Photodiode Thin-Film Phase Modulation for NIR Quantum Efficiency
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Solution Overview
Problem
Silicon-based CMOS image sensors have insufficient sensitivity and low Quantum Efficiency (QE) for near-infrared wavelengths due to low light absorption, with most incident power passing through without being absorbed, necessitating improved photon management techniques to reach 50% or greater QE.
Innovation Solution
The integration of phase-modulating thin-film optics with metasurfaces and nanostructures, which provide a unidirectional π phase shift and spatially localized resonances, enhancing light absorption within the photodetector by reflecting incident NIR light back into the photodiode, thereby increasing absorption efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of Si is increased to improve quantum efficiency, then light absorption is improved, but manufacturing cost increases, jitter time increases, and dark-noise from recombination increases
Solution Approach 1:
The patent changes the optical parameters of the system by introducing a phase-modulating thin-film layer that imparts a unidirectional π phase shift to light. This phase modulation alters the interference conditions for light waves within the photodiode, enhancing absorption probability without requiring increased Si thickness. The phase shift parameter transforms the optical field distribution to maximize photon absorption in the existing detector volume.
Solution Approach 2:
The phase-modulating thin-film layer acts as an intermediary element between the incident light and the photodiode active region. This thin-film mediator modifies the optical properties of incident light through phase modulation, creating constructive interference patterns that enhance light absorption in the photodiode without requiring the light to traverse a longer path through the Si material itself.
2Reliability
If nanostructures are used to scatter incident NIR light to increase path length, then light absorption is improved, but the scattering angle is limited by the low refractive index and size of nanostructures
Solution Approach 1:
The patent replaces the mechanical/geometric scattering mechanism of traditional nanostructures with an optical phase-modulation mechanism. Instead of relying on physical scattering angles determined by nanostructure geometry and refractive index, the invention uses a thin-film phase modulator to control light propagation through phase interference effects, achieving superior light confinement and absorption enhancement.
Solution Approach 2:
The invention changes the fundamental parameter controlling light scattering from geometric angle (determined by nanostructure size and refractive index) to optical phase shift (controlled by thin-film thickness and refractive index). This parameter transformation enables precise control over light propagation paths and absorption characteristics without being constrained by the physical limitations of nanostructure scattering angles.
3Reliability
If previous metaphotonics techniques are used to bend incident NIR light at high angles, then light absorption is improved, but the implementation is complex and may not be CMOS compatible
Solution Approach 1:
The patent employs a thin-film phase-modulating layer that can be integrated into the CMOS fabrication process. This thin-film structure is mechanically flexible and compatible with standard semiconductor manufacturing techniques, unlike complex metaphotic structures. The thin-film approach achieves high-angle light bending through phase modulation while maintaining CMOS process compatibility and manufacturability.
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 significantly improves near-infrared light absorption in CMOS image sensors, enhancing Quantum Efficiency and making them comparable to RGB sensors, while being CMOS compatible and cost-effective.
Implementation Method 1
The thin-film layer may be on the first side of the photodiode and may provide a unidirectional phase-shift to light passing from the photodiode to the thin-film layer
Implementation Method 2
Integration of phase-modulating thin-film optics with photodiodes, including metasurfaces and nanostructures, to create a unidirectional π phase shift and spatially localized resonances
Implementation Method 3
The reflective layer may be on the second side of the photodiode and may reflect light passing from the photodiode to the reflective layer toward the first side of the photodiode
Implementation Method 4
The photodiode may include a first side and a second side that is opposite the first side and in which the photodiode receives incident light on the first side
Data Source
AI summary
A pixel for an image sensor is disclosed that includes a photodiode, a thin-film layer and a reflective layer. The photodiode includes a first side and a second side that is opposite the first side, and receives incident light on the first side. The thin-film layer is formed on the first side of the photodiode and provides a unidirectional phase-shift to light passing from the photodiode to the thin-film layer. The thin-film layer has a refractive index that less than a refractive index of material forming the photodiode. The unidirectional phase-shift may be a unidirectional it phase shift at a target near-infrared light wavelength. The reflective layer is formed on the second side of the photodiode and reflects light passing from the photodiode to the reflective layer toward the first side of the photodiode. The reflective layer may be a thin-film layer, a Distributed Bragg Reflector layer, or a metal.