Numerical analysis on effective mass and traps density dependence of electrical characteristics of a-IGZO thin-film transistors

We have investigated the effect of electron effective mass (m_e*) and tail acceptor-like edge traps density (N_TA) on the electrical characteristics of amorphous-InGaZnO (a-IGZO) thin-film transistors (TFTs) through numerical simulation. To examine the credibility of our simulation, we found that by adjusting m_e* to 0.34 of the free electron mass (m_o), we can preferentially derive the experimentally obtained electrical properties of conventional a-IGZO TFTs through our simulation. Our initial simulation considered the effect of m_e* on the electrical characteristics independent of N_TA. We varied the m_e* value while not changing the other variables related to traps density not dependent on it. As m_e* was incremented to 0.44 m_o, the field-effect mobility (µ_fe) and the on-state current (I_on) decreased due to the higher sub-gap scattering based on electron capture behavior. However, the threshold voltage (V_th) was not significantly changed due to fixed effective acceptor-like traps (N_TA). In reality, since the magnitude of N_TA was affected by the magnitude of m_e*, we controlled m_e* together with N_TA value as a secondary simulation. As the magnitude of both m_e* and N_TA increased, µ_fe and Ion deceased showing the same phenomena as the first simulation. The magnitude of V_th was higher when compared to the first simulation due to the lower conductivity in the channel. In this regard, our simulation methods showed that controlling m_e* and N_TA simultaneously would be expected to predict and optimize the electrical characteristics of a-IGZO TFTs more precisely.