Fabrication and Electrical Characteristics of ZnSnO/Si Bilayer Tunneling Filed-Effect Transistors

We demonstrate improvement of electrical characteristics of a bilayer tunneling field effect transistor (TFET) composed of an n-type zinc-tin-oxide (ZnSnO) channel with superior thickness uniformity and a p-type Si source. Careful optimization of the deposition condition of the ZnSnO layer leads to the significant improvement of the thickness uniformity thanks to its amorphous structure. It is promising to reduce the average sub-threshold swing (S.S.) of the bilayer TFET. The average S.S. of the amorphous ZnSnO/Si TFET is 87 mV/dec. in a gate voltage swing of 0.3 V, which is lower by 30% than that of the poly-crystalline ZnO/Si TFET with the rough surface. The minimum S.S. value of 80 mV/dec. in the ZnSnO/Si TFET is similar to that in the ZnO/Si TFET. Additionally, the ZnSnO/Si TFET has realized the increase in on-state current (I
_on
) and the achieved Ion of 1.7 μA/μm is approximately 8 times higher than that of the ZnO/Si TFET. We also found that the ZnSnO/Si TFET shows the stronger temperature dependence of bothIon and S.S. than the ZnO/Si TFET. These differences in the electrical characteristics between ZnSnO and ZnO TFETs are discussed in terms of the amorphous and ploy-crystalline natures of the OS channels.