Light scattering studies of organic field effect transistors

Adil, Danish

doi:10.32469/10355/42618

Cited by 1 publication

(2 citation statements)

References 73 publications

(88 reference statements)

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“…Details of the OTS SAM deposition can be found in previous works from our research group. 40 The OTS solution was prepared in a freshly cleaned and dried glassware. Glassware was cleaned using Liquinox Critical Cleaning Detergent (Alconox Inc.) and dried in a closed oven (Model 20 GC Lab Oven) at 120 o C. The glassware was then allowed to cool to room temperature before use.…”

Section: Substrate Preparationmentioning

confidence: 99%

“…It has been shown that the contact angle should be about 80 o . 40 A surface with a contact angle less than this is indicative of incomplete OTS coverage. If the above described protocol ever results in incompletely covered substrates during a particular session, it may be modified by dipping the substrates for a longer time (up to one minute).…”

Section: Substrate Preparationmentioning

confidence: 99%

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Polarization-induced transport in ferroelelctric organic field-effect transistors

Laudari¹

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In this research we study the role of ferroelectric dielectrics in organic field-effect transistors (FETs) to understand the mechanism of charge transport in organic semiconductors. The ferroelectric nature of the polymer, poly(vinylidene fluoride) (PVDF)), has been known for over 45 years. However, its role in interfacial transport in organic/polymeric FETs is not that well understood. PVDF and its copolymer, polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE), as a dielectric in organic FETs is a perfect test-bed for conducting transport studies where a systematic tuning of the dielectric constant with temperature may be achieved. By choosing small molecule organic semiconductors -- pentacene and 6,13 bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) -- along with a copolymer PVDF-TrFE as the dielectric layer, the FET characteristics are monitored as a function of temperature. Pentacene FETs show a weak temperature dependence of the charge carrier mobility in the ferroelectric phase of PVDF-TrFE, which is attributed to polarization fluctuation driven transport resulting from a coupling of the charge carriers to the surface phonons of the dielectric layer. A negative coefficient of carrier mobility is observed in TIPS-pentacene upwards of 200 K with the ferroelectric dielectric, while an activated transport is observed with non-ferroelectric dielectrics. We show that this behavior is correlated with the nature of the trap states in TIPS-pentacene. We also developed the method of dipole engineering of the PVDF-TrFE films to enhance the properties of organic FETs. PVDF-TrFE, despite its applications in a vast range of work (including as a gate dielectric in organic FET and sensing applications) poses concerns such as higher conductivity compared to other polymer non-ferroelectric dielectrics. We have come up with new methods of electrical poling the dielectric layer to enhance FET performance as well as reduce gate leakage issues. We demonstrate the effect of polarization rotation in PVDF-TrFE on the performance of small-molecule-based organic FETs. The subthreshold swing and other transistor parameters in organic FETs can be controlled in a reversible fashion by switching the polarization direction in the PVDF-TrFE layer. We further demonstrate a novel method of selective poling of the dielectric layer. By using solution processed TIPS-pentacene as the organic semiconductor, it is shown that textured poling of the PVDF-TrFE layer dramatically improves FET properties compared to unpoled or uniformly poled ferroelectric films. The texturing is achieved by first vertically poling the PVDF-TrFE film and then laterally poling the dielectric layer close to the gate electrode. TIPS-pentacene FETs show on/off ratios of 105 and hole mobilities of 1 cm2/Vs under ambient conditions with operating voltages well below-4 V. This research opens prospects of achieving low-operating FETs without any expensive patterning techniques.

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Section: Substrate Preparationmentioning

confidence: 99%

Section: Substrate Preparationmentioning

confidence: 99%