Influence of Channel Layer Thickness on the Instability of Amorphous SiZnSnO Thin Film Transistors Under Negative Bias Temperature Stress

Abstract

In this study, amorphous silicon-zinc-tin-oxide thin film transistors (a-SZTO TFTs) are fabricated by radio-frequency magnetron sputtering at room temperature, and the influence of various channel thicknesses on their electrical performance and stability is report. Under the negative bias temperature stress, the transfer curve exhibits threshold voltage shift in the negative direction and degradation of subthreshold swing. In addition, the hump effect occurs in the thick channel, which is primarily due to an increase in total trap density from 5.0 Â 10 11 to 3.5 Â 10 12 cm À2 with an increase in the channel layer thickness from 12 to 72 nm. These results agree well with the increase in the bulk trap density because all a-SZTO TFTs have the same interface; therefore, the interface trap density is excluded. Thicker SZTO TFTs show the hump effect, as they have more donor-like states in the shallow level. Furthermore, temperature stress at 300-333 K and the activation energy (E a ) falling rate are calculated for a-SZTO TFTs. The E a falling rate decreases from 0.103 to 0.010 eV V À1 with increasing channel thickness. Consequently, an a-SZTO TFT with a 12-nm channel layer thickness shows a large E a falling rate (0.103 eV V À1 ) and a small threshold voltage shift of 4.74 V without the hump effect and degraded electrical performance.

Investigation on energy bandgap states of amorphous SiZnSnO thin films

“…The temperature dependency of TS was measured from room temperature to 353 K in intervals of 20 K. As O p increased, the amount of shift of V th (Δ V th ) decreased from 2.16 to 0.55 V. Regardless of the increase in O p , it was confirmed that V th moves toward the negative direction as temperature increases in the TS. It is expected that the thermal energy releases electrons in the trapped state inside the thin film with an increase in temperature 29 . We only applied the temperature parameter to analyze the effect on trap states inside the energy bandgap and did not add any additional stress, such as bias and illumination.…”

“…3(d–f), including the obtained E a falling rate through the slope. The thermally activated drain current in the subthreshold region is obtained using the equation 29 where I D0 is the pre-factor, k is Boltzmann’s constant, T is the absolute temperature, and E a is the activation energy. The calculated E a falling rate increased systematically from 0.077 eV/V to 0.082 eV/V as O p increased.…”

“…The calculated E a falling rate increased systematically from 0.077 eV/V to 0.082 eV/V as O p increased. An increase in the falling rate implies a decrease in the channel and/or interface trap states 29,30 . In other words, in the graph of E a , the state can be changed more quickly if the amount of trap states is small for electrons to transit from the valence band to the conduction band.…”

High‐Performance Thin‐Film Transistors with Nickel‐Doped Indium Zinc Oxide Channel Layers

“…As Ni content increased from 0 to 7.5 at%, the area proportion of O H decreased from 48.7% to 34.5%, indicating that oxygen vacancies were suppressed by Ni doping. The decrease in oxygen vacancies would result in reduced carrier concentration because oxygen vacancies serve as donors in AOSs . Figure shows EDS elemental maps encompassing In, Zn, Ni, and O obtained from the a‐IZNO thin films.…”

“…The decrease in oxygen vacancies would result in reduced carrier concentration because oxygen vacancies serve as donors in AOSs. [23] Figure 7 shows EDS elemental maps encompassing In, Zn, Ni, and O obtained www.advancedsciencenews.com www.pss-a.com www.advancedsciencenews.com www.pss-a.com from the a-IZNO thin films. In this study, an a-IZNO thin film with a Ni content of 6.6 at% was selected as a representative sample.…”