Daniel Siu-Hung Chan

Volatile electrical switching in a functional polyimide containing electron-donor and -acceptor moieties

A solution-processable functional polyimide (PYTPA-PI), containing triphenylamine-substituted diphenylpyridine moieties (PYTPA, electron donors) and phthalimide moieties (PI, electron acceptors), was synthesized. The copolymer exhibits a high glass transition temperature of 342u2009°C. A switching device, based on a solution-cast thin film of PYTPA-PI sandwiched between an indium-tin oxide (ITO) bottom electrode and an Al top electrode, exhibits two accessible conductivity states and can be switched from the low-conductivity (OFF) state to the high-conductivity (ON) state, with an ON/OFF current ratio of more than 103, at the threshold voltage of about 2.7 V. The ON state is volatile and relaxes readily to the OFF state. However, it can be electrically sustained by a refreshing voltage pulse of 2 V. The ON state can also be reset to the initial OFF state by a reverse bias of −0.9 V. The ability to write, erase, read, and refresh the electrical states fulfills the functionality of a dynamic random access memor...

Extraction of metal-oxide-semiconductor field-effect-transistor interface state and trapped charge spatial distributions using a physics-based algorithm

In this article, a new charge-extraction algorithm is proposed for extracting the spatial distributions of hot-carrier-induced interface states and trapped charges in p- and n- metal-oxide-semiconductor field-effect transistors, based on the charge-pumping measurement data. This extraction algorithm is physics based and provides a better understanding of how the presence of hot-carrier-induced trapped charges and interface states affect the charge-pumping curves. The extraction time for this new algorithm is very fast (typically 30 s) and does not require very tedious computer simulation. The verification of this method was performed using TSUPREM-4 and MEDICI simulations. With this new extraction method, one can gain better insight into the degradation mechanisms taking place under different hot-carrier stressing conditions.

Electronic and optical properties of carbon nitride thin films synthesized by laser ablation under ion beam bombardment

Carbon nitride thin films were deposited by 532 nm Nd:YAG laser ablation of graphite assisted by a nitrogen ion beam bombardment on silicon substrates. Different nitrogen ion beam energies (200, 400, and 600 eV) were used while the laser parameters remained fixed. X-ray photoelectron spectroscopy (XPS) and ellipsometry measurements were carried out to analyze the electronic and optical properties. The XPS Cu20091s spectrum for the C–N binding is at 286.5 eV while the Nu20091s spectrum has a corresponding peak of C–N binding at 396.9 eV. The optical gap Eopt is on the order of magnitude of 10−1u2009eV and increases with the N/C ratio in the deposited film. Linear dependence of the refractive index n and the extinction coefficient k on photon energy E in the range of 1.5–3.5 eV are established.

Synthesis and memory properties of a conjugated copolymer of fluorene and benzoate with chelated europium complex

A conjugated copolymer of diethylhexylfluorene and europium complex-chelated benzoate (PF8Eu) was synthesized. The device based on an Al/PF8Eu/indium-tin-oxide sandwich structure exhibited nonvolatile, write-once read-many-times (WORM) memory behavior. The fluorene moiety served as the backbone and electron donor, while the europium complex served as the electron acceptor. The as-fabricated device was in its low conductivity state. After applying a voltage of ∼3V, the device underwent a transition to the high conductivity state, which could not be erased by a reverse bias. In the initial low conductivity state, the device showed a charge injection controlled current. At the high conductivity state, the current-voltage characteristics were dominated by a space-charge-limited current. The device had a switching time of ∼1μs and an on/off current ratio as high as 106. No degradation in device performance was observed after 107 read cycles at a read voltage of 1V under ambient conditions. The device also exhi...

Removal of submicron particles from nickel-phosphorus surfaces by pulsed laser irradiation

Abstract Pulsed laser cleaning was demonstrated to be an efficient way for removing submicron particles from the nickel-phosphorus (NiP) surface both experimentally and theoretically. Experimentally, it is found that using KrF excimer laser with a pulse width of 23 ns the cleaning threshold is about 20 mJ / cm 2 for removing quartz particles from the NiP surface and laser cleaning efficiency increases rapidly with increasing laser fluence. The theoretical analysis shows that the peak cleaning force (per unit area) is larger than the adhesion force (per unit area) for submicron quartz particles on the NiP surface when it is irradiated by excimer laser with a fluence above 10 mJ / cm 2 . Therefore, it is possible to remove submicron quartz particles from NiP surfaces by laser irradiation. The difference between the cleaning force (per unit area) and the adhesion force (per unit area) increases with increasing laser fluence, leading to a higher cleaning efficency for quartz particles on the NiP surface.

Studies of Carbon Nitride Thin Films Synthesized by KrF Excimer Ablation of Graphite in Nitrogen Atmosphere

Carbon nitride thin films were deposited on silicon wafers by pulsed KrF excimer laser (wavelength 248 nm, duration 23 ns) ablation of graphite in nitrogen atmosphere. Different fluences of the excimer laser and pressures of the nitrogen atmosphere were used in order to achieve a high nitrogen content in the deposited thin films. Fourier Transform Infra-red (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to identify the binding structure and the content of the nitrogen species in the deposited thin films. The highest N/C ratio 0.42 was achieved at an excimer laser fluence of 0.8 Jcm -2 with a repetition rate of 10 Hz under the nitrogen pressure of P N =100 mTorr. A high content of C=N double bond instead of C-N triple bond was indicated in the deposited thin films. Ellipsometry was used to analyze the optical properties of the deposited thin films. The carbon nitride thin films have amorphous-semiconductor-like characteristics with the optical band gap Eop, as high as 0.42 eV.

Carbon nitride thin films deposited by nitrogen-ion-assisted KRF excimer ablation of graphite

Abstract Carbon nitride thin films were deposited on silicon wafers by pulsed KrF Excimer (wavelength 248 nm, duration 23 ns) ablation of graphite. Different laser fluences and pressures of the nitrogen atmosphere were used in order to achieve a high nitrogen content in the deposited thin films. A Kaufmann-type ion source was used to produce a nitrogen ion beam to assist the deposition process. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to identify the binding structure and the content of the nitrogen species in the deposited thin films. The thin films deposited in nitrogen atmosphere had N/C ratio of 0.42, similar to those deposited with assistance of nitrogen ion beam bombardment with N/C=0.43. A high content of Cue605N double bond was indicated in both thin films deposited in nitrogen atmosphere and with nitrogen ion-beam assistance. The dependence of the optical band gap on nitrogen ion energy was studied by Ellipsometry.