Study On ZnO And In₂O₃Thin Film Transistors

The thin film transistor is the core part of display, whose characteristics are directlyrelated with the performance of display. Used as largely applied electronic devices, theresearch we do about them are not only restricted in improving of device characteristics, weshould also pay attention to these aspects such as preparation cost, preparation conditions andthe source of raw materials. The main work of this article can be divided into three parts:The zinc oxide film transistor was deposited by Spray Pyrolysis techniques: SiO2/Si assubstrate, the backside of which is heavily doped P-type silicon, a300nm thick SiO2insulating layer was obtained through oxidizing in front side and made indium ion doping. Wehave obtained optical conditions for preparation of zinc oxide film through a series ofexperiments. We can draw a conclusion through the analysis of film internal structure andsurface morphology the zinc oxide films we prepared have uniform and dense surface. Zincoxide in the film have polycrystalline structure and have growth orientation of (111) and (112),while the doped indium oxide did not form crystal structure since there is no diffraction peaksof indium oxide in the XRD patterns. The optical transmittance of the film in visible region ismore than85%, indicating the zinc oxide can be prepared as transparent conductive film.Then we prepared source and drain electrodes on the film through thermal evaporation andshadow mask technology. Al as electrode evaporation source, mask technology changes theindium oxide semiconductor layer into conducted channel which have fixed length and width.Electrical characters are detected with our prepared In-ZnO film transistor: the ZnO filmtransistor prepared by spray thermal decomposition method have obvious n-type field effecttransistor characters, and the output curve include cut-off region, linear region and saturationregion, with the minimum current1.02×10-8A, and the saturation current6.3×10-4A. Thetransistors have smaller threshold voltage of-5.1V and saturation mobility about0.61cm2/Vs.We deposited indium oxide film transistor through Spray Pyrolysis techniques: SiO2/Sias substrate, we obtained indium oxide film with optical characters through adjusting andoptimizing experiment conditions. Based on the symbol of film characters we can find crystalparticle of indium oxide are arranged uniformly and densely on substrate through the spraydecomposition technology. Indium oxide crystal has the growth orientation (111) and betteroptical transmittance in visible wavelength region. Then we prepared Al electrode as sourceand drain on indium oxide film through thermal evaporation and mask technology. Electrical characteristics are tested with the prepared In2O3: performed better n-type field effecttransistor characters, with minimum current1.9×10-10A, saturation current1.15×10-6A.Transistor has smaller threshold voltage3.7V and saturation mobility0.03cm2/Vs.We prepared indium oxide film and transistor by magnetron sputtering deposition.Compared with film characters and electrical characters of transistors in different experimentconditions, we analyze and discuss the effects of some related parameters on film andtransistor.1)with increasing the thickness in channel layer, the optical transmittance of indiumoxide film gradually reduced, carrier concentration of semiconductor gradually increase,saturation current of indium oxide film transistor also increase linearly. When the indiumoxide film is thin, the saturation current of transistor is too small to guarantee larger on-offratio. When the thickness of channel layer is too large, the device can obtain larger on statecurrent. The device can not step into off state and the minimum current is so large that can notobtain better transistor characteristics. Only the thickness of channel layer is appropriately,the transistor will be better comprehensive characteristic.2) The post annealing treatment canpromote crystalline of indium oxide but will reduce optical transmittance of film in visibleregion.3)365nm illumination has greater impact on the cut-off region of device while theimpact can ignore in saturation region. Photo-generated carriers can be formed when thesemiconductor was illuminated under360nm. The carrier concentration in channel layer ofcut-off region is very low, the number of photo-generated carriers is larger than intrinsiccarriers in channel layer so resulted to the current of cut-off state increase greatly and evendozens of times than original current. When device in saturation region, the current in channellayer is so large that the photo-generated current can ignore, that is to say light illuminationhave little effect on saturation current.