Tunnel Junction Photo Detector for High-Sensitivity Image Sensors
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Solution Overview
Problem
Conventional image sensors face challenges in generating high sensitivity and high-speed frame operations, especially in low-light environments, due to limited photoelectric efficiency and noise issues, and struggle to maintain clear video rendering across varying illumination levels.
Innovation Solution
A unit pixel with a tunnel junction photo detector is implemented, utilizing a {100} type silicon substrate with V- or U-shaped grooves and a light-blocking layer, allowing for increased photoelectric current generation through tunneling effects and efficient light absorption, enabling high-speed frame operations and clear video rendering from low to high illumination levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a conventional photo diode is used as the light-absorbing part, then the structure is simple and manufacturing is easy, but the photoelectric current intensity is low and the electrostatic capacity is small causing easy saturation
Solution Approach 1:
The patent changes the material parameter from conventional silicon to compound semiconductor materials (GaAs, InGaAs, InP) with different band gaps, enabling detection of different wavelength ranges and generating higher photoelectric currents through superior material properties
Solution Approach 2:
The patent employs compound semiconductor materials that combine elements from different groups in the periodic table (Ga-As, In-Ga-As, In-P) to create materials with optimized optical and electrical properties for enhanced photoelectric conversion efficiency
2Quantity of substance
If the area of the light-absorbing part is increased to generate more photoelectric charge, then the photoelectric efficiency improves, but the area for transistor arrangement is reduced and manufacturing high-density sensors becomes difficult
Solution Approach 1:
The patent changes the material composition to compound semiconductors with higher quantum efficiency, enabling sufficient photoelectric charge generation from smaller light-absorbing areas, thus maintaining transistor density while improving signal generation
Solution Approach 2:
The patent uses epitaxial growth techniques to create highly ordered, defect-free crystal structures that maximize photoelectric conversion efficiency per unit area, allowing compact pixel designs with adequate signal generation
3Measurement precision
If a P-N junction interface is formed to detect green rays (550nm), then green light detection efficiency improves, but photoelectric efficiency for short wavelengths (blue) and long wavelengths (near infrared) deteriorates
Solution Approach 1:
The patent varies the material band gap parameters by selecting different compound semiconductor compositions (GaAs for infrared, InGaAs for visible, InP for extended range) to detect different wavelength ranges, replacing the fixed P-N junction approach
Solution Approach 2:
The patent creates a family of compound semiconductor materials that can be tuned for different spectral responses, enabling a single sensor platform to detect across blue, green, red, and near-infrared wavelengths by material selection
4Quantity of substance
If the photoelectric charge accumulation time is extended to generate minimum electric charge for signal processing, then signal processing capability improves, but frame rate decreases and high-speed operation becomes difficult
Solution Approach 1:
The patent changes the material quantum efficiency parameter to generate higher photoelectric currents per unit time, providing sufficient signal charge in shorter accumulation periods, thus enabling high-speed frame rates without sacrificing signal quality
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 tunnel junction photo detector achieves significantly higher photoelectric currents compared to conventional photo diodes, enabling high-sensitivity and high-speed image sensing with reduced noise and parasitic capacitance, allowing for efficient video rendering across a wide range of illumination levels without the need for additional signal amplification devices.
Implementation Method 1
When light irradiates a light-absorbing part inside a unit pixel of an image sensor chip, the image sensor detects the light incident at each unit pixel and the amount of the light and transforms an optical signal to an electrical signal
Implementation Method 2
A unit pixel with a tunnel junction photo detector is implemented, utilizing a {100} type silicon substrate with V- or U-shaped grooves and a light-blocking layer, allowing for increased photoelectric current generation through tunneling effects
Data Source
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AI summary
A unit pixel of an image sensor and a photo detector are disclosed. The photo detector can include: a substrate in which a V-shaped groove having a predetermined angle is formed; a light-absorbing part formed in a floated structure above the V-shaped groove and to which light is incident; an oxide film formed between the light-absorbing part and the V-shaped groove and in which tunneling occurs; a source formed adjacent to the oxide film on a slope of one side of the V-shaped groove and separated from the light-absorbing part by the oxide film; a drain formed adjacent to the oxide film on a slope of the other side of the V-shaped groove and separated from the light-absorbing part by the oxide film; and a channel interposed between the source and the drain along the V-shaped groove to form flow of an electric current between the source and the drain.