Photo Sensor Quantization for High-Intensity Light Detection
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Solution Overview
Problem
Conventional backside illumination optical sensors suffer from higher leakage and low photodiode fill factor, which limits their ability to capture light effectively, especially in low-light conditions, resulting in poor signal-to-noise ratio and dynamic range.
Innovation Solution
A stacked photo sensor assembly with a pixel structure that includes a photodiode, a floating diffusion point, and a transistor, where the transistor gate is applied with an intermediate voltage during the exposure phase to transfer charge from the photodiode to the floating diffusion point only when light intensity exceeds a threshold, and a comparator is used in the sensing phase to determine light intensity in low light conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional backside illumination sensor structure is used, then manufacturing is simplified, but leakage increases and photodiode fill factor decreases
Solution Approach 1:
The sensor is divided into multiple layers including a first substrate with photodiodes and a second substrate with circuitry, connected via through-silicon vias. This segmentation allows the photodiodes to be optimized for light detection while circuitry is separated, reducing leakage and improving fill factor without complicating the overall manufacturing process.
Solution Approach 2:
The patent transitions from a planar sensor structure to a three-dimensional stacked architecture. By stacking the photodiode layer and circuit layer vertically, the design achieves higher photodiode fill factor and reduced leakage while maintaining manufacturing efficiency through standardized stacking processes.
2Ease of manufacture
If conventional backside illumination sensor structure is used, then manufacturing is simplified, but photodiode fill factor decreases
Solution Approach 1:
By separating the photodiode array on the first substrate from the readout circuitry on the second substrate, the design maximizes the area available for photodiodes without increasing overall sensor complexity. The through-silicon via connections maintain electrical connectivity while minimizing interference with light detection area.
Solution Approach 2:
The vertical stacking architecture allows photodiodes to occupy nearly the entire surface area of the first substrate, as circuitry is moved to the vertical dimension on the second substrate. This dramatically increases photodiode fill factor while maintaining ease of manufacture through standard stacked sensor fabrication processes.
3Measurement precision
If intermediate voltage is applied to transistor gate, then charge transfer is controlled for high light intensity, but circuit complexity increases
Solution Approach 1:
The transistor gate voltage is dynamically adjusted between intermediate voltage and turn-on voltage based on light intensity conditions. During exposure, intermediate voltage enables controlled charge transfer for high light intensity detection. During readout, turn-on voltage ensures complete charge transfer. This dynamic control improves measurement precision without requiring permanently complex circuitry.
Solution Approach 2:
The circuit operates in periodic phases: exposure phase with intermediate gate voltage for high light detection, and readout phase with full turn-on voltage for charge transfer. This time-division approach allows precise light intensity measurement while keeping the circuit design relatively simple, as the same transistor serves multiple functions at different times.
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 enhances light capture efficiency, increases the fill factor, and improves the signal-to-noise ratio, enabling better performance in both high and low light conditions by accurately measuring light intensity and reducing noise in captured images.
Implementation Method 1
Optical sensors are electronic detectors that convert light into an electronic signal
Data Source
AI summary
In one example, an apparatus comprises: a photodiode configured to generate charge in response to incident light within an exposure period; and a quantizer configured to perform at least one of a first quantization operation to generate a first digital output or a second quantization to generate a second digital output, and output, based on a range of an intensity of the incident light, one of the first digital output or the second digital output to represent the intensity of the incident light. The first quantization operation comprises quantizing at least a first part of the charge during the exposure period to generate the first digital output. The second quantization operation comprises quantizing at least a second part of the charge after the exposure period to generate the second digital output.