Pentacene thin film transistors on inorganic dielectrics: Morphology, structural properties, and electronic transport

Abstract

The structural and transport properties of evaporated pentacene organic thin film transistors (TFTs) are reported, and they show the influence of the deposition conditions with different inorganic dielectrics. Dielectrics compatible with large area fabrication were explored to facilitate low cost electronics on glass or flexible plastic substrates. X-ray diffraction and atomic force microscopy show a clear correlation between the morphology and the structure of the highly polycrystalline films for all dielectrics investigated. The roughness of the dielectric has a distinct influence on the morphology and the structural properties, whereas the films on smooth thermal oxide are in general highly ordered and independent of the deposition conditions. The ordered films exhibit a “thin film” and a bulk phase, and the bulk phase volume fraction increases with the deposition temperature and the film thickness. Careful control of the deposition conditions gives virtually identical films on thermal oxide and silicon nitride dielectrics. The electronic properties of inverted staggered transistors show that the TFT mobility is correlated with the morphology and structure of the films. The TFTs exhibit very similar mobilities of ∼0.4 cm2/Vs and on/off ratios >108 on thermal oxide and silicon nitride. The impact of the dielectric on the device parameters of mobility, threshold voltage, and subthreshold voltage slope is discussed. Temperature dependent measurements of the mobility were performed to study the influence of traps on electronic transport. Bias stress experiments were carried out to investigate the stability of the TFTs, and to gain understanding of the transport mechanisms of thermally evaporated pentacene TFTs.

Threshold voltage shift in organic field effect transistors by dipole monolayers on the gate insulator

“…The film morphology has been shown to influence the charge carrier mobility [4][13] [22] [23]. Especially the morphology of the first few monolayers where charge transport occurs [9][24] is expected to strongly influence the mobility [23] [25].…”

“…In addition to the charge carrier mobility, the threshold voltage (V t ) is an important parameter that needs to be controlled to ensure proper operation of the circuits. The threshold voltage can depend on the time a gate voltage has been applied (bias stress) [4][5] [6] [7] [8], on the exposure of the device to light [9] or it can be shifted using a polarizable gate insulator [10]. Furthermore, a dependence on the work function of the gate electrode [11] and the thickness of the active layer material [12] has been reported.…”

Evidence of water-related discrete trap state formation in pentacene single-crystal field-effect transistors

“…Bias stress measurements can provide insight on charge trapping. [1][2][3][4][5] For example, the formation of a hydrogen-related metastable hole trap in pentacene under bias stress has been reported. 6 An important aspect of charge trapping in organic semiconductors is the influence of ambient conditions.…”

Effect of curing conditions of a poly(4-vinylphenol)gate dielectric on the performance of a pentacene-based thin film transistor

“…Many groups have reported field-effect mobilities greater than 1 cm 2 /Vs for OFETs in which pentacene is used as the active layer. [1][2][3][4] The surface characteristics of the gate dielectric strongly influence the quality of the gate dielectric-semiconductor interface hence the device performance. [5][6][7] In the last decade, considerable effort has been devoted to the fabrication of OTFTs using organic gate dielectrics [8][9][10][11][12] for use as switching devices for flexible displays.…”