ESD Human Body Model step stress distributions of GaN HEMTs and the correlation with one level test results

Abstract

Evaluation of the Electro Sensitivity Discharge (ESD) robustness of Radio Frequency (RF) GaN HEMTs can result in different Human Body Model (HBM) ESD classifications due to different sample sizes, batch-to-batch variations, different test methodology and differences in the test set-up. For example, a low sample sizes per voltage level can lead to a higher classification level.

Two GaN HEMTs processed in the same technology with different power ratings were investigated with (i) step stress testing, and (ii) with testing at one voltage level, using different test set-ups and different wafer and assembly batches. A lognormal distribution gives a good fit for the HBM failure voltages acquired from step stress testing and can quantify the differences between GaN HEMTs, test set-ups and different batches.

The failure percentages observed with one level testing can be significantly lower than what is expected based on the step stress HBM failure distribution. Furthermore, the spread observed in the HBM failure distributions acquired by testing at one voltage level is significantly larger than the spread observed in the HBM failure distribution as determined by step stress testing.

The differences between one level and the step stress failure distribution can be explained by presence of traps inside the GaN HEMT devices.

Furthermore, the ESD classification according to JS-001 [1] is discussed and how Operating Characteristics (OC) curves can be used to compare ESD test plans with different sample sizes and number of failures observed.