LDMOS Trench Shield Gate Reduces Hot Carrier Injection
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Solution Overview
Problem
Conventional LDMOS devices with dielectric trenches suffer from hot carrier injection issues, leading to reduced long-term reliability and increased switching loss due to electric field concentration at the trench corners, which worsens under high-speed and high-magnetic field conditions.
Innovation Solution
The introduction of a drain field plate and a shield gate electrode within the dielectric trench, connected to the drain and source electrodes respectively, modifies the electric field direction to impact carrier motion and reduces hot carrier injection, while the shield gate also lowers gate-drain capacitance and assists in depletion during the OFF state, thereby improving device reliability and switching efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a dielectric trench is introduced in the LDMOS drift region to reduce device size and improve integration, then the device can be compactly integrated, but electric field concentrates at the trench corner causing hot carrier injection that reduces long-term reliability
Solution Approach 1:
A shield gate electrode is introduced as an intermediary element within the dielectric trench, positioned between the gate and drain. This shield gate modifies the electric field distribution by providing a gradual potential transition, preventing field concentration at the trench corner while maintaining the compact device structure. The shield gate acts as a mediator that reconciles the conflicting requirements of device miniaturization and reliability.
Solution Approach 2:
The electric field distribution parameter is changed by introducing the shield gate electrode with a specific potential (connected to source or ground). This changes the potential gradient in the drift region, transforming the concentrated field at the trench corner into a more distributed field, thereby reducing hot carrier generation while preserving the compact geometry.
2Power
If the differential voltage applied to source-drain increases to improve power handling, then power capability is enhanced, but the integral of impact ionization coefficient reaches 1 causing avalanche breakdown and hot carrier injection
Solution Approach 1:
The shield gate electrode provides preliminary anti-action by pre-modifying the electric field distribution before avalanche conditions can develop. By establishing a more uniform potential gradient in advance, the shield gate prevents the formation of high-field regions that would lead to impact ionization and hot carrier injection when high differential voltages are applied.
Solution Approach 2:
The shield gate transforms the potentially harmful concentrated electric field at the trench corner into a beneficial distributed field pattern. The region that would otherwise be a hot spot for carrier generation becomes a controlled potential transition zone, converting the structural feature causing problems into a field-management mechanism.
3Speed
If the overlapping area of gate-drain region is decreased to reduce gate-drain capacitance, then switching speed is improved, but device performance is compromised
Solution Approach 1:
The shield gate electrode introduces a new spatial dimension within the existing gate-drain overlap region. By placing the shield gate vertically within the trench structure, the solution addresses the capacitance issue in the vertical dimension while maintaining the horizontal overlap area, thus preserving device performance while enabling faster switching.
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 solution effectively reduces hot carrier injection and gate-drain parasitic capacitance, enhancing the long-term reliability and switching performance of LDMOS devices by altering the carrier trajectory and electric field distribution within the trench.
Implementation Method 1
the shield gate electrode 120 entirely positioned between gate and drain positioned at one side of the dielectric trench 107 close to a source electrode... the shield gate electrode 120 in the dielectric trench 107 is connected to a source electrode 111, having a same low electric potential or ground connection
Implementation Method 2
the dielectric trench 107 comprises a drain field plate 115 positioned at one side of the dielectric trench 107 close to a drain... the drain field plate 115 in the dielectric trench is connected to a drain electrode 110, having a same electric potential
Implementation Method 3
The electric potential of the shield gate is connected to the ground, such that the shield gate performs the function of a Faraday cage, thereby shielding connection of electric potential between gate and drain and also improving the gate-drain capacitance Cgd to a certain extent
Data Source
AI summary
A power semiconductor device for improving a hot carrier injection is provided. A drain field plate is introduced at one side of a drain in a dielectric trench and connected to a drain electrode, having identical electric potential, thereby improving hole injection effects at a drain side of the dielectric trench. A shield gate field plate is introduced at one side of a source electrode in the dielectric trench and is connected to the source electrode or ground, thereby forming a shield gate. While decreasing gate drain parasitic capacitance Cgd, electron injection effects at a source electrode side of the dielectric trench are improved. With a trench etching method, the improvement of hot carrier injection can also be achieved by making carriers avoid a side wall of the dielectric trench on a path.