Gate-Controlled Thyristor Base-Width Latching Control
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Solution Overview
Problem
Thyristor devices face challenges in turning off due to positive feedback relationships and high manufacturing costs associated with small gate-to-gate distances and thin trench gate oxides, requiring complex power circuits different from IGBTs.
Innovation Solution
The design changes the NPN transistor from a wide-base to a narrow-base configuration by forming an inversion layer at the trench sidewalls and bottom, allowing the gate to control conduction without latching, using wider trench distances and thicker trench gate oxides, and reducing manufacturing costs by eliminating the need for precise gate-to-gate alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the gate-to-gate distance is reduced to less than the Debye length (1 micron or less) to enable turn-off capability, then the thyristor can be turned off by negative gate voltage, but the manufacturing cost increases significantly
Solution Approach 1:
The patent changes the fundamental parameter of base width from narrow (less than Debye length) to wide (greater than Debye length). This parameter change allows the device to achieve turn-off capability through a different mechanism - by controlling the product of bipolar transistor gains to be less than unity, rather than requiring sub-Debye-length gate spacing. This resolves the contradiction by enabling turn-off capability without the high manufacturing costs associated with precise sub-micron fabrication.
Solution Approach 2:
The patent applies different doping concentrations and base widths in different regions of the device. Specifically, the n-base region has a width greater than the Debye length, while the p-base region is configured to achieve the desired gain product. This local differentiation allows the device to achieve both turn-on and turn-off capabilities without requiring uniformly small dimensions throughout, thereby reducing manufacturing costs.
2Reliability
If the trench gate oxide thickness is reduced to 10 nm or so to improve device performance, then the turn-on and turn-off characteristics are enhanced, but the manufacturing cost increases and yield decreases
Solution Approach 1:
The patent changes the oxide thickness parameter from thin (10 nm) to thick (greater than 10 nm). This parameter change is coupled with a change in base width from narrow to wide. The thicker oxide, combined with the wide base configuration, achieves the desired device performance through the gain product mechanism rather than relying on extremely thin oxides, thereby improving manufacturability and yield while maintaining reliability.
3Ease of manufacture
If the n-base region width is made greater than the Debye length, then the manufacturing cost decreases and alignment precision requirements are relaxed, but the device requires a different turn-off mechanism compared to conventional thyristors
Solution Approach 1:
The patent utilizes feedback control through the bipolar transistor gain product mechanism. By configuring the device so that the product of the NPN and PNP transistor gains (βNPN·βPNP) is less than unity in the wide-base configuration, the device automatically prevents latching and enables turn-off through controlled feedback reduction. This feedback-based mechanism, while different from conventional thyristors, provides a systematic and controllable turn-off approach that integrates well with the wide-base structure.
4Manufacturing precision
If the thyristor uses a wide-base configuration (base width greater than Debye length), then the manufacturing precision requirements are relaxed, but the device cannot be turned off by simply returning the turn-on terminal to 0 Volts or small negative voltage
Solution Approach 1:
The patent changes the base width parameter to be greater than the Debye length, which relaxes manufacturing precision requirements. Simultaneously, it changes the control mechanism parameter by designing the bipolar transistor gains to have a product less than unity. This dual parameter change enables the device to achieve both relaxed manufacturing tolerances and effective turn-off capability through gate control, resolving the contradiction between manufacturing ease and operational control.
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 enables low ON voltage, high performance, decreased manufacturing costs, and the use of the same drive circuit as IGBTs, while allowing wider trench distances and thicker trench gate oxides, improving the thyristor's controllability and efficiency.
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
Holes will pass from the p+ anode region through the n-base region into the p-base region, and thence into the n+ cathode (where they will typically recombine with the majority carriers, which in the n+ region are electrons).
Implementation Method 3
If the trench gate is turned on (driven sufficiently positive), 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
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.