SiN Membrane Research Articles

Sub-10-nm-thick SiN nanopore membranes fabricated using the SiO2 sacrificial layer process

In our previous studies, ultrathin SiN membranes down to 3 nm in thickness were fabricated using the poly-Si sacrificial layer process, and nanopores were formed in those membranes. The region of the SiN membrane fabricated using this process was small, and the poly-Si sacrificial layer remained throughout the other region. On the other hand, to reduce the noise of the current through the nanopore, it is preferable to reduce the capacitance of the nanopore chip by replacing the poly-Si layer with an insulator with low permittivity, such as SiO2. Thus, in this study, the fabrication of SiN membranes with thicknesses of 3–7 nm using the SiO2 sacrificial layer process was examined. SiN membranes with thicknesses of less than 5 nm could not be formed when the thickness of the top SiN layer deposited onto the sacrificial layer was 100 nm. In contrast, SiN membranes down to 3.07 nm in thickness could be formed when the top SiN layer was 40 nm in thickness. This is thought to be due to the difference in membrane stress. Nanopores were then fabricated in the membranes via dielectric breakdown. The current noise of the nanopore membranes was approximately 3/5 that of membranes fabricated using the poly-Si sacrificial layer process. Last, ionic current blockades were measured when poly(dT)60 passed through the nanopores, and the effective thickness of the nanopores was estimated based on those current-blockade values. The effective thickness was approximately 4.8 nm when the deposited thickness of the SiN membrane was 6.03 nm. On the other hand, the effective thickness and the deposited thickness were almost the same when the deposited thickness was 3.07 nm. This suggests it became difficult to form a shape in which the thickness of the nanopore edge was thinner than the deposited membrane thickness as the deposited thickness decreased.

Active feedback cooling of a SiN membrane resonator by electrostatic actuation

Feedback-based control techniques are useful tools in precision measurements as they allow us to actively shape the mechanical response of high quality factor oscillators used in force detection measurements. In this paper, we implement a feedback technique on a high-stress low-loss SiN membrane resonator, exploiting the charges trapped on the dielectric membrane. A properly delayed feedback force (dissipative feedback) enables the narrowing of the thermomechanical displacement variance in a similar manner to the cooling of the normal mechanical mode down to an effective temperature Teff. In the experiment reported here, we started from room temperature and gradually increasing the feedback gain, we were able to cool down the first normal mode of the resonator to a minimum temperature of about 124mK. This limit is imposed by our experimental setup and, in particular, by the injection of the read-out noise into the feedback. We discuss the implementation details and possible improvements to the technique.

In‐Situ Observation of the Formation of NiSi/Ni2Si Heterojunction in SiGe Nanowire with Al2O3 Diffusion Barrier Layer

AbstractIn complementary metal‐oxide‐semiconductor technology, the metal silicides/germanides have prominent advantages such as low resistivity, high thermal and chemical stability. Here, a study to probe the phase transformations and the diffusion behaviors of Ni in Si1‐xGex nanowire (NW) by in situ transmission electron microscopy is conducted. The Si1‐xGex NWs are dispersed on Si3N4 membrane and contacted with Ni by E‐beam lithography process for in situ study. The sample is heated to 723 K, Ni is diffused into Si1‐xGex NW and Ni2Si is formed accordingly. The diffusion mechanism is confirmed to be reaction‐controlled and the activation energy can be extracted to be 0.708 eV. On the other hand, in this study Al2O3 layer‐coated Si1‐xGex NW is probed for comparison, while the Al2O3 layer serves as the diffusion barrier to modulate the diffusion rate of Ni. This increases the activation energy to 1.38 eV. Importantly, it is found that the NiSi/Ni2Si heterojunction is formed at the diffusion front. The results provide the insights for fabrication of semiconducting devices.

Fabrication of Plasmonic Nano-Slit Pore Double Layer for Single Molecule Detection

We fabricated the plasmonic nano-slit pore platforms for single molecule detection and other various applications. The nano-apertures on the Au/insulator/Au/SiN flat membrane, in addition to the 200 nm thick Au film on ~ 20 nm thick SiN membrane were fabricated using a focused ion beam drilling technique. The insulating materials of SiO2 or Al2O3 were deposited using an atomic layer epitaxy technique. The nanopores with a few nanometer size were fabricated under the proper control of drilling depth and pore opening. Optical characteristics were carried out dependent upon the pore opening width and sample thickness. The broad emission spectra from the (7x 7) slit pore array are obtained via spp-mediated emission on the ~200 nm thick Au/~ 20 nm thick SiN flat samples. A sharp strong infrared emission peak is also obtained due to Au nanoparticle. The fabricated Au double layer platform will be investigated for a single molecule sensor device and a possible radiative thermal energy transfer device.

Fabricating Ultra-thin Silicon Nitride Membranes Suspended on Silicon Wafer

Ultrathin silicon nitride SiNx membrane suspended on a silicon wafer is a popular two-dimensional platform in MEMS applications. The unsupported membrane has a low thermal conductivity, is electrically insulated, and very robust against mechanical impact. Remarkably thin, it is difficult to fabricate and manipulate. Recently equipped with a dual chamber system for plasma enhanced chemical vapor deposition (PECVD) and reactive ion etching, we calibrate it to deposit silicon nitride Si3N4, silicon dioxide SiO2, and to dry etch these materials. Based on the superb quality of Si3N4, we perform a through-wafer etch that creates suspended Si3N4 membranes. The recipe is reliable and reproducible. We analyze the membrane’s chemical composition and optical properties. Although created by PECVD, the membrane is so robust that it survives multiple lithography steps. It extends our capability to study thermal transport at the submicron scale as well as to fabricate micron size devices for MEMS applicati

OMT-Coupled CMB Detector Development at Argonne

Future cosmic microwave background (CMB) experiments will deploy increasing numbers of superconducting detectors with requirements for increased sensitivity and reduced systematics. We report on the ongoing development of OMT-coupled CMB detectors at Argonne National Laboratory. Key areas of development include bolometers with dual Transition Edge Sensors (TES) for easier lab characterization, a hybrid SiN membrane fabrication process, a chemical vapor deposition (CVD) SiN dielectric process, and a new pixel design for improved compatibility with large scale fabrication. These developments enhance our ability to fabricate large-scale (150 mm diameter wafers) detector arrays with the performance necessary for future CMB experiments.

Transmission electron microscopy analysis of reduction reactions and phase transformations in Nb2O5 films deposited by atomic layer deposition

Amorphous films of Nb2O5 composition were deposited by thermal atomic layer deposition on (001) Si substrates and subsequently crystallized by annealing in forming gas at temperatures ranging from 550 °C to 1000 °C. After subjecting these films to an 850 °C anneal, cross-sectional transmission electron microscopy revealed the presence of B-Nb2O5 and T-Nb2O5 phases in the matrix, as well as reduced R-NbO2 in floret-shaped regions. Annealing at 1000 °C completed the reduction process, resulting in the insulator-to-metal transition (IMT) capable T-NbO2 phase throughout the film. ALD films of composition Nb2O5 were also deposited on electron-transparent SiN membranes and then subjected to 550 °C and 1000 °C anneals. Here, the 550 °C anneal induced the B-Nb2O5 and T-Nb2O5 phases without inducing the R-NbO2 phase. The 1000 °C anneal of the films deposited on SiN membranes retained B-Nb2O5 while inducing the R-NbO2 phase, but without bringing the process to completion and inducing the T-NbO2 phase. The effectiveness of the 1000 °C reducing annealing treatment to induce the T-NbO2 phase for Nb2O5 films deposited on (001) Si substrates, while stopping short of this transition for films deposited on SiN membranes, suggests the importance of the SiO2 layer on the Si substrate in contributing to the reduction reaction that results in the technologically important insulator-to-metal transition (IMT)-capable T-NbO2 phase.

Studying the onset of galvanic steel corrosion in situ using thin films: film preparation, characterization and application to pitting

This work reports about a novel approach for investigating surface processes during the early stages of galvanic corrosion of stainless steel in situ by employing ultra-thin films and synchrotron x-radiation. Characterized by x-ray techniques and voltammetry, such films, sputter deposited from austenitic steel, were found representing useful replicas of the target material. Typical for stainless steel, the surface consists of a passivation layer of Fe- and Cr-oxides, a couple of nm thick, that is depleted of Ni. Films of ≈4 nm thickness were studied in situ in an electrochemical cell under potential control (−0.6 to +0.8 V vs Ag/AgCl) during exposure to 0.1 M KCl. Material transport was recorded with better than 1/10 monolayer sensitivity by x-ray spectroscopy. Leaching of Fe was observed in the cathodic range and the therefor necessary reduction of Fe-oxide appears to be accelerated by atomic hydrogen. Except for minor leaching, reduction of Ni, while expected from Pourbaix diagram, was not observed until at a potential of about +0.8 V Cr-oxide was removed from the steel film. After couple of minutes exposure at +0.8 V, the current in the electrochemical cell revealed a rapid pitting event that was simultaneously monitored by x-ray spectroscopy. Continuous loss of Cr and Ni was observed during the induction time leading to the pitting, suggesting a causal connection with the event. Finally, a spectroscopic image of a pit was recorded ex situ with 50 nm lateral and 1 nm depth resolution by soft x-ray scanning absorption microscopy at the Fe L2,3-edges by using a 80 nm film on a SiN membrane, which is further demonstrating the usefulness of thin films for corrosion studies.

Strengthening ultrathin Si3N4 membranes by compressive surface stress

In this work, the effect of compressive surface stress on thin film membrane fracture was studied by bulge test. In order to create membranes with compressive residual stress at the surface, low-pressure chemical vapor deposition (LPCVD) Si3N4 membranes were coated with a 1−8 nm compressive SiNx adlayer or subjected to Ar-ion bombardment. Fracture strength analysis, done using finite element method and Weibull distribution, and microscope inspection of failed membranes showed that the pressure limit of the membranes is determined by the intrinsic fracture mode, caused by high stress induced at the membrane edge near the top surface. By creating compressive residual stress at the membrane surface, the maximum stress induced by the applied pressure was reduced and the fracture strength of the Si3N4 was increased from 17.3 GPa to 18.3 GPa. As a result, membranes with a compressive surface showed a 50 % increase in pressure limit, from 5 kPa/nm to 7.5 kPa/nm.

Irradiation tests of bolometer sensor prototypes for ITER

In ITER, the bolometer diagnostic is foreseen to provide the measurements for the total plasma radiation. Sensors need to withstand the harsh environmental conditions. Most prominent among those is the nuclear environment with neutron fluxes up to 1013ncm2s at the locations of bolometers, which result in a radiation dose of up to 0.3dpa in Si3N4. Original metal resistor bolometer sensors based on Au-absorbers on a mica substrate with Au-meanders failed when exposed to fast neutron fluences corresponding to 0.1 dpa. Various material tests under irradiation identified ceramic materials like Al2O3, AlN or Si3N4 together with Pt meanders as promising alternatives. Based on these ideas a development campaign was initiated to produce a radiation hard bolometer sensor. Two approaches resulted in good mechanical stability under thermal cycling: Au absorbers supported by a Si3N4 membrane and Au absorbers on a silicon base plate which is hung up by flexure hinges. In order to assess their resistance against irradiation, tests have been conducted in the Budapest Neutron Centre. The test campaign demonstrated for the first time that bolometer sensors can withstand irradiation doses corresponding up to 0.3 dpa in Si3N4, which is higher than the value of 0.1 dpa requested by ITER project requirements, while their meander resistance measured after irradiation increased only by 20–30 Ω.

Soft X-ray induced radiation damage in thin freeze-dried brain samples studied by FTIR microscopy

In order to push the spatial resolution limits to the nanoscale, synchrotron-based soft X-ray microscopy (XRM) experiments require higher radiation doses to be delivered to materials. Nevertheless, the associated radiation damage impacts onthe integrity of delicate biological samples. Herein, the extent of soft X-ray radiation damage in popular thin freeze-dried brain tissue samples mounted onto Si3N4 membranes, as highlighted by Fourier transform infrared microscopy (FTIR), is reported. The freeze-dried tissue samples were found to be affected by general degradation of the vibrational architecture, though these effects were weaker than those observed in paraffin-embedded and hydrated systems reported in the literature. In addition, weak, reversible and specific features of the tissue-Si3N4 interaction could be identified for the first time upon routine soft X-ray exposures, further highlighting the complex interplay between the biological sample, its preparation protocol and X-ray probe.

Emergence of amyloidic fibrillation in 2D-ordered Langmuir–Blodgett protein multilayers upon heating

Langmuir–Blodgett protein nanofilms can serve as templates for nucleation and growth of protein crystals. This functionality can be enhanced by thermal annealing. While surface ordering of the multilayered nanofilms and an improvement of the correlation between the layers during thermal annealing have been revealed by atomic force microscopy and grazing-incidence small-angle x-ray scattering, information on the structure developing in the bulk of nanofilms is lacking. In this paper, we report on scanning x-ray nanodiffraction experiments of penicillin-G-acylase multilayers deposited on Si3N4 membranes and annealed at 150 °C. While the annealed multilayer has remained mostly featureless, we observe locally globular aggregates and filamentous spherulites based on nanofibrillar subunits with cross-β amyloidic motifs.

Casimir spring and dilution in macroscopic cavity optomechanics

The Casimir force was predicted in 1948 as a force arising between macroscopic bodies from the zero-point energy. At finite temperatures it has been shown that a thermal Casimir force exists due to thermal rather than zero-point energy and there are a growing number of experiments that characterise the effect at a range of temperatures and distances. Additionally, in the rapidly evolving field of cavity optomechanics there is an endeavor to manipulate phonons and enhance coherence. We demonstrate a new way to achieve this through the first observation of Casimir spring and dilution in macroscopic optomechanics, by coupling a metallic SiN membrane to a photonic re-entrant cavity. The attraction of the spatially-localised Casimir spring mimics a non-contacting boundary condition giving rise to increased strain and acoustic coherence through dissipation dilution. This work invents a new way to manipulate phonons via thermal photons leading to ``in situ'' reconfigurable mechanical states, to reduce loss mechanisms and to create new types of acoustic non-linearity -- all at room temperature.

Current–Voltage Characteristics of SiN Membranes in Solution

Recently, the dielectric breakdown of insulating membranes in aqueous solution has been utilized to fabricate nanopore sensors for various molecular detection applications. Generally, the breakdown...

2-D nanometer thickness mapping applying a reduced bias soft X-ray NEXAFS approach.

We present a 2-D mapping of a sample thickness with nanometer accuracy employing a compact arrangement of near-edge X-ray absorption fine structure (NEXAFS) technique. A NEXAFS spectrum coupled with a scanning system was used to generate a 2-D thickness map of the TiO2 sample (anatase form) deposited on the top of a SiN membrane. The thickness values were retrieved from the experimental data by applying different methods of data processing. In the paper, the detailed analysis of the data processing methods and the identified sources of the errors show that the proposed procedure based on averaging two imperfect estimates reduces the error caused by the uncontrolled bias of the measured signals. This procedure was termed as the average one. The estimates from the proposed average approach and the standard absorption-jump ratio in the absorption edge vicinity were compared with the direct results obtained by applying scanning electron microscopy (SEM). The experimental arrangement of the NEXAFS spectroscopy system, the data acquisition method, as well as the possible error sources, are presented and discussed in detail.

Towards cavity-free ground-state cooling of an acoustic-frequency silicon nitride membrane.

We demonstrate feedback cooling of a millimeter-scale, 40 kHz SiN membrane from room temperature to 5 mK (3000 phonons) using a Michelson interferometer, and discuss the challenges to ground-state cooling without an optical cavity. This advance appears within reach of current membrane technology, positioning it as a compelling alternative to levitated systems for quantum sensing and fundamental weak force measurements.

Piezoelectric Actuation of Graphene-Coated Polar Structures.

Ferroelectric materials based on lead zirconate titanate (PZT) are widely used as sensors and actuators because of their strong piezoelectric activity. However, their application is limited because of the high processing temperature, brittleness, lack of conformal deposition, and a limited possibility to be integrated with the microelectromechanical systems (MEMS). Recent studies on the piezoelectricity in the 2-D materials have demonstrated their potential in these applications, essentially due to their flexibility and integrability with the MEMS. In this work, we deposited a few layer graphene (FLG) on the amorphous oxidized Si3N4 membranes and studied their piezoelectric response by sensitive laser interferometry and rigorous finite-element modeling (FEM) analysis. Modal analysis by FEM and comparison with the experimental results show that the driving force for the piezoelectric-like response can be a polar interface layer formed between the residual oxygen in Si3N4 and the FLG. The response was about 14 nm/V at resonance and could be further enhanced by adjusting the geometry of the device. These phenomena are fully consistent with the earlier piezoresponse force microscopy (PFM) observations of the piezoelectricity of the graphene on SiO2 and open up an avenue for using graphene-coated structures in the MEMS.

Soft X-ray absorption spectroscopy in the low-energy region explored using an argon gas window.

The soft X-ray region below 200 eV is important for investigating chemical and biological phenomena since it covers K-edges of Li and B and L-edges of Si, P, Sand Cl. Helium gas is generally used as the soft X-ray transmission window for soft X-ray absorption spectroscopy (XAS) under atmospheric conditions. However, the helium gas window cannot be applied to XAS in the low-energy region since transmitted soft X-rays mostly consist of high-order X-rays due to the low transmission of first-order X-rays. In this study, the argon gas window isproposed as a new soft X-ray transmission window in the low-energy region. High-order X-rays are removed by the absorption of the Ar L-edge (240 eV), and first-order X-rays become the major contribution of transmitted soft X-rays in the low-energy region. Under atmospheric argon conditions, the double-excitation Rydberg series of helium gas (60 eV), Si L-edge XAS of an Si3N4 membrane (100 eV) and S L-edge XAS of dimethyl sulfoxide gas (170 eV) are successfully measured, indicating that the argon gas window is effective for soft X-ray transmission in the low-energy region from 60 eV to 240 eV.

Interferometric measurements of graphene-based membranes for micromechanical applications

Recent studies on piezoelectricity in 2D materials, such as graphene, have revealed their potential in multiple applications including microelectromechanical systems. In this work, we reveal piezoelectricity in few-layer graphene sheets deposited on amorphous Si3N4 membranes. The response in the center of square membrane of 6.7 × 6.7 mm2 size reaches about 14 nm at resonance and could be further enhanced by adjusting the composite structure. Resonance piezoelectric phenomena are fully consistent with the earlier piezoresponse force microscopy observations on free-standing piezoelectric graphene and open up a possibility of using 2D materials in micromechanical applications.

Fingerprints of homogeneous nucleation and crystal growth in polyamide 66 as studied by combined infrared spectroscopy and fast scanning chip calorimetry

Homogenous crystal nucleation and growth in polyamide 66 (PA66) are followed in situ by means of a combination of FTIR spectroscopy and fast scanning chip calorimetry (FSC). Therefore, a novel setup with a calorimetry chip equipped with an IR-transparent SiN membrane was developed, which enables to examine IR spectroscopic and FSC experiments on the identical specimen. Because of the small amount of sample material (~ 100 ng), it is possible to achieve heating and cooling rates up to 5000 Ks−1, and hence to quench the sample into a fully amorphous state without quenched-in homogeneous crystal nuclei. Annealing the film then allows to determine the onset of homogenous nucleation and crystal growth by means of FSC, whereas molecular interactions are unraveled by FTIR spectroscopy. It is demonstrated that different moieties of PA66 respond distinctly during crystallization; far-reaching interactions such as hydrogen bonding are established prior to onset of short-range steric hindrance.Graphical Crystal nucleation and growth are followed in situ by means of a combination of FTIR spectroscopy and fast scanning chip calorimetry. For this purpose a novel IR-transparent chip enables to examine both measurements on the identical specimen, while heating and cooling rates up to 5000 Ks−1 and hence quenching into a fully amorphous state can be achieved