Vertical IGTO With Segmented P-Base Doping
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Solution Overview
Problem
Existing insulated gate turn-off thyristors (IGTOs) face challenges in independently adjusting gate turn-on voltage and other parameters without affecting maximum turn-off voltage or decreasing breakover voltage, which limits their safe operating area (SOA) and efficiency.
Innovation Solution
A vertical IGTO thyristor with a p-type base doped to have a lightly doped upper portion, a more heavily doped intermediate p+ portion, and a lightly doped lower p portion, allowing for independent control of dopant concentrations and layer depths, along with a highly doped n+ emitter layer for improved electron injection efficiency and reduced contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the p-base is uniformly doped with a single concentration, then the manufacturing process is simple, but the gate turn-on voltage and other parameters cannot be independently adjusted
Solution Approach 1:
The p-base is divided into three distinct doping regions (upper p-type region, intermediate p+ type region, and lower p-type region) with different dopant concentrations. This segmentation allows independent control of gate turn-on voltage and other parameters by adjusting each region's doping profile separately, resolving the contradiction between adjustability and complexity.
Solution Approach 2:
Different regions of the p-base are assigned different doping concentrations tailored to their specific functions: the upper region controls surface characteristics, the intermediate p+ region provides high carrier concentration for turn-on, and the lower region maintains bulk properties. This local quality approach enables independent parameter adjustment while managing complexity through functional specialization.
2Ease of operation
If the gate turn-on voltage is reduced for easier switching, then the operational efficiency improves, but the breakover voltage and maximum turn-off voltage may be compromised
Solution Approach 1:
The segmented doping structure separates the functions of turn-on control and voltage breakdown resistance into different regions. The upper p-type region with lower doping concentration facilitates easier turn-on by reducing the electric field required for inversion layer formation, while the intermediate p+ region and lower p-type region maintain high breakover voltage through their higher carrier concentrations, thus resolving the contradiction between ease of operation and reliability.
Solution Approach 2:
By changing the doping concentration parameter across different regions of the p-base, the patent optimizes both gate turn-on voltage and breakover voltage simultaneously. The upper region uses lower doping (e.g., 1E16 to 1E18 atoms/cm³) for easy turn-on, while the intermediate and lower regions use higher doping (e.g., 1E18 to 1E20 atoms/cm³) for high breakover voltage, resolving the parameter trade-off.
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 achieves a lower gate threshold voltage, higher breakover voltage, and increased maximum turn-off voltage without adversely affecting switching losses, thereby enhancing the safe operating area and operational efficiency of the device.
Implementation Method 1
The p-type base area is doped using a first implant and drive-in, followed by a second implant and drive-in to form the intermediate p+ portion
Implementation Method 2
After the silicon is doped to form the p-type base, n-type dopants are implanted in the lightly doped upper p portion to convert the upper p portion to the n-type layer
Data Source
AI summary
An insulated gate turn-off thyristor has a layered structure including a p+ layer (e.g., a substrate), an n-epi layer, a p-well, vertical insulated gate regions formed in the p-well, and an n-layer over the p-well and between the gate regions, so that vertical npn and pnp transistors are formed. The p-well has an intermediate highly doped portion. When the gate regions are sufficiently biased, an inversion layer surrounds the gate regions, causing the effective base of the npn transistor to be narrowed to increase its beta. When the product of the betas exceeds one, controlled latch-up of the thyristor is initiated. The p-well's highly doped intermediate region enables improvement in the npn transistor efficiency as well as enabling more independent control over the characteristics of the n-type layer (emitter), the emitter-base junction characteristics, and the overall dopant concentration and thickness of the p-type base.