Photodiode Transfer Transistor for Correlated Double Sampling
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Solution Overview
Problem
Conventional CMOS image sensors with embedded nanoparticles for Near Infra-Red (NIR) and Short Wave Infra-Red (SWIR) sensitivity face increased noise due to the lack of a transfer node between the diode and reset node, preventing true correlated double sampling.
Innovation Solution
A photodiode structure is fabricated on a CMOS readout circuit with a transfer transistor between the collection and conversion nodes, utilizing a doped contact diffusion of opposite doping type to facilitate charge transfer and reduce noise, enabling correlated double sampling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a 3T pixel architecture is used without a transfer node, then the device complexity is reduced, but the measurement precision deteriorates due to increased noise and inability to perform true correlated double sampling
Solution Approach 1:
The pixel is segmented into distinct functional nodes: photodiode, collection node, transfer node, and conversion node. This segmentation allows the transfer node to be isolated and dedicated to charge transfer functions, enabling correlated double sampling while maintaining manageable overall complexity through modular design.
Solution Approach 2:
A transfer node with transfer transistor is introduced as an intermediary between the collection node and conversion node. This intermediary component enables precise control of charge transfer timing and facilitates correlated double sampling operations, improving measurement precision without requiring complete redesign of the entire pixel architecture.
2Manufacturing precision
If a highly doped diffusion of the same type as photocarrier is used for contact, then the manufacturing precision is improved, but the object-generated harmful factors increase due to prevention of true correlated double sampling and increased noise
Solution Approach 1:
Instead of using a highly doped diffusion of the same type as photocarrier (conventional approach), the invention uses a lightly doped or oppositely doped contact diffusion. This inversion of the doping approach reduces noise generation while still achieving reliable electrical contact, thereby reducing object-generated harmful factors without sacrificing manufacturing precision.
Solution Approach 2:
The doping concentration and type of the contact diffusion are changed from highly doped same-type to lightly doped or oppositely doped. This parameter change fundamentally alters the electrical characteristics at the contact interface, reducing noise generation and enabling true correlated double sampling while maintaining manufacturability.
3Use of energy by moving object
If the photodiode is made thin for NIR and SWIR sensitivity, then the use of energy is improved, but the reliability deteriorates due to interface defects between interconnect layers and semiconductor material
Solution Approach 1:
A doped contact diffusion layer is introduced as an intermediary between the thin photodiode and the interconnect layers. This intermediary layer acts as a buffer that isolates the photodiode from interface defects, maintaining reliability while allowing the photodiode to remain thin for energy efficiency and NIR/SWIR sensitivity.
Solution Approach 2:
The doping parameters of the contact diffusion are optimized to create a transition region that protects against interface defects. By adjusting doping concentration and depth, the system maintains electrical performance while shielding the thin photodiode from reliability-degrading interface 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 design reduces noise by allowing minority carrier injection and integration of signal charge, enabling true correlated double sampling and improved sensitivity in NIR and SWIR ranges.
Implementation Method 1
Organic photodiodes including ones which are made light sensitive by the use of embedded nanoparticles have demonstrated ability to have response that is better than silicon into the Near Infra-Red (NIR) and Short Wave Infra-Red (SWIR)
Implementation Method 2
the interconnect being in contact with a doped contact diffusion disposed proximate to the collection node... the doped contact diffusion isolates aid collection node from defects... enabling minority carrier injection
Data Source
AI summary
A pixel, is provided the pixel comprising: a photodiode structure built on top of an integrated circuit generating a charge; the integrated circuit comprising at least one semiconductor material and at least one interconnect layer; the at least one interconnect layer comprises an interconnect to facilitate charge flowing into a collection node disposed in the semiconductor material; the interconnect being in contact with a doped contact diffusion disposed proximate to the collection node; a transfer transistor disposed between the collection node and a conversion node, the conversion node coupled to an active transistor; the pixel having a reset configured to reset the conversion node.