seed projects

Sarah Swisher: Origins of Improved Field-effect Mobility in Metal Oxide Semiconductors on High-κ Gate Dielectrics :

Metal oxide semiconductors based on In, Ga, Zn, and Sn are poised to replace amorphous silicon (a-Si) and low-temperature polysilicon (LTPS) for high-performance thin-film transistors (TFTs), which are ubiquitous in flat panel displays. It has been widely reported in literature that – unlike silicon MOSFETs – metal oxide semiconductor TFTs actually exhibit higher mobility when used with high-κ gate dielectrics (ZrO₂, HfO₂, etc.). Very few studies have investigated the underlying cause of this phenomenon, and it remains poorly understood.

In this seed project, Swisher will explore the origin of this enhanced mobility for metal oxide thin films derived from colloidal nanocrystal inks. She fabricates solution-processed metal oxide (In₂o₃, ZnO, and IZO) TFTs using various gate dielectrics: thermally-grown SiO₂, ALD HfO₂, and ALD ZrO₂ (κ = 3.9, 16, and 26, respectively). In addition to varying the gate dielectric material, experiments will be designed to vary the TFT gate stack to independently examine the dielectric constant (κ), the total gate capacitance (C_ox), and the semiconductor-dielectric interface. The electrical performance of the TFTs (mobility, subthreshold swing, turn-on voltage, and hysteresis) will be characterized in conjunction with film morphology and density of trap states. With a better understanding of the materials interactions that enhance electron transport, the semiconductor-gate dielectric interface can be engineered to take full advantage of metal oxide semiconductors for high-performance flexible electronics.

Funded by the National Science Foundation through the University of Minnesota MRSEC under Award Number DMR-1420013