Simultaneous measurement of temperature, stress, and electric field in GaN HEMTs with micro-Raman spectroscopy

Abstract

As semiconductor devices based on silicon reach their intrinsic material limits, compound semiconductors, such as gallium nitride (GaN), are gaining increasing interest for high performance, solid-state transistor applications. Unfortunately, higher voltage, current, and/or power levels in GaN high electron mobility transistors (HEMTs) often result in elevated device temperatures, degraded performance, and shorter lifetimes. Although micro-Raman spectroscopy has become one of the most popular techniques for measuring localized temperature rise in GaN HEMTs for reliability assessment, decoupling the effects of temperature, mechanical stress, and electric field on the optical phonon frequencies measured by micro-Raman spectroscopy is challenging. In this work, we demonstrate the simultaneous measurement of temperature rise, inverse piezoelectric stress, thermoelastic stress, and vertical electric field via micro-Raman spectroscopy from the shifts of the E (high), A longitudinal optical (LO), and E (low) optical phonon frequencies in wurtzite GaN. We also validate experimentally that the pinched OFF state as the unpowered reference accurately measures the temperature rise by removing the effect of the vertical electric field on the Raman spectrum and that the vertical electric field is approximately the same whether the channel is open or closed. Our experimental results are in good quantitative agreement with a 3D electro-thermo-mechanical model of the HEMT we tested and indicate that the GaN buffer acts as a semi-insulating, p-type material due to the presence of deep acceptors in the lower half of the bandgap. This implementation of micro-Raman spectroscopy offers an exciting opportunity to simultaneously probe thermal, mechanical, and electrical phenomena in semiconductor devices under bias, providing unique insight into the complex physics that describes device behavior and reliability. Although GaN HEMTs have been specifically used in this study to demonstrate its viability, this technique is applicable to any solid-state material with a suitable Raman response and will likely enable new measurement capabilities in a wide variety of scientific and engineering applications.

Wide-Field Magnetic Field and Temperature Imaging Using Nanoscale Quantum Sensors

“…The resulting temperature profile is obtained simultaneously. Significant temperature rise is localized around the gate, which agrees with previous experimental observations 8,[16][17][18] . Particularly, attributed to the high spatial resolution and wide-field nature of Q-CAT imaging, a sharp temperature drop is well-resolved at the end of the gate along the channel direction ( Fig.5d-e), indicating limited leakage current at the channel's end.…”

“…We measure a thermal resistance of 73 ± 0.8 • C/W, which agrees with previous measurements of the same model(75 • C/W) 8 . These results elucidate device physics at a spatial resolution that is competitive with in situ methods, at wide-field.…”

“…The extremely high power density (> 5 W/mm) in GaN HEMTs gives rise to a concentrated (∼1 µm) channel temperature (>200 • C), which leads to device failure 8,[16][17][18] . The operation of GaN HEMTs involves non-linear coupling between electromagnetism and heat transport, making their dynamics difficult to capture by simulation, especially when considering device variations.…”

Characterization of thin film evaporation in micropillar wicks using micro-Raman spectroscopy

“…It has been widely that reported the heat transfer of evaporation can be significantly enhanced by micro/nanostructures [5][6][7][8][9] . For this reason, thin film evaporation on microstructured surfaces has attracted particular interest for high heat flux thermal management, especially for cooling high-performance electronic devices [6][7][8][9] (e.g., micro-processors 1 and highpower radio-frequency amplifiers 10,11 with highly concentrated heat generation > 100 W/cm 2 ).…”

“…In this work, we developed a non-contact, in situ temperature measurement approach using micro-Raman thermometry to investigate thin film evaporation from microstructured surfaces. Due to the superior spatial resolution (≈ 1 µm) and high temperature sensitivity (≈ 0.5 °C), micro-Raman thermometry has been widely used to measure the localized temperature rise 11,12 for various semiconductor materials [17][18][19] and microelectronic devices 20,21 . Meanwhile, the capability of micro-Raman in studying phase change heat transfer has not yet been demonstrated.…”