MCT Thyristor Gate-Controlled Latching and Turn-Off Mechanism
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Solution Overview
Problem
Existing gate-controlled thyristor devices face challenges in turning off the conductive latchup state due to high manufacturing costs and the requirement for precise trench gate dimensions and negative gate voltage for turn-off, which is different from IGBTs and difficult to fabricate consistently.
Innovation Solution
The solution involves modifying the thyristor structure to change the NPN transistor from a wide-base to a narrow-base configuration by applying a positive gate voltage, creating an inversion layer that acts as a virtual emitter, allowing for lower ON voltage, higher performance, and reduced manufacturing costs, with wider trench distances and thicker trench gate oxides, enabling control with the same drive circuit as IGBTs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the Rodov et al. device uses a mesa width of less than the Debye length to enable turn-off, then the device can be turned off by negative gate voltage, but the gate-to-gate distance becomes very small (1 micron or less) resulting in high manufacturing cost
Solution Approach 1:
The patent changes the fundamental parameter of gate-to-gate distance from sub-micron (less than Debye length) to wider dimensions (5-20 microns), enabling the use of thicker gate oxide (50-200 nm instead of 10 nm) and significantly reducing manufacturing cost while maintaining turn-off capability through the alternative mechanism of depleting the n-base region
2Reliability
If the Rodov et al. device uses trench gate oxide thicknesses as small as 10 nm to achieve turn-off, then the device can be turned off by negative gate voltage, but this further increases manufacturing costs and lowers the yield
Solution Approach 1:
The patent increases the gate oxide thickness from 10 nm to 50-200 nm, which dramatically improves manufacturing yield and reduces cost. The turn-off capability is maintained not by thin oxide but by the field effect of the gate voltage depleting the n-base region, eliminating the need for ultra-thin oxide
3Reliability
If the Rodov et al. device requires negative gate voltage to turn off, then the device can be turned off, but this is different from IGBTs and requires different power circuitry
Solution Approach 1:
The patent makes the device compatible with standard IGBT drive circuits by using positive gate voltage to turn on (like IGBTs) rather than negative voltage to turn off. The turn-off is achieved by the gate voltage depleting the n-base region, allowing the device to be controlled by the same drive circuitry used for IGBTs, enhancing versatility
4Power
If the thyristor is turned on, then it draws current up to maximum supply, but it stays on as long as it can draw minimum holding current and cannot be turned off by returning terminal to 0 Volts or small negative voltage
Solution Approach 1:
The patent introduces the gate-controlled depletion region as an intermediary mechanism between the anode and cathode. The gate voltage creates a depletion region in the n-base region that acts as a controllable barrier, enabling turn-off without requiring large negative voltages or complex external circuits, simply by modulating the intermediate n-base region
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 approach allows for efficient control of the thyristor device with lower ON voltage, high performance, decreased manufacturing costs, and the ability to use wider trench distances and thicker trench gate oxides, while maintaining the same drive circuit compatibility as IGBTs, effectively addressing the turn-off challenge and reducing manufacturing complexities.
Implementation Method 1
The voltage on the gate electrode can cause depletion of the p-type material in these mesas, which 'pinches off' the connection to the cathode terminal, and thereby interrupts conduction
Implementation Method 2
an inversion layer forms at the trench sidewalls and bottom. In this inversion layer, electrons are the majority carriers, so the population of electrons at the bottom of the trench provides a 'virtual emitter' for the NPN bipolar transistor
Data Source
Figure 1
Figure 1A
Figure 1B~3B
AI summary
Methods and systems for a gate-controlled thyristor which switches between narrow-base operation in the ON state and wide -base operation in the OFF state, and which can only sustain latch-up in the narrow-base ON state.