| PhD Viva

Name of the Speaker: Fiheon Imroze (EE16D301)
Guide: Dr. Soumya Dutta
Online meeting link: https://meet.google.com/dhq-tnbc-avp
Date/Time: 22nd August 2022, 3:15 PM
Title: Charge injection-assisted performance improvement of solution-processed organic field-effect devices

Abstract

Solution-processed organic field-effect devices have been a low-cost alternative to conventional device technologies specifically for low-frequency flexible electronics, rigid electronics, and specific large area applications. Organic metal-insulator-semiconductor capacitors (OMISCAP) and organic thin-film transistors (OTFT) are fundamental building blocks in organic circuits. It is required to counter some fundamental limitations in OMISCAP and OTFT, i.e., frequency response, mobility, and contact effect. These fundamental limitations exist due to inferior charge injection from the metal to the semiconductor bulk.

In the first part of the presentation, the frequency response of an OMISCAP will be discussed. The cut-off frequency of dispersion (f­T) for an OMISCAP typically decides the bandwidth of organic field-effect devices, which is a crucial parameter for circuits. The f­T dependency on the dielectric constant of polyvinyl-4-phenol (PVP) polymer dielectric and on the injection barrier at the metal-semiconductor interface will be discussed. Impact of charge injection through the metal-semiconductor interface is equally important in deciding the performance of OTFT in terms of contact resistance, mobility etc. which will be discussed in the second part of the presentation. Typically, in solution-processed bottom gate bottom contact (BGBC) OTFT, the metal thickness elevated above the substrate leads to poor morphology and thus high contact resistance. Contact resistance usually leads to deterioration of performance such as high switch-on voltage and hysteresis, which are the fundamental bottleneck for circuit applications. The ways to mitigate the contact resistance by varying the electrode thickness and fabricating recessed electrodes on polymer dielectric will be discussed further. The planar OTFT substrate by fabricating the recessed source, drain and gate was found to reduce the contact resistance by two orders and improve the mobility by three-fold along with a significant reduction in hysteresis and switch-on voltage close to zero.