CMOS-Integrated SPAD Pixel Structure for Low Dark Count Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional photodiodes face challenges such as difficulty in manufacturing, poor signal-to-noise ratios, high power consumption, and limited integration with complex integrated circuit devices, which restrict their application in sensitive sensing applications like LiDAR and time-of-flight measurements.
Innovation Solution
A single photon avalanche diode device integrated with CMOS technology, featuring a semiconductor substrate with epitaxially grown silicon, implanted p-type and n-type materials, and deep trench regions, operates above breakdown voltage to multiply electron-hole pairs, enhancing sensitivity and reducing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional photodiodes are used, then manufacturing is simpler, but device yields are lower and integration with CMOS is difficult
Solution Approach 1:
The patent combines the photodiode sensor substrate with CMOS logic circuitry on a single integrated device. The sensor substrate containing pixel elements is bonded to a logic substrate with CMOS circuits, achieving monolithic integration that improves device yields while maintaining manufacturability through standard semiconductor fabrication processes
Solution Approach 2:
The integrated device performs multiple functions: the sensor substrate detects photons and generates signals, while the CMOS logic substrate processes, stores, and outputs the detected data. This multi-functional integration eliminates the need for separate discrete components and improves overall device yields
2Device complexity
If conventional photodiodes are used, then device complexity is lower, but signal-to-noise ratios are poor
Solution Approach 1:
The device is segmented into distinct functional regions: sensor substrate with pixel elements for photon detection, deep trench isolation regions for noise reduction, and CMOS logic regions for signal processing. This segmentation allows each region to be optimized for its specific function, improving signal-to-noise ratios while managing complexity
Solution Approach 2:
The deep trench isolation structures serve as intermediary elements between the sensor substrate and logic substrate. These trenches filled with dielectric material and containing charge layers act as electrical isolators and noise barriers, improving signal-to-noise ratios by preventing crosstalk and reducing background noise
3Use of energy by moving object
If conventional photodiodes are used, then power consumption is lower, but sensitivity is insufficient for single photon detection
Solution Approach 1:
The photodiode operates in avalanche breakdown mode by applying a high reverse bias voltage close to the breakdown voltage. This parameter change enables internal gain through avalanche multiplication, allowing single photon detection with high sensitivity while maintaining relatively low power consumption due to the pulsed detection mode and low dark current
4Ease of manufacture
If conventional photodiodes are used, then ease of manufacture is better, but integration with complex integrated circuit devices is limited
Solution Approach 1:
The patent merges the sensor substrate with pixel elements with the logic substrate containing CMOS circuitry into a single integrated device. The substrates are bonded together through standard semiconductor fabrication processes, achieving seamless integration that maintains ease of manufacture while enabling complex functionality
Solution Approach 2:
The device employs a nested structure where the sensor substrate with pixel elements is integrated with the CMOS logic substrate. The deep trench isolation regions are nested within the substrate structure, and the charge layers are nested within the trench regions, creating a multi-layered integrated architecture that combines simplicity with complexity
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 provides improved device yields, reduced dark count rates, and compatibility with conventional technology, enabling higher sensitivity and efficiency in sensing applications without substantial equipment modifications.
Implementation Method 1
When a photo-generated electron-hole pair reaches an avalanche region (which is a region where the electric field is above the avalanche breakdown threshold), both electrons and holes have a probability of breaking a silicon covalent bond to free another electron-hole pair in a process. The process results in a multiplication of electron-hole pairs with a gain typically larger than 10^5-10^6.
Implementation Method 2
When a photon of sufficient energy strikes the diode, it creates an electron-hole pair. This mechanism is also known as the inner photoelectric effect.
Implementation Method 3
The trench region comprises a fill material, a surrounding charge material, and a surrounding insulating material. reduced dark count rates
Data Source
AI summary
The present invention provides a single photon avalanche diode device. The device has a logic substrate comprising an upper surface. The device has a sensor substrate bonded to an upper surface of the logic substrate. In an example, the sensor substrate comprises a plurality of pixel elements spatially disposed to form an array structure. In an example, each of the pixel elements has a passivation material, an epitaxially grown silicon material, an implanted p-type material configured in a first portion of the epitaxially grown material, an implanted n-type material configured in a second portion of the epitaxially grown material, and a junction region configured from the implanted p-type material and the implanted n-type material.