Resonant Cavity Image Sensor for 940 nm Quantum Efficiency
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Solution Overview
Problem
Conventional image sensors, particularly those using silicon photodiodes, face challenges in achieving high quantum efficiency at specific wavelengths like 940 nm due to the thick detector layers required, which lead to crosstalk issues in small pixels and limited speed in charge carrier collection, especially in near-infrared imaging applications.
Innovation Solution
The implementation of a resonant cavity enhanced image sensor with dielectric mirrors forming a resonating optical cavity between the top and bottom reflecting layers, allowing for high quantum efficiency and rapid charge carrier collection, enabling the design of small pixels with minimal crosstalk and optimized for wavelengths between 900 nm to 980 nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick detector layer is used to achieve high quantum efficiency at 940 nm, then photon absorption efficiency is improved, but pixel crosstalk increases due to carrier diffusion
Solution Approach 1:
The patent introduces a vertical resonant cavity structure with top and bottom mirrors to enhance light absorption in a thin detector layer. By utilizing optical resonance in the vertical dimension, the effective optical path length is extended without increasing the physical thickness of the charge-collecting layer, thereby maintaining high quantum efficiency while preventing carrier diffusion-induced crosstalk between pixels.
Solution Approach 2:
The patent modifies the optical parameters by introducing a resonant cavity with specific mirror configurations and optical path lengths that resonate at the target wavelength (940 nm). This changes the light-matter interaction parameters, allowing enhanced absorption efficiency in a thin layer through constructive interference of light waves within the cavity, without requiring a thick detector layer that would cause crosstalk.
2Reliability
If a thick detector layer is used to increase quantum efficiency, then photon detection capability is improved, but charge carrier collection speed decreases
Solution Approach 1:
The resonant cavity structure enhances the optical interaction time and absorption probability through multiple passes of light within the cavity, effectively decoupling the absorption efficiency from the physical thickness of the charge-collecting layer. This allows thin layers to achieve high quantum efficiency while maintaining short carrier collection distances and fast response speeds.
Solution Approach 2:
The resonant cavity enables continuous optical interaction through multiple reflections and passes of light within the cavity structure. This continuous interaction increases the probability of photon absorption without requiring a thick detector layer, thereby maintaining both high quantum efficiency and fast carrier collection speed.
3Reliability
If backside bias technique is used to increase detector thickness without crosstalk, then quantum efficiency is improved, but manufacturing complexity increases
Solution Approach 1:
Instead of using electrical field manipulation (backside bias) to extend the effective detection depth, the patent uses optical resonance in the vertical dimension to enhance absorption in a thin layer. This optical approach achieves the same goal of improved quantum efficiency without requiring complex electrical field control or additional processing steps for biasing.
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 approach achieves high quantum efficiency and fast carrier collection, allowing for small pixel pitches with reduced crosstalk, compatible with standard CMOS image sensor manufacturing processes, and suitable for applications like time-of-flight imaging and hyperspectral imaging.
Implementation Method 1
a resonant cavity enhanced image sensor with dielectric mirrors forming a resonating optical cavity between the top and bottom reflecting layers
Implementation Method 2
Fabry-Perot interferometer or etalon is formed by two reflecting mirrors placed at a specified distance. In case when the optical path length between the mirrors is a multiple of the wavelength of the light in the material inside the cavity, a constructive interference occurs.
Implementation Method 3
silicon photodiodes as commonly used in CMOS and CCD image sensors
Data Source
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AI summary
The semiconductor image sensor device comprises a semiconductor layer (SL) having a main surface (MS) and an opposite rear surface (RS), and a charge carrier generating component (CG) at the main surface. The charge carrier generating component is arranged between a top reflecting layer (R1) and a bottom reflecting layer (R2), which are arranged outside the semiconductor layer.