The advent and success of electronics based on wide bandgap (WBG) semiconductors such as GaN and SiC have incited research for the development of device technologies based on ultra-wide bandgap (UWBG) semiconductor materials, characterized by bandgaps larger than 3.4 eV such as β-Ga~2~O~3~. The ultra-wide bandgap of these materials can be exploited for the fabrication of devices capable of withstanding larger electric fields and higher temperature operation. This will enable significant improvements in the size, weight, and power (SWaP) of RF and power electronics beyond current state-of-the-art devices based on WBG semiconductors. However, the increased operating power densities realized by UWBG devices may result in enhanced levels of device heating that can ultimately restrict their operation through performance degradation, reliability issues, and failure. For UWBG β-Ga~2~O~3~, this self-heating is anticipated to be further exacerbated by the low thermal conductivity of the base material. Therefore, effective thermal characterization methods are required to understand the interplay between the coupled thermal and electrical physics to provide data for device manufacturers and improve device performance and reliability.

In this work, a novel optical thermography scheme utilizing 2D transition metal dichalcogenide (TMD) monolayers as surface temperature transducers was used to study β-Ga~2~O~3~ lateral transistors. Molybdenum disulfide (MoS~2~) monolayers were transferred to the surface of (AlGa)~2~O~3~/Ga~2~O~3~ modulation doped field effect transistors (MODFETs) to enable surface temperature measurements using Raman spectroscopy. While standard Raman spectroscopy can directly probe the β-Ga~2~O~3~ channel layer, significant underestimation of the peak temperature occurs due to through-thickness depth averaging since the β-Ga~2~O~3~ channel is homoepitaxially grown on a β-Ga~2~O~3~ substrate. In contrast, the 2D nature of the MoS~2~ monolayers allows for 2D thermal imaging of the device surface near the device channel. Effectively, the developed 2D material assisted Raman thermometry (2DRT) technique converts the standard point-based measurement capabilities of Raman thermometry into a non-intrusive thermal mapping technique, similar to infrared thermography but with significantly enhanced (10X) spatial resolution.

The developed thermal metrology technique enables study and analysis of the coupled electro-thermal physics governing the device self-heating in UWBG technologies. This is significant because it will enable electro-thermal co-design in the development of next generation β-Ga~2~O~3~-based microelectronics, which will result in power conversion systems relevant to both military and civilian energy sectors with heretofore unrealized performance and efficiency.


2d Material Assisted Raman Thermometry for Thermal Characterization of Ultra-Wide Bandgap Electronics

Division / Sponsors: 
Electronic & Photonic Packaging Division (EPPD)

Paper Proceedings: https://asmedigitalcollection.asme.org/InterPACK/InterPACK2020/volume/84041

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