Dual-Workfunction LDMOS Drift Region for Higher Breakdown Voltage
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Solution Overview
Problem
LDMOS devices face limitations in achieving high drain-source breakdown voltage (BVDSS) and Ron characteristics while minimizing leakage, particularly in RF power amplifiers, due to the challenges in doping profiles and electric field management in the drift region.
Innovation Solution
Incorporating a gate structure with a first workfunction metal in the channel region and a second workfunction metal in the trench of the drift region, along with a sidewall spacer, to enhance the doping profile and electric field management, thereby improving BVDSS and reducing leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional LDMOS structure is used, then the device can operate in RF power amplifiers, but the drain-source breakdown voltage is limited and leakage is high
Solution Approach 1:
The gate structure is segmented into two distinct workfunction metals: a first workfunction metal in the channel region and a second workfunction metal in the trench within the drift region. This segmentation allows independent optimization of electrical characteristics in different regions, enabling higher drain-source breakdown voltage while reducing leakage through the drift region
Solution Approach 2:
Different workfunction metals are applied to different regions of the gate structure based on local requirements. The first workfunction metal optimizes channel region performance, while the second workfunction metal specifically addresses drift region characteristics. This local quality approach enables tailored electrical properties in each region to simultaneously achieve high breakdown voltage and low leakage
2Reliability
If the drain-source breakdown voltage is increased, then high-power RF applications are enabled, but the device complexity increases due to additional doping profile requirements
Solution Approach 1:
The invention changes the workfunction parameter by introducing a second workfunction metal with different electrical properties in the drift region trench. This parameter change modifies the electric field distribution and potential profile in the drift region, enabling higher breakdown voltage without requiring complex multi-step doping profiles
Data Source
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Figure 3A~3B
AI summary
The present disclosure relates to semiconductor structures and, more particularly, to a device with workfunction metal in a drift region and methods of manufacture. The structure includes: a gate structure having at least a first workfunction metal in a channel region and a second workfunction metal, which is different from the first workfunction metal, in a trench in a drift region; and a sidewall spacer adjacent to the gate structure within the trench in the drift region.