3D Image Sensor Dark Current Suppression via Segmented Architecture
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Solution Overview
Problem
Conventional image sensors face challenges in achieving high photoconductive gain and sensitivity without increasing dark current levels, and they struggle with compact integration of pixels with control units across various spectral ranges due to limitations in noise reduction and exposure time, especially in infrared and ultraviolet ranges.
Innovation Solution
A monolithic three-dimensional integrated circuit architecture is employed, where the photosensitive element is placed in the upper level and the active device in the lower level, utilizing a two-dimensional material transport layer and a photosensitizing layer to achieve high photoconductive gain and responsivity, while a dark current suppressing circuit minimizes dark current, allowing for efficient integration and extended spectral sensitivity without deep cooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If photodetectors with photoconductive gain (avalanche photodiodes or image intensifiers) are used, then photoconductive gain and sensitivity are improved, but device complexity and difficulty of integration increase
Solution Approach 1:
The image sensor is divided into two separate levels: the first level contains the photodetector array, and the second level contains the control unit with readout circuitry. This segmentation allows each level to be optimized independently, enabling the use of photodetectors with photoconductive gain without increasing overall device complexity
Solution Approach 2:
The patent transitions from a planar two-dimensional integration architecture to a three-dimensional stacked architecture. By stacking the photodetector level and control unit level vertically, the patent achieves compact integration while maintaining the photoconductive gain capability of the photodetectors
2Measurement precision
If pre-amplification stage is placed close to photodiode, then noise levels are reduced, but device complexity increases
Solution Approach 1:
The control unit with readout circuitry is positioned in a second level directly above the photodetector array in the first level. This three-dimensional arrangement places the amplification stages physically close to the photodiodes for noise reduction, while the vertical stacking keeps the overall device compact and simplifies routing
3Measurement precision
If exposure time is increased, then signal-to-noise ratio is improved, but frame rate decreases and thermal noise increases
Solution Approach 1:
The patent employs photodetectors with photoconductive gain capability, which amplify the photo signal internally. This parameter change in detection mechanism allows achieving high signal-to-noise ratios with shorter exposure times, thereby maintaining high frame rates without suffering from thermal noise accumulation
4Measurement precision
If photodetectors with high photoconductive gain are used, then sensitivity is improved, but dark current levels increase
Solution Approach 1:
The patent extracts and addresses the dark current issue separately by implementing a dedicated dark current suppression circuit in the control unit. This circuit is specifically designed to compensate for and reduce the dark current generated by the photodetectors, allowing the system to maintain high sensitivity while minimizing dark current effects
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 results in a compact image sensor with high sensitivity and signal-to-noise ratios across a wide spectral range, including infrared and ultraviolet, without the need for deep cooling, by effectively managing dark current and optimizing pixel design.
Implementation Method 1
a transport layer including at least one layer of a two-dimensional material... The high carrier mobility of graphene and the long carrier lifetime in the quantum dots make it possible for the phototransistor disclosed therein to obtain a large photoconductive gain
Implementation Method 2
The sensitizing layer absorbs incident light and induces changes in the conductivity of the transport layer to which is associated
Data Source
Figure 1a
Figure 1b
Figure 2a~2b
AI summary
The invention relates to an image sensor (100) comprising a plurality of pixels (101) operatively connected to a control unit that includes a readout circuit (102), wherein it comprises a monolithic three-dimensional integrated circuit (104) comprising an upper level (105) and a lower level (106); wherein each pixel comprises: a photosensitive element (107) arranged in said upper level and comprising a photosensitizing layer (108) associated to a transport layer (109); an active device (110) arranged in said lower level and operatively coupled to the photosensitive element; and a first intermediate terminal and an output terminal circuitally connected, respectively, to the photosensitive element and to the readout circuit; wherein the image sensor further comprises a dark current suppressing circuit; and wherein the control unit is configured to, upon readout of a pixel, circuitally connect the first intermediate terminal of said pixel with its output terminal through the dark current suppressing circuit. The invention also relates to an optoelectronic system comprising said image sensor and to a method of manufacturing said image sensor.