Silicon Nitride Buffer Layer Research Articles

TEM sample preparation of lithographically patterned permalloy nanostructures on silicon nitride membranes.

We have prepared ferromagnetic nanostructures intended for the investigation of high-frequency magnetization dynamics in permalloy (Py) nanodisks using Lorentz transmission electron microscopy (LTEM) and electron holography. Py nanodisks were fabricated on thin silicon nitride (SiN) membranes using three different fabrication methods: lift-off, ion beam etching (IBE), and stencil lithography. They were further analyzed using different instruments, including scanning electron microscopy, LTEM, and electron holography. A bilayer of positive PMMA resist was utilized in the first fabrication method to form an undercut structure that guarantees a clean lift-off procedure. The second approach used dry etching with an Ar beam to etch a thin Py film, while an electron-beam-patterned negative resist mask kept the desired structure. In the third process, nanostencils (shadow masks) with submicrometer apertures were milled on SiN membranes using a focused ion beam. Furthermore, we have developed a new TEM sample preparation method, where we fabricated Py nanostructures on a bulk substrate with a SiN buffer layer and etched the substrate to create a thin SiN membrane under the Py nanostructure. Finally, we observed the vortex dynamics of the Py nanodisk under magnetic fields using LTEM and off-axis electron holography. A correlation between preparation methods and the properties of the Py nanostructures was made.

Polarization beam splitter on lithium niobate on insulator using a silicon nitride assisted waveguide

A polarization beam splitter (PBS) is proposed based on an asymmetric directional coupler consisting of a silicon nitride assisted waveguide and two ridge waveguides on a lithium niobate on insulator. Due to the silicon nitride buffer layer, the phase-matching condition is satisfied for TE polarization, whereas TM polarization has a significant phase mismatch by choosing reasonable widths of three waveguides. A 112.2-μm-long PBS is designed, and the gap width is chosen to be 300 nm to make it easy to fabricate. Numerical simulations show that the designed PBS has a broad bandwidth (>80 nm) for an extinction ratio of >15 dB and an ultralow insertion loss (<0.35 dB).

Impact of substrate nitridation on the photoluminescence and photovoltaic characteristics of GaN grown on p-Si (100) by molecular beam epitaxy

This report focuses on the structural and optical properties of the GaN films grown on p-Si (100) substrates along with photovoltaic characteristics of GaN/p-Si heterojunctions fabricated with substrate nitridation and in absence of substrate nitridation. The high resolution X-ray diffraction (HRXRD), atomic force microscopy (AFM), Raman and photoluminescence (PL) spectroscopic studies reveal that the significant enhancement in the structural as well as in the optical properties of GaN epifilms grown with silicon nitride buffer layer when compared with the sample grown without silicon nitride buffer layer. The low temperature PL shows a free excitonic (FX) emission peak at 3.51 eV at the temperature of 5 K with a very narrow line width of 35 meV. Temperature dependent PL spectra follow the Varshni equation well and peak energy blue shifts by ~63 meV from 300 to 5 K. Raman data confirms the strain free nature and reasonably good crystallinity of the films. The GaN/p-Si heterojunctions fabricated without substrate nitridation show a superior photovoltaic performance compared to the devices fabricated in presence of substrate nitridation. The discussions have been carried out on the junction properties. Such single junction devices exhibit a promising fill factor and conversion efficiency of 23.36 and 0.12 %, respectively, under concentrated AM1.5 illumination.

Thermal stability of an ultrathin hafnium oxide film on plasma nitrided Si(100)

We report on the thermal stability of an ultrathin hafnium oxide film on a plasma nitrided Si(100) surface. The ultrathin silicon nitride buffer layer was produced by an ECR-plasma ion source. Onto this buffer layer a thin hafnium oxide film was prepared by electron beam evaporation. The thermal stability of the layer stack was checked by systematic annealing steps. A detailed angle resolved X-ray photoelectron spectroscopy study of the interfaces is presented. For chemical surface studies high-resolution spectra of the Si 2p and Hf 4f signals were taken. It is demonstrated that the thermal stability of hafnium oxide thin films can be increased by a smooth and homogenous buffer layer of silicon nitride.

Substrate nitridation induced modulations in transport properties of wurtzite GaN/p-Si (100) heterojunctions grown by molecular beam epitaxy

Phase pure wurtzite GaN films were grown on Si (100) substrates by introducing a silicon nitride layer followed by low temperature GaN growth as buffer layers. GaN films grown directly on Si (100) were found to be phase mixtured, containing both cubic (β) and hexagonal (α) modifications. The x-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy studies reveal that the significant enhancement in the structural as well as in the optical properties of GaN films grown with silicon nitride buffer layer grown at 800 °C when compared to the samples grown in the absence of silicon nitride buffer layer and with silicon nitride buffer layer grown at 600 °C. Core-level photoelectron spectroscopy of SixNy layers reveals the sources for superior qualities of GaN epilayers grown with the high temperature substrate nitridation process. The discussion has been carried out on the typical inverted rectification behavior exhibited by n-GaN/p-Si heterojunctions. Considerable modulation in the transport mechanism was observed with the nitridation conditions. The heterojunction fabricated with the sample of substrate nitridation at high temperature exhibited superior rectifying nature with reduced trap concentrations. Lowest ideality factors (∼1.5) were observed in the heterojunctions grown with high temperature substrate nitridation which is attributed to the recombination tunneling at the space charge region transport mechanism at lower voltages and at higher voltages space charge limited current conduction is the dominating transport mechanism. Whereas, thermally generated carrier tunneling and recombination tunneling are the dominating transport mechanisms in the heterojunctions grown without substrate nitridation and low temperature substrate nitridation, respectively.

Reduction of oxygen impurity at GaN/β-Si 3N 4/Si interface via SiO 2 to Ga 2O conversion by exposing of Si surface under Ga flux

The removal of native oxide from Si (1 1 1) surfaces was investigated by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectra (SIMS) depth profiles. Two different oxide removal methods, performed under ultrahigh-vacuum (UHV) conditions, were carried out and compared. The first cleaning method is thermal desorption of oxide at 900 °C. The second method is the deposition of metallic gallium followed by redesorption. A significant decrease in oxygen was achieved by thermal desorption at 900 °C under UHV conditions. By applying a subsequent Ga deposition/redesorption, a further reduction in oxygen could be achieved. We examine the merits of an alternative oxide desorption method via conversion of the stable SiO 2 surface oxide into a volatile Ga 2O oxide by a supply of Ga metals. Furthermore, ultra thin films of pure silicon nitride buffer layer were grown on a Si (1 1 1) surface by exposing the surface to radio-frequency (RF) nitrogen plasma followed by GaN growth. The SIMS depth profile shows that the oxygen impurity can be reduced at GaN/β-Si 3N 4/Si interfaces by applying a subsequent Ga deposition/redesorption.

The impact of ultra thin silicon nitride buffer layer on GaN growth on Si (1 1 1) by RF-MBE

Ultra thin films of pure silicon nitride were grown on a Si (1 1 1) surface by exposing the surface to radio-frequency (RF) nitrogen plasma with a high content of nitrogen atoms. The effect of annealing of silicon nitride surface was investigated with core-level photoelectron spectroscopy. The Si 2 p photoelectron spectra reveals a characteristic series of components for the Si species, not only in stoichiometric Si 3N 4 (Si 4+) but also in the intermediate nitridation states with one (Si 1+) or three (Si 3+) nitrogen nearest neighbors. The Si 2 p core-level shifts for the Si 1+, Si 3+, and Si 4+ components are determined to be 0.64, 2.20, and 3.05 eV, respectively. In annealed sample it has been observed that the Si 4+ component in the Si 2 p spectra is significantly improved, which clearly indicates the crystalline nature of silicon nitride. The high resolution X-ray diffraction (HRXRD), scanning electron microscopy (SEM) and photoluminescence (PL) studies showed a significant improvement of the crystalline qualities and enhancement of the optical properties of GaN grown on the stoichiometric Si 3N 4 by molecular beam epitaxy (MBE).

Thermal stability and surface modifications of detonation diamond nanoparticles studied with X-ray photoelectron spectroscopy

Detonation nanodiamond (ND) particles were dispersed on silicon nitride (SiN x ) coated sc-Si substrates by spin-coating technique. Their surface density was in the 10 10–10 11 cm − 2 range. Thermal stability and surface modifications of ND particles were studied by combined use of X-ray Photoelectron Spectroscopy (XPS) and Field Emission Gun Scanning Electron Microscopy (FEG SEM). Different oxygen-containing functional groups could be identified by XPS and their evolution versus UHV annealing temperature (400–1085 °C) could be monitored in situ. The increase of annealing temperature led to a decrease of oxygen bound to carbon. In particular, functional groups where carbon was bound to oxygen via one σ bond (C–OH, C–O–C) started decomposing first. At 970 °C carbon–oxygen components decreased further. However, the sp 2/sp 3 carbon ratio did not increase, thus confirming that the graphitization of ND requires higher temperatures. XPS analyses also revealed that no interaction of ND particles with the silicon nitride substrate occurred at temperatures up to about 1000 °C. However, at 1050 °C silicon nitride coated substrates started showing patch-like damaged areas attributable to interaction of silicon nitride with the underlying substrate. Nevertheless ND particles were preserved in undamaged areas, with surface densities exceeding 10 10 cm − 2. These nanoparticles acted as sp 3-carbon seeds in a subsequent 15 min Chemical Vapour Deposition run that allowed growing a 60–80 nm diamond film. Our previous study on Si(100) showed that detonation ND particles reacted with silicon between 800 and 900 °C and, as a consequence, no diamond film could be grown after Chemical Vapour Deposition (CVD). These findings demonstrated that the use of a thin silicon nitride buffer layer is preferable insofar as the growth of thin diamond films on silicon devices via nanoseeding is concerned.

Effect of a silicon nitride buffer layer on the electrical properties of tantalum pentoxide films

Ta 2O 5 films with a buffer layer of silicon nitride of various thicknesses were deposited on Si substrate by reactive sputtering and submitted to annealing at 700 °C in nitrogen atmosphere. The microstructure and the electrical properties of thin films were studied. It was found that with a buffer layer of silicon nitride the electrical properties of Si x N y /Ta 2O 5 film can be improved than Ta 2O 5 film. When the thickness of the buffer layer was 3 nm, the Si x N y /Ta 2O 5 film has the highest dielectric constant of 27.4 and the lowest leakage current density of 4.61 × 10 −5 A/cm 2 (at −1 V). For the Si x N y (3 nm)/Ta 2O 5 film, the conduction mechanism of leakage current was also analyzed and showed four types of conduction mechanisms at different applied voltages.

Fabrication of AlN/Si SAW delay lines with very low RF signal noise

In this work we investigate the influence of the substrate resistivity and of different buffer layers on the out-of-band insertion losses in AlN SAW devices fabricated on (1 0 0) silicon substrates. The measurements have shown that the out-of-band insertion loss is improved by increasing the substrate resistivity but also by the introduction of an insulating buffer layer material. An out-of-band insertion loss as low as −75 dB has been achieved by the device realized on a silicon nitride buffer layer. This can be explained in terms of inhibition of the diffusion of silicon atoms in the AlN film. Our results show that silicon nitride represents a good solution in terms of low out-of-band insertion loss and cost effectiveness for the realization of nitride-based piezoelectric MEMS devices on silicon substrates.

Influence of buffer layer thickness on memory effects of SrBi2Ta2O9∕SiN∕Si structures

We deposited SrBi2Ta2O9 (SBT) thin films on silicon–nitride (SiN) buffered Si(100) substrates to form metal–ferroelectric–insulator–semiconductor structures and observed a significant influence of the buffer layer thickness on the magnitude and direction of the capacitance–voltage (C–V) memory window. As the SiN buffer layer thickness was decreased from 6nm to 2nm, the C–V memory hysteresis direction changed from memory direction dominated by ferroelectric polarization (i.e., counterclockwise for n-Si) to a trapping-related hysteresis direction (i.e., clockwise for n-Si). The memory windows for both cases exhibited a similar temperature dependence. The memory window approached zero at temperatures from 340°C to 380°C, which corresponds to the Curie temperature (TC) of the ferroelectric SBT films. When the temperature was returned to room temperature, the hysteresis windows were recovered. A detailed study has led us to believe that the switching of polarization of the ferroelectric SBT plays a key role in the observed temperature dependence, for both the ferroelectric polarization-dominated and the trapping-dominated memory window.

GaN heteroepitaxial growth on silicon nitride buffer layers formed on Si (111) surfaces by plasma-assisted molecular beam epitaxy

Wurtzite GaN films were grown on silicon nitride buffer layers formed on Si (111) substrates by radio frequency plasma-assisted molecular beam epitaxy. Reflection high energy electron diffraction, Auger electron spectroscopy, transmission electron microscopy, and photoluminescence results indicate that the single crystalline wurtzite GaN was grown on the buffer layers of amorphouslike silicon nitride formed on Si (111) substrates by taking the following relationship with the substrate: GaN [0001]//Si [111] and GaN (1̄1̄20)//Si (11̄0). Both faces of the silicon nitride buffer layer were found to be flat and sharp, the thickness of the buffer layer (1–1.5 nm) being constant across the interface. Efficient bound exciton emission was observed at 3.46 eV. The growth technique described was found to be simple but very powerful for growing high quality GaN films on Si substrates.

Memory effects of SrBi2Ta2O9 capacitor on silicon with a silicon nitride buffer

The memory effects of SrBi2Ta2O9 (SBT) films deposited on Si substrates with an ultra-thin silicon nitride buffer layer have been investigated. The Capacitance-Voltage (C-V) measurements indicate low densities of interface traps, suggesting a good interface between the silicon nitride buffer layer and the Si substrate. The C-V characteristics show hysteresis that is consistent with the polarization of the SBT film, but opposite to that due to the electron injection/trapping effect. When swept back and forth between -7V and + 7V, a sizable hysteresis window of ± 2V is observed. The results from a single-pulse programming experiment suggest that the switching time is shorter than 8 ns, the shortest pulse available for the experiment. These results are all obtained on samples that exhibit remanent polarizations as low as 0.15 μC/cm2. Fatigue tests show only modest degradation of the memory window after 1011 switching cycles. Results from forming gas annealing experiments indicate no degradation up to 400°C of annealing temperature.

Sol-gel derived thin films on GaAs

Sol-gel derived thin films of lead zirconate titanate (PZT) have been fabricated on a platinized GaAs substrate using a propane-1,3-diol based sol-gel route. PZT can be used as the piezoelectric component in bulk acoustic wave devices for monolithic microwave integrated circuit applications. A 100 nm silicon nitride buffer layer was deposited onto the GaAs by plasma-enhanced chemical vapour deposition in order to prevent gallium and arsenic outdiffusion during film fabrication. Rapid thermal processing (RTP) techniques were employed to decompose thermally the sol-gel layer to PZT in a further effort to minimize problems of gallium and arsenic outdiffusion. Adhesion between the bottom electrode and substrate was found to improve when an intermediate titanium layer deposited between the platinum and silicon nitride was oxidized prior to deposition of the platinum electrode. A crystalline PZT film was produced on the substrate configuration by firing the sol-gel coating at C for 10 s using RTP. A single deposition of sol resulted in a film having a thickness of . Ferroelectric hysteresis measurements yielded average values of remanant polarization and coercive field of and respectively.