Investigation of Indium Gallium Oxide Thin Film Fabricated by RF Sputtering System and Their Applications

Abstract

In this thesis the indium gallium oxide (InGaO) is deposited by RF magnetron sputtering and the films are applied to photodetectors thin film transistors and EGFET pH sensors The properties of the devices are discussed in detail First InGaO films are deposited under different oxygen partial pressure and researched into structural optical and surface/depth element analysis For the structural analysis the surface of films is dense With the increasing of oxygen partial pressure the crystalline phase gradually appears and is consistent with In2O3 The peak intensities increased indicating that the crystalline qualities are improved It can also be observed from XPS analysis that the oxygen vacancies decrease as the partial oxygen pressure increases For the optical analysis owing to the large bandgap of gallium InGaO thin films could be used as wide bandgap material absorbing ultraviolet light Furthermore the transmittance in the visible region is more than 80% For surface/depth element analysis AFM measurement is used to observe the surface The smooth surface of the films leads to lower surface density of states which is beneficial for the performance of the devices Next InGaO photodetectors are fabricated under various oxygen flow ratios to investigate influence on these devices The dark current could be suppressed effectively with the increasing oxygen flow Also the Ohmic contact is tuned to Schottky contact and the photoresponse time decreases For the photodetectors fabricated under 20% oxygen partial pressure dark current can be reduced to 8 1 × 10-12 amps the response rises to 0 31 amperes / watt and the photoresponse time is reduced to 21/27 seconds On the other hand we also make a research on the different indium to gallium ratio At first the responsivity is 10-5 amperes/watt however the atoms in the film rearrange after the annealing process and the responsivity rises to about 10-2 amperes/watt In the third part of the experiment we fabricated InGaO TFT with silicon oxide gate dielectric layer The optimized parameters of In0 9Ga0 1O TFT is fabricated under pO2= 20% The field effect mobility is 434 9 cm2/V?S Ion/Ioff ratio is 5 order and SS is 0 31V/decade In addition we compare the difference of TFTs produced by various indium to gallium ratio targets When the proportion of indium is too much the active layer becomes a conductor leading to large leakage current and the TFR cannot be turned off On the other hand when the proportion of gallium is too much the device becomes dielectric In this way the device performs satisfactory Ion/Ioff ratio but the mobility drops at the same time Therefore the ratio of indium to gallium is a very critical point on fabricating TFTs In the last part of the experiment we apply In0 9Ga0 1O in the extended gate field effect transistors because of its low-resistance The sensitivity is up to 56 24 uA / pH as VD = 3 43 7uA / pH as ID = 200 These values are superior to the EGFET published previously

Date of Award	2017 Jun 29
Original language	English
Supervisor	Shoou-Jinn Chang (Supervisor)