Hybrid Bonded Image Sensor Noise Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Hybrid bonded image sensors face challenges with increased node parasitic bonding pad capacitance, pixel to pixel uniformity, and kTC reset noise due to chip-to-chip connections in Hybrid Chip Stacking Technology, limiting further performance improvements in image sensor design.
Innovation Solution
The solution involves a hybrid bonded image sensor architecture where photodiode chips and circuit carrying chips are connected at the Floating Diffusion node level, using inter-chip bonding techniques to minimize capacitance effects and optimize both photodiode and circuit fabrication technologies independently, incorporating P-channel MOS transistors and feedback capacitors to reduce noise and enhance charge storage capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If chip-to-chip bonding is used to separate photodiodes and circuits onto different chips, then manufacturing precision and fabrication optimization are improved, but node parasitic bonding pad capacitance increases
Solution Approach 1:
The patent extracts the photodiode functions onto a separate photodiode chip from the circuit chip, allowing independent optimization of photodiode fabrication while removing circuit-related parasitic effects from the photodiode processing path. This separation enables specialized fabrication processes for each chip type without mutual interference.
Solution Approach 2:
The patent introduces an intermediate transfer mechanism where charge is transferred from the photodiode chip to the circuit chip through controlled bonding interfaces. This intermediary approach manages the parasitic capacitance by controlling charge transfer timing and pathways, isolating the photodiode node from excessive parasitic effects during the critical charge accumulation phase.
2Device complexity
If chip-to-chip bonding is used to separate photodiodes and circuits, then device complexity is reduced for independent optimization, but pixel to pixel uniformity deteriorates
Solution Approach 1:
The patent applies local quality by optimizing each chip separately for its specific function - the photodiode chip is optimized for light sensing with uniform photodiode characteristics, while the circuit chip is optimized for signal processing. The bonding interface is designed with localized precision features to maintain pixel-to-pixel uniformity despite the separation, using matched bonding pad geometries and controlled placement tolerances.
3Ease of manufacture
If chip-to-chip bonding is used, then ease of manufacture is improved for separate fabrication, but kTC reset noise increases
Solution Approach 1:
The patent segments the image sensor into two independently fabricated chips: a photodiode chip and a circuit chip. This segmentation allows each chip to be manufactured using optimized processes for its specific function, improving ease of manufacture. The kTC reset noise is managed by implementing the reset function on the circuit chip after charge transfer, where the larger capacitance of the bonding pad helps reduce the relative impact of kTC noise.
Solution Approach 2:
The patent changes the capacitance parameter at the bonding interface by designing the bonding pad structure to provide sufficient capacitance for noise reduction. By adjusting the bonding pad area and geometry, the system optimizes the balance between maintaining low parasitic effects and providing enough capacitance to reduce kTC reset noise through the relationship between capacitance and thermal noise.
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 configuration results in efficient photodiode performance with high charge storage capacity and quantum efficiency, reducing kTC reset noise and fixed pattern noise, while allowing for optimized fabrication technologies for both photodiodes and circuits, enabling improved image sensor performance in both rolling shutter and global shutter scanning modes.
Implementation Method 1
image sensors sense light by converting impinging photons into electrons
Implementation Method 2
the collected charge is converted into a voltage
Data Source
AI summary
In one form, a hybrid bonded image sensor comprises a photodiode chip, a circuit carrying chip, and an interconnection. The photodiode chip provides charge to a first floating diffusion in response to incident light, wherein the first floating diffusion is coupled to a first terminal on a first surface of the photodiode chip. The circuit carrying chip has a first terminal aligned with the first terminal of the photodiode chip, the circuit carrying chip forming an output voltage based on charge transferred on the first floating diffusion sensed from the first terminal thereof. The interconnection connects the first terminal of the photodiode chip to the first terminal of the circuit carrying chip.