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Characterization of Lateral 4H-SiC MOSFETs in the Temperature Range of 25°C to 600°C for Harsh Environment Applications
Keywords: 4H-SiC, MOSFET, harsh environment
The efforts to increase energy efficiency and reduce green-house gas emissions demand robust sensor and electronic devices to be operated in harsh environments. The most common application scenarios are found in the automotive, aerospace, and avionics industries. Silicon carbide (SiC) is a promising material for harsh environment sensors and electronics due to its outstanding properties and the high level of maturity of the related process technology. This work investigates SiC-based field-effect transistors (FET) for the use as transducer in sensor applications in harsh environments. SiC-FETs are typically known to suffer from low channel mobility, which was attributed to the high density of states at the SiC/SiO2 interface. Yet, a throughout understanding of the underlying phenomena is still lacking. Also, reliability at high temperatures is a concern. To clarify these aspects, we frabricated and compared different channel layouts (inversion and implanted channels). The devices were electrically characterized in the [25-600]°C temperature range. All transistors had stacked dielectrics, Ti-based ohmic contacts, and sputtered Ti/TiN/Pt interconnects. The I-V characteristics were stable up to 500°C. At higher temperatures, degradations of ohmic contacts and gate metallizations occurred. Effective barrier heights were calculated from fitting the leakage current characteristics to the Fowler-Nordheim formula. The values decreased from 2.7eV at 25°C to 1.3eV at 500°C. The Poole-Frenkel analysis of the characteristics yielded a linear behavior at T > 300°C, indicating that this mechanism is dominant at high temperatures. In inversion-channel devices, the field effect mobility peak increased with increasing temperature. The mobility is, therefore, dominated by Coulomb scattering in this case. For implanted-channel devices, instead, a decrease of the FE mobility peak with increasing temperature was found. Hence, Coulomb scattering does not play a dominant role for these devices. We relate this to a buried channel that is formed below the SiC/SiO2 interface.
Walter Daves,
Robert Bosch GmbH
Stuttgart, Baden Württemberg 70049,
Germany


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