Trench Transistor Drift Length Optimization
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Solution Overview
Problem
Conventional techniques for achieving high breakdown voltage in lateral double-diffused transistors result in increased drain-to-source on-resistance, which undesirably decreases switching speed, making it challenging to achieve both high breakdown voltage and fast switching speed simultaneously.
Innovation Solution
The method involves forming a semiconductor device with a buried doped region below the gate and a surface doped region adjacent to the gate, along with first and second device doped wells, to optimize the drift length and channel length, allowing for a longer drift region without increasing device area laterally, thereby enhancing breakdown voltage and reducing on-resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional techniques are used to achieve high breakdown voltage by increasing the distance between drain and gate, then breakdown voltage is improved, but drain-to-source on-resistance increases and switching speed decreases
Solution Approach 1:
The patent transitions from a planar transistor structure to a trench transistor structure where the channel is formed on the sidewall of a trench. This vertical dimensionality change allows the drift region to extend vertically beneath the gate rather than horizontally, enabling longer drift length for high breakdown voltage without increasing lateral device area or drain-to-source distance, thus maintaining fast switching speed while achieving high breakdown voltage
2Reliability
If the drift length is increased to enhance breakdown voltage, then breakdown voltage is improved, but device area increases laterally
Solution Approach 1:
The trench structure enables the drift region to extend in the vertical dimension beneath the gate rather than expanding laterally. The channel forms on the trench sidewall, allowing the drift length to be increased vertically without increasing the lateral footprint of the device, thus achieving high breakdown voltage with compact device area
3Speed
If drain-to-source distance is reduced to decrease on-resistance and improve switching speed, then switching speed is improved, but breakdown voltage decreases
Solution Approach 1:
By forming the channel on the trench sidewall and extending the drift region vertically beneath the gate, the patent decouples the relationship between drift length and lateral device dimensions. This allows short lateral drain-to-source distance for low on-resistance and fast switching, while maintaining long vertical drift length for high breakdown voltage through the trench structure
Data Source
AI summary
A method of forming a device is disclosed. A substrate defined with a device region is provided. A buried doped region is formed in the substrate in the device region. A gate is formed in a trench in the substrate in the device region. A channel of the device is disposed on a sidewall of the trench. The buried doped region is disposed below the gate. A distance from the buried doped region to the channel is a drift length LD of the device. A surface doped region is formed adjacent to the gate.