SPAD Pixel Trench Layout for Stable Avalanche Gain
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The generation of a tunneling effect between the PN junction region and the contact in solid-state imaging devices, which prevents avalanche amplification due to recombined electron-hole pairs generated by the tunneling current.
Innovation Solution
A solid-state imaging device with a grid-shaped first trench and a second trench along the bottom of the first trench, where the photoelectric conversion elements have a specific semiconductor region structure and contact configuration to stabilize avalanche amplification while maintaining pixel size and resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a contact is formed close to the PN junction region to discharge large current, then current discharge capability is improved, but a strong electric field is generated causing tunneling effect that prevents avalanche amplification
Solution Approach 1:
The patent introduces a third dimension (depth) by forming the first contact at the bottom of a first trench and the second contact at a different depth level, rather than placing contacts side-by-side at the same depth. This vertical separation in the depth direction allows sufficient distance between contacts to prevent tunneling while maintaining compact pixel area.
Solution Approach 2:
The patent employs a nested trench structure where a second trench is formed along the bottom of the first trench, creating a nested configuration. The first contact is formed in the first trench while the second contact is formed at the bottom of the second trench, allowing compact arrangement that prevents tunneling without increasing pixel area.
2Reliability
If the distance between contacts is increased to avoid tunneling effect, then avalanche amplification stability is improved, but pixel size increases and resolution decreases
Solution Approach 1:
By utilizing the depth dimension through trench structures, the patent achieves sufficient contact separation distance without increasing the lateral footprint of the pixel. The first contact at the bottom of the first trench and the second contact at the bottom of the second trench are separated in the depth direction, maintaining compact pixel size while preventing tunneling.
Solution Approach 2:
The patent creates different local regions with different depths and functions: the first trench region contains the first contact for current discharge, while the second trench region contains the second contact positioned to avoid tunneling. This localized structural differentiation achieves both current discharge capability and tunneling prevention within a compact area.
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 proposed solution effectively suppresses the tunneling effect without increasing pixel size, thereby stabilizing avalanche amplification and maintaining high resolution in solid-state imaging devices.
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
a single photon avalanche diode (SPAD) has been developed that amplifies a charge generated by photoelectric conversion by avalanche multiplication (also referred to as avalanche amplification) and outputs the amplified charge as an electric signal. 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
Data Source
Figure 1~2
Figure 3
Figure 4~5
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 (102) that is provided in an element region defined by a trench in a semiconductor substrate (101), a first semiconductor region (104) that surrounds the photoelectric conversion region, a first contact (108) that is configured to make contact with the first semiconductor region at a bottom of the trench, a second semiconductor region (105) that is provided in a region making contact with the first semiconductor region and has a first conductivity type the same as the first semiconductor region, a third semiconductor region (106) that is a region making contact with the second semiconductor region, is provided between the second semiconductor region and a first surface, and has a second conductivity type opposite to that of the first conductivity type, and a second contact (107) that is provided on the first surface so as to make contact with the third semiconductor region, and in the solid-state imaging device, a height of the first contact from the first surface is different from a height of the third semiconductor region from the first surface.