LDMOS Drain Oxide Gradient for Breakdown and Rdson Trade-Off
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Solution Overview
Problem
Lateral double-diffused metal oxide semiconductor (LDMOS) transistors in switching voltage regulators face a trade-off between specific on-resistance (Rdson) and drain-to-source breakdown voltage (BVd_s), where improving one parameter often compromises the other, leading to suboptimal performance in voltage regulation for low-power devices.
Innovation Solution
The design incorporates a field oxide layer structure adjacent to a drain region, with at least one drain oxide layer structure having a thickness less than the field oxide layer, and a gradually decreasing thickness along the lateral direction from the drain to the channel region, along with a drift region with decreasing junction depth, to enhance breakdown voltage performance and reduce on-resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the oxide layer thickness is increased to improve breakdown voltage, then the on-resistance increases, compromising the trade-off between Rdson and BVd_s
Solution Approach 1:
The patent applies local quality by implementing a non-uniform oxide layer thickness distribution along the lateral direction. The oxide layer thickness gradually decreases from the drain region toward the channel region, creating different local properties: thicker oxide near the drain for high breakdown voltage, and thinner oxide near the channel for lower on-resistance. This resolves the contradiction by optimizing each region's oxide thickness according to its specific functional requirements.
Solution Approach 2:
The patent employs parameter changes by systematically varying the oxide layer thickness parameter along the lateral direction. Instead of using a constant thickness, the oxide layer thickness is continuously adjusted from the drain to the channel region, enabling simultaneous optimization of breakdown voltage and on-resistance through controlled parameter variation.
2Ease of manufacture
If a uniform oxide layer is used, then the manufacturing process is simpler, but the electric field distribution becomes non-uniform, causing the bird's beak effect
Solution Approach 1:
The patent implements local quality by creating a spatially varying oxide layer thickness profile. The oxide layer is designed with different thicknesses at different lateral positions, with thicker regions near the drain and thinner regions near the channel. This non-uniform structure achieves uniform electric field distribution and eliminates the bird's beak effect while remaining manufacturable through standard semiconductor processing techniques.
3Reliability
If the oxide layer thickness is reduced to lower on-resistance, then the breakdown voltage decreases, worsening the Rdson-BVd_s trade-off
Solution Approach 1:
The patent applies dimensionality change by transitioning from a one-dimensional (vertical) oxide layer structure to a two-dimensional (lateral gradient) structure. The oxide layer thickness varies continuously in the lateral direction from drain to channel, adding a spatial dimension to the design. This enables simultaneous optimization of both breakdown voltage and on-resistance by exploiting the lateral thickness gradient rather than being constrained to a single uniform thickness.
Data Source
AI summary
An LDMOS transistor can include: a field oxide layer structure adjacent to a drain region; and at least one drain oxide layer structure adjacent to the field oxide layer structure along a lateral direction, where a thickness of the drain oxide layer structure is less than a thickness of the field oxide layer, and at least one of a length of the field oxide layer structure and a length of the drain oxide layer structure is adjusted to improve a breakdown voltage performance of the LDMOS transistor.