Stepped-Drift MOSFET With Shallow Trench Insulator
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Solution Overview
Problem
There is a fundamental trade-off between breakdown voltage and on-resistance in power metal-oxide semiconductor field effect transistors (MOSFETs), with low-voltage MOSFETs having low on-resistance due to active drift regions and high-voltage MOSFETs having increased on-resistance due to field drift regions, necessitating a structure that optimizes this trade-off.
Innovation Solution
A MOSFET structure incorporating a stepped drift region with a shallow trench insulator partially overlapped by the gate and a silicide block extending from the shallow trench isolation (STI) to the drain region, combining active and field drift structures to improve the breakdown voltage and on-resistance trade-off.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a field drift region (shallow trench isolation) is used in high voltage MOSFETs, then breakdown voltage is improved, but on-resistance increases
Solution Approach 1:
The drift region is segmented into two distinct zones: an active drift region with lower on-resistance and a field drift region with shallow trench isolation for higher breakdown voltage. This segmentation allows each zone to optimize for its specific function, resolving the contradiction between low on-resistance and high breakdown voltage
Solution Approach 2:
Different regions of the drift zone are assigned different qualities: the active drift region maintains surface conduction for low resistance, while the field drift region uses shallow trench isolation for voltage withstand capability. This local differentiation enables simultaneous optimization of both parameters in different spatial locations
2Object-generated harmful factors
If an active drift region is used in low voltage MOSFETs, then on-resistance is reduced, but breakdown voltage is limited
Solution Approach 1:
The drift region is divided into active and field drift portions, enabling the device to achieve low on-resistance through the active region while attaining high breakdown voltage through the field drift region with shallow trench isolation, thus overcoming the voltage limitation of traditional active drift structures
3Reliability
If shallow trench isolation is used to reduce gate stress, then breakdown voltage is improved, but surface conduction is removed increasing on-resistance
Solution Approach 1:
The drift region is segmented such that the active drift portion maintains surface conduction for low resistance while the field drift portion uses shallow trench isolation for voltage breakdown protection, allowing both functions to coexist without interfering with each other
Solution Approach 2:
Shallow trench isolation is applied locally only to the field drift region rather than the entire drift zone, preserving surface conduction in the active region while providing voltage withstand capability where needed, thus maintaining low on-resistance while improving breakdown voltage
Data Source
AI summary
A power metal-oxide-semiconductor field effect transistor (MOSFET)(100) incorporates a stepped drift region including a shallow trench insulator (STI)(112) partially overlapped by the gate (114) and which extends a portion of the distance to a drain region (122). A silicide block extends from and partially overlaps STI (112) and drain region (122). The STI (112) has a width that is approximately 50% to 75% of the drift region.