SPAD Pixel Isolation Structure for Consistent Charge Arrival
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Solution Overview
Problem
Existing optical detection apparatuses with single-photon avalanche diodes (SPAD) suffer from variations in the time it takes for photocharges to reach the P-N junction, leading to low temporal resolution due to inconsistent potential gradients in the P-type semiconductor region, affecting the detection efficiency.
Innovation Solution
The apparatus incorporates a trench isolation portion with a conductor and insulator between photoelectric conversion elements, featuring specific semiconductor regions and a second conductivity type layer on the trench sidewall to manage potential gradients and facilitate faster charge movement to the avalanche multiplication region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a P-type semiconductor region is used to isolate pixels, then pixel isolation is achieved, but potential gradient becomes inconsistent causing variation in photocharge arrival time
Solution Approach 1:
The patent applies local quality by creating a second conductivity type layer specifically on the sidewall of the trench isolation portion, rather than uniformly modifying the entire P-type semiconductor region. This localized modification generates a targeted potential gradient in the charge collection region, ensuring consistent photocharge arrival times at the P-N junction while maintaining effective pixel isolation through the trench structure.
2Reliability
If photocharges are collected in a P-type semiconductor region without potential gradient control, then charge collection is achieved, but variation in arrival time reduces detection speed
Solution Approach 1:
The patent implements preliminary action by pre-establishing a potential gradient through the second conductivity type layer on the trench sidewall before photocharges are generated. This预先 created electric field guides the movement of photocharges through the charge collection region, ensuring they reach the P-N junction in consistent time intervals and improving detection speed without compromising 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 design enhances the temporal resolution of optical detection by reducing charge diffusion and ensuring consistent potential gradients, improving the speed and efficiency of signal detection.
Implementation Method 1
In each of the SPAD pixels, in a P-N junction region in a semiconductor region, a photocharge resulting from a single photon causes avalanche multiplication.
Implementation Method 2
an optical detection apparatus that performs photoelectric conversion
Data Source
AI summary
An optical detection apparatus includes a trench isolation portion provided in a substrate and disposed between a plurality of photoelectric conversion elements. Each of the plurality of photoelectric conversion elements includes an avalanche diode. The avalanche diode includes a first semiconductor region of a first conductivity type, a second semiconductor region of a second conductivity type, and a third semiconductor region having an impurity concentration lower than impurity concentrations of the first and second semiconductor regions. The trench isolation portion includes a conductor and an insulator disposed between the conductor and the avalanche diode, and on a sidewall of the trench isolation portion, a second conductivity type layer is formed in which charges of the second conductivity type are accumulated, and the second conductivity type layer and the second semiconductor region are in contact with each other.