SPAD Sensor Chip Layout With Dummy Edge Pixels for Stable Bias
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Solution Overview
Problem
The periodicity of SPAD pixels collapses near the peripheral edge of the pixel area in sensor chips, leading to abnormal device characteristics, bias variations, and increased electric currents, which affect the overall performance of the sensor chip.
Innovation Solution
A sensor chip design that includes a pixel array with a dummy pixel area near the peripheral edge, where the cathode and anode electric potentials of the avalanche photodiode elements are the same or in a floating state, and a wiring layer covering the high electric field area to insulate and separate pixels, preventing abnormal functioning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If SPAD pixels are arranged in an array in the pixel area, then the pixel density and sensing area are improved, but the periodicity collapses near the peripheral edge causing abnormal device characteristics and bias variation
Solution Approach 1:
The patent applies preliminary action by introducing dummy pixels in advance near the peripheral edge of the pixel area. These dummy pixels are configured with the same structure as normal SPAD pixels but are electrically isolated through floating potential connections. This preliminary structural preparation prevents the periodicity collapse from affecting the main pixel array, thereby maintaining device characteristics stability while maximizing pixel density in the central region.
2Measurement precision
If SPAD pixels are arranged densely in the pixel area, then the sensing accuracy is improved, but electric current increases near the peripheral edge due to periodicity collapse
Solution Approach 1:
The patent applies segmentation by dividing the pixel area into two distinct zones: the main pixel array region with fully functional SPAD pixels for high-precision sensing, and the peripheral dummy pixel region with electrically isolated pixels. This segmentation allows the functional pixels to operate at optimal current levels for high sensing accuracy while the dummy pixels act as buffers that prevent current anomalies from propagating into the main array, thus controlling overall power consumption.
3Productivity
If the peripheral area is minimized to increase pixel area, then the productivity is improved, but the periodicity collapse and abnormal characteristics occur more frequently
Solution Approach 1:
The patent applies local quality by assigning different functional characteristics to different regions of the pixel array. The central region contains fully functional SPAD pixels optimized for high-density sensing, while the peripheral region contains dummy pixels with floating potential connections specifically designed to maintain structural periodicity without active sensing function. This local differentiation allows maximum pixel area utilization in the functional region while the peripheral region serves as a protective buffer against periodicity collapse.
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 design stabilizes the SPAD pixels, suppresses large electric currents, reduces power consumption, and enhances sensing accuracy by isolating defective pixels, thereby improving the sensitivity and accuracy of distance measurements.
Implementation Method 1
an avalanche photodiode element that amplifies a carrier by a high electric field area provided for the each of the pixels
Data Source
Figure 1
Figure 2(A)~2(C)
Figure 3
AI summary
Provided are a sensor chip and an electronic device for which the enhancement of the characteristics of SPAD pixels each including an avalanche photodiode element has been achieved. The sensor chip includes a pixel array section including a pixel area in which a plurality of pixels is arranged in rows and columns, 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 the each of the pixels from another pixel adjacent to the each of the pixels in a semiconductor substrate in which the avalanche photodiode element is formed, and a wiring that is arranged in a wiring layer laminated on a surface being opposite to a light receiving surface of the semiconductor substrate in such a way as to cover at least the high electric field area. The pixel array section includes a dummy pixel area located near a peripheral edge of the pixel area, and a cathode electric potential and an anode electric potential of the avalanche photodiode element that is arranged in the dummy pixel area are a same electric potential, or at least one of the cathode electric potential and the anode electric potential is in a floating state.