Effects of high-k gate dielectrics on the electrical performance and reliability of an amorphous indium–tin–zinc–oxide thin film transistor (a-ITZO TFT): an analytical survey
This study is a numerical simulation obtained by using Silvaco Atlas software to investigate the effect of different types of dielectric layers, inserted between the channel and the gate, on the performance and reliability of an a-ITZO TFT. Replacing the SiO2 oxide layer with a high-k dielectric layer gives the concept of the electrical thickness, known by the equivalent oxide thickness (EOT) in which the physical thickness (PT) can be increased to improve the device reliability without increasing the effective thickness of the gate dielectric. A range of different high-k dielectric materials was suggested. For low-k SiO2 (k = 3.9), the electrical parameters extracted are: Ci = 3.45 × 10−8 F cm−2, Ion = 2.23 × 10−6 A, Ioff = 2.17 × 10−13 A, Ion/Ioff = 1.02 × 107, EOT = 100 nm, VT = −0.61 V, μFE = 29.75 cm2 V−1 s−1, SS = 7.91 × 10−2 V per decade and Von = −0.95 V. Replacing SiO2 by a high-k dielectric material, such as SrTiO3 (k = 300), leads to effects similar to the effects of reducing the physical thickness of the gate dielectric but without actually reducing this physical thickness. This allows improving the outputs of the a-ITZO TFT as it leads to an increase in Ci, Ion and Ion/Ioff to the values Ci = 2.66 × 10−6 F cm−2, Ion = 2.86 × 10−4 A, and Ion/Ioff = 8.80 × 109, respectively, and the decrease in EOT, Ioff, VT, μFE, SS and Von to the values EOT = 1.3 nm, Ioff = 3.25 × 10−14 A, VT = −0.428 V, μFE = 26.66 cm2 V−1 s−1, SS = 6.12 × 10−2 V per decade and Von = −0.75 V, respectively, without leakage effects.