Photo Diode Array With V-Shaped Buried Channel Mirror
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Solution Overview
Problem
Photo diode arrays face challenges in achieving high aperture ratios while preventing band deterioration and signal-to-noise ratio degradation due to issues like edge breakdown, electrical cross-talk, and inefficient light absorption.
Innovation Solution
A photo diode array design featuring a substrate with parallel, linearly arrayed photo diodes, a buried layer with a V-shaped separating channel, and metal mirrors on the channel's inclines to reflect incident light into the light-absorbing layers, ensuring efficient light absorption and reducing slow response components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a light shielding film is provided to prevent stray light deterioration, then reliability is improved, but electrical cross talk occurs and S/N ratio deteriorates
Solution Approach 1:
The invention divides the light receiving surface into multiple independent light receiving regions using separating channels. These channels physically segment the continuous light receiving surface, preventing electrical cross talk between adjacent elements while maintaining optical isolation. The segmentation is achieved through etching grooves that extend through the light absorbing layer, creating electrically isolated regions that can be independently biased and read out.
Solution Approach 2:
The invention introduces an intermediate layer (separating channel) filled with reflective material or doped semiconductor between adjacent light receiving regions. This intermediary structure serves dual purposes: electrically isolating adjacent elements to prevent cross talk, and optically managing stray light through reflection or absorption, thereby improving S/N ratio without sacrificing reliability.
2Reliability
If a separating channel is formed to electrically separate elements, then electrical cross talk is prevented, but aperture ratio decreases
Solution Approach 1:
The invention addresses the aperture ratio issue by transitioning from a two-dimensional planar separation to a three-dimensional structure. The separating channels are formed as deep grooves that extend through the light absorbing layer but leave the top surface relatively intact. This vertical separation allows light to incident on the surface without being blocked by wide lateral separation structures, thereby maintaining high aperture ratio while achieving effective electrical isolation.
Solution Approach 2:
The separating channels are strategically positioned only where electrical isolation is needed, rather than creating uniform wide spacing between all elements. The channel width and depth are locally optimized to provide sufficient electrical isolation while minimizing the lateral footprint. This localized approach to separation allows adjacent light receiving regions to remain closely spaced, preserving overall aperture ratio.
3Area of moving object
If the separating channel width is reduced to maintain aperture ratio, then light receiving area is improved, but manufacturing difficulty increases
Solution Approach 1:
The invention changes the critical parameters from lateral channel width to channel depth and aspect ratio. By making the channels sufficiently deep relative to their width, effective electrical isolation is achieved even with narrow lateral dimensions. The depth parameter becomes the dominant factor for isolation effectiveness, allowing narrow channels to provide sufficient isolation without requiring complex ultra-precise width control.
Solution Approach 2:
The separating channels are formed with curved or tapered profiles rather than sharp rectangular cross-sections. The curved walls reduce stress concentration and improve etch uniformity, while the tapered shape (wider at top, narrower at bottom) facilitates easier formation through standard semiconductor etching processes. This geometric optimization makes narrow channel fabrication more manufacturable without compromising isolation effectiveness.
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 achieves a high aperture ratio and prevents band and signal-to-noise ratio deterioration by ensuring efficient light absorption and minimizing slow response components, thereby enhancing the reliability and sensitivity of the photo diode array.
Implementation Method 1
a first metal mirror on a incline of the separating channel, reflecting an incident light entering from the back face of the substrate, and leading the incident light to light-absorbing layers of the plurality of photo diodes
Implementation Method 2
a plurality of photo diodes separated from each other and arrayed in parallel on the major face of the substrate... light-absorbing layers of the plurality of photo diodes
Data Source
AI summary
A photo diode array includes: a substrate having a major face and a back face; photo diodes separated from each other and arrayed in parallel on the major face of the substrate and being linear in a plan view facing the major face of the substrate; a buried layer between the photo diodes and including a separating channel having a V-shape cross section; and a first metal mirror on an inclined face of the separating channel, reflecting incident light entering from the back face of the substrate, and leading the incident light to light-absorbing layers of the photo diodes. Band gap energy of the buried layer is wider than band gap energies of the light-absorbing layers.