Reliability Of Flexible LTPS TFTs Under Mechanical Stress And Instability Of A-IGZO TFTs Under NBTS

Mechanical reliability of flexible p-channel LTPS TFTs is investigated under repetitive bending and stretchy stress. It is found that their degradation behaviors are similar, where threshold voltage of TFTs shifts positively without much change in the subthreshold region. The degradation is attributed to electron generate during the mechanical process, which causes the IV shift. The faster bending frequencies and the larger stretchy stress will accelerate degradation of device. But part of the device is damaged during the mechanical process. Damage is generally caused by the breaking of wire, gate insulating layer or the channel layer, which lead to device failure. Location of damage is typically located at the interface of two kinds of materials. The stress mutation can be found at this location by ANSYS simulation, which makes the device easy to damage at this location. We can solve this problem by adding the stress buffer layers on top of the device.Then, we investigated the degradation behaviors of a-IGZO TFTs under negative bias temperature stress(NBTS). Transfer curve has a negative shift and subthreshold swing degrades seriously. The degradation is attributed to the ionized oxygen vacancies which can move under the electric field, and accumulate at the interface. Besides, the degradation of the threshold voltage induced by NBTS under different stress voltages and temperatures can all be described by the stretched exponential model. The extract parameter reveal that effective energy barrier values are nearly a constant of 0.74?0.3eV, which represents the average energy that ionized oxygen vacancies move to interface.