Stacked Image Sensor Pixel Structure for Low-Noise Color Detection
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Solution Overview
Problem
Existing photo-sensitive devices, particularly those using silicon substrates, suffer from limitations such as reduced detectable wavelengths, high noise characteristics, and loss of resolution due to inefficient light absorption and processing.
Innovation Solution
The development of a thin-film, stacked, fully depleted pixel structure with a common floating electrical connection, integrated with a read-out integrated circuit (ROIC), which allows for improved light absorption and signal processing across various wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a color filter array is stacked on top of a pixel to selectively absorb each color signal, then color detection capability is improved, but light signal loss increases and resolution decreases
Solution Approach 1:
The patent transitions from a planar color filter array to a vertically stacked three-dimensional architecture where multiple photodetector layers are stacked along the vertical dimension. Each layer detects different wavelengths, eliminating the need for lateral color filters and enabling full light utilization without signal loss.
Solution Approach 2:
The patent implements nested photodetector layers where shorter wavelength detectors (e.g., blue) are positioned above longer wavelength detectors (e.g., red, infrared). Each layer is nested within the vertical stack, allowing sequential detection of different wavelength components as light passes through the stack from top to bottom.
2Measurement precision
If a three-transistor pixel circuit is used with quantum dot detector material, then detection sensitivity is improved, but reset noise increases and dark current increases
Solution Approach 1:
The patent extracts and removes the problematic three-transistor pixel circuitry from directly under the photodetector area. Instead, a simplified readout circuit is implemented that eliminates the sources of reset noise and uncorrelated readout errors, while maintaining detection sensitivity through the stacked photodetector architecture.
Solution Approach 2:
The patent introduces an intermediate charge transfer mechanism where photogenerated charges are transferred vertically between stacked photodetector layers before being read out. This intermediary charge transfer process eliminates the need for complex pixel-level transistor circuits that generate noise, while preserving detection sensitivity.
3Ease of manufacture
If photodiode area is directly connected to pixel circuit below the photodiode area, then readout integration is improved, but dark current increases due to defective contact region
Solution Approach 1:
The patent separates the photodetector active area from the readout circuitry by utilizing the vertical dimension. Charges are transferred vertically through dedicated transfer regions rather than through lateral contacts, eliminating defective contact regions that generate dark current while maintaining integrated readout capability.
4Adaptability or versatility
If a layered photodiode structure is used, then wavelength-specific detection is improved, but noise characteristics worsen and resolution is lost
Solution Approach 1:
The patent applies local quality optimization by creating fully depleted regions in each photodetector layer with tailored doping profiles and thicknesses. Each layer is optimized for its specific wavelength range with appropriate depletion depths, improving signal-to-noise ratio and maintaining high resolution through localized charge collection regions.
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 solution enhances light absorption, reduces noise, and improves resolution, enabling more efficient and compact photo-sensitive devices capable of detecting a broader range of wavelengths.
Implementation Method 1
an active layer (113), configured to generate electrical charges in response to a first predefined range of wavelengths of light incident on the device (100)
Implementation Method 2
a bottom electrode (116) separated by a dielectric material (115) from the second charge transport layer (114) wherein the bottom electrode (116) is configured to provide a first electrical voltage for at least partially depleting the first portion (114a) of the corresponding second charge transport layer (114)
Data Source
AI summary
An image sensor comprises at least two vertically stacked photo-sensitive devices wherein each respective photo-sensitive device comprises a stack of a top electrode, a first charge transport layer and an active layer. Each respective stack generates electrical charges in response to a corresponding predefined range of wavelengths of light incident on the image sensor.Each photo-sensitive device further comprises a second charge transport layer having a first portion, vertically aligned underneath the active layer, and a second portion, transfer region, protruding laterally to extend beyond the active layer. A dielectric layer separates the first portion from a bottom electrode providing a voltage for depleting the first portion, and the transfer region from a transfer gate providing a voltage for transferring the generated electrical charge to a floating electrical connection, shared by all stacked photo-sensitive devices.The floating electrical connection couples to a read-out-circuitry.