We studied annealing effects on perpendicular anisotropy in CoFeB-MgO magnetic tunnel junctions. The results show that annealing is an effective method to improve the perpendicular anisotropy of a CoFeB-MgO system. It is found that a thicker CoFeB layer requires a higher annealing temperature to buildup its perpendicular anisotropy. However, perpendicular anisotropy could be seriously degraded if the annealing temperature is more than 350 °C. Our study suggests that CoFeB thickness should be optimized so that the required annealing temperature window for perpendicular anisotropy could match the annealing temperature for high magnetoresistance. In this work, the perpendicular anisotropy energy density of 2.5 × 106 erg/cm3 was achieved with tunnel magnetoresistive value exceeding 70%. The use of CoFeB films will enable the development of high density nonvolatile memory with size down to 30 nm.

Annealing effects on CoFeB-MgO magnetic tunnel junctions with perpendicular anisotropy

Two conjugated polymers based on poly(phenylenethiophene) and poly (fluorenethiophene) main chain functionalized with pendant trithiocyanato ruthenium terpyridine complexes were synthesized by the Suzuki coupling reaction. The ruthenium complexes can extend the absorption band to longer wavelength and enhance the photosensitivity in this region. The polymers exhibit very broad absorption band spanning from 400 to 750 nm due to the presence of π-conjugated system and the ruthenium complexes. Such enhancement in optical absorption enables the utilization of solar light in the near IR region. By space charge limited current modeling, the hole carrier mobilities of the polymers were calculated to be in the order of 10−4 cm2 V−1 s−1, which greatly facilitate the transport of charges after the separation of excitons. Heterojunction photovoltaic cells with simple structure ITO/polymer/C60/Al were fabricated. Under simulated AM1.5 solar light illumination, the short circuit currents, open circuit voltages, and power conversion efficiencies of the photovoltaic cells were measured to be 1.53–2.58 mA cm−2, 0.12–0.24 V, and 0.084–0.12%, respectively. Deposition of PEDOT:PSS on ITO surface did not show significant difference in device performance. Plot of incident photon to charge efficiency as the function of wavelength suggests that absorption by both conjugated main chain and ruthenium complex are essential to the photocurrent generation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1305–1317, 2008

Synthesis of conjugated polymers with pendant ruthenium terpyridine trithiocyanato complexes and their applications in heterojunction photovoltaic cells

In this paper, we propose an analytic model for inverted-staggered organic thin-film transistors, and we use the proposed model to investigate the dependence of contact effect on the voltage bias, the film thickness of the organic semiconductor, and the channel length In our model, the variable-range-hopping transport is adopted for the conduction in the horizontal direction to the semiconductor-insulator interface, and the space-charge-limited conduction is adopted for the conduction in the vertical direction by considering the molecular orientations Qualitative agreement is obtained between simulation and measurement in the steady-state characteristics From simulation study, we notice that the contact resistances vary with the source-gate voltage and with the source-drain voltage, the film thickness requires to be optimized to improve the on-current and the linearity in the linear operating regime, and the overlap length between the gate electrode and the source/drain contact needs to be guaranteed for the short-channel devices because it would not be scaled as much as the channel length

Analysis of Contact Effects in Inverted-Staggered Organic Thin-Film Transistors Based on Anisotropic Conduction

We report on the investigations of the differences in the measured current characteristics of source/drain top contact (TOC) and bottom contact (BOC) organic field-effect transistors (OFETs). The active layer was made from poly[1,4-phenylene-(4-methylphenyl)imino-4,48-diphenylene-(4-methylphenyl)imino-1,4-phenylenevinylene-2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene] and a highly doped silicon wafer with a thermal oxide was used for the gate and the insulator, respectively. Both transistors show a good subthreshold behavior characterized by a threshold voltage of Vth≈−5 V and an inverse subthreshold increase of S≈0.25 V∕dec. The estimated mobility is in the range of 10−3 cm2∕V s. The main difference between the TOC and the BOC transistors is a nonlinear increase of the drain current at small drain voltages in the output characteristics of the TOC OFETs. Numerical two-dimensional simulations show that a high concentration of donor-like traps with a Gaussian or exponential distribution are the reas...

Influence of traps on top and bottom contact field-effect transistors based on modified poly(phenylene-vinylene)

How small the contacts could be optimal for nanoscale organic transistors

The horizontal and vertical hole mobility of amorphous spin-coated electroluminescent conjugated films are studied. It is found that the horizontal mobility is about four orders of magnitude larger than the vertical mobility. The horizontal mobility increases daily with the aging of the polymer solution from which the film is spun. Low temperature and photoluminescence study reveal that the giant mobility anisotropy is a result of the alignment of the aggregates, formed during aging, by the centrifugal force of the spin.

https://ir.nctu.edu.tw:443/bitstream/11536/12746/1/000234606900080.pdf

Kuo-Chen Tzeng

Papers

Giant anisotropy of carrier mobility in electroluminescent conjugated polymer