Diffractive Silicon Pixel Structure for Near-IR Quantum Efficiency
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The quantum efficiency of existing silicon photodiodes in integrated image sensors is low, particularly for near-infrared wavelengths, limiting their performance in converting light into electrical charges.
Innovation Solution
A pixel design featuring a silicon photodiode with a diffractive structure and refractive index-matched layers to reflect and diffract light, increasing the light pathlength within the photodiode, comprising a substrate with refractive index lower than silicon, and a diffractive structure with trenches filled with dielectric materials, arranged to diffract light mainly in two orthogonal directions, enhancing light absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a silicon photodiode is used for near infrared operation, then the pixel can operate at near infrared wavelengths, but the quantum efficiency remains low due to poor light absorption
Solution Approach 1:
The patent introduces a diffractive structure with trenches that redirects light into oblique paths, effectively adding a spatial dimension to light propagation. This causes light to travel through the photodiode in a zigzag pattern rather than a straight line, increasing the optical path length and absorption probability without changing the photodiode material or geometry
Solution Approach 2:
The diffractive structure employs periodically arranged trenches that create repeated refraction and reflection events as light passes through. This periodic modulation of light paths ensures multiple interaction opportunities with the photodiode material, significantly enhancing absorption efficiency at near infrared wavelengths
2Area of stationary object
If the photodiode area is increased to capture more light, then the light collection area increases, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The photodiode is divided into multiple regions separated by trenches in the diffractive structure. Each segment independently processes light, and the trenches act as optical isolators. This segmentation allows for modular design and manufacturing while maintaining overall light collection efficiency
Solution Approach 2:
The diffractive structure with trenches serves as an intermediary element between the incident light and the photodiode active area. It mediates the light paths, redirecting and concentrating light onto the photodiode surface without requiring direct enlargement of the photodiode itself, thus avoiding associated manufacturing complexities
3Reliability
If reflective layers are added to increase light reflection, then the quantum efficiency improves, but the device complexity increases
Solution Approach 1:
The diffractive structure with trenches utilizes the photodiode's own refractive index difference with surrounding materials to create total internal reflection. This self-service mechanism generates the necessary light redirection and reflection without requiring additional reflective coating layers, thereby improving quantum efficiency while minimizing increases in device complexity
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 solution significantly improves quantum efficiency by increasing light absorption, achieving a quantum efficiency improvement of over two times compared to similar pixels without these features, effectively addressing the low efficiency of existing silicon photodiodes in near-infrared wavelengths.
Implementation Method 1
a diffractive structure disposed on a face of the photodiode on the side of the second face of the substrate... the diffractive structure is configured to diffract light at an operating wavelength of the pixel
Implementation Method 2
each of the first and second materials is configured so that light at an operating wavelength of the pixel reaching an interface between the photodiode and said material with an angle of incidence greater than 30° is fully reflected
Data Source
AI summary
The present disclosure relates to a pixel comprising: a photodiode comprising a portion of a substrate of a semiconductor material, extending vertically from a first face of the substrate to a second face of the substrate configured to receive light; a layer of a first material covering each of the lateral surfaces of the portion; a layer of a second material covering the portion on the side of the first face, first and second material having refractive indexes lower than that of the semiconductor material; and a diffractive structure disposed on a face of the photodiode on the side of the second face.