Experimental Investigations on the Electrical Properties of 4H-SiC Power MOSFETs Under Biaxial and Uniaxial Mechanical Strains

Abstract

In this letter, we comprehensively investigate the electrical properties of the 1200 V planner-gate 4H-SiC power metal–oxide–semiconductor field-effect transistors under the mechanical strains. Three kinds of strains, including the biaxial strain, uniaxial strain parallel to the gate channel, and uniaxial strain perpendicular to the gate channel, are applied using the wafer bending system. It is found that all kinds of compressive strains improve the drain current ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_d</i> ) under the same gate voltage ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V_g</i> ) and shift the threshold voltage ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> ) negatively, while the tensile strains decrease <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_d</i> and shift <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> positively. The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> shift mainly results from the strain modulated band structure in the poly-Si gate. Under the same overdrive gate voltage ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ov</sub> ), biaxial strains merely change <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_d</i> , while both the parallel and perpendicular uniaxial compressive strains enhance <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_d</i> . The uniaxial compressive strain elevates the electron mobility in the inverted channel by repopulating more electrons into the valleys with a smaller conduction effective mass, which results in the current improvement.