Backside Illuminated CMOS Sensor Heat Management
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Solution Overview
Problem
Backside illuminated CMOS image sensors experience performance degradation due to heat buildup from peripheral circuitry, leading to increased dark current and reduced signal-to-noise ratio, especially in high-temperature environments, as existing heat management techniques are ineffective in dissipating heat through the thin silicon substrate.
Innovation Solution
Integration of metal heat sinks and through-silicon heat management structures that directly contact the silicon substrate to enhance thermal conduction, including large area metal pads and vias, and through-silicon heat sinks that extend through the substrate to improve heat dissipation away from the pixel array region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If backside illuminated CMOS image sensor structure is used, then light sensitivity is improved, but heat dissipation capability deteriorates
Solution Approach 1:
The patent introduces through-silicon vias (TSVs) that extend vertically through the substrate thickness dimension, creating new thermal conduction pathways in the depth direction. This dimensional approach allows heat to escape from the backside of the substrate, complementing the frontside heat dissipation and effectively addressing the thermal management challenge without compromising the BSI structure's light sensitivity.
Solution Approach 2:
The patent employs composite thermal management structures combining copper heat sinks, aluminum heat dissipation layers, and thermal interface materials. These composite materials with different thermal conductivity properties work together to optimize heat conduction from the substrate to the heat sink, achieving effective thermal management while maintaining the BSI CMOS sensor's optical performance.
2Device complexity
If peripheral circuitry is placed close to photodiodes, then device integration is improved, but heat generation at photodiode sites increases
Solution Approach 1:
The patent divides the device into distinct thermal zones by placing heat sinks and heat dissipation structures specifically under high-heat-generation peripheral circuits. This segmentation allows differential thermal management, where heat-intensive regions receive enhanced cooling while photodiode regions maintain their optical performance, thus preserving high device integration without compromising photodiode thermal environment.
Solution Approach 2:
The patent implements localized heat management by positioning heat sinks and thermal conduction structures specifically beneath peripheral circuit regions that generate excessive heat. This local quality approach ensures that heat dissipation resources are concentrated where most needed, allowing close integration of peripheral circuits with photodiodes while preventing heat from degrading image quality at photodiode sites.
3Volume of moving object
If substrate thickness is reduced, then device miniaturization is improved, but thermal conduction path length is reduced
Solution Approach 1:
The patent compensates for reduced substrate thickness by introducing vertical through-silicon via (TSV) structures that extend thermal conduction pathways through the entire substrate depth. This dimensional approach creates efficient heat escape routes in the vertical dimension, offsetting the limited thermal conduction path length caused by substrate miniaturization and enabling effective heat dissipation in thin BSI CMOS sensors.
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
Effectively reduces heat buildup and operating temperature, minimizing dark current and improving image quality by facilitating better thermal conductivity and dissipation of heat generated by peripheral circuits.
Implementation Method 1
Integration of metal heat sinks and through-silicon heat management structures that directly contact the silicon substrate to enhance thermal conduction
Implementation Method 2
A Peltier device will transport heat from one side of the device, known as the cold side, to the other side of the device, known as the hot side, when current flows through the Peltier device
Data Source
AI summary
An image sensor includes a device wafer substrate of a device wafer, a device layer of the device wafer, and optionally a heat control structure and/or a heat sink. The device layer is disposed on a frontside of the device wafer substrate and includes a plurality of photosensitive elements disposed within a pixel array region and peripheral circuitry disposed within a peripheral circuits region. The photosensitive elements are sensitive to light incident on a backside of the device wafer substrate. The heat control structure is disposed within the device wafer substrate and thermally isolates the pixel array region from the peripheral circuits region to reduce heat transfer between the peripheral circuits region and the pixel array region. The heat sink conducts heat away from the device layer.