Graded SiGe Image Sensor for Infrared Absorption
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Solution Overview
Problem
Conventional image sensors poorly absorb infrared light due to the band structure of semiconductor materials, requiring thick semiconductors which complicate fabrication and reduce performance, and materials that can absorb IR light are often expensive, toxic, or less sensitive to the visible spectrum.
Innovation Solution
A graded-semiconductor image sensor is developed using epitaxially grown silicon-germanium (SiGe) with increasing germanium concentration from the illuminated surface to the non-illuminated surface, creating a potential energy gradient that enhances IR light sensitivity and reduces electrical crosstalk, allowing for thinner layers to effectively absorb IR light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional semiconductor materials are used, then the sensor structure is simple and fabrication is easy, but IR light absorption is poor
Solution Approach 1:
The patent changes the compositional parameter of the semiconductor material by creating a graded SiGe structure where the germanium concentration varies continuously from 0% at the first surface to 30-50% at the second surface. This gradual parameter change modifies the band structure to improve IR light absorption while maintaining compatibility with conventional fabrication processes
Solution Approach 2:
The patent uses a composite semiconductor structure combining silicon and germanium in a graded composition. The SiGe alloy combines the advantages of both materials, achieving improved IR absorption characteristics while maintaining the structural integrity and manufacturability of silicon-based devices
2Reliability
If semiconductor thickness is increased to improve IR absorption, then IR light absorption improves, but fabrication becomes more complex and performance decreases
Solution Approach 1:
The patent changes the compositional parameter to achieve enhanced IR absorption in a thinner layer. The graded SiGe structure with increasing germanium concentration toward the non-illuminated surface creates favorable band conditions for IR absorption, allowing effective detection in reduced thickness compared to conventional uniform semiconductor materials
3Reliability
If materials capable of absorbing IR light are used, then IR light sensitivity improves, but cost increases and toxicity increases
Solution Approach 1:
The patent uses parameter changes in material composition (graded SiGe) to achieve IR sensitivity comparable to specialized materials while avoiding their drawbacks. The silicon-germanium alloy provides a cost-effective and non-toxic alternative to exotic IR-sensitive materials by optimizing the compositional gradient
4Reliability
If graded SiGe structure is implemented, then IR light sensitivity and charge transfer improve, but manufacturing precision requirements increase
Solution Approach 1:
The patent implements controlled parameter changes during the epitaxial growth process to achieve the desired germanium concentration gradient. By carefully controlling the germanium incorporation rate as a function of layer depth, the process achieves the required compositional profile with acceptable precision for device fabrication
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
The SiGe image sensor improves IR light sensitivity and reduces electrical crosstalk, enabling efficient charge transfer and absorption of IR light in thinner layers, addressing the limitations of conventional sensors while maintaining performance and simplifying fabrication.
Implementation Method 1
the germanium concentration increases in a direction from the illuminated surface to the non-illuminated surface of the semiconductor material. The increasing germanium concentration in the direction of the non-illuminated surface of the semiconductor material results in a potential energy gradient from the illuminated surface to the non-illuminated surface
Implementation Method 2
Detection of infrared (IR) light is useful in automotive and night vision applications. However, conventional image sensor devices may poorly absorb infrared light due to the band structure of semiconductor materials used in modern microelectronic devices
Implementation Method 3
A plurality of photodiodes is disposed in the semiconductor material to receive incident image light
Data Source
AI summary
A method of image sensor fabrication includes growing a semiconductor material having an illuminated surface and a non-illuminated surface, where the semiconductor material includes silicon and germanium and a germanium concentration increases in a direction of the non-illuminated surface. The method further includes forming a plurality of photodiodes, including a doped region and a heavily doped region, in the semiconductor material, where the doped region is of an opposite majority charge carrier type as the heavily doped region. A plurality of isolation regions are formed and disposed between individual photodiodes in the plurality of photodiodes, where the plurality of isolation regions surround, at least in part, the individual photodiodes and electrically isolate the individual photodiodes.