Contact-Induced Oxygen Scavenging in Indium Tin Oxide Transistors

Semiconducting oxide transistors are promising for several applications due to their ultralow leakage current and compatibility with silicon processing. However, their stability and performance degradation at short channel lengths are often poorly understood. Here, for the first time, we use x-ray absorption spectroscopy to probe oxygen migration in metal-insulator-semiconductor-metal (MISM) test structures, as a cause for the instability of indium tin oxide (ITO) transistors.

Using x-ray absorption spectroscopy and metals with four different work functions (Ti/Pt, Ni, Pd, or Pt) enables us to uncover that oxygen scavenging from ITO occurs with a trend consistent with the reactivity of the metal contact. Such oxygen scavenging (by the contacts) from the ITO channel in a transistor creates more oxygen vacancies, i.e. higher carrier concentration, which can shift the threshold voltage negative, especially at short channel lengths where the contacts are closer together. The observed trend with metal reactivity is consistent with our previous reports of ITO transistors with Ni vs. Pd contacts, where Ni contacts showed a more negative threshold voltage shift at shorter channel lengths compared to Pd contacts.

In summary, using x-ray characterization, our results provide new understanding of device operation and threshold voltage (in)stability of ITO transistors, which is essential for optimizing transistor performance and reliability.