Front-Side Image Sensor With Double BOX for Biasing and Reflectivity
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Solution Overview
Problem
Existing front-side imagers face a compromise between the reflectivity of the buried oxide layer and its ability to polarize pixels, with optimal thickness ranges for these functions not coinciding, leading to suboptimal performance and cost considerations.
Innovation Solution
A front-side imager design featuring a semiconductor carrier substrate, two electrically insulating separating layers, and an intermediate semiconductor or conductive layer, where the first separating layer is thin for biasing and the second is thicker for reflectivity, with an optical confinement layer and epitaxially grown active layer to enhance photon absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If the buried oxide layer is made thin (smaller than 100 nm), then the ability to polarize pixels by applying low potential difference is improved, but the reflectivity of the buried oxide deteriorates
Solution Approach 1:
The single buried oxide layer is segmented into two separate layers: a first electrically insulating layer with thickness of 10-100 nm for polarization function, and a second electrically insulating layer with thickness of 100-300 nm for reflectivity function. This segmentation allows each layer to be optimized for its specific function, resolving the contradiction between low potential difference requirement and reflectivity requirement.
Solution Approach 2:
Different regions of the insulating structure are assigned different thicknesses to perform different functions: the first layer (closer to active layer) is thin to enable efficient electrical polarization with low potential difference, while the second layer (closer to substrate) is thick to provide high reflectivity for photon confinement. This local differentiation of quality resolves the functional contradiction.
2Ease of manufacture
If the buried oxide layer is made thick (100 to 200 nm or more), then the reflectivity and photon confinement ability is improved, but the potential difference required for polarization increases
Solution Approach 1:
The thick buried oxide structure is segmented into two functional layers: a thin first layer (10-100 nm) that requires low potential difference for polarization, and a thick second layer (100-300 nm) that provides high reflectivity. This segmentation allows the system to achieve both high reflectivity and low polarization voltage simultaneously, resolving the contradiction.
Solution Approach 2:
The first electrically insulating layer acts as an intermediary between the active layer and the second insulating layer, enabling electrical polarization to occur at a low potential difference while the second layer provides the thick-oxide reflectivity function. This intermediary structure allows both functions to coexist without direct conflict.
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 design improves photon absorption and reflectivity, enhancing image capture efficiency while being cost-effective by optimizing the thickness and material properties of the layers, particularly using a double BOX structure and silicon-germanium active layers to minimize crystal defects.
Implementation Method 1
a first electrically insulating separating layer (2a)
Implementation Method 2
it has reflective optical properties and allows incident photons to be reflected so as to confine them in the active layer
Implementation Method 3
improves photon absorption and reflectivity, enhancing image capture efficiency
Implementation Method 4
epitaxially grown active layer
Data Source
AI summary
The invention relates to a front-side imager comprising in succession: —a semiconductor carrier substrate, a first electrically insulating separating layer, and a single-crystal semiconductor layer, called the active layer, comprising a matrix array of photodiodes, wherein the imager further comprises between the carrier substrate and the first electrically insulating layer: —a second electrically insulating separating layer, and —a second semiconductor or electrically conductive layer, called the intermediate layer, arranged between the second separating layer and the first separating layer, the second separating layer being thicker than the first separating layer.