Vertical Bidirectional IGTO Device for High Reverse Voltage
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Solution Overview
Problem
Existing insulated gate turn-off (IGTO) devices are unidirectional and prone to breakdown under high reverse voltage, making them unsuitable for applications requiring bidirectional current switching, which can be achieved by connecting two IGTO devices in parallel but at the cost of increased real estate and complexity.
Innovation Solution
An integrated, vertical bidirectional IGTO device is designed with a mirror-image structure on both sides of a substrate, allowing independent control of gates for bidirectional current flow, reducing the need for additional components and minimizing area requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If two IGTO devices are connected in parallel to achieve bidirectional current switching, then bidirectional current flow is enabled, but device area and structural complexity increase
Solution Approach 1:
The patent merges two IGTO devices into a single integrated structure by forming a first IGTO device on a first surface of the substrate and a second IGTO device on a second surface of the substrate, with the gate structures interconnected through the substrate. This integration enables bidirectional current switching while reducing the overall device area compared to using two separate devices.
Solution Approach 2:
The patent utilizes the third dimension (vertical depth) by forming gate structures that extend through the substrate and interconnecting them via conductive paths through the substrate thickness. This dimensional approach allows bidirectional control without requiring lateral expansion of the device area.
2Adaptability or versatility
If two IGTO devices are connected in parallel to achieve bidirectional current switching, then bidirectional current flow is enabled, but device structural complexity increases
Solution Approach 1:
The patent combines the gate control structures of both IGTO devices into a unified system where gate electrodes on both surfaces are interconnected through the substrate via conductive paths. This merging reduces structural complexity compared to maintaining two independent gate control systems.
Solution Approach 2:
The substrate serves multiple functions: it acts as the base for both IGTO devices, provides the medium for interconnecting gate structures, and enables bidirectional current flow control. This multi-functionality reduces the need for additional components and simplifies the overall structure.
3Device complexity
If a unidirectional IGTO device is used, then device structure is simple, but the device is prone to breakdown under high reverse voltage
Solution Approach 1:
The patent segments the device into two symmetrical IGTO structures, each optimized for one direction of current flow. The first IGTO device on the first surface handles forward current, while the second IGTO device on the second surface handles reverse current, with both structures having equivalent breakdown voltage ratings. This segmentation allows each structure to be optimized for its specific direction, improving overall reliability under reverse voltage conditions.
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 bidirectional IGTO device effectively switches currents in both directions without the strain of high reverse voltage, reducing the device's size and cost while maintaining robustness, and operates efficiently by controlling current flow based on voltage polarity.
Implementation Method 1
The gate material in the bus trenches is electrically conductive and is connected to the metal gate electrode
Implementation Method 2
an oxide layer 39 within the trenches
Implementation Method 3
The p+ guard rings 57 and 58, formed in the n− epitaxial (epi) layer 50 near the edge of the die, reduce electric field crowding near the edges of the die to improve the breakdown voltage
Implementation Method 4
When there is a sufficient positive voltage applied to the gate, and there is a sufficient anode-cathode voltage, electrons from the n+ layer 40 become the majority carriers along the sidewalls and below the bottom of the trenches in an inversion layer
Data Source
AI summary
A vertical bidirectional insulated gate turn-off (IGTO) device includes a top half formed over a top surface of a substrate and a bottom half formed over the bottom surface of the substrate. A top electrode is formed over the top half, and a bottom electrode is formed over the bottom half. The layered structure forms vertical NPN and PNP transistors. Each half includes trenched gates. When a first polarity voltage is applied across the electrodes, one of the halves may be turned on by biasing its gates to conduct current between the top and bottom electrodes. When a voltage of an opposite polarity is applied across the electrodes, the other one of the halves may be turned on by biasing its gates to conduct current between the two electrodes. In one embodiment, biasing the gates increases the beta of the NPN transistor to turn on the device.