Local strain modification effects on global properties of AlGaN/GaN high electron mobility transistors

Performance and reliability of microelectronic devices are governed by the mechanical strain within the device layers. Typically, this is studied with uniformly distributed strain applied externally or internally. The focus of this study is on AlGaN/GaN high electron mobility transistors (HEMTs), which is expected to be more sensitive to strain due to its piezo-resistive and piezo-electric nature. Accordingly, we hypothesize that even small but localized strain may have significant impact on the overall behavior of a HEMT. To investigate this hypothesis, we introduce highly localized strain relief by milling a 20 × 30 μm² micro trench about 70 μm deep on the backside of an 800 × 840 μm² size HEMT die. The resulting local relaxation of in-plane residual strain was mapped using micro-Raman technique. Our results show that a decrease of only 0.02% strain can decrease the overall output saturation current up to ~20%. The drop of output current is attributed to reduced two-dimensional electron gas (2DEG) sheet carrier density and electron mobility due to the strain relief in the device layers. However, the mechanistic process of strain relief also causes defect generation at the interfaces, which increases leakage current. Our technique for localized strain re-distribution could be an effective tool to surrogate the influence of inherent localized strain build-up across the channel of electronic devices.