Schottky Diode Integration in Power MOSFET Termination
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Solution Overview
Problem
Power MOSFET devices using P-N junction diodes exhibit high forward conduction loss, charge storage, and voltage overshoots, which are undesirable in DC-DC converter applications, whereas Schottky diodes offer lower forward drop and reduced conduction loss but are not typically integrated into these devices.
Innovation Solution
The integration of Schottky diodes into power MOSFET devices within the termination region, using a self-aligned contact scheme and a four-mask fabrication process, which allows for improved device characteristics and reduced production costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If P-N junction diodes are used in power MOSFET devices, then the devices can provide rectification function, but the forward conduction loss increases and charge storage effects occur
Solution Approach 1:
The patent changes the fundamental parameter of the diode structure from P-N junction to Schottky junction, which fundamentally alters the conduction mechanism from minority carrier diffusion to majority carrier transport, thereby reducing forward conduction loss and eliminating charge storage effects
Solution Approach 2:
The patent creates a composite structure integrating Schottky diode and power MOSFET on the same semiconductor substrate, combining the rectification function of Schottky diode with the switching function of MOSFET to achieve both low conduction loss and good switching performance
2Loss of energy
If P-N junction diodes are used, then rectification is achieved, but minority carrier charge storage causes voltage overshoots
Solution Approach 1:
The patent changes the diode junction type from P-N to Schottky, which changes the conduction mechanism from minority carrier diffusion to majority carrier transport, eliminating charge storage and the associated voltage overshoots during switching transitions
3Loss of energy
If Schottky diodes are integrated into power MOSFET devices, then conduction loss is reduced, but the device structure becomes more complex
Solution Approach 1:
The patent merges the Schottky diode and power MOSFET into a single integrated device structure, where the Schottky diode is formed within the same semiconductor substrate and shares common regions with the MOSFET, reducing overall device complexity despite the advanced functionality
Solution Approach 2:
The integrated structure serves multiple functions simultaneously - the Schottky diode provides rectification with low conduction loss while the MOSFET provides switching control, and both share common semiconductor regions and fabrication processes
4Ease of manufacture
If four-mask fabrication process is used, then manufacturing cost is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent employs preliminary action by forming the Schottky diode regions and MOSFET structures in a predetermined sequence using self-aligned processes, where earlier fabrication steps automatically define the positions for subsequent steps, reducing the need for precise mask alignment while maintaining manufacturing precision
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 integration of Schottky diodes in power MOSFET devices reduces power dissipation and conduction loss, eliminates minority carrier charge storage effects, and enhances switching performance, leading to improved device characteristics and efficiency.
Implementation Method 1
Schottky diodes, on the other hand, exhibit several desirable characteristics which make it preferable over P-N junction diodes, particularly in power MOSFET configurations. The low forward drop of the Schottky diode during forward conduction reduces power dissipation of the device and leads to lower conduction loss. The conduction of the Schottky is carried out by majority carriers, so minority carrier charge storage effects do not occur during switching of the device.
Data Source
AI summary
A semiconductor device includes a plurality of trenches including active gate trenches in an active area and gate runner/termination trenches and shield electrode pickup trenches in a termination area outside the active area. The gate runner/termination trenches include one or more trenches that define a mesa located outside an active area. A first conductive region is formed in the plurality of trenches. An intermediate dielectric region and termination protection region are formed in the trenches that define the mesa. A second conductive region is formed in the portion of the trenches that define the mesa. The second conductive region is electrically isolated from the first conductive region by the intermediate dielectric region. A first electrical contact is made to the second conductive regions and a second electrical contact to the first conductive region in the shield electrode pickup trenches. One or more Schottky diodes are formed within the mesa.