SPAD Pixel Contact Height Offset for Stable Avalanche Imaging
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The generation of avalanche amplification in single photon avalanche diodes (SPADs) is hindered by the tunneling effect caused by a strong electric field between the PN junction region and the contact, leading to recombination of photoelectrically generated electron-hole pairs, and increasing the distance between contacts to avoid this effect results in increased pixel size and decreased resolution.
Innovation Solution
A solid-state imaging device with a grid-shaped trench structure in the semiconductor substrate, where the anode contact is positioned at a different height than the cathode contact and N+ type semiconductor region, allowing for increased distance without expanding pixel size, and forming an ohmic contact to stabilize avalanche amplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the distance between the PN junction region and the contact is increased to avoid the tunneling effect, then the tunneling effect is suppressed and avalanche amplification can be generated, but the pixel size increases and resolution decreases
Solution Approach 1:
The patent introduces a third dimension (depth) by forming the first contact at the bottom of a trench structure, allowing the contact to be positioned deeper in the substrate. This vertical separation increases the distance between the PN junction and contact without increasing lateral pixel dimensions, thereby suppressing the tunneling effect while maintaining high resolution.
Solution Approach 2:
The patent embeds the first contact within a trench structure that is formed within the semiconductor substrate. The trench itself is nested within the substrate, and the contact is nested within the trench, creating a hierarchical structure that achieves spatial separation without expanding the overall pixel footprint.
2Power
If a high voltage is applied to the PN junction in the reverse-bias direction to generate avalanche amplification, then the field strength is sufficient for avalanche amplification, but a strong electric field between the PN junction region and the contact generates a tunneling effect
Solution Approach 1:
The patent extracts the harmful strong electric field interaction by physically separating the PN junction region from the contact through the trench structure. By removing the direct proximity between these elements, the tunneling effect caused by the strong electric field is eliminated while the high voltage can still be applied for avalanche amplification.
3Ease of manufacture
If the first contact is formed at the same height as the second contact and N+ type semiconductor region, then the manufacturing process is simplified, but the distance between contacts cannot be increased without expanding pixel size
Solution Approach 1:
The patent resolves this contradiction by moving the first contact to a different vertical level (depth) rather than the same plane. The first contact is formed at the bottom of the trench while the second contact remains on the surface, creating a vertical offset that increases the distance between contacts without requiring lateral expansion of the pixel structure.
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
Stable generation of avalanche amplification is achieved while maintaining high resolution by suppressing the tunneling effect and ensuring a uniform electric field across the photoelectric conversion region.
Implementation Method 1
a photoelectric conversion region that is provided in an element region defined by the first trench and the second trench in the first semiconductor substrate, and is configured to photoelectrically convert incident light to generate charges
Implementation Method 2
The avalanche amplification is a phenomenon in which electrons accelerated by an electric field collide with lattice atoms in an impurity diffusion region of a PN junction to cut bonds of the lattice atoms, and newly generated electrons further collide with other lattice atoms to cut bonds thereof, multiplying a current by repeating the above
Implementation Method 3
a small distance from the PN junction region to the contact causes a strong electric field between the PN junction region and the contact, generating a tunneling effect
Data Source
AI summary
To stably generate avalanche amplification while suppressing a reduction in resolution. A solid-state imaging device according to an embodiment includes a photoelectric conversion region in an element region defined by a trench in a semiconductor substrate, a first semiconductor region surrounding the photoelectric conversion region, a first contact that contacts the first semiconductor region at a bottom of the trench, a second semiconductor region contacting the first semiconductor region and having a first conductivity type the same as the first semiconductor region, a third semiconductor region that contacts the second semiconductor region, between the second semiconductor region and a first surface, and having a second conductivity type, and a second contact on the first surface and contacting the third semiconductor region, wherein a height of the first contact from the first surface is different from a height of the third semiconductor region from the first surface.