SiNx Membrane Research Articles

Synchronous Optical and Electrical Measurements of Single DNA Molecules Translocating Through a Solid State Nanopore

Nucleic acids and proteins are increasingly being analyzed using solid-state nanopores. The nanopore method relies on the measurement of transient conductance changes of the nanopores as charged biomolecules are being electrophoretically driven into it. Although electrical detection is highly appealing for the label-free analysis of biological samples, our understanding of the dynamics of charged biopolymers through such nanoconfined geometries is limited by the information captured by the electrical signal alone.We report the development of an instrument capable of interrogating solid-state nanopore devices by simultaneous electrical and optical measurements. Instead of the conventional TEM-drilled nanopores, we used a method pioneered by our group, and fabricate nanopores in a thin SiNx membrane via dielectric breakdown in solution . In this presentation, we show how a range of odd behaviors of the ionic current can be explained with parallel fluorescence imaging of the nanopore. Our custom instrument allows us to: (i) study these anomalous events; (ii) probe the dynamics of DNA capture; (iii) monitor, for the first time, the creation process of a nanopore; and (iv) determine its location on the dielectric membrane;.A better understanding of these anomalous single-molecule events during DNA passage through solid-state nanopores is essential to increase reliability of nanopore-based sensing.

Noise and its reduction in graphene based nanopore devices

Ionic current fluctuations in graphene nanopore devices are a ubiquitous phenomenon and are responsible for degraded spatial and temporal resolution. Here, we descriptively investigate the impact of different substrate materials (Si and quartz) and membrane thicknesses on noise characteristics of graphene nanopore devices. To mitigate the membrane fluctuations and pin-hole defects, a SiNx membrane is transferred onto the substrate and a pore of approximately 70 nm in diameter is perforated prior to the graphene transfer. Comprehensive noise study reveals that the few layer graphene transferred onto the quartz substrate possesses low noise level and higher signal to noise ratio as compared to single layer graphene, without deteriorating the spatial resolution. The findings here point to improvement of graphene based nanopore devices for exciting opportunities in future single-molecule genomic screening devices.

3D hierarchical architectures based on self-rolled-up silicon nitride membranes

This study presents the superior structural versatility of strained silicon nitride (SiNx) membranes as a platform for three-dimensional (3D) hierarchical tubular architectures. The effects of compressive and tensile stressed SiNx layer thickness on the self-rolled-up tube curvature, the sacrificial layer etching anisotropy on rolling direction and chirality, and stress engineering by localized thickness control or thermal treatment, are explored systematically. Using strained SiNx membranes as an electrically insulating and optically transparent mechanical support, compact 3D hierarchical architectures involving carbon nanotube arrays and passive electronic components are demonstrated by releasing the functional structures deposited and patterned in 2D. These examples highlight the uniqueness of this platform that exploits 2D processing and self-assembly to achieve highly functional 3D structures.

Formation mechanisms of embedded nanocrystals in SiNx

We have investigated the formation of embedded nanocrystals (NCs) in SiNx using Ga+ focused-ion beam irradiation of SiNx membranes, followed by rapid thermal annealing (RTA). During irradiation, redeposition is enhanced by developing side walls, leading to enhanced near-surface [Ga] and [Si]. Subsequent RTA leads to the formation of Si and Ga NCs embedded in SiNx. When the ratio of the irradiated area to the sidewall area is increased, redeposition is limited, and SiNx and GaN NCs are also apparent. We discuss the effect of limited redeposition on NC formation and the catalytic effect of Ga on Si NC nucleation and growth.

Role of radiative decay of valence plasmons in transmission spectra of Si, SiNx and PET membranes

Membranes of Si, SiNx and polyethylene terephthalate (PET) were investigated via vacuum ultraviolet (VUV) transmission measurements. The transmission spectra show maxima at energies equal to energies of valence plasmons (VPs) which are interpreted as signatures of radiative decay of VPs. Resonant generation and radiative decay mechanism of valence plasmons and their effects on transmission spectra are discussed. Furthermore, the energy of VPs in SiNx was also confirmed by photo electron spectroscopy (PES) measurements on SiNx thin film. The presented results demonstrate the light induced resonant generation and radiative decay of both, valence bulk and valence surface plasmons.

MEMS solid propellant thruster array with micro membrane igniter

A microigniter with improved membrane for MEMS solid propellant thruster array is proposed. Although existing igniters using dielectric SiNx membranes consume low power, they cannot withstand shocks during the propellant charging process. A glass wafer is selected as the material for the igniter. A glass membrane is fabricated by the anisotropic wet etching of photosensitive glass. Platinum is used for the ignition coil. A 30–40-μm thick glass membrane exhibited sufficient strength to withstand accidental impacts during the propellant charging process. Further, the microigniter using the glass membrane had an appropriate power consumption to ignite the solid propellant. The thermal, electrical, and mechanical characteristics of the fabricated microigniter were measured. The proposed microigniter provided the sufficient heat for the propellant to be ignited with the given electric power. The fracture pressure of the glass membrane was thrice higher than the conventional microigniter. A solid propellant lead styphnate was filled into the microigniter without any additional processes. Ignition tests with fully assembly MEMS thrusters were performed successfully. Thus, it is demonstrated that a simpler, robust, and low-cost fabrication process of an igniter that performs well when assembled into a micro solid propellant thruster (MSPT) array is possible.

Phonon Transport and Thermoelectricity in Defect-Engineered InAs Nanowires

ABSTRACTThere have been reports of improvements in the thermoelectric figure of merit through the use of nanostructured materials to suppress the lattice thermal conductivity. Here, we report on a fundamental study of the combined effects of defect planes and surface scattering on phonon transport and thermoelectric properties of defect-engineered InAs nanowires. A microfabricated device is employed to measure the thermal conductivity and thermopower of individual suspended indium arsenide nanowires grown by metal organic vapor phase epitaxy. The four-probe measurement device consists of platinum resistance thermometers and electrodes patterned on two adjacent SiNx membranes. A nanowire was suspended between the two membranes, and electrical contact between the nanowire and the platinum electrodes was made with the evaporation of a Ni/Pd film through a shadow mask. The exposed back side of the device substrate allows for characterization of the crystal structure of the suspended nanowire with transmission electron microscopy (TEM) following measurement. The 100-200 nm diameter zincblende (ZB) InAs nanowire samples were grown with randomly spaced twin defects, stacking faults, or phases boundaries perpendicular to the nanowire growth direction, as revealed by transmission electron microscopy (TEM) analysis. Compared to single-crystal ZB InAs nanowires with a similar lateral dimension, the thermal conductivity of the defect-engineered nanowires is reduced by fifty percent at room temperature.

3D fabrication by stacking prepatterned, rigidly held membranes

The authors describe an approach to fabricating high resolution, complex 3D structures based on the stacking of thin membranes that have been patterned in advance. The membranes are attached to a rigid frame by means of tethers that are strong enough to permit normal handling but can be cleaved after bonding. The tether shape was designed using finite-element analysis to enable clean cleavage at a specific location so that fragments are avoided that would interfere with the bonding of subsequent layers. The authors used 12 × 12 mm SiNx membranes, 350 nm thick, patterned with a square array of holes at 600 nm pitch and demonstrate the stacking of three layers.

Substrate-dependent quasiparticle recombination time in superconducting resonators

We demonstrate an increased quasiparticle recombination time in superconducting resonators on a SiNx membrane, compared to identical resonators on a SiNx/Si wafer. An interpretation is given using a thermal model of the membrane. Using an array of tunnel junctions to cool or heat the membrane, we show that the resonators on the membranes are extremely sensitive to small changes of the phonon temperature, which renders them excellent phonon thermometers with a noise level equivalent to 5μK/Hz. The experimental set-up is in principle an ideal platform to study the interplay of quasiparticles and phonon populations in superconductors.

Evidence that small proteins translocate through silicon nitride pores in a foldedconformation

The interaction of three proteins (histidine-containing phosphocarrier protein, HPr,calmodulin, CaM, and maltose binding protein, MBP) with synthetic silicon nitride (SiNx) membranes has been studied. The proteins which have a net negative charge wereelectrophoretically driven into pores of 7 and 5 nm diameter with a nominal length of 15 nm.The % blockade current and event duration were measured at three different voltages. For atranslocation event it was expected that the % block would be constant with voltage whilstthe event duration would decrease with increasing voltage. On the basis of these criteria,we deduce that MBP whose largest dimension is 6.5 nm does not translocate whereas upto 40% of CaM molecules can translocate the 7 nm pore as can a majority ofHPr molecules, with some translocations being observed for the 5 nm pore. Fortranslocation events the magnitude of the % blockade current is consistent with afolded conformation of the proteins surrounded by a hydration shell of 0.5–1.0 nm.

Thermopile Infrared Detector with Detectivity Greater Than 108 cmHz(1/2)/W

In this paper, the design, fabrication and experimental results of the thermopile infrared detector, with a single layer of low-stress SiNx membrane, instead of thin sandwich layer membrane of SiO2–Si3N4 are presented. Thermal isolation is achieved by using back etching of bulk silicon. Thermopiles are consisted of serially interconnected p-poly-Si/Al thermocouples supported by the single layer of SiNx membrane with low stress. Au/Ti reflective coating was evaporated on the surface of cold junctions of the thermopile to block incident radiation. In the measurement, we find that infrared absorbance of SiNx membrane to different wavelength is diverse and less than 100%, which has great influence on calculating the actual absorbing power of the detector, so the infrared (IR) transmission spectrum is measured to calibrate the actual infrared absorbing amount of the detector. The analysis result shows that only 43.72% infrared radiation is absorbed by the detector. Based on the measurement of IR transmission spectrum and output voltage of the detector, the response sensitivity of the detector is calculated as 31.65 V/W, detectivity of the detector is 1.16 × 108 cmHz(1/2)W−1, and response time of the detector is 126 ms.

Discriminating Bases by Stretching Double-Stranded DNA in a Nanopore

We report a new method for trapping a single molecule of double-stranded DNA (dsDNA) in a solid-state nanopore in SiNx membrane and describe the prospects for sequencing it. It is possible to trap a single dsDNA molecule in a nanopore <3nm in diameter by first applying a voltage larger than this threshold and forcing the molecule to translocate through the pore. If the electric field is then rapidly switched to a value below threshold, the DNA becomes trapped for seconds in the pore, compared to a sub-millisecond translocation if the field is maintained above threshold. Moreover, if the duration in the trap is commensurate with the bandwidth we can discriminate distinct signatures of C-G and A-T base-pairs by simply measuring the pore current. Molecular dynamics simulations of these experiments reveal that, when trapped, the dsDNA is stretched in the pore in a specific tilted orientation, depending on the orientation of the leading nucleotides, while the B-form canonical structure is preserved outside the pore. Finally, we show using streptavidin bound biotinylated dsDNA (Fig. 1a) that it's possible to discriminate stretched basepairs in the trapped configuration (Fig. 1b,c) between A-T and C-G.View Large Image | View Hi-Res Image | Download PowerPoint Slide

Fabrication of large area ultrathin silicon membrane: Application for high efficiency extreme ultraviolet diffraction gratings

Silicon membranes of 100nm thick (and below) over several mm2 have been fabricated for high efficiency extreme ultraviolet (EUV) transmission grating. The perfect planarity (&amp;lt;1nm) and the high transparency (&amp;gt;80%) at 13.5nm wavelength have been measured. In comparison to SiNx membranes (40% transmission), the silicon membranes allow high resolution EUV interference lithography using the second order diffraction of the molybdenum grating. The fabrication of such phase gratings has been performed and the diffraction efficiency measurement is 27% for the silicon membrane and the Mo grating.

On-chip characterization of low-noise microstrip-coupled transition edge sensors

Transition edge sensors (TESs) are used extensively in millimeter-wave and submillimeter-wave astronomy. The next technological push is to reduce the noise equivalent powers from 10−17 to 10−20 W Hz−1/2 in order to take full advantage of the exceptionally low backgrounds associated with cooled-aperture space telescopes. We describe a lab-on-a-chip (LoC) for measuring the small-signal and noise properties of ultralow-noise microstrip-coupled TESs. The LoC comprises two suspended SiNx membranes, one of which supports a single-mode, variable-temperature blackbody source, and the other a microstrip-coupled TES. The two devices are connected by a superconducting microstrip transmission line. The temperature of the source is determined by Johnson noise thermometry using superconducting quantum interference device readout. In this paper, we describe the theory, layout, operation, and calibration of the experimental system and report on two prototype devices. The LoC concept has many advantages, and already we have been able to assess the optical efficiencies of our TESs. We have started to gain an appreciation of the losses associated with 100–300 GHz microminiature superconducting microstrip transmission lines at low temperatures. The next phase of our work is to apply the technique to ultralow-noise detectors, to study fluctuation phenomena in multimode devices, and to investigate the behavior of more complicated integrated circuits.

Thermal models and noise in transition edge sensors

Detectors based on transition edge sensors (TESs) must achieve theoretically predicted noise levels if they are to be suitable for the next generation of space-borne astronomical telescopes. The noise of an ideal detector is determined by the sum of three contributions: (i) thermal-fluctuation noise in the heat link to the bath, (ii) Johnson noise in the sensor itself, and (iii) noise in the electrical read-out circuit. Many groups have reported TESs with noise levels significantly above the theoretical predictions. We use two well-defined experimental configurations to measure the read-out noise spectra of Mo–Cu TESs with transition temperatures of 370 and 200mK. The TESs are geometrically simple, comprising superconducting and normal metal films on a silicon nitride (SiNx) membrane. The measurements are compared with a multiparameter noise model, which is based on a physical model of the thin-film devices. Taking into consideration separate, accurate measurements of the heat capacity of identical SiNx membranes, we are able to provide a good account of both the magnitude and frequency dependences of the measured current-noise spectra. We find that an important excess noise mechanism involves the random exchange of heat between the heat capacity of the bilayer and the heat capacity of the nitride membrane, with either the thermal conductance of the membrane, or in some cases the thermal conductance of the bilayer, being the mediating path. Clear design recommendations are given to achieve the best possible noise performance.

Phonon transport in suspended silicon nitride membranes at low temperatures

We have studied experimentally the nature of phonon transport in 750 nm and 200 nm thick free-standing silicon nitride (SiNx) membranes over a temperature range of 0.1–1K. Measurements were performed by using a radially symmetric DC heater and several normal metal-insulator-superconductor (NIS) tunnel junction thermometers to detect the phonon temperature Tp at several different distances from the heater. Our data indicates that phonon transport is three dimensional in both membranes, and mostly ballistic at the low temperature range of our experiment. At temperatures above 0.5 K there are indications of a transition to a more diffusive regime.

Low stress nanoporous SiN&lt;SUB align=right&gt;x membrane for cell culture

Micromachined nanoporous membrane for cell culture is one of the promising applications for biomolecular separation and immunoisolation, in which Silicon Nitride (SiNx) receives particular interest due to its several advantages compared to polymeric membranes. Our works focused on fabricating nanoporous SiNx layer with near zero residual stress. This paper investigated the influence of Radio Frequency (RF), power and reactant gases to the SiNx deposition rates and residual stress, and developed the optimised process to produce near zero stress SiNx layer. By applying this technique, nanoporous SiNx membranes have been fabricated and tested for cell culture. By cultivating the mouse D1 mesenchymal stem cells on top of the nanoporous membrane, the results showed that mouse D1 mesenchymal stem cells were able to grow well. This shows that the nanoporous membrane can be used as the platform for interfacing with living cells to become biocapsules for biomolecular separation and immunoisolation.

A close proximity self-aligned shadow mask for sputter deposition onto a membrane or cavity

In this paper we report on the fabrication of a close proximity shadow mask designed for sputtering into cavities or onto the back surface of freestanding silicon nitride (SiNx) membranes. Sputtering into a well-defined area on a fragile surface is difficult since sputter deposition through a shadow mask separated from the deposition surface typically results in spreading of the deposited material. The area of spreading beyond the desired area of deposition depends on the vertical separation between the shadow mask and the surface of the membrane. In our design, a high degree of accuracy (±5 µm) in the separation (25 µm) between the shadow mask and the deposition surface is achieved. The shadow mask is made from SiNx-coated silicon wafers, using potassium hydroxide (KOH) etching on both sides of the wafer. The design rules chosen to maintain accuracy of the fit between the shadow mask and the deposition surface over various etch conditions, fabrication and methods used for convex-corner compensation and the alignment to the wafer crystal axis, which also contribute to an accurate fit, are discussed. Spreading of deposited material due to sputtering is limited to about 40 µm when this shadow mask is used.

Spectral Analysis of Nanomaterials using a Transition-Edge Sensor Microcalorimeter Mounted on a Field-Emission Scanning Electron Microscope

A prototype transition-edge sensor (TES) microcalorimeter is successfully integrated into a commercial field-emission scanning electron microscope (FE-SEM). The microcalorimeter is composed of a gold (Au) absorber, a Au/Ti bilayer thermometer and a thermal isolation structure with a SiNx membrane. Operating temperatures of 100–150 mK are obtained with a dilution refrigerator. The measured energy resolution was between 19–22 eV for Al Kα at an acceleration voltage of 5 keV. The newly developed system was applied to the analysis of nanosheets for the first time at a low acceleration voltage (≤ 5 kV). The energy dispersive spectrometer (EDS) spectra of Nb3O8 nanosheets of different thicknesses (less than 20 nm) were successfully detected. Moreover, Au particles on carbon nanotubes with a thickness less than 1 nm are detected clearly. With further improvement of both energy resolution and count rate, this system holds the promise for practical X-ray compositional characterization of nanomaterials with high image spatial resolution in the low-acceleration-voltage regime.

Large Anisotropy of Electrical Properties in Layer-Structured In2Se3 Nanowires

Layer-structured indium selenide (In 2Se 3) nanowires (NWs) have large anisotropy in both shape and bonding. In 2Se 3 NWs show two types of growth directions: [11-20] along the layers and [0001] perpendicular to the layers. We have developed a powerful technique combining high-resolution transmission electron microscopy (HRTEM) investigation with single NW electrical transport measurement, which allows us to correlate directly the electrical properties and structure of the same individual NWs. The NW devices were made directly on a 50 nm thick SiN x membrane TEM window for electrical measurements and HRTEM study. NWs with the [11-20] growth direction exhibit metallic behavior while the NWs grown along the [0001] direction show n-type semiconductive behavior. Excitingly, the conductivity anisotropy reaches 10 (3)-10 (6) at room temperature, which is 1-3 orders magnitude higher than the bulk ratio.