Isolator ICs with Cavity for Reduced Capacitive Coupling

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Solution Overview

Problem

Conventional opto-isolators using glass for electrical isolation suffer from capacitive coupling and high manufacturing costs, particularly in high-speed data communications and high common-mode slew rate applications, and face degradation over time.

Innovation Solution

An integrated circuit design featuring a molded package structure with a cavity that magnetically couples coil structures, eliminating solid materials and using sacrificial sublimation to create a solid-free optical path for reduced capacitance and cost, while maintaining desired voltage isolation and optical transmission efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If glass is used for electrical isolation in opto-isolators, then dc electrical isolation and optical transmission are provided, but capacitive coupling occurs and manufacturing cost increases

Engineering Contradiction:

Improveelectrical isolationVSAvoidcapacitive coupling

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent removes the glass isolation barrier from the opto-isolator structure, extracting the harmful capacitive coupling effect while maintaining electrical isolation through alternative means (air gap and magnetic coupling architecture). The glass element that caused parasitic capacitance is completely eliminated from the signal path.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces air as an intermediary medium between the primary and secondary coils, replacing glass as the isolation barrier. This air gap provides electrical isolation while having negligible capacitive coupling effects compared to glass, thus resolving the contradiction between isolation and capacitance.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If glass is used for electrical isolation in opto-isolators, then optical transmission is achieved, but manufacturing cost increases

Engineering Contradiction:

Improveoptical transmissionVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent extracts the expensive glass component from the device structure, eliminating the need for precision glass fabrication, assembly, and sealing processes. This dramatically simplifies manufacturing while the optical transmission function is maintained through alternative magnetic coupling mechanisms.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces expensive, difficult-to-manufacture glass with inexpensive air gap structures that can be formed through standard PCB and coil fabrication processes. The air gap is a passive, inherent feature of the construction rather than a separate component requiring special handling.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Strength

If solid materials are used in the optical path, then structural support is provided, but capacitance increases and performance degrades in high-speed applications

Engineering Contradiction:

Improvestructural supportVSAvoidhigh-speed performance

Core Design Contradiction:

StrengthVSProductivity

Solution Approach 1:

The patent uses air (a gas) as the primary isolation medium between primary and secondary circuits, exploiting the properties of gaseous dielectrics to provide electrical isolation with minimal capacitive coupling. This pneumatic approach enables high-speed signal transmission while maintaining structural integrity through the air gap geometry.

Inventive Principle:

Principle #29Pneumatics and hydraulics

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 reduces capacitive coupling and manufacturing costs, enhances optical transmission, and improves performance in high-speed communications by controlling the gap distance between optical sensor and transmitter, offering improved electrical isolation and breakdown voltage.

Implementation Method 1

sacrificial sublimation to create a solid-free optical path

Methodology Applied

Scientific EffectSublimation: Sublimation

Implementation Method 2

The molded package structure includes a cavity to magnetically couple portions of the first and second coil structures

Methodology Applied

Scientific EffectMagnetic coupling: Electromagnetic Induction

Data Source

PatentUS11264369B2Isolator integrated circuits with package structure cavity and fabrication methods

Publication Date: 2022.03.01 TEXAS INSTRUMENTS INC

AI summary

In described examples, an integrated circuit includes a leadframe structure, which includes electrical conductors. A first coil structure is electrically connected to a first pair of the electrical conductors of the leadframe structure. The first coil structure is partially formed on a semiconductor die structure. A second coil structure is electrically connected to a second pair of the electrical conductors of the leadframe structure. The second coil structure is partially formed on the semiconductor die structure. A molded package structure encloses portions of the leadframe structure. The molded package structure exposes portions of the first and second pairs of the electrical conductors to allow external connection to the first and second coil structures. The molded package structure includes a cavity to magnetically couple portions of the first and second coil structures.