Buried Field Shield for High Voltage MOSFET Reliability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High voltage MOSFET devices suffer from large avalanche multiplication, leading to device degradation due to hot-carrier injection into the gate oxide, especially when biased in the off or weakly-on state, resulting in potential device failure.
Innovation Solution
Incorporating a buried electrically conductive field shield within the n-type drift region, parallel to the gate electrode, to reduce peak electric fields and suppress avalanche multiplication, thereby enhancing the integrity of the gate oxide and preventing device failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high voltage MOSFET devices operate at larger voltage potentials, then power handling capability is improved, but avalanche multiplication increases leading to device degradation
Solution Approach 1:
A buried field shield member is introduced as an intermediary conductive structure within the n-type drift region. This shield member, positioned between the gate electrode and the drift region, mediates the electric field distribution by providing an intermediate potential that reduces peak electric fields at critical interfaces, thereby suppressing avalanche multiplication while allowing high voltage operation
Solution Approach 2:
The invention changes the electrical parameter distribution within the drift region by introducing a conductive shield member with a specific potential (typically tied to source or bulk potential). This parameter change modifies the electric field profile, reducing the peak field strength at the gate oxide interface while maintaining the overall high voltage blocking capability of the device
2Power
If high voltage MOSFET devices operate at larger voltage potentials, then voltage handling capability is improved, but hot-carrier injection into gate oxide increases causing device failure
Solution Approach 1:
The buried field shield acts as an intermediary that reduces the direct interaction between high voltage stress and the gate oxide. By positioning the conductive shield between the high voltage drift region and the gate electrode, it mediates the electric field, preventing excessive field penetration into the gate oxide that would cause hot-carrier injection
Solution Approach 2:
The field shield member provides beforehand cushioning by pre-reducing the electric field strength in the drift region before avalanche multiplication can occur. This protective measure is in place during normal high voltage operation, cushioning the gate oxide from harmful hot-carrier injection events before they can cause damage
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 buried field shield effectively reduces avalanche multiplication, allowing high voltage MOSFETs to operate at larger voltage potentials without compromising device integrity, thus extending the lifespan and reliability of the MOSFETs.
Implementation Method 1
an electrically conductive field shield member disposed within the n-type drift region at least partially beneath the p-type body region and generally parallel to the gate electrode
Data Source
AI summary
A structure includes a laterally diffused (LD) MOSFET with an n-type drift region disposed on a surface of a substrate and a p-type body region contained in the drift region. The structure further includes an n-type source region contained in the p-type body region; an n-type drain region contained in the n-type drift region; a gate electrode disposed on a gate dielectric overlying a portion of the p-type body region and the n-type drift region and an electrically conductive field shield member disposed within the n-type drift region at least partially beneath the p-type body region and generally parallel to the gate electrode. The electrically conductive buried field shield member is contained within and surrounded by a layer of buried field shield oxide and is common to both a first LD MOSFET and a second LD MOSFET that are connected in parallel. Methods to fabricate the structure are also disclosed.