Silicon Nitride Layer Research Articles

Silicon nitride assisted 1×64 optical phased array based on a SOI platform

We demonstrate a 1×64 optical phased array (OPA) based on a silicon on insulator (SOI) platform with integrated silicon nitride. The input port of the OPA is fabricated using a silicon nitride waveguide due to its advantage of allowing more optical power. The phase shifter is a silicon waveguide with heater because of the higher thermo-optic coefficient of silicon. And a double layer silicon nitride assisted grating is used in the emitter to reduce the emission strength and then increase the length of emitter to reduce the spot size. The length of the grating emitter is 1.5 mm and the measured field of view of this optical phased array is 35.5°×22.7° with spot size of 0.69°×0.075°.

Novel Low-Loss Fiber-Chip Edge Coupler for Coupling Standard Single Mode Fibers to Silicon Photonic Wire Waveguides

Fiber-to-chip optical interconnects is a big challenge in silicon photonics application scenarios such as data centers and optical transmission systems. An edge coupler, compared to optical grating, is appealing to in the application of silicon photonics due to the high coupling efficiency between standard optical fibers (SMF-28) and the sub-micron silicon wire waveguides. In this work, we proposed a novel fiber–chip edge coupler approach with a large mode size for silicon photonic wire waveguides. The edge coupler consists of a multiple structure which was fulfilled by multiple silicon nitride layers embedded in SiO2 upper cladding, curved waveguides and two adiabatic spot size converter (SSC) sections. The multiple structure can allow light directly coupling from large mode size fiber-to-chip coupler, and then the curved waveguides and SSCs transmit the evanescent field to a 220 nm-thick silicon wire waveguide based on the silicon-on-insulator (SOI) platform. The edge coupler, designed for a standard SMF-28 fiber with 8.2 μm mode field diameter (MFD) at a wavelength of 1550 nm, exhibits a mode overlap efficiency exceeding 95% at the chip facet and the overall coupling exceeding 90%. The proposed edge coupler is fully compatible with standard microfabrication processes.

Vertical Engineering for Large Brillouin Gain in Unreleased Silicon-Based Waveguides

Strong acousto-optic interaction in silicon-based waveguides generally requires releasing of the silicon core to avoid mechanical leakage into the underlying silica substrate. This complicates fabrication, limits thermalization, reduces the mechanical robustness and hinders large area optomechanical devices on a single chip. Here, we overcome this limitation by employing vertical photonic-phononic engineering. Specifically, the insertion of a thick silicon nitride layer between the silicon guiding core and the silica substrate contributes to reduce GHz-frequencies phonon leakage enabling large values of the Brillouin gain in an unreleased platform. We get values of the Brillouin gain around 300 (Wm)$^{-1}$ for different configurations, which could be further increased by operation at cryogenic temperatures. These values should enable to observe Brillouin-related phenomena in cm-scale waveguides or in more compact ring resonators. This finding could pave the way towards large-area unreleased cavity and waveguide optomechanics on silicon chips.

Test Structure for Measuring the Selectivity in XeF2 and HF Vapour Etch Processes

Etch selectivity between layers is an important parameter in the fabrication of microelectronics and microsystems. This is particularly true in the case of isotropic gas/vapour etching methods used to release free standing structures through the selective etching of sacrificial layers. Commonly used structural materials have been reported to be largely inert when exposed to a given vapour etchant, indicating high selectivity when measured against typical sacrificial layers. However, there is growing evidence that these structural layers are actually etched at an enhanced rate if they are located in the proximity of the sacrificial layer being removed. Hence, removal rates given in the literature, which have resulted from measurements of layers that have been etched in isolation, can no longer be trusted to characterize critical etch processes in device fabrication. In this paper, a test structure is reported that enables a far more appropriate determination of the etch selectivity between sacrificial and structural materials. The method is demonstrated with the two most common vapour etch processes. Firstly, the XeF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> vapour etch of a polysilicon sacrificial layer located above a silicon nitride structural layer, and secondly, the HF vapour etch of silicon dioxide placed above a silicon nitride structural layer. Both test structure datasets are presented. The polysilicon and silicon nitride layers, etched with XeF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> show a selectivity of 5:4. The silicon dioxide and silicon nitride layers etched with HF, show a selectivity of 6:1 to 8:1.

Tunnel nitride passivated contacts for silicon solar cells formed by catalytic CVD

An ultra-thin silicon nitride (SiN x ) layer formed by catalytic chemical vapor deposition (Cat-CVD) is used to replace the Si dioxide (SiO2) layer of a tunnel oxide passivated contact solar cell. The passivation quality of crystalline Si (c-Si) with a stack of the ultra-thin SiN x and n-type hydrogenated amorphous Si (a-Si:H) or microcrystalline Si (μc-Si:H), also formed by Cat-CVD, is significantly improved by annealing at 850 °C, probably due to the formation of a back surface field layer. Cat-CVD SiN x with thicknesses of up to 2.5 nm can have sufficient tunneling conduction. The ultra-thin SiN x having functions of surface passivation and carrier tunneling, and the unification of the formation method for the tunnel SiN x and conductive layers will lead to the realization of tunnel nitride passivated contact solar cells.

Two-step fabrication of thin film encapsulation using laser assisted chemical vapor deposition and laser assisted plasma enhanced chemical vapor deposition for long-lifetime organic light emitting diodes

A thin film encapsulation layer was fabricated through two-sequential chemical vapor deposition processes for organic light emitting diodes (OLEDs). The fabrication process consists of laser assisted chemical vapor deposition (LACVD) for the first silicon nitride layer and laser assisted plasma enhanced chemical vapor deposition (LAPECVD) for the second silicon nitride layer. While SiN x thin films fabricated by LAPECVD exhibits remarkable encapsulation characteristics, OLEDs underneath the encapsulation layer risk being damaged during the plasma generation process. In order to prevent damage from the plasma, LACVD was completed prior to the LAPECVD as a buffer layer so that the laser during LACVD did not damage the devices because there was no direct irradiation to the surface. This two-step thin film encapsulation was performed sequentially in one chamber, which reduced the process steps and increased fabrication time. The encapsulation was demonstrated on green phosphorescent OLEDs with I–V-L measurements and a lifetime test. The two-step encapsulation process alleviated the damage on the devices by 19.5% in external quantum efficiency compared to the single layer fabricated by plasma enhanced chemical vapor deposition. The lifetime was increased 3.59 times compared to the device without encapsulation. The composition of the SiNx thin films was analyzed through Fourier-transform infrared spectroscopy (FTIR). While the atomic bond in the layer fabricated by LACVD was too weak to be used in encapsulation, the layer fabricated by the two-step encapsulation did not reveal a Si–O bonding peak but did show a Si–N peak with strong atomic bonding. • Thin film encapsulation by laser assisted plasma enhanced chemical vapor deposition. • Buffer layer by laser assisted chemical vapor deposition prior to encapsulation. • Increase of stability and protection of plasma damage through in-line pre-deposition. • 3.59 times increased LT80 in green phosphorescent organic light emitting diodes.

Research on Sapphire Deep Cavity Corrosion and Mask Selection Technology.

Aimed at the problem of the small wet etching depth in sapphire microstructure processing technology, a multilayer composite mask layer is proposed. The thickness of the mask layer is studied, combined with the corrosion rate of different materials on sapphire in the sapphire etching solution, different mask layers are selected for the corrosion test on the sapphire sheet, and then the corrosion experiment is carried out. The results show that at 250 °C, the choice is relatively high when PECVD (Plasma Enhanced Chemical Vapor Deposition) is used to make a double-layer composite film of silicon dioxide and silicon nitride. When the temperature rises to 300 °C, the selection ratio of the silicon dioxide layer grown by PECVD is much greater than that of the silicon nitride layer. Therefore, under high temperature conditions, a certain thickness of silicon dioxide can be used as a mask layer for deep cavity corrosion.

An Optical Planar Waveguide-Based Immunosensors for Determination of Fusarium Mycotoxin Zearalenone.

A planar waveguide (PW) immunosensor working as a polarisation interferometer was developed for the detection of mycotoxin zearalenone (ZON). The main element of the sensor is an optical waveguide consisting of a thin silicon nitride layer between two thicker silicon dioxide layers. A combination of a narrow waveguiding core made by photolithography with an advanced optical set-up providing a coupling of circular polarised light into the PW via its slanted edge allowed the realization of a novel sensing principle by detection of the phase shift between the p- and s-components of polarised light propagating through the PW. As the p-component is sensitive to refractive index changes at the waveguide interface, molecular events between the sensor surface and the contacting sample solution can be detected. To detect ZON concentrations in the sample solution, ZON-specific antibodies were immobilised on the waveguide via an electrostatically deposited polyelectrolyte layer, and protein A was adsorbed on it. Refractive index changes on the surface due to the binding of ZON molecules to the anchored antibodies were detected in a concentration-dependent manner up to 1000 ng/mL of ZON, allowing a limit of detection of 0.01 ng/mL. Structurally unrelated mycotoxins such as aflatoxin B1 or ochratoxin A did not exert observable cross-reactivity.

Reduced power degradation in bifacial PERC modules by a rear silicon oxide additive layer

In this paper, we investigate the influence of silicon oxide (SiOx) layer on the potential induced degradation (PID) of P-type monocrystalline PERC cells and modules. A SiOx layer was added between the aluminum oxide (AlOx) and silicon nitride (SiNx) layers on the rear side of PERC cells using a newly designed plasma enhanced chemical vapor deposition (PECVD) tool, MAiA from Meyer Burger. The performance of cells and modules with this AlOx + SiOx + SiNx stack was characterized by electrical breakdown (EBD), cell degradation indicator (CDi) and climate chamber PID tests. The EBD test results indicate that the AlOx + SiOx + SiNx stack has higher breakdown voltage than the typically used AlOx + SiNx stack. After undergoing CDi tests, power degradation is more severe in PERC cells with AlOx + SiNx passivation stack than those with AlOx + SiOx + SiNx passivation stack, as evidenced by darker photoluminescence. Bifacial modules made from PERC cells with the AlOx + SiOx + SiNx rear passivation stack demonstrate a significant reduction in rear PID from 12.3% to 4.2%. The results above depict that the addition of a SiOx layer between the AlOx and SiNx layers could effectively reduce the transfer of positive charges from the SiNx layer into the AlOx layer.

Evolution of the surface passivation mechanism during the fabrication of ex-situ doped poly-Si(B)/SiOx passivating contacts for high-efficiency c-Si solar cells

Passivating the contacts of crystalline silicon (c-Si) solar cells (SC) with a poly-crystalline silicon (poly-Si) layer on top of a thin silicon oxide (SiOx) is currently sparking interest for reducing carrier recombination at the interface between the metal electrode and the c-Si substrate. However, due to the interrelation between different mechanisms at play, a comprehensive understanding of the surface passivation provided by the poly-Si/SiOx contact in the final SC has not been achieved yet. In the present work, we report on an original ex-situ doping process of the poly-Si layer through the deposition of a B-rich dielectric layer followed by an annealing step to diffuse B dopants in the layer. We propose an in-depth investigation of the passivation scheme of the resulting B-doped poly-Si/SiOx contact by first comparing the surface passivation provided by ex-situ doped and intrinsic poly-Si/SiOx contacts at different steps of the fabrication process. The excellent surface passivation properties obtained with the ex-situ doped poly-Si(B) contact (iVoc = 733 mV and J0 = 6.1 fA cm−2) attests to the good quality of this contact. We then propose further STEM, ECV and ToF-SIMS characterizations to assess: i) the evolution of the microstructure and B-doping profile through ex-situ doping and ii) the diffusion profile of hydrogen in the poly-Si contact. Our results show a gradual filling of the poly-Si layer with active B dopants with increasing annealing temperature (Ta), which strengthens the field-effect passivation and enables an iVoc increase after annealing up to 800 °C. We also observe a diffusion of O from the SiON:B doping layer to the interfacial SiOx layer during annealing, that likely enhances the passivation stability of our ex-situ doped poly-Si contact with increasing Ta. Finally, we conclude that the mechanism dominating the surface passivation changes during the fabrication process of the poly-Si/SiOx contact from field-effect passivation after annealing (performed for B-diffusion in the contact) to chemical passivation after following hydrogenation of the samples (performed by depositing a H-rich silicon nitride layer).

Lithium Niobate Fabry-Perot microcavity based on strip loaded waveguides

In this work, we combine Lithium Niobate on insulator with a silicon nitride layer to form strip-loaded waveguides that can take advantage of the strong nonlinear optical coefficients of lithium niobate and of the high refractive contrast and ease of processing of silicon nitride. We describe the design and fabrication of a Fabry-Perot cavity formed by Distributed Bragg Reflectors. We discuss the design trade-offs implicit in the realisation of such microcavities of this nature and demonstrate an experimental quality factor of 2300, which is to our knowledge, the highest experimentally reported result for such type of waveguide based Fabry-Perot cavity.

Sensitivity enhancement with anti-reflection coating of silicon nitride (Si3N4) layer in silver-based Surface Plasmon Resonance (SPR) sensor for sensing of DNA hybridization

This work presents a highly sensitive silver (Ag) based Surface Plasmon Resonance (SPR) sensor with graphene-coated over Silicon nitride (Si3N4) for sensing of Deoxyribonucleic acid (DNA) hybridization. The design consists of five layers namely Ag, Si3N4, graphene, and sensing medium along with BK7 glass prism that couple light at the metal–dielectric interface. The performance of the present structure has been evaluated using the angular interrogation method. The present investigation reveals the difference in complementary DNA strands and mismatched DNA strands as well as single-nucleotide polymorphisms (SNP) event by examining the variation of resonance angle in the reflectivity spectrum. The performance of the present structure is compared with the contemporary structures and found better than existing sensors. Therefore, the proposed structure is suitable in the biochemical field for the detection of biomolecules interactions.

Silicon nitride deposited by laser assisted plasma enhanced chemical vapor deposition for next generation organic electronic devices

Deposition of stoichiometric silicon nitride without damage and stress at low temperature using plasma enhanced chemical vapor deposition (PECVD) is an important issue in the application to various areas such as microelectronics, micro-electromechanical system (MEMS), etc. In this study, the effects of laser assistance during PECVD (LAPECVD) of silicon nitride on the physical and chemical characteristics of deposited Si3N4 film were investigated. The LAPECVD assisted by 193 nm laser at 80 °C showed higher deposition ratescompared to PECVD due to the enhanced dissociation of the reactant gases. In addition, the stoichiometric ratio of N/Si and the residual stress of the deposited silicon nitride film were improved. When the silicon nitride was directly deposited on the organic light emitting diode (OLED) for thin film passivation, no electrical damage was observed for LAPECVD possibly due to the coverage of a thin silicon nitride layer on the OLED surface by laser assisted deposition while conventional PECVD showed a damage of the device due to ion bombardment by direct exposure to plasma. We believe the LAPECVD system can be used for various next-generation microelectronic industries where high quality film deposition with minimized damage during PECVD at low temperature is required.

Investigation of Passivating and Protecting Methods for Multijunction Solar Cells

Methods for passivation and protection of p–n junctions at places of their emergence at the lateral surface of a mesa structure and for sealing-off of multijunction solar cells based on a GaInP/GaAs/Ge structure have been studied. Protective coatings based on silicon nitride and silicone layers were examined by analyzing dark current–voltage characteristics of the solar cells. The distribution of the electroluminescence was analyzed.

Optimization of front SiNx/ITO stacks for high-efficiency two-side contacted c-Si solar cells with co-annealed front and rear passivating contacts

In this contribution, we present an electron selective passivating contact metallised with a low temperature process to target front side applications in crystalline silicon (c-Si) solar cells. In addition to an interfacial silicon oxide (SiOx) and an in-situ phosphorous doped micro-crystalline silicon (μc-Si(n)) layer, it comprises an ultra-thin indium tin oxide (ITO) layer of 15 nm for lateral conductivity and a hydrogen rich silicon nitride (SiNx:H) layer which serves as hydrogen (H) reservoir and as anti-reflection coating. We use one single thermal treatment for 30 min at 350 °C to sinter the screen-printed paste, to recover sputtering damage induced during ITO deposition, and to diffuse hydrogen from the SiNx:H layer towards the c-Si/SiOx interface where it passivates interfacial defects.Applied to symmetrically processed textured samples, we find implied open-circuit voltage (iVOC) > 728 mV for optimal ITO thickness of 15 nm and annealing temperatures of 350 °C. The developed stack was applied on the front textured side of co-annealed (800 °C) p-type c-Si solar cells in combination with a tunnel oxide hole selective passivating contact on the rear side. We demonstrate solar cells with fill factor (FF) up to 81.9% and an open-circuit voltage (VOC) up to 719 mV. With a short-circuit current density (JSC) of 38.6 mA/cm2, we obtain a final cell efficiency to 22.8%. We find that the annealing of the SiNx:H/ITO stack strongly increases the ITO free carrier density penalizing the solar cell spectral response at high wavelengths.

TiO2 microring resonators with high Q and compact footprint fabricated by a bottom-up method.

Titanium dioxide (TiO2) microring resonators (MRRs) with high quality factors (Qs) are demonstrated by using a new, to the best of our knowledge, bottom-up fabrication method. Pattern platforms with a T-shaped cross section are first defined by etching a thin top layer of silicon nitride and a thick bottom layer of silica and partially undercutting the silica. Then, TiO2 is deposited on the platforms to form the TiO2 waveguides and devices. TiO2 MRRs with different bending radii, waveguide widths, and gaps in the bus waveguide are fabricated and measured. The intrinsic Q(Qint) is achieved to be ∼1.1×105 at the telecommunication wavelengths, corresponding to a bend waveguide loss of 3.9 dB/cm while the compact MRR with a radius of 10 µm can still sustain a Qint of ∼105. These results not only unfold the feasibilities of the proposed bottom-up method for fabricating TiO2 waveguides and MRRs with high Qs and compact footprints but also suggest a new approach for fabricating waveguides in other materials, of which direct etching is not easily accessible.

Degradation of copper‐plated silicon solar cells with damp heat stress

AbstractCrystalline silicon solar cells with copper‐plated contacts are fabricated, encapsulated in ethylene‐vinyl acetate (EVA), and subject to extended damp heat stress (85° C and 85% relative humidity). We source cell precursors from several different cell manufacturers and employ several different patterning methods of the silicon nitride layer and deposit a plated front contact stack of nickel, copper, and tin using light‐induced plating. Across different Cu‐plated samples, we find similar degradation that impacts both series resistance and diode quality of the cells, indicating that there is some degradation of the p‐n junction. The overall degradation is on the order of 15%–20% of maximum power (PMP), and roughly half of this degradation is attributable to degradation of the p‐n junction. Control samples with silver‐screenprinted contacts do not exhibit the same degradation, and p‐n junction degradation in copper‐plated samples is prevented by changing the encapsulant from EVA to a polyolefin. The degradation mode is hypothesized to be the diffusion of copper from the contact, followed by the transport of this copper into the silicon cell via some mechanism facilitated by the degraded EVA encapsulant.

Highly sensitive silicon nitride biomedical sensor using plasmonic grating and ZnO layer

A biomedical sensor that sense concentration of glycerol in a deionized water with a high sensitivity is introduced in this work. A silicon nitride layer is added to the grated substrate, glass, then a plasmonic layer has been used before adding a zinc oxide layer on the top of the plasmonic gratings. The dimensions of all layers have been optimized to obtain the maximum refractive index sensitivity. Finite difference time domain method is used to calculate a transmitted signal from the proposed structure with and without analyte material. Figure of merit, quality factor and full width half maximum are also calculated at different duty cycle. The best performance of the senor has been obtained at duty cycle 35%, figure of merit 57.6, quality factor 57.3 and linewidth 14 nm. The maximum refractive index sensitivity is 806 nm/RIU which calculated at the same duty cycle. Detecting the glycerol concentration in deionized water is simulated at the maximum sensitivity and measured at different incident light angle. Finally, electric and magnetic fields and optical power, distributed along the structure are illustrated and discussed.

Efficiency Enhanced Grating Coupler for Perfectly Vertical Fiber-to-Chip Coupling.

In this work, a bidirectional grating coupler for perfectly vertical coupling is proposed. The coupling efficiency is enhanced using a silicon nitride (Si3N4) layer above a uniform grating. In the presence of Si3N4 layer, the back-reflected optical power into the fiber is diminished and coupling into the waveguide is increased. Genetic algorithm (GA) is used to optimize the grating and Si3N4 layer simultaneously. The optimal design obtained from GA shows that the average in-plane coupling efficiency is enhanced from about 57.5% (−2.5 dB) to 68.5% (−1.65 dB), meanwhile the average back-reflection in the C band is reduced from 17.6% (−7.5 dB) to 7.4% (−11.3 dB). With the help of a backside metal mirror, the average coupling efficiency and peak coupling efficiency are further increased to 87% (−0.6 dB) and 89.4% (−0.49 dB). The minimum feature size of the designed device is 266 nm, which makes our design easy to fabricate through 193 nm deep-UV lithography and lowers the fabrication cost. In addition, the coupler proposed here shows a wide-band character with a 1-dB bandwidth of 64 nm and 3-dB bandwidth of 96 nm. Such a grating coupler design can provide an efficient and cost-effective solution for vertical fiber-to-chip optical coupling of a Wavelength Division Multiplexing (WDM) application.

Al diffusion at AlN/Si interface and its suppression through substrate nitridation

One of the challenges for GaN-on-Si radio frequency (RF) device applications is the RF loss, which is mainly associated with a parasitic channel formed at the interface of AlN and high-resistivity Si substrates. However, the type of conductivity and formation mechanism of the parasitic channel remains controversial. Here, we report unambiguous evidence of Al diffusion at the AlN/Si interface and its effect on RF loss. Hall measurements reveal p-type conductivity at the interface. By combining with secondary ion mass spectroscopy measurements, the p-type conductivity is attributed to the Al diffusion from the AlN layers into the Si substrates, with Al being an acceptor in Si. Experimental data and simulations are in good agreement. We also demonstrate that substrate nitridation can indeed promote the formation of an amorphous silicon nitride layer, which plays a role in suppressing the Al diffusion and, thus, reducing the RF loss.