Weight-Update Characteristics Dependent on Deposition Temperature of Defective Gate Oxides in Synaptic Thin-Film Transistors

We present a study on the weight-update characteristics in Hf-ZnO thin-film transistors dependent on deposition temperature of the defective gate oxide. Here, interface trap density ($\mathbf{D}_{\text {it }}$) between a gate oxide and channel layer (e.g., $\mathrm{HfO}_{\mathrm{x}}$ and $\mathrm{Hf}-\mathrm{ZnO}$) are varied depending on different insulator deposition temperature (e.g., 100 and $200^{\circ} \mathrm{C}$), which can affect the weight-update characteristics. To verify this, the static and pulsed characteristics of the fabricated Syn-TFTs at each deposition temperature are experimentally monitored. From experimental results, the Syn-TFT fabricated at a higher temperature (e.g., $200^{\circ} \mathrm{C}$) is found to be a larger dynamic ratio ($\mathbf{d r}_{\mathbf{w}}$) compared to the lower temperature (e.g., $100^{\circ} \mathrm{C}$). This can be because, when the insulator deposition temperature is increased, the larger thermal energy is provided, leading to the stronger chemical bonding between Hf and O. This effect contributes to the smaller $D_{\text {it }}$, which results in the lower average subthreshold swing (SS ${ }_{\text {avg }}$).