SPAD Pixel Structure for Lower Hole Resistance and Higher Quantum Efficiency
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Solution Overview
Problem
Known SPAD pixels have high hole current resistance and insufficient quantum efficiency, limiting their performance in time-of-flight distance measurement applications.
Innovation Solution
The introduction of an avalanche multiplication region at the junction surface between N-type and P-type diffusion layers, a hole accumulation layer surrounding the lateral and light reception surfaces, a pinning layer outside the hole accumulation layer, and an in-pixel trench structure with the pinning layer covering its outer peripheral surface, which reduces hole current resistance and increases quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional SPAD pixel structure is used, then the device complexity is low, but the hole current resistance is high and quantum efficiency is insufficient
Solution Approach 1:
The pixel structure is segmented into multiple functional regions including an avalanche multiplication region, hole accumulation layer, pinning layer, and in-pixel trench structure. This segmentation allows each region to perform its specific function optimally, reducing hole current resistance and improving quantum efficiency without creating an uncontrollably complex device
Solution Approach 2:
The invention introduces a vertical dimension by creating an avalanche multiplication region at a junction surface between N-type and P-type diffusion layers on the opposite side of the light reception surface. This three-dimensional structure enables photons to travel through a longer optical path while maintaining effective charge collection, thereby improving quantum efficiency without proportionally increasing device complexity
2Reliability
If the avalanche multiplication region is provided at the junction surface between N-type and P-type diffusion layers on the opposite side of the light reception surface, then the optical path length is increased, but the hole current resistance increases
Solution Approach 1:
A hole accumulation layer is introduced as an intermediary structure between the avalanche multiplication region and the pinning layer. This hole accumulation layer acts as a mediator that collects and transports holes efficiently, reducing hole current resistance despite the increased distance caused by the extended optical path through the avalanche multiplication region
Solution Approach 2:
The invention replaces reliance on simple geometric distance with an engineered charge transport system. Instead of depending solely on the physical path length, the hole accumulation layer and pinning layer create an optimized electrical field distribution that facilitates efficient hole collection, substituting mechanical distance considerations with controlled electrical field mechanisms
3Reliability
If the pinning layer is formed all over the outer peripheral surface of the in-pixel trench structure, then the hole current resistance is reduced, but the manufacturing process complexity increases
Solution Approach 1:
The pinning layer is designed to serve multiple functions simultaneously: it provides surface passivation to reduce surface recombination, establishes proper electrical potential distribution to guide hole current, and forms a protective barrier on the trench structure. This multi-functionality justifies the additional manufacturing step by delivering multiple performance benefits from a single structural element
Solution Approach 2:
The pinning layer modifies the electrical and physical parameters of the trench outer peripheral surface, transforming it from a potentially harmful surface (high recombination, uncontrolled potential) to a beneficial structure (low recombination, controlled potential distribution). This parameter transformation achieves reduced hole current resistance while the manufacturing complexity is managed through standard semiconductor processing techniques
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 enhances the performance of SPAD pixels by reducing hole current resistance and increasing quantum efficiency, leading to improved accuracy and sensitivity in distance measurement.
Implementation Method 1
when one photon enters a PN junction region of a high electric field with a voltage much larger than a breakdown voltage applied, avalanche amplification occurs
Implementation Method 2
when one photon enters a PN junction region of a high electric field
Implementation Method 3
a hole accumulation layer provided so as to surround a lateral surface and a light reception surface of a well provided in the sensor substrate
Implementation Method 4
the pinning layer being formed all over an outer peripheral surface of the in-pixel trench structure
Data Source
AI summary
The present disclosure relates to a light reception element and an electronic device that make it possible to achieve better performance.Provided is a SPAD element including an avalanche multiplication region provided at a junction surface between an N-type diffusion layer and a P-type diffusion layer provided on a side of a sensor substrate opposite from a light reception surface of the sensor substrate, a hole accumulation layer provided so as to surround a lateral surface and a light reception surface of a well provided in the sensor substrate, a pinning layer provided outside the hole accumulation layer, and an in-pixel trench structure provided in a pixel region, the pinning layer being formed all over an outer peripheral surface of the in-pixel trench structure. The present technology is applicable to, for example, a distance image sensor that performs time-of-flight (ToF)-based distance measurement.