Silicon Substrate Research Articles

Alleviating internal stress in diamond-like carbon films for enhanced tribological performance under high contact pressure via interface texturing

Diamond-like carbon (DLC) films have found widespread applications across numerous fields due to their exceptional properties. Nevertheless, their significant internal stress has restricted their further utility, particularly in scenarios involving high-contact pressure conditions. In response to this challenge, we fabricated diamond-like carbon films with nano-depth interface texture. This nano-depth interface texturing technique helps alleviate the internal stress within the carbon film, thereby enhancing the tribological performance of diamond-like carbon films with textured interfaces, especially under high contact pressure. We successfully fabricated textured carbon films with a thickness of 1 μm, which exhibited excellent tribological performance even under pressures exceeding 1 GPa. Through atomistic molecular dynamics simulations, internal stress testing, and cross-sectional transmission electron microscopy imaging, we observed that the incorporation of nano-depth interface texturing resulted in an approximate 47.62 % increase in the thickness of the transition layer between the silicon substrate and the carbon film. Furthermore, there was a notable reduction of about 30 % in the internal stress exhibited by the carbon films. These findings are expected to expand the application of carbon films under higher contact pressure and facilitate the production of thicker films.

Novel approach of SERS sensors AgNPs/PSi by incorporated MWCNT

In this study, two types of nano photonics sensors silver nanoparticles/porous silicon (AgNPs/PSi) and silver nanoparticles/multi wall carbon nanotube/porous silicon (AgNPs/MWCNT/PSi) were formed and tested extensively. The porous silicon (PSi) substrate was formed by laser assisted chemical etching process at laser intensity 150 mW/cm2 and wavelength 630 nm respectively. The formation of these types of nano photonics SERS sensors were carried out by a simple and low cost dipping process of porous silicon (PSi) in silver nitrate (AgNO3) and multi wall carbon nanotube (MWCNT) solution fixed concentration of AgNO3 about (10−3 M). These sensors were tested at different concentrations of difenoconazole, 10−5, 10−7, 10−9 and 10−10 M at room temperature. The research results showed an excellent sensing behavior of silver nanoparticles/multi wall carbon nanotube/porous silicon (AgNPs/MWCNT/PSi) comparing with the silver nanoparticles/porous silicon (AgNPs/PSi) nanoparticles sensors. Higher enhancement factor with lower limit of detection with multi wall carbon nanotube (MWCNT) were improved by two orders of magnitude, due to the high value of the sensing area after incorporating multi wall carbon nanotube (MWCNT) to nano photonics sensors.

Flexible Nanoscale Amorphous Oxide Transistors with a Gold-Assisted Transfer Method.

We present a new approach to achieve nanoscale transistors on ultrathin flexible substrates with conventional electron-beam lithography. Full devices are first fabricated on a gold sacrificial layer covering a rigid silicon substrate, and then coated with a polyimide film and released from the rigid substrate. This approach bypasses nanofabrication constraints on flexible substrates: (i) electron-beam surface charging, (ii) alignment inaccuracy due to the wavy substrate, and (iii) restricted thermal budgets. As a proof-of-concept, we demonstrate ∼100 nm long indium tin oxide (ITO) transistors on ∼6 μm thin polyimide. This is achieved with sub-20 nm misalignment or overlap between source (or drain) and gate contacts on flexible substrates for the first time. The estimated transit frequency of our well-aligned devices can be up to 3.3 GHz, which can be further improved by optimizing the device structure and performance.

Effect of Ultraviolet Radiation on Properties of Ge2Sb2Te5 Phase Change Films.

With the expanding utilization of space technology, the stability of electronic components' performance in radiation environments has garnered significant attention. In this study, we prepared Ge2Sb2Te5 phase change films and memory units on silicon substrates to explore the influence of ultraviolet (UV) radiation on their characteristics. The experimental findings revealed that UV irradiation at a power density of 450 mW/cm2 decreased the amorphous resistance and thermal stability of Ge2Sb2Te5 films, impeding their multistage storage performance. Nevertheless, the amorphous state could still undergo effective transformation into a crystalline state. Furthermore, UV irradiation triggered the photoelectric effect, narrowing the band gap and causing a redshift of the Raman peak in amorphous films. Remarkably, the surface properties of Ge2Sb2Te5 films remained unchanged under irradiation. The phase change memory device based on Ge2Sb2Te5 film retained its SET-RESET conversion capability at a pulse width of 100 ns post-UV irradiation, demonstrating resilience against UV radiation. This study offers the practical insights for the application of phase change memory in space radiation environments.

Resistive random-access memories using quasi-2D halide perovskites for wafer-scale reliable switching behaviors

In this study, we propose the (PEA)2MA3Pb4I13, a quasi-two-dimensional (2D) halide perovskite, in the realm of resistive switching memory devices. A quasi-2D perovskite film (PEA)2MA3Pb4I13, with a thickness measuring 450 nm, has been effectively fabricated on a silicon substrate coated with platinum through an all-solution process conducted at low temperatures. The constructed resistive switching memory devices, incorporating an Ag/(PEA)2MA3Pb4I13/Pt/Ti/SiO2/Si configuration, display dependable and consistent bipolar switching attributes. The device shows an ultra-low operating voltage of less than +0.1 V, an impressive high ON/OFF ratio exceeding 108, reversible resistive switching via pulse voltage operation, and the capability for multilevel data storage. In addition, there is little variation in device characteristics depending on the location on a wafer or device size.

Fabrication of high-performance nanostructured CsPbI3/Si perovskite photodetector by pulsed laser deposition: Challenges and prospects

The inorganic perovskite CsPbI3 is a promising material for optoelectronic applications like photodetectors and solar cells due to its suitable bandgap and excellent properties. In this work, nanostructured CsPbI3 thin films were deposited on glass and silicon substrates by pulsed laser deposition (PLD) at laser fluences ranging from 5.7 to 10 J/cm2. Systematic characterization revealed that increasing the laser fluence significantly enhances the crystallinity, phase purity, optical emission intensity, charge carrier concentration (up to 1.38 × 1012 cm−3), and mobility (up to 164.7 cm2/Vs) of the CsPbI3 films. An optimal laser fluence of 10 J/cm2 resulted in large, elongated grains over 280 nm, tightly packed films with minimal defects, and a suitable bandgap of 1.83 eV CsPbI3/Si heterojunction photodetectors were fabricated, with the device made at 8.5 J/cm2 exhibiting maximum responsivity of 8 A/W at 600 nm, detectivity exceeding 1014 Jones, external quantum efficiency up to 17.5 × 102 %, and a high ON/OFF ratio of 225 under illumination. The photodetector performance was strongly correlated with the optimized structural order, morphology, and optoelectronic quality achieved by careful control of the laser fluence during PLD. This work highlights PLD as an effective technique for realizing high-quality CsPbI3 films with tailored properties for advanced photodetection and photovoltaic applications.

Narrow nano-beam generation inside of silicon photonic chip with a hemi-cylinder

A photonic nanojet (PNJ) can be shrunk using a high index dielectric micro-particle to generate a narrow nano-beam. Considering silicon has a high refractive index and low absorption in near-infrared waves, here, we present a narrow nano-beam generation inside of a silicon photonic chip with a hemi-cylinder. The proposed design consists of a silicon hemi-cylinder on a silicon substrate with a micro-hole. At first, we investigate the narrow PNJ inside of the silicon substrate produced by a silicon hemi-cylinder on a silicon substrate. In order to make the PNJ inside of the silicon substrate usable, the properties of the PNJ influenced by the position of the added micro-hole filled with water are studied. A narrow nano-beam can be obtained when the position of the added micro-hole is well-chosen. Then, the narrow nano-beam affected by the silicon hemi-cylinder immersed different mediums is presented. Finally, we discuss the influence of the perturbation of illumination angle on the properties of the nano-beam. The proposed structure may have potential applications in enhanced Raman spectroscopy and optofluidic chips.

Charge Trapping and Emission during Bias Temperature Stressing of Schottky Gate GaN-on-Silicon HEMT Structures Targeting RF/mm Wave Power Amplifiers.

For operation as power amplifiers in RF applications, high electron mobility transistor (HEMT) structures are subjected to a range of bias conditions, applied at both the gate and drain terminals, as the device is biased from the OFF- to ON-state conditions. The stability of the device threshold voltage (Vt) condition is imperative from a circuit-design perspective and is the focus of this study, where stresses in both the ON and OFF states are explored. We see rapid positive threshold voltage increases under negative bias stress and subsequent recovery (i.e., Vt reduces), whereas conversely, we see a negative Vt shift under positive stress and Vt increase during the subsequent relaxation phase. These effects are correlated with the thickness of the GaN layer and ultimately result from the deep carbon-acceptor levels in the C-GaN back barrier incorporated to screen the buffer between the silicon substrate and the epitaxially grown GaN layer. Methods to mitigate this effect are explored, and the consequences are discussed.

High Performance Porous Silicon Substrate for the Integration of Millimeter-Wave Passive Devices

High Performance Porous Silicon Substrate for the Integration of Millimeter-Wave Passive Devices

A Time-Domain Perspective on the Structural and Electronic Response in Epitaxial Ferroelectric Thin Films on Silicon.

This operando study of epitaxial ferroelectric Pb(Zr0.48Ti0.52)O3 capacitors on silicon substrates studies their structural response via synchrotron-based time-resolved X-ray diffraction during hysteresis-loop measurements in the 2-200 kHz range. At high frequencies, the polarization hysteresis loop is rounded and the classical butterfly-like strain hysteresis acquires a flat dumbbell shape. We explain these observations from a time-domain perspective: The polarization and structural motion within the unit cell are coupled to the strain by the piezoelectric effect and limited by domain wall velocity. The solution of this coupled oscillator system is derived experimentally from the simultaneously measured electronic and structural data. The driving stress σFE(t) is calculated as the product of the measured voltage U(t) and polarization P(t). Unlike the electrical variables, σFE(t) and η(t) of the ferroelectric oscillate at twice the frequency of the applied electrical field. We model the measured frequency-dependent phase shift between η(t) and σFE(t).

Microstructure and reflectance of porous GaN distributed Bragg reflectors on silicon substrates

Distributed Bragg reflectors (DBRs) based on alternating layers of porous and non-porous GaN have previously been fabricated at the wafer-scale in heteroepitaxial GaN layers grown on sapphire substrates. Porosification is achieved via the electrochemical etching of highly Si-doped layers, and the etchant accesses the n+-GaN layers through nanoscale channels arising at threading dislocations that are ubiquitous in the heteroepitaxial growth process. Here, we show that the same process applies to GaN multilayer structures grown on silicon substrates. The reflectance of the resulting DBRs depends on the voltage at which the porosification process is carried out. Etching at higher voltages yields higher porosities. However, while an increase in porosity is theoretically expected to lead to peak reflectance, in practice, the highest reflectance is achieved at a moderate etching voltage because etching at higher voltages leads to pore formation in the nominally non-porous layers, pore coarsening in the porous layers, and in the worst cases layer collapse. We also find that at the high threading dislocation densities present in these samples, not all dislocations participate in the etching process at low and moderate etching voltages. However, the number of dislocations involved in the process increases with etching voltage.

Effect of N2 reactive gas flow rate on the structural, optical and wettability properties of silicon carbon oxynitride thin films

In the current research, the silicon carbon oxynitride (SiCON) thin film was deposited on the silicon (Si) substrate by radio frequency (RF) reactive magnetron sputtering method. To comprehensively assess the impact of nitrogen flux rate on thin film characteristics, a suite of advanced analytical methods was utilized. The GIXRD analysis confirmed that the SiCON thin film is amorphous in structure. Additionally, Raman spectroscopy detected no graphite nanocrystals within the film. Ellipsometry measurements further showed that the refractive index of the thin films rises with increased nitrogen flux in the reactive gas, indicating a direct correlation between nitrogen concentration during deposition and optical properties. Based on the designs made with McLeod's software, the amount of reflection can be reduced up to 5.7 % at the wavelength of 4 μm and up to 8.5 % in the wavelength range of 3–5 μm for an optimal thickness thin film. The atomic force microscopy (AFM) examination revealed that the surface roughness of the thin films decreases as the nitrogen flux in the reactive gas mixture increases. Additionally, measurements of the water contact angle (WCA) indicated that the SiCON thin films exhibit a hydrophilic state.

In silico monitoring of non-reactive gas blistering on crystalline substrates

Blistering from gas aggregation occurs very rarely on solid substrates; however, it is commonly observed under high-pressure gas or plasma environments. This is due to the repeated aggregation process of gas molecules penetrating beneath the surface, but it has been difficult to find cases that demonstrate the dynamic mechanism on the atomic level. In this study, the dynamics of physical bombardment of argon atoms on the flat monocrystalline silicon substrate are simulated to propose an initiation principle for gas-aggregate formation. Simulations of extremely large numbers of argon atoms bombarding a limited area of single crystal silicon revealed inhomogeneous aggregation properties consistent with the experimental observations. Particularly, the results suggest that momentum transfer formed by collisions between argon trapped in the surface grooves and the argon used for bombardment is the governing factor for the aggregation behavior. The aggregated argon clusters grow in the in-plane direction while generating stress propagation in the thickness direction, ultimately causing an expansion pressure that lifts the adjacent silicon surface upwards. Our work provides a deterministic understanding of the initiation process of blister formation, which rarely occurs in physical sputtering on defect-free substrates.

Tackling residual tensile stress in AlN-on-Si nucleation layers via the controlled Si(111) surface nitridation

This work is devoted to the study of the influence of controlled Si(111) surface nitridation on the epitaxial growth of AlN-on-Si nucleation layers with reduced tensile stress on ordered crystalline silicon nitride phase. The Si(111) surface nitridation process was performed at low ammonia flux and substrate temperatures in the range of 700–900 °C and was studied using RHEED and STM techniques. A universal criterion, namely the stage of the nitridation process completion is introduced, taking into account the influence of substrate temperature, ammonia flux and nitridation time. The 100 nm AlN nucleation layer on silicon substrates grown by ammonia molecular beam epitaxy is studied using AFM, XRD, HR-TEM and Raman spectroscopy techniques. The Raman data show that reducing the nitridation temperature from 900 °C to 700 °C not only deteriorates the crystalline quality of the subsequent AlN nucleation layers, but also reduces the residual tensile stress by almost 30 %. In the present contribution, micro-Raman spectroscopy is used to determine the nature of the defects formed during the high temperature growth of the AlN nucleation layers and confirms them to be inversion domains. The HR-TEM technique was used to study the AlN/Si interface in AlN-on-Si nucleation layers grown on a nitridated silicon surface at 700 °C and 900 °C at the optimum stage of the nitridation process completion. HR-TEM images of AlN nucleation layers revealed regions with different AlN/Si(111) interfaces: 1) AlN/amorph-Si3N4/Si, 2) AlN/SiN(8 × 8)/Si, and 3) AlN/Si with a sharp interface boundary. Using fast Fourier transform image analysis, it is shown that the presence of amorphous Si3N4 phase inclusions in the AlN/Si interface boundary introduces tensile stresses in the AlN nucleation layer which can be reduced by lowering the nitridation temperature. The results obtained clearly show that one of the causes of cracks in III-nitride layers grown on silicon substrates is the formation of tensile AlN layers with a high content of the amorphous Si3N4 phase at the AlN/Si interface, which is characteristic of silicon nitridation at elevated temperatures (> 700 °C).

Patterning optimization for device realization of patterned GaAsSbN nanowire photodetectors

Vertically grown nanowires (NWs) are a research interest in optoelectronics and photovoltaic applications due to their high surface to volume ratio and good light trapping capabilities. This study presents the effects of process and design parameters on self-catalyzed GaAsSbN NWs grown by plasma-assisted molecular beam epitaxy on patterned silicon substrates using electron beam lithography. Vertical alignment of the patterned NWs examined via scanning electron microscopy show the sensitivity of patterned NW growth to the parameters of NW diameter, pitch, dose time, etching techniques and growth plan. Diameters range from 90 nm to 250 nm. Pitch lengths of 200 nm, 400 nm, 600 nm, 800 nm, 1000 nm, and 1200 nm were examined. Dry etching of the oxide layer of the silicon substrate and PMMA coating is performed using reactive ion etching (RIE) for 20 s and 120 s respectively. Comparisons of different HF etch durations performed pre and post PMMA removal are presented. Additionally, the report of an observed surfactant effect in dilute nitride GaAsSbN NWs in comparison to non-nitride GaAsSb is presented. Optimizations to patterning, RIE, and HF etching are presented to obtain higher vertical yield of patterned GaAsSbN NWs, achieving ∼80% of the expected NW µm2. Room temperature and 4 K photoluminescence results show the effect of nitride incorporation for further bandgap tuning, and patterned pitch on the optical characteristics of the NWs which gives insights to the compositional homogeneity for NWs grown at each pitch length.

Biologically inspired piezoresistive MEMS acoustic vector sensor for underwater applications

Underwater acoustics has assumed a pivotal role in the detection, navigation, communication, and target identification of ships and submarines. In recent years, advancements in noise reduction from marine vessels have underscored the significance of underwater acoustic vector sensors. This paper presents a novel approach to the design, fabrication, and characterization of a two-dimensional Micro-Electro Mechanical Systems (MEMS) vector acoustic sensor tailored for underwater environments. Traditional underwater acoustic vector sensors often employ doped polysilicon or silicon/germanium sensing films on rigid silicon substrates. The inflexible nature of silicon substrates necessitates labor-intensive and costly chemical-mechanical polishing processes to achieve submicron thickness, often requiring extended clean-room usage. In contrast, this work proposes a simplified, cost-effective, and scalable alternative. The sensor design utilizes reduced graphene oxide (rGO) as the sensing material and Kapton as the substrate, chosen for their unique properties. rGO exhibits high carrier mobility and low intrinsic noise, ensuring clear signals with minimal external interference, thereby improving measurement accuracy in challenging environments. Kapton provides excellent thermal stability, mechanical strength, and chemical resistance, along with superior insulating properties that reduce electrical noise, enhancing the signal-to-noise ratio. The designed vector sensor leverages the piezoresistive transduction principle, incorporating a thin piezoresistive film of rGO on a flexible Kapton substrate via a straightforward drop-casting method. Inspired by the sensory mechanisms of aquatic life, the two-dimensional vector sensor not only detects pressure associated with acoustic signals but also discerns the direction from which these low and ultralow frequency signals originate. The device's performance characteristics, sensitivity, and directivity are comprehensively evaluated through static, dynamic, and acoustic tests conducted in both air and water mediums. Static tests reveal the piezoresistive behavior of rGO under applied displacement, yielding displacement sensitivities of 0.0279 V/mm and 0.0276 V/mm for axial and radial displacements, respectively. Dynamic and acoustic tests demonstrate the sensor's capability to detect low-frequency signals spanning from 0.25 Hz to 200 Hz, exhibiting a smooth and favorable frequency response. In air, the sensor exhibits receiving sensitivities ranging from −15.18 dB to −19.75 dB (X-channel) and −13.67 dB to −16.67 dB (Y-channel). In the underwater environment, these values range from −134.40 dB to −138.93 dB (X-channel) and −131.83 dB to −136.93 dB (Y-channel). Notably, the variation in receiving sensitivity across channels in both air and water is limited to within 6 dB. Furthermore, the device showcases a symmetrical directivity pattern resembling the shape of an "8," with an approximate sensitivity of −136.66 dB, a significant improvement compared to the −165 dB sensitivity of conventional polysilicon underwater vector sensors. These experimental findings affirm the feasibility of the proposed underwater vector sensor, based on the piezoresistive effect and MEMS technology, highlighting its two-dimensional directivity capabilities.

A quad-port triple-band high isolation terahertz MIMO antenna for short-distance THz communication links

This paper introduces an arrangement of a Multiple-Input Multiple-Output antenna array implemented specifically for operating within the THz frequency bands. The antenna is designed for short-distance THz communication links. A quad-port MIMO antenna configuration has been chosen to function across three frequency bands. Each cell element is situated on top of a silicon substrate. The combined cross-sectional surface of the MIMO antenna is 70 × 50 µm². The proposed MIMO antenna device reaches the following three frequency bands: 2.6–7.9 THz, 9.66–10.3 THz and 11.5–14.1 THz. In addition, the mutual coupling coefficient is less than − 20 dB, indicating strong isolation between antenna elements. This high isolation is obtained by using a defected sibstrat structure and a specifique distance between antenna elements. The MIMO array antenna attains peak gains of 11.88 dBi, 8.78 dBi and 10.65 dBi when operating over the three cited bandwidth. Furthermore, the suggested MIMO structure exhibits favorable characteristics with CCL < 0.5 bps/Hz/sec, MEG ≤ –3.0 dB, ECC < 0.01, and DG ≈ 10 dB, over the operating bands. Based on the results obtained and compared to several works reported in the literature, the proposed implementation maintains a good size-performance compromise which allows better adaptation to applications requiring versatile performance in various communication scenarios.

Achieving γ‐Phase CsPbI3 by Reducing Underlayer Surface Roughness

AbstractCesium lead iodide (CsPbI3) exhibits great potential in developing photovoltaic cells due to suitable optical bandgap and thermal stability. However, the photoactive γ‐phase normally exists at high‐temperatures ≈180 °C, and it is challenging to obtain γ‐phase CsPbI3 at room temperature. Here, it discovers that γ‐phase CsPbI3 is achievable by reducing the underlayer surface roughness to a certain level. This method is universal as demonstrated on the surface of poly(3,4‐ethylenedioxythiophene) poly(styrene sulfonate) (PEDOT:PSS), poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine] (PTAA), polystyrene (PS), and silicon substrates. Moreover, it is found that lower surface roughness resulted in smaller crystallite size in the CsPbI3 film, which is an important reason for achieving γ‐phase because the decrease in crystallite size will increase grain surface energy to suppress tilting of PbI6 octahedra and lattice distortion. This study offers a universal approach to obtain γ‐phase CsPbI3 for the development of high‐performance all‐inorganic perovskite solar cells and other optoelectronic devices.

Polystyrene Brush Evolution by Grafting to Reaction on Deglazed and Not-Deglazed Silicon Substrates.

Two model substrates for the grafting to reaction are considered: not-deglazed silicon, whose surface is coated by a thin oxide layer with reactive silanol groups on its surface; and deglazed silicon, where the oxide layer is removed by treatment with hydrofluoric acid. The reactive polymers are hydroxy-terminated polystyrenes with molecular weights ranging from 3.9 to 13.9kgmol⁻1. The grafting to reaction is carried out at different temperatures and for different periods of time on the two different substrates. The thickness and the thermal stability of the resulting brushes are evaluated. Furthermore, the grafting of a highly dispersed system is simulated by blending two polymers with different molecular weights. Although the brush thickness growth is found to be faster on deglazed silicon, the preferential grafting of short chains occurs with equal chain selection propensity on both substrates.

Low-temperature stabilization of rutile in W-doped Titania thin films deposited by magnetron Co-Sputtering

Tungsten doped Titania thin films were sputtered on a silicon substrate by magnetron co-sputtering. The influence of tungsten on Vickers hardness and crystallographic changes was studied in films subjected to stepped annealing treatments. Rutile is the dominant phase with crystallite size ∼ 10 nm after 500 °C annealing. The films, doped with 1.79 % W, exhibit the highest hardness (20.88 GPa), a rutile-anatase mixture (80:20) and a preferential shift in crystallographic orientation from (101) to (110). The homogeneous distribution of tungsten in TiO2 stabilizes rutile at 500 °C, providing an innovative and simple strategy for its synthesis, thus expanding the options for substrate materials.