Jon-Yiew Gan

Dielectric property of (TiO2)x−(Ta2O5)1−x thin films

(TiO2)x−(Ta2O5)1−x thin films were prepared with radio-frequency magnetron sputtering deposition in this study. The dielectric constant measured from these films appears to critically depend on the amount of TiO2 incorporated into the film and post-anneal condition. The composition dependence was found similar to that reported on (TiO2)x−(Ta2O5)1−x bulk. The highest value of dielectric constant is about 55 for a TiO2 content of 8% and annealing at 800 °C. Compared to pure Ta2O5 thin films, significant enhancement in dielectric constant is obtained by adding small quantity of TiO2.

Ferroelectric properties of (117)- and (001)-oriented Bi3.25La0.75Ti3O12 polycrystalline thin films

Highly (117)- and (001)-oriented Bi3.25La0.75Ti3O12 (BLT) thin films were fabricated on Pt/TiO2/SiO2/Si(100) substrates by chemical solution deposition under the appropriate baking and crystallization conditions. The (117)-oriented BLT films exhibited higher remanent polarization (2Pr=24 μC/cm2), than did (001)-oriented BLT films, which exhibited only a slight amount of polarization (2Pr=6.6 μC/cm2). The results of fatigue and retention tests revealed that neither film was fatigued up to 1×1010 switching cycles, and the retained charge was unchanged for 1×104 s.

Formation and instability of silver nanofilament in Ag-based programmable metallization cells.

In this paper, we report on the formation and rupture of Ag nanofilament on planar Ag/TiO2/Pt cells using visual observation. During the forming process, the filament tends to stay very thin. Specifically, it is so thin that it breaks up into a chain of nanospheres (according to Rayleigh instability) right after the formation has been completed. Similar mechanical breakup may also impact vertically stacked cells, causing reliability concerns.

ZnO-based one diode-one resistor device structure for crossbar memory applications

This letter reports the development of a ZnO-based one diode-one resistor (1D1R) device consisting of a Pt/ZnO:Al/ZnO/Pt Schottky-type diode and a Pt/ZnO/Pt memristor using a room-temperature sputtering process. The proposed 1D1R device exhibits stable switching for more than 103 cycles, good retention up to 104 s at 85 °C, and desirable anti-crosstalk characteristics. Thus, the proposed design shows potential for integration in a crossbar memory array.

Thermally stable amorphous (AlMoNbSiTaTiVZr)50N50 nitride film as diffusion barrier in copper metallization

Results on copper metallization diffusion barriers using high-entropy alloy (HEA) nitride are reported. The HEA nitride (AlMoNbSiTaTiVZr)50N50 is amorphous in the as-deposited state and remains its noncrystallinity up to a high temperature of 850°C. To evaluate its diffusion barrier characteristics, Cu∕(AlMoNbSiTaTiVZr)50N50∕Si test structures were prepared and annealed under 750–900°C for 30min. The results show that the current nitride prevents the reaction between Cu and Si before its failure at 900°C. The outstanding barrier performance and high thermal stability of amorphous structure are suggested to originate from multiprincipal-element effects.

In situ epitaxial growth of TiO2 on RuO2 nanorods with reactive sputtering

In this work, TiO2 deposition on RuO2 nanorods with reactive sputtering was studied. The TiO2 deposition was performed in situ after the RuO2 nanorod deposition at the same substrate temperature of 450 °C. The morphology examination and structure analysis have indicated a uniform and pure rutile TiO2 deposition on RuO2 nanorods. High-resolution transmission electron microscopy images also revealed an epitaxial growth of TiO2 on RuO2 nanorods. Such a low-temperature fabrication technique for one-dimensional (1D) heteronanostructure may apply to other functional materials. Since RuO2 is a good electric conductor, 1D heteronanostructures made from RuO2 nanorods are expected to exhibit enhanced functionality particularly in electrical and electrochemical applications.

Field emission from a composite structure consisting of vertically aligned single-walled carbon nanotubes and carbon nanocones

Vertically aligned single-walled carbon nanotubes (VA-SWCNTs) have been fabricated on carbon nanocones (CNCs) in a gravity-assisted chemical vapour deposition (CVD) process. The CNCs with nanoscale Co particles at the top were first grown on the Co/Si(100) substrate biased at 350?V in a plasma enhanced chemical vapour deposition process. The CNCs typically are ~200?nm in height, and their diameters are ~100?nm near the bottom and ~10?nm at the top. The nanoscale Co particles ~10?nm in diameter act as catalysts which favour the growth of VA-SWCNTs out of CNCs at 850??C in the gravity-assisted CVD process. The average length and the growth time of VA-SWCNTs are ~150?nm and 1.5?min, equivalent to a growth rate of ~6??m?h?1. The diameters of VA-SWCNTs are estimated to be 1.2?2.1?nm. When VA-SWCNTs are fabricated on CNCs, the turn-on voltage is reduced from 3.9 to 0.7?V??m?1 and the emission current density at the electric field of 5?V??m?1 is enhanced by a factor of more than 200. The composite VA-SWCNT/CNC structure is potentially an excellent field emitter. The emission stability of the VA-SWCNT/CNC field emitter is discussed.

RuO2/MnO2 core–shell nanorods for supercapacitors

RuO2/MnO2 NRs as an electrode for supercapacitors show a high electrochemical performance with a specific capacitance of 793 F g−1 (based on MnO2) by cyclic voltammetry (CV) at a scan rate of 2 mV s−1 in 1 M Na2SO4 aqueous solution. A good rate capability with a specific capacitance of 556 F g−1 at a current density of 1 A g−1 and a good cycling stability (20% degradation after 1000 cycles) were also achieved. The enhancement of capacitive behavior can be attributed to the conductive RuO2 template with a series resistance of 0.75 Ω and a charge transfer resistance of 0.75 Ω. The results show that an active material such as a MnO2 hybrid with highly conductive 1D nanowires may greatly improve the electrochemical performance for supercapacitors.

Effects of nitrogen flow ratio on the structure and properties of reactively sputtered (AlMoNbSiTaTiVZr)Nx coatings

(AlMoNbSiTaTiVZr)Nx films are reactively sputtered from an AlMoNbSiTaTiVZr equimolar target under varied nitrogen flow ratio (RN). The concentration of nitrogen increases rapidly at lower RN and then saturates at around 50 at% when RN reaches 33% and above. At lower RN (0% and 3%), film structures are amorphous and their cross-sectional microstructures are featureless. When RN is 11%, FCC nitride nanocrystals coexist with the amorphous phase. At higher RN (33% and above), films exhibit a single NaCl-type FCC structure having fine column structures and nanograins. The texture of the FCC structures changes from (1 1 1) to (2 0 0) as RN increases from 33% to 66%. Enhanced hardness is observed upon the addition of nitrogen due to the strong bondings between N and target elements. Compared with reported high-entropy alloy (HEA)/nitride films deposited without bias, (AlMoNbSiTaTiVZr)Nx exhibits the highest hardness and modulus both in its alloy and nitride states. This not only confirms the effectiveness of the present alloy design but also demonstrates that HEA design could provide a new route to enhance the mechanical properties of alloy and nitride films.

Growth of RuO2 nanorods in reactive sputtering

The synthesis of RuO2 nanorods with reactive sputtering was demonstrated in this work. The synthesis process is very much like the metal organic chemical vapor deposition, except that RuO3 generated with reactive sputtering under high oxygen-to-argon flow ratio (>5SCCM∕15SCCM) (SCCM denotes cubic centimeter per minute at STP) and high substrate temperature (>300°C) is used in place of the metal organic precursor. RuO2 nanorods tend to grow steadily with constant aspect ratio (∼27) and the field-emission characteristics appear very sensitive to their spatial distribution.