Trenched Faraday Shield for LDMOS Hot Carrier Injection
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Solution Overview
Problem
High operating voltages in LDMOS transistor devices lead to high energy charge carriers, causing device degradation through hot carrier injection (HCI) into the gate oxide, which affects operational characteristics and performance, especially at high frequencies.
Innovation Solution
A trenched Faraday shield is disposed in a semiconductor substrate trench below the surface, reducing drain-gate capacitance and shielding the gate electrode from the electric field, thereby minimizing HCI and improving device ruggedness without significantly affecting other parameters like breakdown voltage or on-state resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high operating voltages are applied between source and drain electrodes, then power handling capability and RF performance are improved, but hot carrier injection into gate oxide increases causing device degradation
Solution Approach 1:
A Faraday shield structure is introduced as an intermediary element between the gate electrode and drain region. This shield, connected to ground or a fixed potential, mediates the electric field interaction by providing a shielding effect that reduces the direct coupling between high-voltage drain and the gate, thereby reducing hot carrier generation while maintaining power handling capability
Solution Approach 2:
The Faraday shield extends in the vertical dimension below the gate electrode into the substrate, creating a three-dimensional shielding structure. This vertical extension allows the shield to intercept and redirect electric field lines that would otherwise directly couple the drain to the gate, reducing hot carrier injection without affecting the lateral power handling dimensions
2Reliability
If a Faraday shield is added to reduce hot carrier injection, then device ruggedness is improved, but device complexity increases
Solution Approach 1:
The Faraday shield's effectiveness is optimized by adjusting parameters such as its depth below the surface, lateral dimensions, and distance from the gate electrode. By carefully controlling these geometric parameters, the shield achieves optimal hot carrier reduction with minimal impact on device performance and acceptable complexity
Solution Approach 2:
The Faraday shield utilizes the substrate itself as part of the shielding structure, effectively copying and extending the shielding function into the existing substrate region. This approach leverages available material and space rather than introducing entirely new complex structures
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 trenched Faraday shield effectively reduces HCI and drain-gate capacitance, enhancing RF LDMOS transistor performance by decoupling the gate and drain terminals, improving device ruggedness, and maintaining or increasing breakdown voltage while minimizing impact on on-state resistance and other capacitances.
Implementation Method 1
A Faraday shield may be disposed between a gate structure and a drain terminal in a laterally diffused metal-oxide-semiconductor (LDMOS) transistor device. At least a portion of the Faraday shield may be disposed below a surface of a semiconductor substrate. The Faraday shield may shield the gate structure from an electric field arising from an operating voltage applied between a source terminal and the drain terminal
Implementation Method 2
The trenched Faraday shield may reduce a capacitance (e.g., feedback capacitance) between a biased conduction terminal and the control electrode structure
Data Source
AI summary
A device includes a semiconductor substrate having a surface with a trench, first and second conduction terminals supported by the semiconductor substrate, a control electrode supported by the semiconductor substrate between the first and second conduction terminals and configured to control flow of charge carriers during operation between the first and second conduction terminals, and a Faraday shield supported by the semiconductor substrate and disposed between the control electrode and the second conduction terminal. At least a portion of the Faraday shield is disposed in the trench.