TiO2 is commonly used as the active switching layer in resistive random access memory. The electrical characteristics of these devices are directly related to the fundamental conditions inside the TiO2 layer and at the interfaces between it and the surrounding electrodes. However, it is complex to disentangle the effects of film “bulk” properties and interface phenomena. The present work uses hard X‐ray photoemission spectroscopy (HAXPES) at different excitation energies to distinguish between these regimes. Changes are found to affect the entire thin film, but the most dramatic effects are confined to an interface. These changes are connected to oxygen ions moving and redistributing within the film. Based on the HAXPES results, post‐deposition annealing of the TiO2 thin film was investigated as an optimisation pathway in order to reach an ideal compromise between device resistivity and lifetime. The structural and chemical changes upon annealing are investigated using X‐ray absorption spectroscopy and are further supported by a range of bulk and surface sensitive characterisation methods. In summary, it is shown that the management of oxygen content and interface quality is intrinsically important to device behavior and that careful annealing procedures are a powerful device optimisation technique.
We report a new method for electrodeposition of device-quality metal chalcogenide semiconductor thin films and nanostructures from a single, highly tuneable, non-aqueous electrolyte. This method opens up the prospect of electrochemical preparation of a wide range of functional semiconducting metal chalcogenide alloys that have applications in various nano-technology areas, ranging from the electronics industry to thermoelectric devices and photovoltaic materials. The functional operation of the new method is demonstrated by means of its application to deposit the technologically important ternary Ge/Sb/Te alloy, GST-225, for fabrication of nanostructured phase change memory (PCM) devices and the quality of the material is confirmed by phase cycling via electrical pulsed switching of both the nano-cells and thin films.
The
neutral, distorted octahedral complex [TiCl4(SenBu2)2] (1), prepared
from the reaction of TiCl4 with the neutral SenBu2 in a 1:2 ratio and characterized by
IR and multinuclear (1H, 13C{1H}, 77Se{1H}) NMR spectroscopy and microanalysis, serves
as an efficient single-source precursor for low-pressure chemical
vapor deposition (LPCVD) of titanium diselenide, TiSe2,
films onto SiO2 and TiN substrates. X-ray diffraction patterns
on the deposited films are consistent with single-phase, hexagonal
1T-TiSe2 (P3̅m1),
with evidence of some preferred orientation of the crystallites in
thicker films. The composition and structural morphology was confirmed
by scanning electron microscopy (SEM), energy dispersive X-ray, and
Raman spectroscopy. SEM imaging shows hexagonal plate crystallites
growing perpendicular to the substrate, but these tend to align parallel
to the surface when the quantity of reagent is reduced. The resistivity
of the crystalline TiSe2 films is 3.36 ± 0.05 ×
10–3 Ω·cm with a carrier density of 1
× 1022 cm–3. Very highly selective
film growth from the reagent was observed onto photolithographically
patterned substrates, with film growth strongly preferred onto the
conducting TiN surfaces of SiO2/TiN patterned substrates.
TiSe2 is selectively deposited within the smallest 2 μm
diameter TiN holes of the patterned TiN/SiO2 substrates.
The variation in crystallite size with different diameter holes is
determined by microfocus X-ray diffraction and SEM, revealing that
the dimensions increase with the hole size, but that the thickness
of the crystals stops increasing above ∼20 μm hole size,
whereas their lengths/widths continue to increase.
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