Dynamics of negative bias thermal stress-induced threshold voltage shifts in indium zinc oxide transistors: impact of the crystalline structure on the activation energy barrier

The kinetics of the negative bias thermal stress (NBTS)-induced Vth variations of indium zinc oxide (IZO) transistors with different crystallographic qualities were examined based on the stretched-exponential formalism. A poly-crystalline IZO device had a 0.64 eV lower activation barrier energy than an amorphous IZO device under NBTS conditions. This was attributed to the difference in the migration energy barrier between poly-crystalline and amorphous IZO films. For the recovery process, however, the activation energy barriers (∼0.75 eV) were independent of the crystal structure. A plausible microscopic mechanism to account for the experimental results is proposed. (paper)