Study On Ultrahigh-mobility Heterojunction Amorphous Oxide Semiconductor Thin Film Transistors

In recent years,active matrix organic light emitting diodes?AMOLED?have shown great promise in displays.The metal oxide thin film transistor?MOTFT?has drawn great attention due to the advantages of relatively high electron mobility,excellent uniformity,good transparency,and low process temperature.However,with the continuous development of display technology,the requirements for the device mobility becomes higher.The existing materials mobility has failed to meet this technical requirement,which requires us to develop high mobility TFT materials or device structures.The active layer material used in this paper is indium zinc oxide?IZO?.In order to improve the mobility,we preparerd a double layer IZO?HIZO/LIZO?active layer,in which HIZO is a high indium layer,LIZO is a low indium layer,forming HIZO/LIZO Heterojunction structure.We investigated the optical properties and electrical properties of HIZO and LIZO films respectively.Both HIZO and LIZO films are still amorphous even though at the process temperatures of 350?.As the thickness reduces,films exhibit higher transmittance with apparent blue-shift which implies widening of the optical bandgap.The optical bandgap of HIZO is wider than that of LIZO with corresponding thickness.According to UPS and Kelvin data,we found that the decrease in film thickness resulted in a decrease in E_F,indicating the decreasing of the carrier concentration,and E_offset of HIZO was found to be larger than LIZO.In addition,the XPS test shows that HIZO has higher oxygen vacancies than LIZO,indicating that HIZO films have higher carrier concentration,which means that HIZO TFT have higher mobility.In this paper,three kinds of TFTs including HIZO,LIZO and heterojunction HIZO/LIZO were prepared.It was found that the mobility of HIZO/LIZO heterojunction TFTs was much higher than that of the other two TFTs.The C-V tests showed that the carrier concentration of heterojunction TFT were higher than others.Moreover,two peaks in Heterojunction TFT have been found by the conductance-film thickness curve.It's proved that the heterojunction TFT have a double-layer conductive channels,thus indicating high mobility.During the low temperature test,the output and transfer characteristics is normal.The performance of the device is excellent even at the temperature of 4.2 K.The performance and initial performance of the device are almost unchanged from low temperature to room temperature,indicating that the device has good temperature stability.