Low voltage metal oxide transistors
Airio, Anna-Sofia (2020)
2020
Degree Programme in Electrical Engineering, MSc (Tech)
Informaatioteknologian ja viestinnän tiedekunta - Faculty of Information Technology and Communication Sciences
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Hyväksymispäivämäärä
2020-06-01
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202005215553
https://urn.fi/URN:NBN:fi:tuni-202005215553
Tiivistelmä
In this thesis the objective is to determine if a functional thin film transistor (TFT) with a bottom gate – top contact structure is possible to make with Evonik’s commercial semiconductor. Ixsenic is a solution processable indium oxide -based metal oxide semiconductor. Another goal is to determine how storing the transistor in different gases affects its performance and how the density of interface states is changed during the storing.
The transistors were optimized by changing the processing parameters concerning the semiconductor layer formation. The gate dielectric was deposited by anodization of Al and the semiconductor was deposited by spin-coating and annealed with ultraviolet (UV) light and hotplate. The optimized transistors have a mobility of 1-3 cm^2/Vs, on-off ratio of 10^4, subthreshold swing of 0,2-0,3 V/dec, threshold voltage of 0,9-1,4 V and gate leakage current of 0,7-3 µA. This compares favorably with Evonik’s reported mobility, up to 10 cm2/V·s, using Evonik’s spin-on dielectric.
Samples were stored either in nitrogen, or air, for two weeks to see the difference the gas has in the changes happening within the transistor. The on current of the transistor stored in air was an order of magnitude lower after storing and the off-current of the transistors stored in nitrogen rose considerably. A Matlab-code was developed to characterize changes in the density of interface states at the anodized Al and Ixsenic interface, but the work was not finished in this thesis.
The transistors made in this thesis have a high enough on-off ratio to be used in circuits. The mobility value is corrected with reliability calculations, which gives it more credibility. The work on the density of interface states should be continued to determine the changes happening in the interface while storing the transistors.
The transistors were optimized by changing the processing parameters concerning the semiconductor layer formation. The gate dielectric was deposited by anodization of Al and the semiconductor was deposited by spin-coating and annealed with ultraviolet (UV) light and hotplate. The optimized transistors have a mobility of 1-3 cm^2/Vs, on-off ratio of 10^4, subthreshold swing of 0,2-0,3 V/dec, threshold voltage of 0,9-1,4 V and gate leakage current of 0,7-3 µA. This compares favorably with Evonik’s reported mobility, up to 10 cm2/V·s, using Evonik’s spin-on dielectric.
Samples were stored either in nitrogen, or air, for two weeks to see the difference the gas has in the changes happening within the transistor. The on current of the transistor stored in air was an order of magnitude lower after storing and the off-current of the transistors stored in nitrogen rose considerably. A Matlab-code was developed to characterize changes in the density of interface states at the anodized Al and Ixsenic interface, but the work was not finished in this thesis.
The transistors made in this thesis have a high enough on-off ratio to be used in circuits. The mobility value is corrected with reliability calculations, which gives it more credibility. The work on the density of interface states should be continued to determine the changes happening in the interface while storing the transistors.