SOI Drift Region Drop Structure for 1200V Breakdown
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Solution Overview
Problem
Conventional silicon-on-insulator (SOI) integrated high-voltage devices struggle to achieve breakdown voltages above 1200V due to limitations in increasing the thickness of the buried oxide layer, which affects thermal conductivity and increases costs, while thickening the top silicon does not solve the issue of longitudinal early breakdown.
Innovation Solution
A silicon-on-insulator semiconductor device with a drift region featuring a drop structure, where the thickness at the high-voltage end is greater than at the low-voltage end, and electrodes configured to apply higher voltage to the second electrode, allowing complete exhaustion of the drift region without increasing the buried oxide layer thickness, accompanied by a protective layer to manage electric field concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of the buried oxide layer is increased to achieve higher breakdown voltage, then the breakdown voltage increases, but the thermal conductivity deteriorates and manufacturing cost increases
Solution Approach 1:
The drift region is designed with non-uniform thickness, featuring a first region with greater thickness and a second region with lesser thickness. This local variation in thickness allows different parts of the drift region to serve different functions: the thicker first region provides higher breakdown voltage capability where needed, while the thinner second region maintains better thermal conductivity and reduces overall device cost. This resolves the contradiction by applying the principle of local quality differentiation.
Solution Approach 2:
Instead of increasing breakdown voltage solely through vertical thickness increase of the buried oxide layer, the invention introduces a lateral dimension variation in the drift region thickness. The drift region transitions from a uniform thickness to a varying thickness profile across the device area, utilizing the lateral dimension to achieve voltage control while maintaining thermal performance.
2Reliability
If the thickness of the buried oxide layer is increased to achieve breakdown voltage above 1200V, then the breakdown voltage reaches the target, but manufacturing cost increases
Solution Approach 1:
The drift region employs non-uniform thickness distribution with a first region having greater thickness and a second region having lesser thickness. This allows the device to achieve high breakdown voltage (above 1200V) in the critical first region while reducing material consumption and manufacturing cost in the second region, thereby resolving the contradiction between performance and cost.
3Reliability
If the thickness of the top silicon is increased to prevent longitudinal early breakdown, then the breakdown voltage improves, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
Rather than uniformly increasing the top silicon thickness throughout the device, the invention implements a non-uniform thickness profile in the drift region with a first region of greater thickness and a second region of lesser thickness. This localized thickness variation prevents longitudinal early breakdown in the critical first region while avoiding the added complexity and manufacturing difficulty associated with uniform thickening.
Data Source
AI summary
In one aspect, a silicon-on-insulator semiconductor device includes: a substrate; a buried dielectric layer disposed on the substrate; a first electrode; a second electrode; and a drift region disposed on the buried dielectric layer. An upper surface of the drift region forms a drop structure including a first side adjacent to the first electrode, a second side adjacent to the second electrode, and a transition region between the first side and the second side. An upper surface of the second side is higher than a bottom surface of the first side, such that a thickness of the drift region at the second side is greater than that at the first side. The first electrode and the second electrode are configured such that a voltage applied to the second electrode is greater than a voltage applied to the first electrode when a reverse bias voltage is applied to the device.