Dual-Circuit Digital Isolator Shield Layout for Lower Parasitic Capacitance
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Solution Overview
Problem
Signal isolators face challenges in reducing parasitic capacitance between coupling capacitors and substrates, leading to signal loss and operational disturbances during common mode transient immunity events.
Innovation Solution
The use of a silicon shield layer between buried oxide layers with an oxide trench structure defines silicon islands for electronic circuits, and conductive vias couple the silicon shield layer to ground, reducing parasitic capacitance by forming series capacitors that act as a capacitive divider.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If coupling capacitors are used to transfer signals across isolation barriers, then signal transmission is enabled, but parasitic capacitance causes signal loss and operational disturbances
Solution Approach 1:
A silicon shield layer is introduced as an intermediary component between the coupling capacitors and the substrate. This shield layer, when connected to ground through conductive vias, acts as a mediator that redirects parasitic capacitance paths to ground, preventing signal loss while maintaining reliable signal transmission across the isolation barrier.
Solution Approach 2:
The shield layer is selectively positioned only in regions where parasitic capacitance problems occur, specifically between the coupling capacitors and the substrate. This localized approach reduces signal loss in critical areas without adding unnecessary complexity to the entire device structure.
2Reliability
If traditional isolator structures are used, then device simplicity is maintained, but resistance to common mode transient immunity events is reduced
Solution Approach 1:
The substrate is segmented into isolated regions using oxide trenches that define separate silicon islands. This segmentation electrically isolates different functional blocks, enhancing common mode transient immunity by preventing noise propagation between regions while maintaining a relatively simple overall device structure.
Solution Approach 2:
The silicon shield layer serves as an intermediary ground reference that stabilizes the isolator during common mode transient events. By providing a dedicated ground path through conductive vias, the shield mediates between the signal paths and substrate, improving transient immunity without significantly increasing device 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
This configuration effectively minimizes signal loss and increases resistance to common mode transient immunity events by reducing overall parasitic capacitance and noise cross-coupling between electronic circuits.
Implementation Method 1
reducing parasitic capacitance by forming series capacitors that act as a capacitive divider
Data Source
AI summary
An apparatus including; a substrate; an isolator that is formed over the substrate, the isolator including a silicon shield layer that is formed between a first buried oxide (BOX) layer and a second BOX layer; a silicon layer having an oxide trench structure formed therein, the oxide trench structure being arranged to define a first silicon island and a second silicon island; a first electronic circuit that is formed over the first silicon island; and a second electronic circuit that is formed over the second silicon island, the first electronic circuit being electrically coupled to the first electronic circuit.