SOI Image Sensor Dark Current Reduction
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Solution Overview
Problem
Conventional CMOS image sensors using bulk silicon substrates face limitations in sensitivity and noise characteristics due to parasitic stray capacitance and dark current, leading to decreased sensitivity and response speed.
Innovation Solution
The development of a high-sensitivity image sensor on a silicon-on-insulator (SOI) substrate involves etching and implanting P-type ions to form PN junctions, gate oxide layers, and gate electrodes, along with source and drain regions, to create a photodiode structure that minimizes dark current and enhances light conversion efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a bulk silicon substrate is used for CMOS image sensor fabrication, then the manufacturing process is simpler, but the sensitivity and noise characteristics deteriorate due to parasitic stray capacitance and dark current
Solution Approach 1:
The patent uses a silicon-on-insulator (SOI) substrate consisting of a silicon active layer on top of a buried oxide layer. This composite structure combines the electrical properties of silicon with the insulating properties of the oxide layer, achieving both good manufacturability and improved sensitivity/noise characteristics by eliminating parasitic stray capacitance and reducing dark current.
2Reliability
If the photodiode area is increased to improve light absorption, then the sensitivity improves, but the sensor size increases
Solution Approach 1:
The patent optimizes the thickness of the silicon active layer in the SOI substrate to control the depletion region depth and electric field distribution. By adjusting this parameter, the photodiode achieves high light absorption efficiency in a compact area, improving sensitivity without increasing sensor size. The buried oxide layer also confines the electric field, enhancing charge collection efficiency.
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 results in a high-sensitivity image sensor with improved noise reduction and increased response speed, capable of sensitively detecting low light levels while maintaining a compact sensor size.
Implementation Method 1
implanting P-type ions into the exposed N-type silicon substrate to form P-type regions
Implementation Method 2
The photodiode 3 is constructed by using a PN junction that is an interface between the P-type silicon substrate 1 and the N-type silicon substrate 2
Data Source
AI summary
A method of fabricating a high-sensitivity image sensor and the same are disclosed. The disclosed method comprises: etching predetermined regions of active silicon and a buried oxide layer of a SOI substrate by using a mask to expose an N-type silicon substrate; implanting P-type ions into the exposed N-type silicon substrate to form P-type regions; forming a gate oxide layer and a gate electrode on the middle part of the active silicon not etched while the active silicon is etched to expose the N-type silicon substrate; forming a P-type gate electrode, and P-type source and drain regions by implanting P-type ions into the active silicon and the gate electrode above the buried oxide layer; and constructing a connection part to connect the P-type regions to the gate electrode. The disclosed high-sensitivity sensor comprises: a photodiode region having a PN junction between an N-type silicon substrate and a P-type region thereon; a monocrystalline silicon region from a SOI substrate in which source and drain regions, and a channel are placed, having a distance to the photodiode region; a gate oxide layer and a gate electrode on the silicon region; and a connection part connecting the P-type region of the photodiode to the gate electrode.