Avalanche Photodiode Array Read Wire Height Optimization
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Solution Overview
Problem
Conventional photodiode arrays have insufficient signal read speed due to voltage drops across quenching resistors, which impede the multiplication effect in avalanche photodiodes, leading to slower signal processing.
Innovation Solution
A photodiode array design with avalanche photodiodes operating in Geiger mode, featuring a read wire positioned between neighboring photodiodes and electrically connected through a quenching resistor and surface electrode, allowing increased width of the read wire without reducing the fill factor, thus decreasing the time constant and enhancing signal read speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the read wire width is increased to decrease the time constant and improve signal read speed, then the signal read speed is improved, but the fill factor of the photodiode is reduced
Solution Approach 1:
The read wire is moved from the same plane as the photodiode surface to a higher layer structure. This spatial relocation in the vertical dimension allows the read wire to overlap with the surface electrode region without occupying additional lateral space. Consequently, the read wire width can be increased to reduce the time constant and improve signal read speed while maintaining the original fill factor of the photodiode array.
2Measurement precision
If the quenching resistor value is increased to improve photon detection sensitivity, then the detection sensitivity is improved, but the signal read speed is reduced due to increased time constant
Solution Approach 1:
The patent changes the physical parameters of the read wire by increasing its width through relocation to a higher layer. This parameter change reduces the RC time constant of the readout circuit, thereby improving signal read speed. The broader read wire provides lower resistance, which compensates for the high quenching resistor value, allowing both high detection sensitivity and fast signal read speed to be achieved simultaneously.
3Reliability
If the surface electrode size is increased to improve electrical connection, then the electrical connection is improved, but the dead space for light incidence is increased
Solution Approach 1:
The read wire is relocated to a higher layer where it can overlap with the surface electrode region. This vertical separation allows the surface electrode to maintain its necessary size for reliable electrical connection without creating excessive dead space, as the read wire no longer competes for the same lateral space. The overlapping configuration in the higher layer utilizes the surface electrode region more efficiently.
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 significantly increases signal read speed and reduces resistance, resulting in faster signal transfer and improved output characteristics without compromising the fill factor.
Implementation Method 1
When an APD is operated in the Geiger mode, a feeble light (photon) can be detected. That is, when a photon enters the APD, a carrier generated in the APD is output to the outside
Implementation Method 2
electric current flows through a pixel in which an electron avalanche in an APD has occurred, a voltage drop occurs through a quenching resistor of about hundreds kΩ sequentially connected to the pixel. This voltage drop lowers the voltage applied to an amplification region of the APD, which terminates a multiplication effect by the electron avalanche
Data Source
AI summary
Each light detecting unit includes a semiconductor region that outputs a carrier, and a surface electrode. In a photodiode array, a read wire is positioned between neighboring avalanche photodiodes. When a plane including a surface of the semiconductor region is set as a reference plane, a distance tb from the reference plane to the read wire is larger than a distance to from the reference plane to the surface electrode.