Optical Sensor Trench Capacitors for Wider Dynamic Range
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Solution Overview
Problem
Conventional image sensors suffer from saturation issues when imaging scenes with both bright and dark portions, leading to uniform brightness in captured images that do not accurately reflect actual brightness levels.
Innovation Solution
Incorporation of deep trench capacitors with sidewall structures, such as sidewall scallops, to increase per-pixel capacitance in optical sensors, allowing for improved dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional image sensors are used, then the sensor can capture images, but the sensor saturates when imaging bright portions, resulting in uniform brightness that does not accurately reflect actual brightness levels
Solution Approach 1:
The patent transitions from planar capacitor structures to three-dimensional trench capacitors with sidewall extensions. By etching deep trenches into the substrate and forming capacitive structures along the sidewalls, the design adds a vertical dimension to charge storage, significantly increasing capacitance per pixel and enabling HDR capability.
Solution Approach 2:
The trench capacitor structure embeds multiple functional layers within a vertical trench. The conductive plates are positioned along the sidewalls of the trench, with dielectric materials filling the space between them, creating a nested configuration that maximizes capacitance within a compact footprint.
2Adaptability or versatility
If the sensor increases per-pixel capacitance to store more charge, then the dynamic range improves, but the device complexity increases due to deep trench structures with sidewall features
Solution Approach 1:
The capacitor structure is divided into multiple segments along the trench sidewalls. Conductive plates are formed at different heights and positions along the trench, creating segmented capacitive elements that collectively provide high capacitance while allowing independent optimization of each segment's function.
Solution Approach 2:
By extending capacitor structures vertically along the trench sidewalls rather than using only horizontal plate arrangements, the design exploits the third dimension to increase capacitance without proportionally increasing the lateral footprint, thereby managing device complexity.
3Quantity of substance
If deep trench capacitors with sidewall structures are formed, then the per-pixel capacitance increases, but the manufacturing precision requirements increase due to sidewall recess formation
Solution Approach 1:
The patent performs preliminary actions by forming the trench structure and sidewall recesses before final capacitor plate deposition. This sequence allows the trench geometry to be established first, providing a template that guides subsequent material deposition and ensures consistent capacitance values across pixels.
Solution Approach 2:
The sidewall recesses are formed with specific local geometries that optimize the electric field distribution and capacitance characteristics. By controlling the depth, width, and shape of recesses at specific locations along the trench sidewalls, the design achieves high capacitance with manageable manufacturing tolerances.
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
Enhances the dynamic range of optical sensors, enabling them to capture a wider luminance range by storing more charge, thus maintaining accurate brightness representation in images.
Implementation Method 1
increase a per-pixel capacitance of an optical sensor through the use of deep trench capacitors with sidewall structures
Implementation Method 2
a microlens
Implementation Method 3
a color filter disposed adjacent the microlens
Implementation Method 4
When photons impinge on the photosensor, electron-hole pairs are generated
Data Source
AI summary
An optical sensor and included pixel circuits of an array of pixel circuits are described. Each pixel circuit may include a microlens, a color filter disposed adjacent the microlens, and an epitaxial substrate layer disposed adjacent the color filter opposite the microlens. An isolation trench may be formed in the epitaxial substrate layer to provide a trench capacitor for the pixel circuit, and having sidewalls with sidewall recesses formed therein that increase a surface area, and therefore a capacitance, of the trench capacitor.