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Kim, Hyunwoo,Kim, Sangsub,Kim, Hyunki,Lee, Jaeseob,Kim, Sangsoo,Choi, Byoungdeog American Scientific Publishers 2017 Journal of Nanoscience and Nanotechnology Vol.17 No.10
<P>We investigated the electrical properties of solution-processed nanolaminates composed of zirconium oxide (ZrO2) and aluminum oxide (Al2O3) as gate insulator materials for thin-film transistors (TFTs). We fabricated MOS capacitors using Al2O3/ZrO2/Al2O3 and ZrO2/Al2O3/ZrO2 nanolaminate stacks through solution processing. The fabricated nanolaminates showed low leakage current densities and high dielectric constants. Also, solution-processed InSnZnO (ITZO) TFTs were fabricated on nanolaminates. Among these devices, the Al2O3/ZrO2/Al2O3 stack showed the best performance in terms of its switching operation, with a high on/off current ratio (>10(6)), high mu(sat) (0.28 cm(2)/Vs), and low subthreshold swing (0.25 V/dec). The superior characteristics of these nanolaminates originated from the high dielectric constant of ZrO2 (>20) and the high band gap energy of Al2O3 (8.9 eV), which generates a large band offset between the gate insulator and active layer to effectively block the leakage current.</P>
Kim, Sangsub,Choi, Pyungho,Kim, Hyunki,Kim, Soonkon,Shin, Junyong,Lee, Jaeseob,Kim, Sangsoo,Choi, Byoungdeog American Scientific Publishers 2017 Journal of Nanoscience and Nanotechnology Vol.17 No.10
<P>In this research, we investigated the interface traps of poly-Si TFTs using charge pumping methods and analyzed effect of hot carrier stress by comparing interface trap distribution. These methods applied three types of pulse shapes, which were square, triangular, and trapezoidal. The interface state density, D-it, was measured by varying the frequency, pulse amplitude, and rise/fall times from the square pulse method. We found that Dit decreased due to the decreasing recombination of trapped carriers, and the majority carriers decreased by thermal emission depending on the temperature. We also confirmed the relation between space charge region and source-drain region according to reverse bias. Additionally, the mean interface-state density and capture cross-section, Q(ss), were extracted from the recombined charge versus pulse frequency curve created by the triangle pulse method. To explain the effects of the HC stress of poly TFTs, the interface trap states were measured before and after application of the hot carrier stress. The experimental results showed that the capture cross-section was doubled from 1.1 x 10(-14) cm(2) to 2.27 x 10(-14) cm(2) and interface trap distribution was changed after the HC stress. Finally, we confirmed that, after applying the hot carrier stress, the energy distribution of the interface state reflected the location of the induced damage region caused by the hot carrier stress and the observed shift of deep trap states affected the drain current in the subthreshold region and increased the subthreshold swing.</P>
Kim, Soonkon,Choi, Pyungho,Kim, Sangsub,Park, Hyoungsun,Baek, Dohyun,Kim, Sangsoo,Choi, Byoungdeog American Scientific Publishers 2016 Journal of nanoscience and nanotechnology Vol.16 No.5
<P>We investigated the carrier transfer and luminescence characteristics of organic light emitting diodes (OLEDs) with structure ITO/HAT-CN/NPB/Alq(3)/Al, ITO/HAT-CN/NPB/Alq(3)/Liq/Al, and ITO/HAT-CN/NPB/Alq(3)/LiF/Al. The performance of the OLED device is improved by inserting an electron injection layer (EIL), which induces lowering of the electron injection barrier. We also investigated the electrical transport behaviors of p-Si/Alq(3)/Al, p-Si/Alq(3)/Liq/Al, and p-Si/Alq(3)/LiF/Al Schottky diodes, by using current-voltage (I-V) and capacitance-voltage (C-V) characterization methods. The parameters of diode quality factor n and barrier height phi(b) were dependent on the interlayer materials between Alq(3) and Al. The barrier heights phi(b) were 0.59, 0.49, and 0.45 eV, respectively, and the diode quality factors n were 1.34, 1.31, and 1.30, respectively, obtained from the I-V characteristics. The built in potentials V-bi were 0.41, 0.42, and 0.42 eV, respectively, obtained from the C-V characteristics. In this experiment, Liq and LiF thin film layers improved the carrier transport behaviors by increasing electron injection from Al to Alq(3), and the LiF schottky diode showed better I-V performance than the Liq schottky diode. We confirmed that a Liq or LiF thin film inter-layer governs electron and hole transport at the Al/Alq(3) interface, and has an important role in determining the electrical properties of OLED devices.</P>
Choi, Pyungho,Kim, Hyunjin,Kim, Sangsub,Kim, Soonkon,Javadi, Reza,Park, Hyoungsun,Choi, Byoungdeog American Scientific Publishers 2016 Journal of nanoscience and nanotechnology Vol.16 No.5
<P>In this study, pulse frequency and reverse bias voltage is modified in charge pumping and advanced technique is presented to extract oxide trap profile in hot carrier stressed thin gate oxide metal oxide semiconductor field effect transistors (MOSFETs). Carrier trapping-detrapping in a gate oxide was analyzed after hot carrier stress and the relationship between trapping depth and frequency was investigated. Hot carrier induced interface traps appears in whole channel area but induced border traps mainly appears in above pinch-off region near drain and gradually decreases toward center of the channel. Thus, hot carrier stress causes interface trap generation in whole channel area while most border trap generation occurs in the drain region under the gate. Ultimately, modified charge pumping method was performed to get trap density distribution of hot carrier stressed MOSFET devices, and the trapping-detrapping mechanism is also analyzed.</P>
Choi, Pyungho,Kim, Dongsoo,Kim, Sangsub,Kim, Hyunwoo,Choi, Byoungdeog American Scientific Publishers 2016 Journal of nanoscience and nanotechnology Vol.16 No.10
<P>In this study, we characterized the interface and oxide charge generation in p-MOSFETs under negative bias temperature stress (NBTS). Thin (2.5 nm) and thick (6 nm) gate oxide MOSFETs were utilized to induce direct and Fowler-Nordheim (FN) tunneling, respectively. The threshold voltage and subthreshold swing in the thick oxide MOSFET was more significantly affected by NBTS than that of the thin oxide MOSFETs. The direct-current current-voltage (DCIV) method was implemented to investigate changes in trapped charges at the SiO2/Si interface. The change in oxide charges in the SiO2 bulk was obtained from the midgap voltage shift. The interface and oxide charges are predominantly affected by FN tunneling with less impact from direct tunneling, because of not only the hole-induced impact ionization at the SiO2/Si interface, but also the larger number of broken hydrogen atoms from the Si-H bonds, which are induced by the high applied gate bias. We conclude that devices' electrical performance can be significantly degraded when the MOSFETs are predominantly affected by FN tunneling rather than by direct tunneling under NBTS.</P>