Biased Deep Trench Isolation for SPAD Dark Current Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Miniaturization of image sensors leads to increased dark current rates and premature edge breakdown in single photon avalanche diodes (SPADs), requiring guard rings or isolation that increase pixel cell area and reduce fill factor.
Innovation Solution
The implementation of biased deep trench isolation (DTI) structures, which provide capacitive type isolation without the need for guard rings, allowing pixels to be placed closer together and reducing dark current by biasing the DTI with polysilicon and separating the SPAD from its quenching circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If guard ring or isolation structures are used to overcome premature edge breakdown and interference between adjacent pixels, then reliability is improved, but area of pixel cell increases and fill factor decreases
Solution Approach 1:
The invention extracts the isolation function from traditional guard ring structures and implements it through deep trench isolation structures that physically separate adjacent pixels. By removing the need for lateral guard rings and using vertical trench isolation, the pixel cell area is reduced while maintaining reliability through effective electrical isolation between adjacent pixels.
Solution Approach 2:
The invention transitions from two-dimensional guard ring isolation (lateral separation) to three-dimensional deep trench isolation (vertical separation). The deep trenches extend into the substrate, providing isolation in the depth dimension rather than relying on peripheral guard rings, thereby reducing the lateral area required while maintaining effective isolation.
2Volume of moving object
If image sensors are miniaturized to reduce size, then volume of image sensor decreases, but dark current rate increases
Solution Approach 1:
The invention applies deep trench isolation structures at critical locations where dark current generation occurs, such as around the periphery of pixel cells and at interfaces between different doped regions. By locally enhancing isolation quality at these specific positions rather than uniformly across the entire pixel, dark current is suppressed while maintaining compact pixel dimensions.
Solution Approach 2:
The deep trench isolation structures utilize composite material structures including doped semiconductor regions, dielectric materials, and conductive polysilicon layers. This composite approach allows simultaneous achievement of electrical isolation, mechanical stability, and controlled electrical characteristics to minimize dark current in miniaturized pixels.
3Area of moving object
If deep trench isolation structures are used to reduce pixel cell area, then area of pixel cell decreases, but device complexity increases
Solution Approach 1:
The deep trench isolation structures serve multiple functions simultaneously: they provide electrical isolation between adjacent pixels, act as mechanical etch stops, define pixel boundaries, and serve as substrates for subsequent metallization layers. By consolidating multiple functions into a single structural element, the overall device complexity is reduced despite the advanced isolation technique employed.
Solution Approach 2:
The isolation structure is segmented into discrete deep trenches that are strategically positioned between pixel cells rather than forming continuous complex patterns. This segmentation approach simplifies the fabrication process and reduces overall structural complexity while effectively isolating adjacent pixels with minimal area overhead.
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 solution reduces pixel cell size, improves resolution, lowers costs, and maintains low dark current rates, thereby enhancing photon detection sensitivity and reducing noise.
Implementation Method 1
the biased deep trench isolation (DTI) structures 222A, 222B, 222C provide capacitive type isolation between pixels and between a single photon avalanche diode (SPAD) 214 and a quenching circuit 218
Implementation Method 2
a single photon avalanche diode (SPAD) 214 having a breakdown junction defined at a planar junction 240 between P doped region 242 and N doped region 244
Data Source
AI summary
A photon detection device includes a photodiode having a planar junction disposed in a first region of semiconductor material. A deep trench isolation (DTI) structure is disposed in the semiconductor material. The DTI structure isolates the first region of the semiconductor material on one side of the DTI structure from a second region of the semiconductor material on an other side of the DTI structure. The DTI structure includes a dielectric layer lining an inside surface of the DTI structure and doped semiconductor material disposed over the dielectric layer inside the DTI structure. The doped semiconductor material disposed inside the DTI structure is coupled to a bias voltage to isolate the photodiode in the first region of the semiconductor material from the second region of the semiconductor material.