Date of Award

Summer 2004

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Micro and Nanoscale Systems

First Advisor

Kody Varahramyan

Abstract

The objectives of this project are to fabricate, characterize, and model organic microelectronic devices by traditional lithography techniques and Technology Computer Aided Design (TCAD).

Organic microelectronics is becoming a promising field due to its number of advantages in low-cost fabrication for large area substrates. There have been growing studies in organic electronics and optoelectronics. In this project, several organic microelectronic devices are studied with the aid of experimentation and numerical modeling.

Organic metal-insulator-metal (MIM) and metal-insulator-semiconductor (MIS) capacitors consisting of insulating polymer poly(4-vinylphenol) (PVP) have been fabricated by spin-coating, photo lithography, and reactive ion etching techniques. Based on the fabricated devices, the dielectric constant of the (PVP) is calculated to be about 5.6–5.94. The MIS capacitor consisting of organic semiconductor pentacene has been investigated. The hole concentration of pentacene is determined to be around 8 × 1016 cm −3.

Schottky diodes consisting of aluminum and a layer of p-type semiconducting polymer poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) have been fabricated. Based on the current-voltage (I-V) and capacitance-voltage (C-V) measurements, the temperature dependence of hole mobility in MEH-PPV has been extracted by the space-charge limited conduction (SCLC) model, from 300 to 400 K. Moreover, the value of the effective hole density for MEH-PPV has been determined to be 2.24 × 1017 cm−3. Numerical simulations have been carried out to identify the parameters which affect the performance of devices significantly.

Organic n- and p-channel field-effect transistors (FETs) have been designed and fabricated. By using Naphthalene-tetracarboxylic-dianhydride (NTCDA) as an organic semiconductor, n-channel FETs have been fabricated and characterized. At room temperature, the device characteristics have displayed electron mobility of 0.016 cm2/Vs, threshold voltage of −32 V, and on/off ratio of 2.25 × 102. Pentacene, an organic semiconductor offering high device performance, has been employed to fabricate the p-channel FETs. At room temperature, the device characteristics have displayed hole mobility of 0.26 cm2/Vs, threshold voltage of −3.5 V, subthreshold slope of 2.5 V/decade, and on/off ratio of 105. The temperature and field dependence of mobility has been studied based on the experimental results. Based on numerical simulations, the influence of bulk traps has also been identified, and the field-dependent mobility model has been used to obtain more accurate simulation results. Furthermore, electrostatically assembled monolayer (poly(dimethyldiallylammonium chloride) (PDDA)) is introduced at the organic/insulator interface to improve the performance of the FETs.

The efforts carried out in this work appear to be the first reported attempt at the investigation of the temperature dependence of mobility for the given organic devices, and the surface modification of organic FETs by electrostatically assembled monolayer.

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