# Assessing the Stress Induced by Novel Packaging in GaN HEMT Devices via Raman Spectroscopy
## 4 Conclusions  
In this article, micro-Raman spectroscopy was employed to assess the stress/deformation induced by packaging in AlGaN/GaN high-electron-mobility transistors (HEMTs) supplied by STMicroelectronics S.r.l. To evaluate the packaging's impact, we acquired 128 micro-Raman spectra by vertically scanning along the AlGaN/GaN heterostructure of the device. The data were analyzed using a fitting procedure employing a model consisting of three or four Lorentzians to accurately measure the frequency shift of the phonon modes' center. Attention was focused on the E2(high) phonon mode, which is highly sensitive to crystalline stress and therefore can be effectively used for its quantification. Two GaN devices supplied by STMicroelectronics S.r.l were studied, one packaged and the other bare, to assess the influence of packaging on the residual stress present within the active layers of the device.  
In the HEMT-PD device, a blue shift of the E2(high) mode near the packaging was observed, while a slight redshift followed by a blue shift was observed for the bare device. A linear correlation between the Raman frequency shift \(\Delta\omega\) and stress \(\sigma\) was used to evaluate the compression stress induced by packaging. The packaged device showed a decrease in stress levels of about 0.1 GPa compared to the bare HEMT. In conclusion, the study states that the compression stress induced by the packaging process strongly mitigates the residual tensile stress present on wafer-level HEMT-B devices. Therefore, packaging, which provides mechanical support and protects the sensitive semiconductor wafer from external environmental factors, can play a dual role by also contributing to stress mitigation, compensating for the inherent tensile stress in these devices, and thereby improving performance in terms of reliability, dynamics, and lifetime.  
**Author Contributions:** Conceptualization, M.C. and S.P.; Methodology, S.P.; Formal analysis, G.M. and M.d.; Investigation, Z.D., A.A.M., M.M. and A.S.; Data curation, Z.D. and M.C.; Writing--original draft, Z.D. and G.M.; Writing--review & editing, M.d., A.A.M., M.M., A.S., M.C. and S.P.; Supervision, S.P.; Funding acquisition, A.A.M. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work has been carried out in the framework of the European Project GaN4 AP (Gallium Nitride for Advanced Power Applications). The project has received funding from the Electronic Component Systems for European Leadership Joint Undertaking (ECSELJU) under grant agreement no. 101007310. This Joint Undertaking received support from the European Union's Horizon 2020 research and innovation programme, and Italy, Germany, France, Poland, Czech Republic, and the Netherlands.  
**Institutional Review Board Statement:** Not applicable.  
**Infrared Consent Statement:** Not applicable.  
**Data Availability Statement:** The raw data supporting the conclusions of this article will be made available by the authors on request.  
**Conflicts of Interest:** Authors [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] were employed by the company ST Microelectronics. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as potential conflicts of interest.