Study of instabilities in amorphous-silicon thin-film transistors by transient current spectroscopy

A study of the metastable changes in a-Si:H/a-SiN:H thin-film transistors (TFTs) caused by prolonged application of high gate voltages by photoinduced discharge (PID) measurements and transient current spectroscopy (TCS) is discussed. Two effects can be distinguished: (1) a pronounced shift of the flatband voltage, which is caused by charge trapping in the dielectric, and (2) the creation of metastable states in the accumulation layer. It is found that PID is unable to detect changes of the density of defect states near the interface N/sub i/. TCS, on the other hand, reveals that voltage stress causes an increase of N/sub i/ by up to a factor of 2. The temperature dependence of this effect indicates an activation energy for defect formation of approximately 0.7 eV.<
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