High-k ZrO_2/Al_2O_3 bilayer on hydrogenated diamond: Band configuration, breakdown field, and electrical properties of field-effect transistors

摘要

A band configuration of a high-k ZrO_2/Al_2O_3 bilayer on hydrogenated diamond (H-diamond), a breakdown field (E_B) of the ZrO_2/Al_2O_3 bilayer, and an effect of gate-drain distance (d_(G-D)) on electrical properties of ZrO_2/Al_2O_3/H-diamond metal-insulator-semiconductor field-effect transistors (MISFETs) have been investigated. The Al_2O_3 and ZrO_2 layers are successively deposited on H-diamond by atomic layer deposition (ALD) and sputtering-deposition (SD) techniques, respectively. The thin ALD-Al_2O_3 buffer layer with 4.0 nm thickness plays a role in protecting the H-diamond surface from being damaged by the plasma discharge during SD-ZrO_2 deposition. The ZrO_2/Al_2O_3 heterojunction has a type I band structure with valence and conduction band offsets of 0.6 ± 0.2 and 1.0 ± 0.2 eV, respectively. The valence band offset between ZrO_2 and H-diamond is deduced to be 2.3 ± 0.2 eV. The E_B of the ZrO_2/Al_2O_3 bilayer is measured to be 5.2 MV cm~(-1), which is larger than that of the single ZrO_2 layer due to the existence of the ALD-Al_2O_3 buffer layer. The dependence of d_(G-D) on drain-source current maximum (I_(DS,max), on-resistance (R_(ON)), threshold voltage (V_(TH)), and extrinsic transconductance maximum (g_(m,max)) of the MISFETs has been investigated. With increasing d_(G-D) from 4 to 18 μm, the absolute I_(DS,max) decreases from 72.7 to 40.1 mA mm~(-1), and the R_(ON) increases linearly from 83.3 ± 5 to 158.7 ± 5 Ω mm. Variation of V_(TH) values of around 1.0 V is observed, and the g_(m,max) is in the range between 8.0 ± 0.1 and 13.1 ± 0.1 mS mm~(-1).