Image Sensor Read Circuitry Over Pixel Zones
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Solution Overview
Problem
Monolithic image sensors face challenges in increasing sensitivity without enlarging the overall size by expanding the active surface area of each pixel, as sharing read circuitry among multiple photodiodes limits the effective capture area.
Innovation Solution
The image sensor design incorporates pixel zones delimited by deep trench isolations, with transistors such as source follower and reset transistors positioned partially over these zones, allowing for increased pixel size without increasing the overall sensor size by using shallow trench isolations and optimizing transistor placement to enhance active area utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the active surface area of each pixel is increased to improve sensitivity, then the sensitivity and photon capture efficiency improve, but the overall size of the image sensor increases
Solution Approach 1:
The patent positions read circuitry transistors vertically over pixel zones using deep trench isolations, transitioning from a planar layout to a three-dimensional arrangement. This allows the active surface area of pixel zones to be enlarged without proportionally increasing the overall sensor footprint, as the read circuitry occupies vertical space above the pixel zones rather than lateral space beside them.
Solution Approach 2:
The patent implements shared read circuitry that serves multiple photodiodes within a pixel zone. A single read circuit can read voltages from multiple sensing nodes, reducing the total number of transistors needed and freeing up lateral space for larger pixel active areas while maintaining sensitivity.
2Device complexity
If read circuitry is shared among multiple photodiodes to reduce component count, then device complexity reduces, but the effective capture area per pixel is limited
Solution Approach 1:
By placing read circuitry transistors vertically over pixel zones using deep trench isolations, the patent enables larger pixel zones with more photodiodes to share the same read circuitry without increasing lateral device footprint. This vertical integration allows greater effective capture area while maintaining reduced component count through sharing.
Solution Approach 2:
The patent nests read circuitry transistors within and over pixel zones by positioning them in the vertical dimension. This nesting allows multiple photodiodes within a pixel zone to share read circuitry while the pixel zone itself can be enlarged to contain more photodiodes, increasing effective capture area without proportionally increasing overall device area.
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 enables a more compact image sensor with larger pixel zones, improving sensitivity and reducing noise spectral density while maintaining or reducing the overall sensor size, thereby enhancing dynamic range and photon capture efficiency.
Implementation Method 1
each having a pinned photodiode coupled to a sensing node by a transfer transistor. A charge accumulated by the photodiode during an integration period can be transferred to the sensing node
Data Source
AI summary
An image sensor having a number of pixel zones delimited by isolation trenches, each pixel zone including a photodiode; a transfer gate associated with each of the pixel zones and arranged to transfer charge from the photodiode to a sensing node; and a read circuit for reading a voltage at one of the sensing nodes, the read circuitry including a number of transistors of which at least one is positioned at least partially over a pixel zone of the pixel zones.