Charge Injection Into Bottom-Contact Pentacene Thin-Film Transistors
- PDF / 689,485 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 79 Downloads / 311 Views
0937-M07-29
Charge Injection Into Bottom-Contact Pentacene Thin-Film Transistors Yi Hong1, Feng Yan1, Piero Migliorato1, S. H. Han2, and Jin Jang2 1 Engineering Department, University of Cambridge, Cambridge, CB3 0FA, United Kingdom 2 Advanced Display Research Center, Kyung Hee University, Seoul, 130-701, Korea, Republic of
ABSTRACT We investigate the contact of bottom-contact pentacene-based thin-film transistors, with Au source/drain electrode. By separating the voltage drop at the contact from the source-drain voltage, the current-voltage characteristic of the injection contact is obtained. The contact characteristics are in a good agreement with a model of carrier injection from a metal electrode into a disordered hopping system. INTRODUCTION The structures of pentacene-based thin-film transistors (TFT) are top-contact and bottom contact (BC). BC TFT is more suitable for fabrication but its performance suffers from the poor contact between source/drain (S/D) electrode and channel. The physical nature of the contact has been widely investigated, including imaging the potential profile of TFT with scanning Kelvin probe microscopy (SKPM) [1-3], extracting contact resistance from device characteristic [4], transmission line method [5], four-terminal measurement [6,7], and 2D electrostatic modeling [8]. Some suggested that the presence of more disordered region near S/D was responsible for the parasite resistance in BC pentacene TFT [9]. Also, the barrier between S/D and pentacene can hamper carrier injection into the channel. Ultraviolet photoelectron spectroscopy (UPS) measurements on Au and pentacene have revealed a hole injection barrier of 0.47 eV [10]. Carrier injection from an electrode into a semiconductor is commonly modeled in the framework of thermionic emission theory [11,12] which does not take into account the energetic disorder in organic semiconductors. A more sophisticated model based on thermally assisted tunnelling of carriers from an electrode into a random hopping system was developed by Arkhipov et al. [13,14]. It was successfully applied in the modeling of the injection current for organic light-emitting-diodes [13,15] and more recently for poly(3-hexylthiophene) (P3HT) TFT [16]. In this work, we measure the characteristics of BC pentacene TFT with Au S/D electrode. By separating the voltage drop at the contact from the source-drain voltage [4], the currentvoltage characteristics of the injection contact are extracted and fitted well with the above hopping injection model. The fitting to Richardson-Schottky emission model was also presented. EXPERIMENT The devices used are Au source/drain electrode, bottom-contact, bottom gate pentacene TFT. AlNd is deposited as gate electrode on poly(ethersulfone) (PES) substrate. Cross-linked poly(4-vinylphenol) (PVP), 450 nm thick, is spin-coated as gate insulator. Cr/Au, 5 nm/50 nm
thick, is sputtered on PVP and then patterned for interdigitated S/D electrodes. After the surface treatment with octadecyltrichlorosilane (OTS), a 600 nm thick pentacene fil
Data Loading...
