SPAD Sensor Chip Dummy Pixel Layout for Edge Bias Stability
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Solution Overview
Problem
In sensor chips with SPAD pixels arranged in an array, the periodicity of SPAD pixels near the peripheral edge often collapses, leading to abnormal device characteristics and bias variations that affect the entire sensor chip's performance.
Innovation Solution
Incorporating a dummy pixel area near the peripheral edge with avalanche photodiode elements having the same electric potential or in a floating state, which prevents the occurrence of large electric currents and maintains the stability of SPAD pixels in the central reference area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If SPAD pixels are arranged in an array in the pixel area, then the pixel array can perform distance measurements, but the periodicity of SPAD pixels near the peripheral edge collapses causing abnormal characteristics and bias variations
Solution Approach 1:
The pixel area is segmented into a reference pixel area (central region) and a dummy pixel area (peripheral region). This segmentation isolates the problematic peripheral pixels from affecting the central reference pixels, allowing the reference pixels to maintain stable characteristics for accurate distance measurements while the dummy pixels absorb the periodicity collapse effects.
Solution Approach 2:
The dummy pixels are extracted from the functional pixel array and placed in the peripheral region. These extracted pixels are configured with the same electric potential at anode and cathode, removing them from the active measurement function while preserving their structural role in maintaining array periodicity and preventing bias variations from propagating to the reference pixels.
2Reliability
If dummy pixel area is added near the peripheral edge, then SPAD pixel stability is maintained, but the device structure becomes more complex
Solution Approach 1:
The dummy pixels serve multiple functions: they maintain the periodic structure of the pixel array, absorb edge effects that would otherwise affect reference pixels, and provide a buffer zone that prevents bias variations from propagating inward. This multi-functionality justifies their inclusion despite the increased structural complexity.
Solution Approach 2:
The dummy pixels are configured with local quality differences from the reference pixels - specifically, their anode and cathode are maintained at the same electric potential, making them non-functional for distance measurement but effective for structural stability. This localized differentiation allows the peripheral region to have different properties than the central region.
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 configuration ensures only stable SPAD pixels contribute to distance measurements, suppressing power consumption and maintaining sensing accuracy by preventing electric current-induced degradations and crosstalk.
Implementation Method 1
avalanche photodiode element that amplifies a carrier by a high electric field area
Implementation Method 2
upon input of one photon into a high electric-field PN junction area, avalanche amplification occurs
Data Source
AI summary
A sensor chip and an electronic device with SPAD pixels each including an avalanche photodiode element. The sensor chip includes a pixel area having an array of pixels, an avalanche photodiode element that amplifies a carrier by a high electric field area provided for the each of the pixels, an inter-pixel separation section that insulates and separates each of the pixels from adjacent pixels, and a wiring in a wiring layer laminated on a surface opposite to a light receiving surface of the semiconductor substrate that covers at least the high electric field area. The pixel array includes a dummy pixel area located near a peripheral edge of the pixel area. A cathode and an anode electric potential of the avalanche photodiode element arranged in the dummy pixel area are the same, or at least one of the cathode and anode electric potential is in a floating state.