Back-Illuminated Sensor Fringe Suppression via Layered Dielectric Coating
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Solution Overview
Problem
Back-illuminated solid state image sensors face challenges in achieving high quantum efficiency (QE) over a broad spectral range (UV-NIR) while minimizing interference fringes caused by internally reflected rays, particularly in the near-infrared spectrum, due to the limitations of conventional anti-reflection coatings which either compromise QE in UV-VIS or are specific to fixed spectral dispersion characteristics.
Innovation Solution
A layered dielectric refractory metal oxides and/or metal fluorides anti-reflection structure is deposited on the photosensitive surface of the image sensor using physical vapor deposition techniques, combined with a wavelength shifting phosphor coating, to minimize etaloning and maintain high QE across the UV-NIR spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single layer anti-reflection coating is deposited on the backside surface to reduce reflectivity at a specific wavelength, then quantum efficiency is improved at that wavelength, but interference fringes are produced in the near-infrared spectrum and quantum efficiency deteriorates over a broad spectral range
Solution Approach 1:
The single layer anti-reflection coating is segmented into multiple layers with different refractive indices and thicknesses. Each layer is optimized to reduce reflectivity at different wavelengths, collectively achieving broadband anti-reflection performance across UV-VIS-NIR spectrum while minimizing interference fringes through destructive interference design.
Solution Approach 2:
The patent uses composite multi-layer structures combining materials with different optical properties (refractive indices). The layered composite coating creates multiple reflection interfaces where reflected waves interfere destructively across a broad wavelength range, achieving broadband anti-reflection without the fringe problems of single-layer coatings.
2Measurement precision
If backside illumination is implemented to achieve high quantum efficiency, then unobscured photosensitive surface is obtained, but interference fringes are produced due to internally reflected rays
Solution Approach 1:
The patent converts the harmful internally reflected rays that cause interference fringes into beneficial destructive interference. By designing the anti-reflection coating with specific thicknesses and refractive indices, the multiple reflected waves are phased to interfere destructively at the detector, canceling out the fringe patterns while maintaining the high quantum efficiency benefits of backside illumination.
Solution Approach 2:
The multi-layer anti-reflection coating introduces periodic variations in refractive index and optical path length. This periodic structure creates controlled interference conditions where reflected waves from different interfaces interfere destructively across broad wavelength ranges, systematically suppressing interference fringes while preserving photon transmission.
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 effectively reduces interference fringes in the NIR spectrum while maintaining high quantum efficiency over a broad spectral range (300-1100 nm), outperforming traditional coatings by achieving minimal reflectivity and reduced fringe amplitude, making it suitable for both spectroscopic and imaging applications with reduced dark current.
Implementation Method 1
The backside, incident surface of illumination, of the sensor and the underlying polysilicon gate structures form two planar optical surfaces where internally reflected light rays may interfere constructively or destructively to produce interference or fringe patterns
Implementation Method 2
A layered sequence of refractory metal oxides and/or fluoride dielectrics is deposited via physical vapor deposition atop of the photosensitive region of the solid state imaging sensor
Implementation Method 3
a wavelength shifting phosphor coating of the group consisting of tetra-phenyl-buthadiene (TPB) or naphthalimide (Lumogen®)
Implementation Method 4
Solid state image sensors produce a digital representation of a visual image by means of converting incident photons into electronic charges
Data Source
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AI summary
A backside - illuminated image sensor (100) is disclosed having improved quantum efficiency (QE) in the near infrared wavelengths (NIR: 750-1100nm) with minimal optical interference fringes produced by multiple reflected rays within the photosensitive Si region of the sensor, which may be a charge - coupled device, a complementary metal oxide sensor or an electron -multiplication sensor. The invention comprises a fringe suppression layer (40) applied to the backside surface (35) of the photosensitive Si region of a detector (Si substrate) whereby the fringe suppression layer functions in concert with the Si substrate (30) to reduce the occurrence of interference fringes in the NIR while maintaining a high QE over a broad range of wavelengths (300-1100nm). The combination of a fringe suppression layer applied to a Si substrate provides a new class of back illuminated solid state detectors for imaging.