The long-term stability of pentacene thin-film transistors (TFTs) encapsulated with a transparent SnO2 thin-film prepared by ion-beam-assisted deposition (IBAD) was investigated. When a buffer layer of 100-nm SnO2 film had been thermally deposited to reduce ion-induced damage prior to the IBAD process, our encapsulated organic thin-film transistors (OTFTs) showed somewhat degraded field-effect mobility of 0.5 cm2 V that was initially 0.62 cm2 V s, while the OTFTs without a buffer layer showed a 60% reduction in field-effect mobility after the IBAD process. However, surprisingly, the mobility was sustained up to one month and then gradually degraded down to 0.35 cm2 V s, which was still three times higher than that of the OTFT without any encapsulation layer after 100 days in air. The encapsulated OTFTs also exhibited superior on/off current ratio of over 105 to that of the unprotected devices (∼ 104), which was reduced from ∼ 106 before aging. Therefore, the enhanced long-term stability of our encapsulated OTFTs should be attributed to good protection of permeation against H2 O into the devices with the IBAD SnO2 thin film, which was identified as having a dense amorphous microstructure with lots of OH groups. Passivation effects on the electrical properties of OTFTs are discussed in terms of the physical and chemical properties of the barrier films.
|Number of pages||6|
|Journal||Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures|
|Publication status||Published - 2005 Nov|
Bibliographical noteFunding Information:
Among the authors, J.L. and S.I. acknowledge financial support from KISTEP (Program No. M1-0214-00-0228) and the BK 21 Program. S.I. also appreciates the discussion with Professor H. W. Yeom for the XPS data. FIG. 1. (a) Schematic drawing of IBAD process. (b) Cross section of the device structure and photographic plan view (length L = 100 μ m , width W = 1000 μ m ). FIG. 2. (a) Output characteristics of reference OTFT after encapsulation. (b) Degradation of the drain current in the saturation regime when V G is − 40 V after 100 days in air. FIG. 3. Plots of − I D vs V G and Log 10 − I D vs V G for the OTFTs without encapsulation (a) and with encapsulation (b). FIG. 4. XPS spectra for O 1 s peaks obtained from the pentacene thin films before and after exposure to air for 100 days. (Inset: comparison of O 1 s peaks from H 2 O ). FIG. 5. Property-endurance limit or aging effect with time of our OTFTs in terms of field-effect mobility (a) and on/off current ratio (b). FIG. 6. (a) XRD results of polycarbonate (PC) as a substrate for reference and thermally evaporated oxide films on PC. (b) WVTR values of the oxides on PC substrates. FIG. 7. (a) XPS spectra for O 1 s peaks of SnO 2 and SiO x (left inset) and Sn 3 d 2 ∕ 3 and 3 d 2 ∕ 5 spectra (right inset) from the SnO 2 thin film prepared by IBAD. (b) Refractive index and according packing density of the oxides before and after the IBAD process. FIG. 8. AFM images and section analyses of 50 nm pentacene thin film (a) and 80 nm IBAD SnO 2 encapsulation layer on top of 100 nm SnO 2 buffer layer (b).
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Electrical and Electronic Engineering