EMI Shield Placement in Stacked ICs for CMOS Image Sensor Noise Reduction
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Solution Overview
Problem
Switching noise between stacked three-dimensional integrated circuits, particularly in CMOS image sensors using through-silicon via technology, degrades image quality due to electromagnetic interference from signal traces, affecting a portion or the entire image sensor.
Innovation Solution
Integration of electromagnetic interference (EMI) shielding within the stacked integrated circuit system, where EMI shields are strategically placed in metal layers or at bonding interfaces to mitigate electrical interference between wafers, reducing noise impact on image sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If through-silicon via technology is used to connect stacked integrated circuits, then device density and performance are improved, but electromagnetic interference and switching noise increase
Solution Approach 1:
The patent introduces an intermediary EMI shield structure positioned between the signal trace and the sensitive image sensor regions. This shield acts as a mediator that blocks electromagnetic fields from coupling into sensitive areas while allowing the through-silicon via connections to function. The shield is connected to ground potential and strategically positioned to intercept electromagnetic interference without disrupting the electrical connections through the silicon substrate.
Solution Approach 2:
The patent applies local quality by creating EMI shields with specific geometric configurations (such as L-shaped, U-shaped, or planar structures) that are positioned only in regions where electromagnetic interference is most problematic. The shields are selectively placed near sensitive pixel regions or trace pathways rather than uniformly throughout the entire device, optimizing noise protection while minimizing impact on signal integrity and device performance.
2Ease of manufacture
If signal traces are routed on the bottom side of the package connecting perimeter vias to inner solder balls, then electrical connectivity is achieved, but switching noise is coupled into the image sensor circuitry
Solution Approach 1:
The EMI shield serves as an intermediary barrier positioned between the switching signal traces and the sensitive image sensor circuitry. The shield intercepts electromagnetic fields generated by rapid switching of pins, preventing these fields from coupling into adjacent sensitive regions. By placing the shield strategically in the signal path, the patent blocks noise propagation while maintaining the necessary electrical connectivity through the traces.
Solution Approach 2:
The patent extracts the harmful electromagnetic interference from the system by introducing EMI shields that capture and redirect noise fields away from sensitive regions. The shields are designed to extract electromagnetic energy from the vicinity of switching traces and dissipate it safely, effectively removing the noise source's impact on image sensor performance while leaving the trace routing intact.
3Length of stationary object
If the run length of traces below the image sensor is increased, then connectivity between perimeter vias and solder balls is improved, but noise coupling into the image sensor increases
Solution Approach 1:
The EMI shield acts as an intermediary structure that spans across or alongside the trace run length, providing continuous electromagnetic shielding along the entire path where noise coupling could occur. The shield is positioned to intercept fields from traces of any length, effectively breaking the coupling path between switching noise sources and sensitive sensor regions regardless of trace extent.
Solution Approach 2:
The patent addresses the trace run length issue by introducing EMI shields that add a vertical dimension to the shielding strategy. Rather than trying to shorten horizontal trace paths, the shields extend vertically or in three-dimensional configurations to block electromagnetic fields from coupling into the sensor plane, effectively neutralizing the noise problem associated with long trace runs.
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 implementation of EMI shielding significantly reduces or eliminates fixed pattern noise in image sensors, enhancing the quality of output image data by minimizing electrical interference between stacked wafers.
Implementation Method 1
a first electromagnetic interference (EMI) shield of the second set of EMI shields is disposed between the second conductor and the second pixel array
Data Source
AI summary
An integrated circuit system includes a first device wafer having a first semiconductor layer proximate to a first metal layer including a first conductor disposed within a first metal layer oxide. A second device wafer having a second semiconductor layer proximate to a second metal layer including a second conductor is disposed within a second metal layer oxide. A frontside of the first device wafer is bonded to a frontside of the second device wafer at a bonding interface. A conductive path couples the first conductor to the second conductor through the bonding interface. A first metal EMI shield is disposed in one of the first metal oxide layer and second metal layer oxide layer. The first EMI shield is included in a metal layer of said one of the first metal oxide layer and the second metal layer oxide layer nearest to the bonding interface.