Highly Stable, Self-Aligned Coplanar a-InGaZnO TFTs With Oxide and Hydrogenated Amorphous Si Contacts

In this study, we have demonstrated the high stability of self-aligned (SA), coplanar amorphous InGaZnO (a-IGZO) TFTs with n+ ohmic contacts by deposition of a- Si:H on the a- IGZO. The sheet resistance of the a- IGZO source/drain contacts is 1.3
$\text{k}\Omega $
/square using a 20 nm a- Si:H layer. The coplanar a- IGZO TFT with
$0.5~\mu \text{m}$
channel length exhibits excellent performance with the subthreshold swing of 0.15 V/dec, threshold voltage of 0.1 V, and field effect mobility of 13.5 cm2/Vs. The threshold voltage shift is 0.5V by positive bias stress at 60°C for 1 h at 20V. The low resistivity and highly stable ohmic contact are due to the existence of stable metal-H bonds by deposition of a- Si:H on a- IGZO at 360°C.