Kwansei Gakuin University
Report of Research Outcome
2024/03/13

To President
Department： Science and Technology
Position： Postdoctoral fellow
Name： Endah Kinarya Palupi
I report the outcome of the research as follows.
□Sabbatical leave with grantName of theFund/Prog ram□KGU Joint Research□Sabbatical leave with no grant□Individual Special Research⊠Postdoctoral fellow※ Please report by designated form as for “Inte rnational Research
Collaboration”.

ResearchTheme
Research
Site/Venue

Research
periodDevelopment of solution-processed oxide thin film transistor: electricalcharacterization of amorphous indium silicon oxide

Fujiwara Labo rato ry, Graduate School of Science and Technology

2023/04/01～

2024/03/31 （12month ）◆ Summary of the research outcome （ appr ox . 2 ,5 00 wo r ds）
Please write down the outcomes in detail regarding the research theme above.
While sputtered amorphous indium- gallium-zinc-oxide (IGZO) semic onductors dominate
industrial applications due to their uniformity and stability, s olution- processed alternatives
hold immense promis e. Solution processing offers advantages such as simplicity,
cost-effectiveness, homogeneity, and prec ise compos itional control. This alter nativeenables cost- effective production and scalability, making them ideal for next- generationelectr onic dev ices. The fascinating pr operties of oxide semiconductor s are delved into witha specific focus on indium silicon oxide (ISO) thin films. Silicon (Si) was introduc ed as adoping mater ial because of its high bond dissociation energy with oxygen (799 kJ/mol).
ISO films are dev eloped using a solution proc ess, which offers the potential for low-costand high-throughput manufacturing. The Fujiwar a Group has initial conc erns centeredaround fabr icating indium silicon oxide (ISO) thin films on a hydr ophilic substrate. The
outcome was nothing s hort of exhilar ating: a s uccessful deposition r esulting in a TFT witha mobility of 8.1 c m²/Vs. Solution processing was starting to liv e up to its promise. Ar med
with accomplishments in hydrophilic, we investigate hydrophobic substrates. Advantages
in ter ms of unifor mity, stability, and pr ocess compatibility are offered by depositing anoxide semiconductor thin film on hydrophobic substrates.
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These cons iderations contr ibute to improved TFT perfor manc e in display applications. My
stand on this research r oadmap was clear: delv e into the structural and electrical properties
of ISO fabricated on a hydrophobic substrate. Extensive r esearch was conducted on thedevice fabrication and post-fabrication treatment.
On devic e fabrication, material ex ploration on indium ox ide and silic on ratios results in
the ISO phase diagram; pur e indium oxide has a polycrystalline s tructure; by adding asilicon doping, s ilicon stabilizes the film str ucture to be an amorphous phase up to 8 at%;above 8 at% silic on doping, it forms a crystalline phas e. Based on the phas e diagram, thestructural model was constructed, and the optimum doped-s ilicon concentr ation wasestimated. In addition to the material ratios, the optimum film thick ness was ex plored byinvestigating spinning speed, spinning time, and lay ers. The optimum annealing
temperature is also determined by the investigation and analysis of the annealing
temperature dependence of crystallization temper atur es.
In the electric al investigation, FET measurements with post-fabric ation treatments wereconducted. The tr ansfer and output curves of ISO TFT dev ice show significant differences
between measurements just after fabrication and 14 days after fabrication. Parameterssuch as mobility, on/off ratio, and thr eshold voltage are analyzed from the transfer
character istics. O n 0th day, a high off-current and a significant negative value of V T H wereobserved. Negative V T H and high off-current will affect trans istor perfor mance and cancause operational pr oblems. After 14 days of storage, off-current decr eased and V T H shiftedin positive directions, indicating better dev ice operations. In addition to that, output
character istics are also analyzed, parameters such as total r esistanc e, contact res istance,and channel resistance are estimated. On 0th day, just a linear zone was observed, whileon the 14th day, the output character istics s how a linear and s atur ation z one, indicatingthat the device is oper ating as desired.
The differenc es between 0th day and 14th day are due to the formation of oxygen
vacancies as an impact of the v acuum treatment. In the fabr ication stage, the thermal
evapor ation deposition method was adopted for the deposited electrodes. This stage
requires a high vacuum at a high temper ature, and it is now known that this condition
causes an oxygen desorption phenomenon, which creates vacancies in the ISO system.
According to analysis of temporal evolution, this vacuum effect can be reduc ed by stor age
in air/ oxygen. Oxygen from the envir onment is adsorbed, res ulting in a decrease in oxygen
vacancies and allowing the devic e to operate with appr opr iate characteristics. The
reduction of oxygen vacancies on the transfer curve was indic ated by the increase in theon/off ratio and thr eshold voltage, which is shifting toward pos itive. Mobility doesn’t change
becaus e it is estimated by a similar slope. Meanwhile, the oxygen vacancies on the output
curve was indicated by a clearly observed linear relations between total r esistance (R T ) andchannel lengths (L). Fr om the s lope of the RT vs. L plot, channel res istanc e (R C H ) can be
estimated, and then contact res istance (R C ) c an be deter mined by extrapolating R T vs. L
relation to L = 0. Detailed relation between R C H and R C , and their gate voltage ( V G )dependenc e will c larify the effect of oxygen vacancy on the TFT dev ice perfor mance.
Deadline： Within two m onths after finishing the research pe riod.
Sabbatical leave with grant: Submit this report t o President with confirm ation by the dean ofschool you belong to.
※ Postdoctoral fellow is required to submit this report with confirmation by the dean of g raduate

school before the end o f employment period.
Where to submit： Orga nization for Research a nd Development and Ou treach (N UC)◆ We put this report o n t he web of KGU. If the re is any problem about it because of difficulties on
your research, please le t us know.
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