Studies on field effect transistors with conjugated polymer and high permittivity gate dielectrics using pulsed plasma polymerization

by Yifan Xu

Institution: The Ohio State University
Department: Electrical Engineering
Degree: PhD
Year: 2005
Record ID: 1761167
Full text PDF: http://rave.ohiolink.edu/etdc/view?acc_num=osu1124219179


The aim of this Ph.D. project is to explore the operating mechanism of polymer field effect transistors (PFETs) to improve their performance. This dissertation presents thin film insulators as new gate dielectric materials to relax the requirement for driving voltages and illustrates some unique features of field dependent mobility in PFETs. Light responsive PFETs based on new polymer semiconductors are also demonstrated as a potential application of PFETs. Pulsed plasma deposited polymer insulating films were investigated for their potential application as the gate dielectric in PFETs. The work on pulsed plasma polymerized (PPP) thin film insulators put emphasis on improving the dielectric constant of the thin polymer films. Early work on PPP allylamine films indicated that the chamber temperature during pulsed plasma polymerization has an effect on the dielectric constant. The dielectric constant, calculated from the C-V data, rose from 3.03 for samples with no heat treatment to 3.55 for samples with an in-situ heat treatment. Later work on PPP dichlorotetramethyldisiloxane (DCTMDS) films demonstrated very high dielectric constants for an organic-based system, in the range of 7 to 10. Poly(3-hexythiophene) (P3HT) FETs using PPP DCTMDS gate dielectric films were fabricated and tested. The field dependent mobility was demonstrated in polythiophene (PT) FETs by varying the gate length. The field effect mobility in polythiophene FETs increases with reduced channel lengths for high driving forces across the source and drain. The longitudinal electric field (across source and drain) dependence of the field effect mobility is believed to create the rise in mobility once the longitudinal electric field exceeds a critical value of 100 KV/cm. The photoresponse of PFET based on the 2,5-bis(dibutylaminostyryl)-1,4-phenylene-b-alkyne-b-1,4-bis(2-ethylhexyl)benzene terpolymer (BAS-PPE) was also investigated. A sweep of VDS shows that BAS-PPE favors hole injection and transport. A sweep of VGS shows an increase in IDS with different light intensities. Overall, this dissertation studied features of PFETs and suggested techniques to improve their performance, which hopefully will contribute to future progress of polymer electronics.