Backside Illuminated CMOS Sensor Infrared Detection Layer
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Solution Overview
Problem
Backside illuminated imaging sensors face a tradeoff between visible and infrared sensitivities due to the absorption of infrared radiation deeper in silicon, resulting in reduced detection of infrared light in thinned substrates.
Innovation Solution
Incorporating an additional infrared sensor and an infrared detecting layer, such as a photodiode formed from hydrogenated amorphous silicon, to improve the detection of both visible and infrared light, with the infrared detecting layer positioned above or within the metal stack to enhance infrared sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If color filters and micro-lenses are added to the back surface to improve sensitivity, then detection sensitivity improves, but device complexity increases
Solution Approach 1:
The sensor is segmented into multiple photodiode regions within the same pixel: a first photodiode region for visible light detection and a second photodiode region for infrared light detection. This segmentation allows each region to be optimized for its respective wavelength range, with the first region positioned closer to the back surface for visible light and the second region positioned deeper in the substrate for infrared light absorption.
Solution Approach 2:
The solution transitions from a two-dimensional surface optimization problem to a three-dimensional depth optimization problem by utilizing different depths within the substrate. The first photodiode is positioned at a first depth from the back surface while the second photodiode is positioned at a second depth greater than the first depth, creating a vertical dimension for wavelength-specific detection.
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 allows for improved detection of infrared light, enhancing the low-light performance and sensitivity of backside illuminated imaging sensors without compromising visible light sensitivity.
Implementation Method 1
infrared radiation is absorbed much deeper in the silicon than it is with visible light
Implementation Method 2
infrared radiation is absorbed much deeper in the silicon
Implementation Method 3
the photodiode must be very close to the back surface of the sensor in order to generate and collect charge
Data Source
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AI summary
A backside illuminated imaging sensor includes a semiconductor layer and an infrared detecting layer. The semiconductor layer has a front surface and a back surface. An imaging pixel includes a photodiode region formed within the semiconductor layer. The infrared detecting layer is disposed above the front surface of the semiconductor layer to receive infrared light that propagates through the imaging sensor from the back surface of the semiconductor layer.