Back-Side Contact Photodiode Array for Crosstalk Reduction
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Solution Overview
Problem
Conventional photodiode arrays suffer from significant crosstalk due to minority carrier diffusion, limiting spatial resolution and requiring complex manufacturing processes, especially in miniaturized and closely spaced detector arrays.
Innovation Solution
The development of a front-side illuminated, back-side contact photodiode array with heavily doped deep regions that form front-to-back electrical connections and achieve active area isolation through deep diffusion, reducing crosstalk and manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional photodiode arrays are used with standard doping levels, then manufacturing is simpler, but crosstalk between adjacent diodes increases significantly
Solution Approach 1:
The patent applies parameter changes by heavily doping deep regions (n+ and p+ types) to alter the electrical properties of the semiconductor substrate. This heavy doping creates strong electric fields that confine minority carriers within their generation regions, preventing diffusion to adjacent diodes and thereby reducing crosstalk while maintaining manufacturing feasibility.
Solution Approach 2:
The patent introduces a depth dimension by forming deep diffused regions that extend vertically through the substrate. This three-dimensional doping structure creates isolation barriers between adjacent diodes, confining carriers in the vertical dimension and preventing lateral diffusion, thus reducing crosstalk without requiring complex lateral isolation structures.
2Measurement precision
If detector arrays are miniaturized with reduced spacing between diodes, then spatial resolution improves, but crosstalk between adjacent diodes increases
Solution Approach 1:
The patent changes the doping parameters by implementing heavy doping in deep regions, which creates strong electric fields that confine carriers even when diodes are closely spaced. This allows miniaturization with reduced pitch while maintaining low crosstalk through enhanced carrier confinement in the heavily doped regions.
Solution Approach 2:
The patent uses vertical deep diffusion to create isolation barriers that extend through the substrate thickness. This three-dimensional approach provides effective isolation between closely spaced diodes, enabling miniaturization without increasing crosstalk by confining carriers in the depth dimension rather than relying solely on lateral spacing.
3Object-generated harmful factors
If heavily doped deep regions are formed for active area isolation, then crosstalk is reduced to near zero, but manufacturing complexity and time increase
Solution Approach 1:
The patent segments the doping process into distinct regions: n+ deep diffused regions, p+ deep diffused regions, and p+ simple diffused regions. This segmentation allows each region to be optimized for its specific function (isolation, contact, or simple doping) while being formed through separate photolithography and diffusion steps, achieving low crosstalk through systematic regional doping.
Solution Approach 2:
The patent performs preliminary actions by forming the n+ and p+ deep diffused regions first to establish the isolation barriers and front-to-back connections before forming shallower structures. This preliminary heavy doping creates the fundamental carrier confinement structure that enables subsequent processing steps to proceed without compromising crosstalk performance.
4Object-generated harmful factors
If conventional isolation structures (trenches, moats, insulating structures) are used between photodiodes, then crosstalk is reduced, but manufacturing complexity and cost increase
Solution Approach 1:
The patent replaces mechanical isolation structures (trenches, moats, insulating layers) with an electrical isolation mechanism based on heavily doped regions. Instead of physically separating diodes with structural barriers, the invention uses strong electric fields from heavy doping to confine carriers, achieving isolation without complex mechanical structures and reducing manufacturing complexity.
Solution Approach 2:
The patent changes the electrical parameters of the semiconductor substrate by heavily doping specific regions, transforming the isolation mechanism from physical/structural to electrical. This parameter change allows carrier confinement through electric field effects rather than physical barriers, simplifying the manufacturing process and reducing costs associated with complex isolation structures.
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 solution effectively minimizes crosstalk and reduces manufacturing time and costs, enabling the production of high-resolution photodiode arrays with virtually zero susceptibility to crosstalk effects.
Implementation Method 1
a first and a second type of heavily doped deep regions that form front to back electrical connections
Implementation Method 2
The problem of crosstalk between diodes becomes even more acute as the size of the detector arrays, the size of individual detectors, the spatial resolution, and spacing of the diodes is reduced... minority carrier current between diodes
Data Source
AI summary
The present application is directed to novel front side illuminated, back side contact photodiodes and arrays thereof. In one embodiment, the photodiode has a substrate with at least a first and a second side and a plurality of electrical contacts physically confined to the second side. The electrical contacts are in electrical communication with the first side through a doped region of a first type and a doped region of a second type, each of the regions substantially extending from the first side through to the second side. In another embodiment, the photodiode includes a wafer with at least a first and a second side; and a plurality of electrical contacts physically confined to the second side, where the electrical contacts are in electrical communication with the first side through a diffusion of a p+region through the wafer and a diffusion of an n+region through the wafer.