Soft-Recovery Power Transistor Body Diode for Lower Switching Loss
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Solution Overview
Problem
Power transistors with built-in body diodes suffer from high snappiness, leading to increased switching times and losses due to conventional design focusing on transistor performance rather than diode characteristics.
Innovation Solution
Designing the transistor with a non-punch through body diode and optimizing minority carrier profiles in the drift layer to reduce snappiness, including increasing the thickness and doping concentration of the drift layer and enhancing carrier lifetime, while reducing minority carriers at the body well-drift layer interface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional transistor design is used, then transistor performance is optimized, but body diode snappiness increases leading to higher switching losses
Solution Approach 1:
The drift layer is designed with non-uniform doping concentration, being higher near the body well interface and lower near the substrate interface. This local variation in doping quality optimizes the body diode's reverse recovery characteristics by controlling minority carrier distribution, reducing snappiness and switching losses without compromising overall transistor performance
Solution Approach 2:
The invention changes key parameters of the drift layer including thickness (2-20 micrometers) and doping concentration (1×10^17 to 5×10^13 cm^-3), along with enhancing carrier lifetime. These parameter modifications transform the body diode from a high-snappiness conventional design to a soft-recovery diode with reduced switching losses
2Reliability
If drift layer thickness and doping concentration are increased, then carrier lifetime is enhanced reducing snappiness, but transistor on-resistance increases
Solution Approach 1:
The drift layer employs localized doping variations with higher concentration regions near the body well and lower concentration regions near the substrate. This spatial differentiation allows enhanced carrier lifetime in critical areas for body diode operation while maintaining lower resistance paths for transistor conduction, balancing switching performance and power loss
Solution Approach 2:
The design dynamically optimizes the drift layer properties by creating a gradient structure that adapts to different operational modes. During body diode conduction, the enhanced carrier lifetime region dominates to reduce snappiness, while during transistor conduction, the overall structure maintains acceptable on-resistance through the graded doping profile
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
Significantly reduces snappiness of the body diode, improving switching performance and reducing switching losses by achieving a softness factor greater than 0.5, enabling faster switching and lower energy losses.
Implementation Method 1
a concentration of minority carriers at an interface between the body well and the drift layer is less than a concentration of minority carriers at an interface between the drift layer and the substrate
Data Source
AI summary
A transistor includes a substrate, a drift layer on the substrate, and a junction implant in the drift layer opposite the substrate. The junction implant includes a body well and a source well within the body well. A source contact is in electrical contact with the source well and the body well. A drain contact is in electrical contact with the substrate. A gate insulator is on the drift layer and over a portion of the body well and the source well. A gate contact is on the gate insulator. A softness of a body diode between the source contact and the drain contact is greater than 0.5. By providing the transistor such that the softness factor of the body diode is greater than 0.5, the switching performance of the body diode and thus switching losses of the transistor when used in a bidirectional conduction application will be significantly reduced.