Optical Sensor Field Plates for Lower Dark Current
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Solution Overview
Problem
Optical sensors, particularly indirect time of flight (iToF) sensors, suffer from high dark current due to electron-hole recombination at shallow trench isolation (STI) interfaces, and exhibit increased full well capacitance in storage nodes.
Innovation Solution
The introduction of field plates supplied with a negative bias voltage to provide electrical isolation for storage nodes, replacing traditional junction or shallow trench isolation, reduces dark current and minimizes the impact on full well capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If shallow trench isolation (STI) structure is used to provide electrical isolation for storage nodes, then electrical isolation is achieved, but dark current increases due to electron-hole recombination at the STI interface
Solution Approach 1:
The patent changes the electrical parameter (bias voltage) applied to the field plates, supplying a negative bias voltage to create a depletion region that provides electrical isolation without the harmful recombination effects at STI interfaces. This parameter change transforms the field plate from a passive structure to an active isolation mechanism that reduces dark current while maintaining electrical isolation functionality
2Reliability
If traditional junction isolation or shallow trench isolation is used, then electrical isolation is provided, but full well capacitance of storage nodes is increased
Solution Approach 1:
The patent changes the electrical parameter (bias voltage) applied to the field plates, supplying a negative bias voltage to create a depletion region that provides electrical isolation without the harmful recombination effects at STI interfaces. This parameter change transforms the field plate from a passive structure to an active isolation mechanism that reduces dark current while maintaining electrical isolation functionality
Solution Approach 2:
The field plates act as intermediary structures between adjacent pixels and storage nodes, providing electrical isolation through a controllable depletion region. This intermediary structure replaces the traditional STI approach and allows for dynamic control of the isolation effect, minimizing impact on storage node capacitance while maintaining effective electrical separation
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 significantly reduces dark current and minimizes full well capacitance, enhancing the performance and efficiency of optical sensors.
Implementation Method 1
a first field plate arranged next to the first storage node at a first lateral side of the pixel and a second field plate arranged next to the second storage node at an opposite second lateral side of the pixel, wherein the first and second field plates are configured to be supplied with a negative bias voltage such that the first and second field plates provide electrical isolation for the first, respectively the second storage node
Implementation Method 2
a photoactive region configured to convert photons into charge carriers
Data Source
Figure 1~2
Figure 3A~3B
Figure 4~5
AI summary
an optical sensor comprises at least one pixel, comprising: a photoactive region configured to convert photons into charge carriers, a first and a second modulation gate configured to be modulated for indirect time of flight measurement, a first and a second storage node arranged on opposite sides of the photoactive region, the first and second storage nodes being configured to pin electrons generated in the photoactive region when the first, respectively the second modulation gate is active, and a first field plate arranged next to the first storage node at a first lateral side of the pixel and a second field plate arranged next to the second storage node at an opposite second lateral side of the pixel, wherein the first and second field plates are configured to be supplied with a negative bias voltage such that the first and second field plates provide electrical isolation for the first, respectively the second storage node.