Wafer-Level Dark Current Pixel Shielding via Segmented Cover Layers
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Solution Overview
Problem
Microelectronic imagers face challenges in accurately isolating dark current pixels due to their close proximity to active pixels, leading to signal scavenging and inaccurate dark current measurement, which complicates calibration and increases device size.
Innovation Solution
A method for wafer-level packaging that involves forming discrete volumes of cover layer material with precise sidewalls aligned with inboard edges of dark current pixels, allowing an opaque material to shield them without covering active pixels, thereby preventing signal scavenging and reducing device footprint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dark reference pixels are positioned at the perimeter of the image sensor to measure dark current, then dark current measurement is enabled, but the pixels scavenge signal from incident light due to close proximity to active pixels
Solution Approach 1:
The patent introduces a physical partition structure (opaque material or deep trench) that segments the image sensor into distinct regions: active pixel region and dark reference pixel region. This segmentation prevents optical crosstalk and signal scavenging by creating an optical barrier between the two functional areas, allowing accurate dark current measurement without contamination from incident light signals.
Solution Approach 2:
The patent employs an intermediary structure (opaque material layer or deep trench filled with reflective material) positioned between active pixels and dark reference pixels. This intermediary acts as an optical barrier that blocks light from reaching dark reference pixels, enabling them to function as true dark current sensors without scavenging signal from adjacent active pixels.
2Reliability
If dark reference pixels are moved further outboard of active pixels to avoid incident light, then signal scavenging is reduced, but the size of the image sensor increases
Solution Approach 1:
The patent transitions from a horizontal spacing solution to a vertical dimension solution by introducing deep trenches or multi-layer opaque structures. Instead of moving dark reference pixels further horizontally (which increases sensor area), the patent uses vertical depth (trench depth) and layered opaque materials to achieve optical isolation, maintaining compact sensor footprint while ensuring measurement accuracy.
3Area of stationary object
If pixels are positioned very close together to reduce device size, then miniaturization is achieved, but accurate partitioning of dark reference pixels from active pixels becomes difficult
Solution Approach 1:
The patent applies preliminary action by forming the opaque partition structure (deep trench or opaque material layer) between active pixels and dark reference pixels during the fabrication process, before final pixel assembly. This preliminary structural division ensures precise spatial separation is maintained throughout subsequent manufacturing steps, enabling accurate pixel partitioning even when pixels are densely packed for miniaturization.
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 approach enhances the precision and performance of microelectronic imagers by accurately shielding dark current pixels, reducing noise, and minimizing device size, making them suitable for compact applications like smartphones and PDAs.
Implementation Method 1
depositing an opaque material on the workpiece between the discrete volumes of cover layer material and over the dark current pixels to shield the dark current pixels
Implementation Method 2
The microlenses focus light onto the initial charge accumulation region of each pixel
Data Source
AI summary
Microelectronic imaging units and methods for manufacturing a plurality of imaging units at the wafer level are disclosed herein. In one embodiment, a method for manufacturing a plurality of imaging units includes providing an imager workpiece having a plurality of imaging dies including integrated circuits, external contacts electrically coupled to the integrated circuits, and image sensors operably coupled to the integrated circuits. The individual image sensors include at least one dark current pixel at a perimeter portion of the image sensor. The method includes depositing a cover layer onto the workpiece and over the image sensors. The method further includes patterning and selectively developing the cover layer to form discrete volumes of cover layer material over corresponding image sensors. The discrete volumes of cover layer material have sidewalls aligned with an inboard edge of the individual dark current pixels such that the dark current pixels are not covered by the discrete volumes.