Reliability Evaluation of Isolated LDMOS Devices and Condition Monitoring Solution

This paper investigates the robustness and performance degradation of isolated Laterally Diffused Metal Oxide Semiconductor (LDMOS) devices under repetitive avalanche breakdown and dynamic reliability tests. To achieve this objective, three custom LDMOS devices with different isolation configurations are designed and taped-out to study the impact of the connection and width of the isolation well over aging. A large-scale accelerated aging setup is designed with a modular and scalable structure, facilitating easy expansion and measurement capabilities. The symmetrical structure of the motherboards ensures even pulse widths and parasitic in the distributed modules. The repetitive avalanche test results indicate a gradual increase in both the on-state resistance and drain leakage current across all devices. In the dynamic tests, however, only the drain leakage current increases over aging. Based on these findings, the drain leakage current is utilized as a reliable precursor for condition monitoring of the LDMOS devices and a circuit is proposed to accurately measure the drain leakage current. In addition, among the three designed devices, the most reliable configuration for LDMOS devices is identified. It is shown that the failure locations and device lifetime vary depending on the isolation well connections due to varying stress on the gate oxide. Furthermore, a detailed analysis of the forward characteristics of the body diode reveals that the distance between the terminals of the n-well and substrate has a notable impact on enhancing the robustness of the diode.