Study of the stability of polycrystalline silicon by means of the behavior of thin film transistors under gate bias stress

The stability of polycrystalline structure is studied by means of the behavior of thin film transistors (TFTs) under gate bias stress with shortened drain and source contacts. Gate bias stress affects the parameters of all TFTs. Experiments show that the stability depends on the importance of the disordered regions that are the grain boundaries, as well as on the behavior of impurities. The behavior of the threshold voltage during the gate bias stress obeys the stretched exponential law exp(t/t0)β. This law, usually encountered in a great variety of situations such as a-Si:H TFTs, single crystal silicon MOSFET and even glasses, is linked to the disordered structure independent of the presence of hydrogen. The structure is less stable when impurities such as hydrogen, oxygen and others, are present.