Stress Silicon Nitride Research Articles

Analysis and stress optimization of a strained germanium tin light-emitting diode with silicon nitride stressor

Analysis and stress optimization of a strained germanium tin light-emitting diode with silicon nitride stressor

Batch Fabrication of Microelectrode Arrays with Glassy Carbon Microelectrodes and Interconnections for Neurochemical Sensing: Promises and Challenges.

Flexible multielectrode arrays with glassy carbon (GC) electrodes and metal interconnection (hybrid MEAs) have shown promising performance in multi-channel neurochemical sensing. A primary challenge faced by hybrid MEAs fabrication is the adhesion of the metal traces with the GC electrodes, as prolonged electrical and mechanical stimulation can lead to adhesion failure. Previous devices with GC electrodes and interconnects made of a homogeneous material (all GC) demonstrated exceptional electrochemical stability but required miniaturization for enhanced tissue integration and chronic electrochemical sensing. In this study, we used two different methods for the fabrication of all GC-MEAs on thin flexible substrates with miniaturized features. The first method, like that previously reported, involves a double pattern-transfer photolithographic process, including transfer-bonding on temporary polymeric support. The second method requires a double-etching process, which uses a 2 µm-thick low stress silicon nitride coating of the Si wafer as the bottom insulator layer for the MEAs, bypassing the pattern-transfer and demonstrating a novel technique with potential advantages. We confirmed the feasibility of the two fabrication processes by verifying the practical conductivity of 3 µm-wide 2 µm-thick GC traces, the GC microelectrode functionality, and their sensing capability for the detection of serotonin using fast scan cyclic voltammetry. Through the exchange and discussion of insights regarding the strengths and limitations of these microfabrication methods, our goal is to propel the advancement of GC-based MEAs for the next generation of neural interface devices.

Enhanced second-harmonic generation in strained germanium-on-insulator microdisks for integrated quantum photonic technologies.

Quantum photonic circuits have recently attracted much attention owing to the potential to achieve exceptional performance improvements over conventional classical electronic circuits. Second-order χ(2) nonlinear processes play an important role in the realization of several key quantum photonic components. However, owing to their centrosymmetric nature, CMOS-compatible materials including silicon (Si) and germanium (Ge) traditionally do not possess the χ(2) response. Recently, second-harmonic generation (SHG) that requires the χ(2) response was reported in Ge, but no attempts at enhancing the SHG signal have been conducted and proven experimentally. Herein, we demonstrate the effect of strain on SHG from Ge by depositing a silicon nitride (Si3N4) stressor layer on Ge-on-insulator (GOI) microdisks. This approach allows the deformation of the centrosymmetric unit cell structure of Ge, which can further enhance the χ(2) nonlinear susceptibility for SHG emission. The experimental observation of SHG under femtosecond optical pumping indicates a clear trend of enhancement in SHG signals with increasing strain. Such improvements boost conversion efficiencies by 300% when compared to the control counterpart. This technique paves the way toward realizing a CMOS-compatible material with nonlinear characteristics, presenting unforeseen opportunities for its integration in the semiconductor industry.

Quality factor comparison between graphene and SiN with triangular lattice phononic crystal structure based on dissipation dilution theory

Nanomechanical resonators attract interests both in fundamental and applied fields, offering outstanding mass and force sensitivity, relying on both the low mass m and high quality factor Q. However, the quality factor typically does not exceed the inverse of the material loss angle φ, related to resonant energy dissipation. Recently, some exceptions breaking the 1/φ limiting rule in a great extent have been reported in use of highly stressed silicon nitride material. Up to now it is interpreted that the pre-stress seems to ‘dilute’ the intrinsic energy dissipation according to Zener model. Dissipation dilution effect could be better if the device dimension is reduced, which implies that the smaller the resonator, the higher the quality factor. Single-layer graphene's thickness is 0.335 nm, which is one hundredth of silicon nitride’ typical thickness about 30 nm, indicating that the dissipation dilution effect of graphene could be much better than that of silicon nitride. Through theoretical calculation, the quality factor amplification coefficient defining the dissipation dilution effect quantitatively of graphene is 2272 times that of SiN. By COMSOL finite element simulation, we further confirm this conclusion. Take the first defect mode for example, the amplification coefficient of graphene and SiN is about 3.02 × 105 and 151 respectively, with the division result about 2004 times. As the overall size increases, the division results gradually converge to a stable value about 2260.

Effect of Pressure on Carbon monoxide Oxidation on Titania Supported Platinum Nanoparticles Catalyst

Thermographic testing methodology was developed to facilitate measurements of particle dimension and substrate influence in heterogeneous catalysts. A screening chip with several areas of less stress silicon nitride membranes which displays less heat conductivity and heat capacity was used. Heat produced during the reaction on catalysts deposited on membranes was established through IR camera which gave the value of the turn over frequency. Effect of pressure on CO conversion on titania supported Pt particles of different dimension was measured on 120 catalysts concurrently. The reaction was studied at various O2 and CO pressures at 170 ℃ and 240 ℃. At these temperature conditions, activity increased with increase of O2 and CO pressure, in agreement with previous reports.

Observing Second Harmonic Generation and Enhancing Second-Order Nonlinearity from Germanium-on-Insulator

Second-order nonlinear χ2 processes hold the key to realizing various promising classical and quantum applications. Only conventional non-centrosymmetric materials like aluminium nitride (AlN) and lithium niobate (LN) exhibit a strong second-order nonlinearity. While germanium (Ge) has the advantage of mature foundry processing due to its complementary metal-oxide-semiconductor (CMOS) compatibility compared to conventional χ2 materials, it has a weak second-order nonlinearity owning to its inversion symmetry. It is predicted that exploiting micro-scale strain gradients induced by silicon nitride (SiN) stressors can break the inversion symmetry of Ge and enable more efficient second harmonic generation (SHG) in mid-infrared (MIR). We herein demonstrate SHG in visible and telecom S-band ranges by pumping our germanium-on-insulator (GOI) sample with a tunable femtosecond pulse laser. The signature quadratic power dependence curve of SHG has also been experimentally observed. In this report, we also propose a novel approach to breaking the inversion symmetry of Ge, which can amplify its weak second-order nonlinearity. We designed a Ge micro-bridge with a periodically changing nano-scale strain gradient that is orders of magnitude higher than the previously proposed structures utilizing SiN stressors. This results in a 3-orders of magnitude enhancement in χ2 according to both a classic anharmonic model and density potential theory. Our work paves the way toward a CMOS compatible and high χ2 nonlinear material for integrated photonic applications.

Structural Optimization of Graphene Triangular Lattice Phononic Crystal Based on Dissipation Dilution Theory.

Nanomechanical resonators offer brilliant mass and force sensitivity applied in many fields, owing to a low mass m and high-quality factor Q. However, in vibrating process, resonant energy is inevitably dissipated. Typically, quality factor does not surpass the inverse of the material loss angle φ. Recently, some exceptions emerged in the use of highly stressed silicon nitride material. As yet, it is interpreted that the pre-stress seems to “dilute” the intrinsic energy dissipation according to the Zener model. Is there any other material that could further break the 1/φ limit and achieve higher quality factors? In our previous research, through theoretical calculation and finite element simulation, we have proved that graphene’s quality factor is two orders of magnitude larger than silicon nitride, on account of the extremely thin thickness of graphene. Based on this, we further optimize the structure of phononic crystals to achieve higher quality factors, in terms of duty cycle and cell size. Through simulation analysis, the quality factor could improve with a larger duty cycle and bigger cell size of triangular lattice phononic crystal. Unexpectedly, the Q amplification coefficient of the 3 × 5-cell structure, which is the least number to compose a phononic crystal with a central defect area, is the highest. In contrast, the minimal cell-number structure in hexagonal lattice could not achieve the brilliant dissipation dilution effect as well as the triangular one. Then we consider how overall size and stress influence quality factor and, furthermore, compare theoretical calculation and finite simulation. Lastly, we start from the primitive 3 × 5 cells, constantly adding cells to the periphery. Through simulation, to our surprise, the largest Q amplification coefficient does not belong to the largest structure, instead originating from the moderate one consisting of 7 × 13 cells.

Tensile Strained Germanium Microstructures: A Comprehensive Analysis of Thermo‐Opto‐Mechanical Properties

The influence of the thermomechanical effects on the optical properties of germanium microstructures is investigated. Finite element method (FEM) calculations allow a complete spatial assessment of mechanical deformations induced by a silicon nitride (SiN) stressor layer deposited on Ge micropillars. Simulated strain maps are confirmed by experimental maps obtained by Raman spectroscopy. The theoretical investigation on strain‐dependent band structure, including the presence of a strain gradient along the longitudinal direction, is exploited to fully capture photoluminescence spectroscopy experiments. Finally, the joint effect of temperature and strain on the fundamental bandgap is also quantified.

PIC-integrable, uniformly tensile-strained Ge-on-insulator photodiodes enabled by recessed SiNx stressor

Mechanical strain engineering has been promising for many integrated photonic applications. However, for the engineering of a material electronic bandgap, a trade-off exists between the strain uniformity and the integration compatibility with photonic-integrated circuits (PICs). Herein, we adopted a straightforward recess-type design of a silicon nitride ( SiN x ) stressor to achieve a uniform strain with enhanced magnitude in the material of interest on PICs. Normal-incidence, uniformly 0.56% tensile strained germanium (Ge)-on-insulator (GOI) metal-semiconductor-metal photodiodes were demonstrated, using the recessed stressor with 750 MPa tensile stress. The device exhibits a responsivity of 1.84 ± 0.15 A / W at 1550 nm. The extracted Ge absorption coefficient is enhanced by ∼ 3.2 × to 8340 cm − 1 at 1612 nm and is superior to that of In 0.53 Ga 0.47 As up to 1630 nm limited by the measurement spectrum. Compared with the nonrecess strained device, additional absorption coefficient improvement of 10%–20% in the C -band and 40%–60% in the L -band was observed. This work facilitates the recess-strained GOI photodiodes for free-space PIC applications and paves the way for various (e.g., Ge, GeSn or III-V based) uniformly strained photonic devices on PICs.

Enhanced room-temperature electroluminescence from a germanium waveguide on a silicon-on-insulator diode with a silicon nitride stressor.

Germanium (Ge) is an attractive material for monolithic light sources on a silicon chip. Introduction of tensile strain using a silicon nitride (SiNx) stressor is a promising means for Ge-based light sources due to the enhancement of direct band gap recombination. We propose a device structure that enables current injection from a silicon-on-insulator (SOI) diode to a Ge waveguide with a SiNx stressor formed by a simple fabrication process. Direct-band-gap electroluminescence and direct-band-gap shrinkage due to the applied SiNx stressor was confirmed. Intensity of electroluminescence from the Ge waveguide with the SiNx stressor was about three times higher than that corresponding to the device without the SiNx stressor.

Stress Engineering for Drive Current Enhancement in Silicon Carbide (SiC) Power MOSFETs

The poor interface quality of the Silicon Carbide/oxide (SiC/SiO2) interface severely degrades the electron surface channel mobility in SiC-based power devices. Based on transfer characteristic simulations (with a deck calibrated to experimental data), this work predicts improved mobility with stress engineering, a well-established technique for performance enhancement in low power silicon (Si) transistor technology. Process simulation of Si and SiC-based devices with Silicon Nitride (Si3N4) stressor layer has been carried out to estimate the stress generated in the channel. SiC D-MOSFET we have also computed the effect of varying stress magnitude, direction, and position in the device.

Analysis of stress distribution in microfabricated germanium with external stressors for enhancement of light emission

In the field of silicon photonics, germanium (Ge) is an attractive material for monolithic light sources. Tensile strain is a promising means for Ge based light sources due to enhancing direct band gap recombination. We investigated strain engineering in Ge using silicon nitride (SiNx) stressors. We found that microfabricated Ge greatly improves the tensile strain because SiNx on the Ge sidewalls causes a large tensile strain in the direction perpendicular to the substrate. Tensile strain equivalent to an in-plane biaxial tensile strain of 0.8% at maximum was applied, and the PL emission intensity was improved more than five times at the maximum.

Membrane sandwich squeeze film pressure sensors

Squeeze film pressure sensors exploit the dynamical modification of the mechanical properties of oscillating elements due to the compression of a fluid in a small gap region and allow for direct and absolute pressure measurements. This Tutorial article discusses the working principles of membrane sandwich squeeze film pressure sensors—i.e., sensors comprised of a parallel arrangement of two large-area, ultrathin suspended films forming a few-micrometer gap, and immersed in a fluid—and focuses on their operation in the free molecular flow regime. The effects of gas pressure on the vibrations of the membrane resonators and their coupled dynamics are discussed in general terms before recent experimental implementations using high tensile stress silicon nitride membranes are presented.

The particle size dependence of CO oxidation on model planar titania supported gold catalysts measured by parallel thermographic imaging

A parallel thermographic screening methodology has been developed which allows the measurements of the particle size and support influences on model planar heterogeneous catalysts. A screening chip was designed and fabricated in order to produce multiple fields of low stress silicon nitride membranes that exhibit low thermal conductivity and heat capacity. The heat generated on supported model catalysts in an exothermic reaction on the membranes was measured using a thermal (infra-red) imaging camera, which in turn provided a measure of the turn over frequency (TOF) for the reaction. The catalytic activity for CO oxidation on titania supported gold model catalysts with varying particle size has been measured on 100 catalysts simultaneously. The reaction has been investigated at 80 °C and 170 °C, and pressures ranging between 0.06 mbar and 1.5 mbar for various O2:CO ratios. Under all conditions investigated, a monotonic increase in the TOF is observed with decreasing particle diameter (d) which is proportional to ca. d−1.8 in the range 6 > d/nm > 1.5. This is in the opposite direction to the number of potentially active perimeter sites which increases linearly with increasing particle size on these catalysts. We show that the surface area specific activity of the gold is increasing even more steeply with reduced particle size, and is proportional to ca. d−4. This rate of increase in activity is significantly higher than one would expect by any increase one may expect as a result of more active low co-ordinate sites on the gold. The steep increase in activity is ascribed to an electronic interaction between the substrate and the particle.

Stresses in thin films: an experimental study

Thin film technology is a relatively young and ever-growing field in the physical and chemical sciences, which is confluence of materials science, surface science, applied physics and applied chemistry. Thin film technology has its objectives in the provision for scientific bases for the methods and materials used in thin film electronics (integrated circuits and micro-electro-mechanical system). Additionally, it provides a sufficient data in the area of applications to permit for understanding of those aspects of the subject that might still be termed an “art”. Thin films of metals were probably first prepared in asystematic manner by Michael Faraday, using electrochemical methods. Thin films go through several distinct stages during growth, each affecting the resulting film microstructure and internal stress. Hence before proceeding to synthesis and characterization, the knowledge of formation, growth and stress generation in thin film is necessary. This paper explains the influence of process parameters on stress in silicon nitride (Si3N4) thin films with experimental results.

Stressor-layer-induced elastic strain sharing in SrTiO3 complex oxide sheets

A precisely selected elastic strain can be introduced in submicron-thick single-crystal SrTiO3 sheets using a silicon nitride stressor layer. A conformal stressor layer deposited using plasma-enhanced chemical vapor deposition produces an elastic strain in the sheet consistent with the magnitude of the nitride residual stress. Synchrotron x-ray nanodiffraction reveals that the strain introduced in the SrTiO3 sheets is on the order of 10−4, matching the predictions of an elastic model. This approach to elastic strain sharing in complex oxides allows the strain to be selected within a wide and continuous range of values, an effect not achievable in heteroepitaxy on rigid substrates.

Mid-infrared light emission > 3 µm wavelength from tensile strained GeSn microdisks.

GeSn alloys with Sn contents of 8.4 % and 10.7 % are grown pseudomorphically on Ge buffers on Si (001) substrates. The alloys as-grown are compressively strained, and therefore indirect bandgap. Undercut GeSn on Ge microdisk structures are fabricated and strained by silicon nitride stressor layers, which leads to tensile strain in the alloys, and direct bandgap photoluminescence in the 3-5 µm gas sensing window of the electromagnetic spectrum. The use of pseudomorphic layers and external stress mitigates the need for plastic deformation to obtain direct bandgap alloys. It is demonstrated, that the optically pumped light emission overlaps with the methane absorption lines, suggesting that GeSn alloys are well suited for mid-infrared integrated gas sensors on Si chips.

Parametric Oscillation, Frequency Mixing, and Injection Locking of Strongly Coupled Nanomechanical Resonator Modes

We study locking phenomena of two strongly coupled, high quality factor nanomechanical resonator modes to a common parametric drive at a single drive frequency in different parametric driving regimes. By controlled dielectric gradient forces we tune the resonance frequencies of the flexural in-plane and out-of-plane oscillation of the high stress silicon nitride string through their mutual avoided crossing. For the case of the strong common parametric drive signal-idler generation via nondegenerate parametric two-mode oscillation is observed. Broadband frequency tuning of the very narrow linewidth signal and idler resonances is demonstrated. When the resonance frequencies of the signal and idler get closer to each other, partial injection locking, injection pulling, and complete injection locking to half of the drive frequency occurs depending on the pump strength. Furthermore, satellite resonances, symmetrically offset from the signal and idler by their beat note, are observed, which can be attributed to degenerate four-wave mixing in the highly nonlinear mechanical oscillations.

Stress Engineering With Silicon Nitride Stressors for Ge-on-Si Lasers

Side and top silicon nitride stressors were proposed and shown to be effective ways to reduce the threshold current Ith and improve the wall-plug efficiency {\eta}wp of Ge-on-Si lasers. Side stressors only turned out to be a more efficient way to increase {\eta}wp than using top and side stressors together. With the side stressors only and geometry optimizations, a {\eta}wp of 30.5% and an Ith of 50 mA (Jth of 37 kA/cm2) can be achieved with the defect limited carrier lifetime of 1 nsec. With the defect limited carrier lifetime of 10 nsec, an Ith of 7.8 mA (Jth of 5.8 kA/cm2) and a wall-plug efficiency of 38.7% can be achieved. These are tremendous improvements from the case without any stressors. These results give strong support to the Ge-on-Si laser technology and provide an effective way to improve the Ge laser performance.

Finite-time Stückelberg interferometry with nanomechanical modes

Stückelberg interferometry describes the interference of two strongly coupled modes during a double passage through an avoided energy level crossing. In this work, we investigate finite-time effects in Stückelberg interferometry and discuss the exact analytical solution of the double passage Stückelberg problem by expanding the finite-time solution of the Landau–Zener problem. Approximating the return probability amplitudes of the double passage in distinct limits reveals uncharted parameter regimes of Stückelberg interferometry where finite-time effects affect the coherent exchange of energy. We find the long-time limit of the exact solution to formally coincide with the well-established adiabatic impulse model which is, to the best of our knowledge, the only regime of Stückelberg interferometry reported so far. Experimentally, we study all predicted regimes using a purely classical, strongly coupled nanomechanical two-mode system of high quality factor. The classical two-mode system consists of the in-plane and out-of-plane fundamental flexural mode of a high stress silicon nitride string resonator, coupled via electric gradient fields. We exploit our experimental and theoretical findings by studying the onset of Stückelberg interference in dependence of the characteristic system control parameters and obtain characteristic excitation oscillations between the two modes even without the explicit need of traversing the avoided crossing. The presented findings are not limited to classical mechanical two-mode systems but can be applied to every strongly coupled (quantum) two-level system, for example a spin-1/2 system or superconducting qubit.