University of Twente Student Theses


The relation between TLP and VSWR to improve the ruggedness of LDMOS transistors

Terbonssen, Bas (2019) The relation between TLP and VSWR to improve the ruggedness of LDMOS transistors.

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Abstract:An analysis is presented to the behavior of laterally diffused metal oxide semiconductor (LDMOS) transistors under normal and mismatch conditions. Mismatch conditions are loads applied to the output of the radio frequency (RF) power amplifier which are not nominal loads, 50 ohms. The mismatch is measured using a voltage standing wave ratio (VSWR) measurement at product level. The robustness to a mismatch is often denoted as the ruggedness of the transistor. Insight of the behavior of the LDMOS transistor under mismatch conditions is used to find a relation between an on-wafer measurement, transmission line pulse (TLP), and the VSWR measurement on product level. A relation between the on-wafer measurement and the measurement on product level will lead to a faster development cycle and will save money and time since a design of the packaged transistor and RF circuit can be avoided. A detailed model of the die, matching, packaging and the RF circuit is created to evaluate the current flows inside the transistor together with the voltages at different nodes. The model can be used to simulate the behavior of the transistor under nominal conditions, 50 ohms, and under mismatch conditions. The failure mode during VSWR measurements at product level is founded to be related to the current flow in breakdown of the transistor. A maximum current flow is reached when a maximum inductive load is applied to the die of the transistor. All measured devices failed in the region were the transistor is in breakdown. The current flow in breakdown is measured on-wafer by TLP and can therefore be used as a measure to determine the ruggedness of the transistors. Further investigations needs to be done to find a clear relation between the onwafer TLP measurements and the VSWR at product level/ A relation is not achieved because the current levels in breakdown of the TLP were too small to find a proper relation. A clear relation is not achieved, although a trend between TLP and VSWR is visible. The VSWR increases when the maximum current in TLP also increases.
Item Type:Essay (Master)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:53 electrotechnology
Programme:Electrical Engineering MSc (60353)
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