Development of ITO/TIO2/PDY-132/Al polymer tunnel diode fabrication process
Ahl, Noa (2026)
2026
Sähkötekniikan DI-ohjelma - Master's Programme in Electrical Engineering
Informaatioteknologian ja viestinnän tiedekunta - Faculty of Information Technology and Communication Sciences
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Hyväksymispäivämäärä
2026-05-04
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202605044842
https://urn.fi/URN:NBN:fi:tuni-202605044842
Tiivistelmä
This master’s thesis investigated the development and optimization of a fabrication process of a polymer tunnel diode. A tunnel diode is a semiconductor device that exploits quantum mechanical tunnelling and exhibits negative differential resistance (NDR), enabling applications in high-frequency oscillators, fast switching circuits, and low-power memory elements.
The objective of this work was to study the influence of titanium dioxide (TiO2) layer thickness on the electrical properties of tunnel diodes based on the indium tin oxide (ITO) / titanium dioxide (TiO2) / PDY-132 polymer / aluminum structure. TiO2 tunnelling layers were deposited by atomic layer deposition (ALD) at three temperatures (250 °C, 275 °C, and 300 °C). Film properties were characterized using ellipsometry, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS).
The most significant finding of this work was the critical importance of contamination control in the fabrication of functional devices. XPS analysis revealed that Kapton tape caused approximately 7–9 at.% silicon contamination in the TiO2 films at ALD temperatures. This contamination resulted in poor measurement reproducibility, electrical noise, and low peak-to-valley current ratios (PVCR < 5). Elimination of this contamination source through the adoption of a metal mask was the critical enabling step for functional device fabrication, improving PVCR values by up to an order of magnitude.
Unexpectedly, the highest PVCR values (for individual device 20–30) were achieved at 6 nm TiO2 thickness rather than at the thinnest 4 nm layer, deviating from the exponential tunnelling probability dependence predicted by conventional tunnelling theory, though the precise reason for this optimum remains unresolved. Capacitance-voltage measurements reveal a double-dip profile consistent with two electrically active junctions, tentatively assigned to the TiO2/PDY-132 and Al/PDY-132 interfaces. Reference samples without the TiO2 layer also exhibited NDR (PVCR 5–6) in some cases, though with substantial batch-to-batch variation, suggesting that the TiO2 layer enhances and stabilizes an NDR phenomenon already present in the ITO/PDY-132/Al stack, the precise origin of which remains an open question.
The objective of this work was to study the influence of titanium dioxide (TiO2) layer thickness on the electrical properties of tunnel diodes based on the indium tin oxide (ITO) / titanium dioxide (TiO2) / PDY-132 polymer / aluminum structure. TiO2 tunnelling layers were deposited by atomic layer deposition (ALD) at three temperatures (250 °C, 275 °C, and 300 °C). Film properties were characterized using ellipsometry, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS).
The most significant finding of this work was the critical importance of contamination control in the fabrication of functional devices. XPS analysis revealed that Kapton tape caused approximately 7–9 at.% silicon contamination in the TiO2 films at ALD temperatures. This contamination resulted in poor measurement reproducibility, electrical noise, and low peak-to-valley current ratios (PVCR < 5). Elimination of this contamination source through the adoption of a metal mask was the critical enabling step for functional device fabrication, improving PVCR values by up to an order of magnitude.
Unexpectedly, the highest PVCR values (for individual device 20–30) were achieved at 6 nm TiO2 thickness rather than at the thinnest 4 nm layer, deviating from the exponential tunnelling probability dependence predicted by conventional tunnelling theory, though the precise reason for this optimum remains unresolved. Capacitance-voltage measurements reveal a double-dip profile consistent with two electrically active junctions, tentatively assigned to the TiO2/PDY-132 and Al/PDY-132 interfaces. Reference samples without the TiO2 layer also exhibited NDR (PVCR 5–6) in some cases, though with substantial batch-to-batch variation, suggesting that the TiO2 layer enhances and stabilizes an NDR phenomenon already present in the ITO/PDY-132/Al stack, the precise origin of which remains an open question.