Flexible Organic Transistors for E-Textile and Memory Applications
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Date
2023-11-04
Researcher
Rahi, Sachin
Supervisor
Tiwari, Prakash
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Publisher
Indian Institute of Tehcnology Jodhpur
Abstract
Flexible electronics has been explored as a low cost technology for numerous applications such as wearable devices, foldable displays, and E-textiles, etc. and offers advantages such as large area applicability, low temperature processing, and adaptability for heterogeneous integration. Organic field effect transistor (OFET) is a crucial device for flexible electronics, which has been explored for various circuit, sensing, and memory applications. Gate dielectric is a crucial component for optimization to achieve high performance and stability in OFETs. This work demonstrates OFET devices with various dielectric combinations for circuit and memory applications. Moreover, a unique strategy for fabrication of devices on textile substrates is demonstrated. To start with, flexible OFETs were demonstrated with bilayer hybrid gate dielectric with various polymers and polyelectrolyte dielectrics such as P(VDF-TrFE), PVP-co-PMMA and polyelectrolyte polyacrylic acid (PAA) in combination with a thin layer of high-k hafnium oxide (HfOx) grown by atomic layer deposition (ALD). TIPS-Pentacene was used as semiconductor. The optimized devices operated at -10 V with decent Ion/Ioff values ranging from ~104 to ~103. The devices with HfOx/PAA dielectric exhibited better performance compared to other counterparts due to higher capacitance density, along with excellent cyclic stability for continuous 500 cycles. Moreover, these devices showed high bending stability upon different radii up to 5 mm causing tensile stress. Further, a bilayer of polyvinyl alcohol (PVA)/(PAA) was used as gate dielectric to demonstrate low voltage high-performance flexible OFETs on a plastic and paper substrate. A super strong hydrogen bonding between PVA and PAA confirmed by fourier-transform infrared (FTIR) spectroscopy makes it a potential solution-processed bilayer dielectric candidate. Fabricated devices with TIPS-Pentacene: PS blend exhibited -5 V operation with nearly zero threshold voltage and high Ion/Ioff of ∼104. High bending stability was achieved upon successive bending in different ways. These devices were also used to demonstrate resistive-load inverter circuit. The devices fabricated on paper showed a significant level of disintegration in soil with a bio fertilizer. OFET devices on fabric substrate were successfully demonstrated by a simple lamination technique. These devices with TIPS-Pentacene:PS blend as active layer and high-k P(VDF-TrFE) gate dielectric showed maximum and average field effect mobility of ∼1.2 and ∼0.5(±0.3) cm2 V-1 s-1 in the saturation regime, and Ion/Ioff of ∼103 with an low operating voltage of -5 V along with excellent bending stability. Excellent cyclic stability for 500 cycles was performed. Moreover, a high shelf life in ambient for 26 weeks was observed from these devices. Finally, solution-processed flexible non-volatile memory (NVM) based on OFETs (OFETNVMs) were demonstrated with TIPS-Pentacene and P(VDF-TrFE) as gate dielectric. These OFET-NVMs showed excellent memory behaviour with very high memory window (MW) of 12 V for VGS sweep of ±15 V and low VDS of -5 V. Moreover, these devices show memory Ion/Ioff ∼103 for 100 continues cycles alongwith stable retention capability for higher than 104 s. These devices showed fairly stable and reliable NVM behaviour even after subjected to 100 repeated bending cycles. Despite of fact that minimal degradation in performance was observed upon bending. These devices are promising candidate for further exploration into flexible electronics due to overall excellent memory performance of the devices.
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Citation
Rahi, Sachin(2019).(PhD)Flexible Organic Transistors for E-Textile and Memory Applications,Indian Institute of Tehcnology Jodhpur