation enables independent optimization of each region's function while maintaining manufacturability through standard CMOS fabrication techniques
Solution Approach 2:
The patent introduces floating diffusion nodes as intermediary elements between the photodetector photosensitive region and the readout circuitry. These floating diffusion nodes serve as charge storage intermediaries that accumulate photo-generated charge during integration and then transfer it to the readout amplifier, enabling signal isolation and reducing dark current impact while maintaining ease of manufacture through standard semiconductor processes
3Measurement precision
If bias voltage is varied during integration and readout, then signal-to-noise ratio is improved, but device complexity increases
Solution Approach 1:
The patent employs periodic switching of the bias voltage between two distinct states: a first bias level during the integration period for optimal signal accumulation, and a second bias level during the readout period for optimal signal transfer and amplification. This periodic modulation of the bias parameter improves signal-to-noise ratio by optimizing conditions for each operational phase while using simple voltage switching rather than complex control 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
This approach significantly reduces dark current, enhances light sensitivity, and improves signal-to-noise ratios, enabling better image detection in low-light conditions and maintaining dynamic range for readout paths.
Implementation Method 1
each pixel region comprising an optically sensitive material over the substrate, the optically sensitive material positioned to receive light
Implementation Method 2
a bias electrode for each pixel region, the bias electrode configured to provide a bias voltage to the optically sensitive material of the respective pixel region
Data Source
AI summary
Image sensors and methods of using image sensors are disclosed. In an embodiment, the image sensor includes pixel regions having optically sensitive material (OSM). A bias voltage is provided to the OSM via a bias electrode for each pixel region. A pixel circuit (PC) for each pixel region includes a read out circuit and a charge store (CS) coupled to the OSM of the respective pixel region. The PC resets voltage on the CS to a reset voltage during a reset period, integrates charge from the OSM to the CS during an integration period, and reads out a signal from the CS during a read out period. The PC includes a reference voltage node coupled to the CS during the reset period and the read out circuit during the read out period, a reference voltage is applied to the reference voltage node and is varied during operation of the PC.