Silicon Nitride Bilayer Research Articles

Phonon and electronic properties of semiconducting silicon nitride bilayers

The two-dimensional (2D) IV-V semiconductors have attracted much attention due to their fascinating electronic and optical properties. In this work, we predicted three phases of silicon nitrides, denoted α-Si2N2, β-Si2N2, and γ-Si4N4, respectively. Both α-Si2N2 and β-Si2N2 consist of two buckled SiN sheets, and γ-Si4N4 consists of two puckered SiN sheets. It is challenging to transform between α-Si2N2 and β-Si2N2 because of the high energy barrier. The three dynamically stable bilayers are semiconductors with fundamental indirect band gaps from 0.25 eV to 2.92 eV. As expected, only the s and p orbitals contribute to the electronic states, and the pz orbitals dominate near the Fermi level. Furthermore, insulator-metal transitions occur in α-Si2N2 and β-Si2N2 under the biaxial strain of 16 %. These materials perhaps have potential applications in microelectronics and spintronics.

­­­­ Ultra-Broadband and Highly Efficient Silicon Nitride Bi-Layer Grating Couplers

­­­­ Ultra-Broadband and Highly Efficient Silicon Nitride Bi-Layer Grating Couplers

Light-induced degradation of native silicon oxide–silicon nitride bilayer passivated silicon

This article reports on the effects of aging and light induced degradation of the passivation quality of the interface formed by the crystalline silicon surface and facile grown oxide—SiNx bilayer. Stable passivation quality against aging and light soaking require thicker oxide layers grown at room temperature, suggesting that thicker oxide layers mitigate the migration of hydrogen from the interface and hence the defect density under light soaking. In addition, the stoichiometry of the PECVD SiNx influences the stability of the passivation quality. Specifically, the rate of degradation in passivation quality is observed to correlate with the optical absorption properties of SiNx; the higher the optical absorption the greater the degradation in passivation. This result is attributed to neutralization of the K+ centers in SiNx. Passivation layers with SiNx deposited with 5% silane in nitrogen to ammonia gas ratio of 7 and facile grown native oxide thickness of ∼1 nm resulted in the most stable passivation scheme within the scope of the reported experiments.

Silicon Nanowires Based Solar Cell Using Native Oxide and Silicon Nitride Bi-Layer Passivation

Silicon nanowires (SiNWs) based solar cells are passivated by native oxide and SiNx bi-layer. In comparison with cells passivated by SiNx single layer, bi-layer passivation exhibits higher effective minority lifetime, illustrating a better surface passivation effect, which leads to a gain of internal quantum efficiency in the short wavelength range, a better output performance with an increase of 0.16% in efficiency. The data obtained from this work is fundamental and has some reference value for future studies.

Realization of 3D Isotropic Negative Index Materials using Massively Parallel and Manufacturable Microfabrication and Micromachining Technology

AbstractIn this paper, we present a method to realize a three dimensional (3D) homogeneous and isotropic negative index materials (3D-NIMs) fabricated using a low cost and massively parallel manufacturable microfabrication and microassembly technique. The construction of self-assembled 3D-NIM array was realized through two dimensional (2-D) planar microfabrication techniques exploiting the as-deposited residual stress imbalance between a bi-layer consisting of e-beam evaporated metal (650nm of chromium) and a structural layer of 500nm of low stress silicon nitride deposited by LPCVD on a silicon substrate.A periodic continuation of a single rectangular unit cell consisting of split-ring resonators (SRR) and wires were fabricated to generate a 3D assembly by orienting them along all three Cartesian axes. The thin chromium and silicon nitride bi-layer is formed as hinges. The strain mismatch between the two layers curls the structural layer (flap) containing the SRR upwards. The self-assembled out-of-plane angular position depends on the thickness and material composing the bi-layer. This built-in stress-actuated assembly method is suitable for applications requiring a thin dielectric layer for the SRR. The split-ring resonators and other structures are created on the membrane which is then assembled into the 3-D configuration.

Electrical characterization of MIS capacitors fabricated from ECR-PECVD silicon oxide and silicon nitride bilayer films

In this study, a comparative electrical characterization of Al/SiNx/Si and Al/SiNx/SiO2/Si MIS structures has been carried out. Both SiO2 and SiNx films have been deposited by using electron-cyclotron resonance plasma-enhanced chemical vapor deposition method. C-V results show that samples without SiO2 have more defects than those with SiO2. Deep-level transient spectroscopy and conductance transient measurements demonstrate that as for the samples containing the SiO2 film, these defects are mostly concentrated in the insulator/semiconductor interface, whereas in the other case defects are spatially distributed into the insulator.

Fabrication of silicon nitride bilayer for roller bearing by plasma activated sintering

Silicon nitride bilayers with the α-phase and the β-phase as outer and inner layers, respectively, were prepared by the plasma activated sintering (PAS) method, under the conditions of 30 MPa and 1 min in nitrogen atmosphere at 1550 °C for the α-phase and 2 min at 1700 °C for the β-phase. The underlying objective was microstructural design of the roller bearing system with optimum mechanical properties; alternating hard layers, for wear resistance, with tough layers, for fracture resistance. Hardness values through Vickers indentation tests on cross-sections of specimen demonstrated the possibility of the thickness control of the bilayer. Fracture toughness of the bilayer with the thickness of the α-phase layer was changed, indicating that the β-phase affected fracture resistance. Implications concerning the fabrication of silicon nitride bilayer for roller bearing application were considered.

Microbridge Testing of Silicon Oxide/Silicon Nitride Bilayer Films

ABSTRACTThe present work further develops the microbridge testing method to characterize mechanical properties of bilayer thin films. A closed-form formula for deflection versus load under small deflection is derived with consideration of the substrate deformation and residual stress in each layer. The analysis shows that the solution for bending a bilayer beam is equivalent to that for bending a single-layer beam with an equivalent bending stiffness, an equivalent residual force and a residual moment. One can estimate the Young's modulus and residual stress in a layer if the corresponding values in the other layer are known. The analytic results are confirmed by finite element calculations. The microbridge tests are conducted on low-temperature-silicon oxide (LTO)/silicon nitride bilayer films as well as on silicon nitride single-layer films. All microbridge specimens are prepared by the microfabricating technique. The tests on the single-layer films provide the material properties of the silicon nitride films. Then, applying the proposed method for bilayer films under small deflection yields the Young's modulus of 37 GPa and the residual stress of -148 MPa for LTO films.

Electrical characterization of ECR enhaced deposited silicon nitride bilayers for high quality Al/SiNx/InP MIS structure fabrication

The interfacial state density existing in metal-insulator-semiconductor (MIS) structures was measured by deep level transient spectroscopy technique. The MIS structures were fabricated on InP substrates by direct deposition of silicon nitride SiNxH) thin films by the electron cyclotron resonance method. In this work, we show that interfacial state density can be diminished without degrading electrical insulator properties by fabricating MIS structures based on a bi-layered insulator with different insulator compositions and different thickness. The effect of rapid thermal annealing treatment has been analysed in detail in these samples. An interface state density as low as 3 × 1011cm−2eV−1 was measured in some structures.

Contact Damage and Strength Degradation in Brittle/Quasi‐Plastic Silicon Nitride Bilayers

A study is made of the damage resistance of silicon nitride bilayers consisting of a hard overlayer (coating) on a soft underlayer (substrate). The two layers are fabricated with different starting powders, to provide distinctive elongate‐grain microstructures, and are cosintered, to provide strong interfacial bonding and thus to minimize subsequent delamination. Contact testing with spherical indenters is used to characterize the damage response. The elastic‐plastic mismatch between the layers is sufficiently high as to produce distinctive damage modes in the two layers: predominantly cone cracking in the coating, and quasi‐plasticity in the substrate. However, the mismatch is also sufficiently low as to preclude secondary transverse cracks of the kind observed in other bilayer systems to initiate immediately beneath the contact at the coating/substrate interface and propagate upward within the coating. The dominant damage mode shifts from coating fracture to substrate quasi‐plasticity with increasing contact load and decreasing coating thickness. Significantly, the presence of the soft underlayer inhibits growth of the coating cone cracks as the latter approach and intersect the interface. The underlayer also substantially diminishes strength losses from the contact‐induced damage, especially in bilayers with thinner coatings. The implication is that bilayer structures with thin, hard coatings can preserve benefits from the inherent toughness of soft substrate materials, and at the same time afford surface protection (high wear resistance) to the underlayer.

Contact‐Induced Transverse Fractures in Brittle Layers on Soft Substrates: A Study on Silicon Nitride Bilayers

An analysis of transverse cracks induced in brittle coatings on soft substrates by spherical indenters is developed. The transverse cracks are essentially axisymmetric and geometrically conelike, with variant forms dependent on the location of initiation: outer cracks that initiate at the top surface outside the contact and propagate downward; inner cracks that initiate at the coating/substrate interface beneath the contact and propagate upward; intermediate cracks that initiate within the coating and propagate in both directions. Bilayers consisting of hard silicon nitride (coating) on a composite underlayer of silicon nitride with boron nitride platelets (substrate), with strong interfacial bonding to minimize delamination, are used as a model test system for Hertzian testing. Test variables investigated are contact load, coating/substrate elastic‐plastic mismatch (controlled by substrate boron nitride content), and coating thickness. Initiation of the transverse coating cracks occurs at lower critical loads, and shifts from the surface to the interface, with increasing elastic‐plastic mismatch and decreasing coating thickness. This shift is accompanied by increasing quasi‐plasticity in the substrate. Once initiated, the cracks pop in and arrest within the coating, becoming highly stabilized and insensitive to further increases in contact load, or even to coating toughness. A finite element analysis of the stress fields in the loaded layer systems enables a direct correlation between the damage patterns and the stress distributions: between the transverse cracks and the tensile (and compressive) stresses; and between the subsurface yield zones and the shear stresses. Implications of these conclusions concerning the design of coating systems for damage tolerance are discussed.

Formation of boron nitride and silicon nitride bilayer films by ion beam enhanced deposition

Bilayer thin films of boron nitride and silicon nitride were prepared by sequential electron beam evaporation of Si or B and simultaneous irradiation with nitrogen ions. The composition and structure of the films were investigated by AES and IR analysis.