Organic Thin-Film Transistor Technology: Properties and Functionality - Analog Organic Electronics - page 20

(a) (b)

Gate Gate

Insulator Insulator

S D

Semiconductor Source Semiconductor Drain

Substrate Substrate

(c) (d)

S D

Semiconductor Source Semiconductor Drain

Insulator Insulator

Gate Gate

Substrate Substrate

Fig. 2.2 The four implementations of a four-layer TFT. a The top-gate architecture with source
and drain contacts on top of the semiconductor. b The top-gate architecture with source and drain
contacts below the semiconductor. c The bottom-gate architecture with source and drain contacts
on top of the semiconductor. d The bottom-gate architecture with source and drain contacts below
the semiconductor

2.2.1 Pentacene

Pentacene (C 22 H 14 ) is an organic small molecule, more specifically a polycyclic
aromatic hydrocarbon that consists of five fused benzene rings, as can be seen on
the drawing in Fig. 2.3 a. The benzene rings are fused in a linear chain and form a
planar molecular structure in which the delocalized electrons can move freely. An
atomic forcemicroscopic photograph of the pentacenemolecule is shown in Fig. 2.3 b.
The uncomplicated structure of the molecule enables a tight molecule stacking in a
planar herringbone crystal structure, as visualized in Fig. 2.3 c. This two-dimensional
herringbone crystal structure is further stacked in the third dimension.