Asymmetric Gate LDMOSFET for High Breakdown Voltage
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Solution Overview
Problem
Current techniques for increasing the breakdown voltage (BV) of lateral double-diffused metal oxide semiconductor field effect transistors (LDMOSFETs), such as implant engineering, are insufficient for emerging technologies like sub-6 GHz WiFi power amplifier applications.
Innovation Solution
An asymmetric replacement metal gate (RMG) structure is introduced, featuring a first section traversing the semiconductor body at the channel region and a second section at the drain drift region, with a first-type work function layer having varying thicknesses in both sections, and a second-type work function layer with a different work function range, to enhance the breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If implant engineering is used to increase breakdown voltage, then breakdown voltage is improved, but it is insufficient for emerging technologies requiring even higher breakdown voltage
Solution Approach 1:
The gate structure is divided into two distinct sections with different work function characteristics: a first section over the channel region with a first work function range, and a second section over the drain drift region with a second work function range. This local differentiation allows optimization of threshold voltage at the channel while managing breakdown voltage at the drain, achieving higher overall breakdown voltage suitable for emerging technologies.
Solution Approach 2:
The gate structure employs asymmetric design where the first section and second section have different work function ranges. The first section may have a lower work function to reduce threshold voltage for efficient switching, while the second section has a higher work function to increase breakdown voltage. This asymmetric configuration resolves the limitation of conventional symmetric gates that cannot simultaneously optimize both threshold voltage and breakdown voltage for high-power RF applications.
2Ease of manufacture
If a uniform gate structure is used, then manufacturing is simplified, but threshold voltage control at the channel region is insufficient
Solution Approach 1:
The gate structure is divided into two distinct sections with different work function characteristics: a first section over the channel region with a first work function range, and a second section over the drain drift region with a second work function range. This local differentiation allows optimization of threshold voltage at the channel while managing breakdown voltage at the drain, achieving higher overall breakdown voltage suitable for emerging technologies.
Data Source
AI summary
Disclosed is a lateral double-diffused metal oxide semiconductor field effect transistor (LDMOSFET) with a replacement metal gate (RMG) structure that includes a first section, which traverses a semiconductor body at a channel region in a first-type well, and a second section, which is adjacent to the first section and which traverses the semiconductor body at a drain drift region in a second-type well. The RMG structure includes, in both sections, a first-type work function layer and a second-type work function layer on the first-type work function layer. However, the thickness of the first-type work function layer in the first section is greater than the thickness in the second section such that the RMG structure is asymmetric. Thus, threshold voltage (Vt) at the first section is greater than Vt at the second section and the LDMOSFET has a relatively high breakdown voltage (BV). Also disclosed are methods for forming the LDMOSFET.