Scanning Capacitance Microscopy Research Articles

Thickness-dependent Relative Dielectric Constant of Organic Ultrathin Films.

In formulas employed for analysis of organic electronic devices, the relative dielectric constant value of the semiconductor organic films is often assumed rather than measured, even though it is a fundamental parameter for a correct interpretation. This is particularly true for ultrathin films made of discrete molecular layers. In this work, Spectroscopy Ellipsometry and Scanning Capacitance Microscopy were used to study thin films made of N,N'-bis(n-octyl)-x:y,dicyanoperylene-3,4:9,10-bis(dicarboximide). The relative dielectric constant presents a non-monotonic trend with thickness: it is equal to 2.1 for one molecular layer, saturating at 3.2 for increasing thickness. This maximum value, equivalent to the bulk one, occurs when the coverage is in between the third to the fourth layer. In this range, the growth switches from a Frank-Van der Merwe (2D growth) to a Volmer-Weber mode (3D growth); in addition, the molecular configuration assumes a bent/distorted geometry with respect to the initial edge-on one. These results establish a morphological dependence of the dielectric constant, especially in the vicinity of the substrate interface, that disappears at a certain distance from it.

Effect of repeating hydrothermal growth processes and rapid thermal annealing on CuO thin film properties.

This paper presents an investigation into the influence of repeating cycles of hydrothermal growth processes and rapid thermal annealing (HT+RTA) on the properties of CuO thin films. An innovative hydrothermal method ensures homogeneous single-phase films initially. However, their electrical instability and susceptibility to cracking under the influence of temperature have posed a challenge to their utilization in electronic devices. To address this limitation, the HT+RTA procedure has been developed, which effectively eliminated the issue. Comprehensive surface analysis confirmed the procedure's ability to yield continuous films in which the content of organic compounds responsible for the formation of cracks significantly decreases. Structural analysis underscored the achieved improvements in the crystalline quality of the films. The implementation of the HT+RTA procedure significantly enhances the potential of CuO films for electronic applications. Key findings from Kelvin probe force microscopy analysis demonstrate the possibility of modulating the work function of the material. In addition, scanning capacitance microscopy measurements provided information on the changes in the local carrier concentration with each repetition. These studies indicate the increased usefulness of CuO thin films obtained from the HT+RTA procedure, which expands the possibilities of their applications in electronic devices.

Threshold voltage mapping at the nanoscale of GaN-based high electron mobility transistor structures using hyperspectral scanning capacitance microscopy

Threshold voltage mapping at the nanoscale of GaN-based high electron mobility transistor structures using hyperspectral scanning capacitance microscopy

30‐3: Direct Observation of 2 Delta L in a‐IGZO TFT Using Scanning Capacitance Microscopy

Herein, we have directly investigated a 2 delta L as the diffusion length in a‐IGZO TFT using a scanning capacitance microscopy (SCM) technique at the cross section of TFTs instead of indirect normal transmission line method (TLM). Moreover, we revealed that the difference of 2 delta L leads the variation of total parastic capacitance in devices, which play a key role in the properites of EL currents in case of display devices.

DC-free Method to Evaluate Nanoscale Equivalent Oxide Thickness: Dark-Mode Scanning Capacitance Microscopy.

This study developed a DC-free technique that used dark-mode scanning capacitance microscopy (DM-SCM) with a small-area contact electrode to evaluate and image equivalent oxide thicknesses (EOTs). In contrast to the conventional capacitance-voltage (C-V) method, which requires a large-area contact electrode and DC voltage sweeping to provide reliable C-V curves from which the EOT can be determined, the proposed method enabled the evaluation of the EOT to a few nanometers for thermal and high-k oxides. The signal intensity equation defining the voltage modulation efficiency in scanning capacitance microscopy (SCM) indicates that thermal oxide films on silicon can serve as calibration references for the establishment of a linear relationship between the SCM signal ratio and the EOT ratio; the EOT is then determined from this relationship. Experimental results for thermal oxide films demonstrated that the EOT obtained using the DM-SCM approach closely matched the value obtained using the typical C-V method for frequencies ranging from 90 kHz to 1 MHz. The percentage differences in EOT values between the C-V and SCM measurements were smaller than 0.5%. For high-k oxide films, DM-SCM with a DC-free operation may mitigate the effect of DC voltages on evaluations of EOTs. In addition, image operations were performed to obtain EOT images showing the EOT variation induced by DC-stress-induced charge trapping. Compared with the typical C-V method, the proposed DM-SCM approach not only provides a DC-free approach for EOT evaluation, but also offers a valuable opportunity to visualize the EOT distribution before and after the application of DC stress.

Characterization of heterogeneity of CVD graphene on copper foil by scanning probe microscopy and Raman spectroscopy

The comparative analysis of the structural, morphological, and local electrical properties of CVD graphene films synthesized at atmospheric and low pressure CVD growth conditions was carried out. The use of electrical techniques of scanning probe microscopy, such as Kelvin probe force microscopy, scanning capacitance microscopy, electrostatic force microscopy, and conductive atomic-force microscopy for investigation of heterogeneous graphene coverage was discussed. A significant change in the surface potential values was observed indicating the formation of p-type multilayered graphene domains on single layer graphene at low pressure and n-type multilayered graphene films at atmospheric pressure CVD. The effect of Ar flow rate increasing during cooling stage in the temperature range of 700–200 °C causing graphite formation was described. The employment of surface potential spectroscopy allows to indicate the presence of nonlinear phenomena in heterogeneous graphene.

Direct Assessment of Defective Regions in Monolayer MoS2 Field-Effect Transistors through In Situ Scanning Probe Microscopy Measurements.

Implementing two-dimensional materials in field-effect transistors (FETs) offers the opportunity to continue the scaling trend in the complementary metal-oxide-semiconductor technology roadmap. Presently, the search for electrically active defects, in terms of both their density of energy states and their spatial distribution, has turned out to be of paramount importance in synthetic transition metal dichalcogenides layers, as they are suspected of severely inhibiting these devices from achieving their highest performance. Although advanced microscopy tools have allowed the direct detection of physical defects such as grain boundaries and point defects, their implementation at the device scale to assess the active defect distribution and their impact on field-induced channel charge modulation and current transport is strictly restrained. Therefore, it becomes critical to directly probe the gate modulation effect on the carrier population at the nanoscale of an FET channel, with the objective to establish a direct correlation with the device characteristics. Here, we have investigated the active channel in a monolayer MoS2 FET through in situ scanning probe microscopy, namely, Kelvin probe force microscopy and scanning capacitance microscopy, to directly identify active defect sites and to improve our understanding of the contribution of grain boundaries, bilayer islands, and defective grain domains to channel conductance.

Scanning probe microscopy and microwave phenomena in composite containing iron nanoparticles and carbon nanotubes

Epoxyamine matrix-based composites containing 15 wt% of Fe nanoparticles and 1.5 or 2 wt% of carbon nanotubes, as well as composites containing only Fe particles, have been studied using microwave methods and various scanning probe microscopy techniques, such as scanning capacitance microscopy and scanning Kelvin probe force microscopy. The composites were prepared using technological methods that improve their homogeneity. Probe current dependences investigated by applying different voltages to the probe in the Kelvin probe force microscopy mode have shown that the falling regions of the dependences at both positive and negative values of the bias voltage are found only for the sample containing both the Fe particles and the CNT in the “soft epoxy” matrix. Microwave measurements of the transmission and reflection coefficients were performed in the frequency range from 26 to 38 GHz. The field dependences of the microwave power dissipation have been plotted. The ferromagnetic resonance in the composites has been investigated. Frequency dependences of the complex dielectric permittivity of the composites have been determined. Microwave properties of the CNT-containing and CNT-free composites have been compared.

Lightly doped In0.53Ga0.47As/InP SWIR photodetectors with diffusion barrier structure

A diffusion barrier structure is proposed to control the accuracies of the Zinc diffusion velocity and depth for lightly doped short-wave infrared (SWIR) InGaAs planar photodetectors. By employing scanning capacitance microscopy and scanning electron microscopy characterizations, the Zinc diffusion profiles were investigated. The introducing of a moderately doped interlayer effectively tailored the diffusion front with reduced depth. In0.53Ga0.47As/InP PIN photodetectors with different structures were fabricated and characterized. Compared with the typical structure, the barrier detector exhibited a significantly lower dark current as well as an approximately three times higher peak detectivity. These results indicated that the diffusion barrier structure is promising for the fabrication of SWIR InGaAs focal plane arrays with both low capacitance and reduced dark current.

Reaction-diffusion effects and spatiotemporal oscillations under SEM, STM and AFM-assisted charging in fiber-like and wire-like systems: From molecular and quantum wires to cooperative ferroelectric nanofibers and microfibers

This review addresses the problem of reaction-diffusion effects and spatiotemporal oscillations in fiber-like and wire-like systems under the electron beam in SEM and in the presence of electric field in some special AFM techniques, such as current sensing atomic force microscopy (CS-AFM)/conductive atomic force microscopy (C-AFM), electrostatic force microscopy (EFM) and Kelvin probe force microscopy (KPFM) also known as surface potential microscopy. Some similar reaction-diffusion effects also can be observed in scanning capacitance microscopy (SCM), scanning gate microscopy (SGM), scanning voltage microscopy (SVM) and piezoresponse force microscopy (PFM). At the end of this paper the authors provide analysis of their own results and approaches. In particular, the possibility of achieving the ion transfer controlled growth of cells along the ion concentration gradients in reaction-diffusion fibers and actuators is indicated. This fundamental idea is discussed within the framework of the implantable fiber “bioiontronics” and “neuroiontronics” controlled by acoustic and electrical signals that regulate the reaction-diffusion or chemical oscillation activity of such fiber structures as reaction-diffusion actuators and sensors. The literature review includes more than 130 references.

Highlighting the role of 3C–SiC in the performance optimization of (Al,Ga)N‒based High‒Electron mobility transistors

AlN nucleation layer is the key issue for the performance of GaN high frequency telecommunication and power switching systems fabricated after heteroepitaxy on Silicon or Silicon Carbide. In this work, we demonstrate and explain both the low level and the origin of propagation losses in GaN/3C–SiC/Si High Electron Mobility Transistors (HEMTs) at microwaves frequencies, in view of providing efficient circuits. First, it is shown that the use of 3C–SiC as an intermediate layer between the Si substrate and the GaN epitaxial layer drastically decreases RF propagation losses. Using Secondary Ion Mass Spectroscopy (SIMS) measurements, we demonstrate that dopant in-diffusion (both Al and Ga) into the 3C–SiC pseudo-substrate remains confined beneath the interface. Furthermore, by combining scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM), the 2D profile shows the presence of a slightly conductive zone beneath the AlN/3C–SiC interface that is highly limited (less than 50 nm) whatever the growth conditions of the (Al, Ga)N layers on 3C–SiC explaining the low propagation losses obtained for such devices. This behavior differs from the one previously observed for GaN growth on Si substrate. This work demonstrates the importance and efficiency of the 3C–SiC intermediate layer when used as a pseudo-substrate increasing not only the crystalline quality of the subsequent (Al, Ga)N layers but also permits to achieve high potential GaN power devices as it is crucial.

Characterization of the parasitic masking layer formed during GaN SA-MOVPE using PECVD SiO2 masks

X-ray photoelectron spectroscopy (XPS) was used to study the surface composition of the parasitic masking layer formed during selective area metalorganic vapor phase epitaxy (MOVPE) of gallium nitride (GaN) using silicon dioxide (SiO2) masks deposited by plasma enhanced chemical vapor deposition (PECVD). It was shown that non-stoichiometric silicon oxynitride layer (SiOxNy) is responsible for the inhibition of GaN nucleation in the vicinity of the SiO2 mask. Atomic force microscopy (AFM) was applied to examine the surface topography, whereas scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM) techniques were used for the purpose of electrical characterization of the parasitic masking layer. The overgrowth of GaN islands through the discontinuities in the SiOxNy film was shown. The SCM imaging showed the presence of a positive electric charge in the parasitic masking layer, indicating the accumulation of defects in the silicon oxynitride film.

Scanning capacitance microscopy of GaN-based high electron mobility transistor structures: A practical guide

The scanning capacitance microscope (SCM) is a powerful tool to characterise local electrical properties in GaN-based high electron mobility transistor (HEMT) structures with nanoscale resolution. We investigated the experimental setup and the imaging conditions to optimise the SCM contrast. As to the experimental setup, we show that the desired tip should be sharp (e.g., with the tip radius of ≤25nm) and its coating should be made of conductive doped diamond. Most importantly, its spring constant should be large to achieve stable tip-sample contact. The selected tip should be positioned close to both the edge and Ohmic contact of the sample. Regarding the imaging conditions, we also show that a dc bias should be applied in addition to an ac bias because the latter alone is not sufficient to deplete the two-dimensional electron gas (2DEG) in the AlGaN/GaN heterostructure. The approximate range of the effective dc bias values was found by measuring the local dC/dV-V curves, yielding, after further optimisation, two optimised dc bias values which provide strong, but opposite, SCM contrast. In comparison, the selected ac bias value has no significant impact on the SCM contrast. The described methodology could potentially also be applied to other types of HEMT structures, and highly-doped samples.

Phosphorus deactivation by hydrogen on hot carrier stressed high-voltage N-channel field effect transistor CMOS device demonstrated by scanning capacitance microscopy imaging

Junction profiles of hot electron stressed high-voltage N-channel field effect transistor (NFET) devices were measured by scanning capacitance microscopy. Deactivation of phosphorous was observed on the drain side. To directly establish a link between phosphorus deactivation and hydrogen, junction profiles were measured on an unstressed NFET (N-type metal-oxide-semiconductor) device with and without H2 plasma treatment and with subsequent 400 °C annealing in helium. Phosphorus deactivation was observed in the device after H2 plasma treatment, while subsequent 400 °C annealing led to dissociation of the P–H (or H–Si–P) bond and recovery of the device junctions.

Hydrothermal Synthesis of Nickel Oxide and Its Application in the Additive Manufacturing of Planar Nanostructures

The hydrothermal synthesis of nickel oxide in the presence of triethanolamine was studied. Furthermore, the relationship between the synthesis conditions, thermal behavior, crystal structure features, phase composition and microstructure of semi-products, and the target oxide nanopowders was established. The thermal behavior of the semi-products was studied using a simultaneous thermal analysis (in particular, using one that involved thermogravimetric analysis and differential scanning calorimetry, TGA/DSC). An X-ray diffraction (XRD) analysis revealed that varying the triethanolamine and nickel chloride concentration in the reaction system can govern the formation of α- and β-Ni(OH)2-based semi-products that contain Ni(HCO3)2 or Ni2(CO3)(OH)2 as additional components. The set of functional groups in the powders was determined using a Fourier-transform infrared (FTIR) spectroscopy analysis. Using microextrusion printing, a composite NiO-(CeO2)0.80(Sm2O3)0.20 anode film was fabricated. Using XRD, scanning electron microscopy (SEM), and atomic force microscopy (AFM) analyses, it was demonstrated that the crystal structure, dispersity, and microstructure character of the obtained material correspond to the initial nanopowders. Using Kelvin probe force microscopy (KPFM) and scanning capacitance microscopy (SCM), the local electrophysical properties of the printed composite film were examined. The value of its conductivity was evaluated using the four-probe method on a direct current in the temperature range of 300-650 °C. The activation energy for the 500-650 °C region, which is of most interest in the context of intermediate-temperature SOFCs working temperatures, has been estimated.

Microplotter Printing of Co3O4 Films as Receptor Component of Hydrogen Sulfide-Sensitive Gas Sensors

A hierarchically organized Co3O4 nanopowder was obtained via programmed chemical precipitation, exhibiting several levels of microstructural self-organization: the initial particles are 40 ± 5 nm in size (average CSR size is 32 ± 3 nm), have a somewhat distorted rounded shape and are combined into curved chains, which, in turn, form flat agglomerates of approximately 350 ± 50 nm in diameter. The thermal behavior of the semiproduct (β-Co(OH)2) was studied by means of a synchronous thermal analysis (TGA/DSC). The obtained powders were examined by X-ray diffraction analysis (XRD) and Fourier-transform infrared spectroscopy (FTIR). Nanopowder of cobalt(II,III) oxide was employed as a functional ink component for the microplotter printing of the corresponding film on the chip surface, and the preservation of the material’s crystal structure was confirmed by XRD and Raman spectroscopy (RS). The microstructural features of the resulting film were analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Kelvin probe force microscopy (KPFM) was utilized to estimate the work function of the material surface, and the scanning capacitance microscopy (SCM) data indicated the intergranular conductivity type. The results of the conducted chemosensor measurements demonstrate that the printed Co3O4 film exhibits hydrogen sulfide selectivity and a rather high sensory response (S = 131% for 100 ppm) to this analyte at an operating temperature of 250 °C. The dependence of the sensor response value and time when detecting H2S in the concentration range of 4–200 ppm was determined and the high reproducibility of the signal was demonstrated.

Charge-Gradient-Induced Ferroelectricity with Robust Polarization Reversal

Developing a ferroelectric tunnel junction with a robust polarization reversal is essential for errorless data storage, but it remains challenging since the second-order phase transition dominates the reversal and introduces intermediate states. This investigation has proposed a charge-gradient-induced ferroelectricity, which is featured with the first-order phase transition. As an order parameter, a charge-gradient-induced polarization is achieved by modulation of stoichiometric oxygen along the Bi2O2Se/Bi2Se3O9 bilayer during pulsed laser deposition. At room temperature, this polarity points out-of-plane and shows an abrupt reversal in the ferroelectric hysteresis loop. The coercive field only increases by 0.04 V/nm after 300 reversals. Fabricated into the ferroelectric tunnel junction, the bilayer ferroelectric exhibits a comparable electroresistance of 100. The ON/OFF state can be switched repeatedly or after a 360 s retention. Characterizations of scanning capacitance microscopy and the current-voltage relation demonstrate that the ON/OFF switching is based on an injection exchange between the tunnelling and the thermionic emission.

Microextrusion Printing of Multilayer Hierarchically Organized Planar Nanostructures Based on NiO, (CeO2)0.8(Sm2O3)0.2 and La0.6Sr0.4Co0.2Fe0.8O3-δ.

In this paper, NiO, La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) and (CeO2)0.8(Sm2O3)0.2 (SDC) nanopowders with different microstructures were obtained using hydrothermal and glycol-citrate methods. The microstructural features of the powders were examined using scanning electron microscopy (SEM). The obtained oxide powders were used to form functional inks for the sequential microextrusion printing of NiO-SDC, SDC and LSCF-SDC coatings with resulting three-layer structures of (NiO-SDC)/SDC/(LSCF-SDC) composition. The crystal structures of these layers were studied using an X-ray diffraction analysis, and the microstructures were studied using atomic force microscopy. Scanning capacitance microscopy was employed to build maps of capacitance gradient distribution over the surface of the oxide layers, and Kelvin probe force microscopy was utilized to map surface potential distribution and to estimate the work function values of the studied oxide layers. Using SEM and an energy-dispersive X-ray microanalysis, the cross-sectional area of the formed three-layer structure was analyzed-the interfacial boundary and the chemical element distribution over the surface of the cross-section were investigated. Using impedance spectroscopy, the temperature dependence of the electrical conductivity was also determined for the printed three-layer nanostructure.

Imaging the Permittivity of Thin Film Materials by Using Scanning Capacitance Microscopy

Recently, great advances had been made by using scanning probe microscopy (SPM) to quantify the relative permittivity of thin film materials on a nanometer scale. The imaging techniques of permittivity for thin film materials with SPM, especially for photoelectric materials, have not been fully researched until now. Here, we presented a method to image permittivity of thin film materials by using a scanning capacitance microscope (SCM). This method combined the quantitative measurement by using SCM with the capacitance gradient–distance fitting curve to obtain the two-dimensional (2D) permittivity image at room temperature under atmospheric conditions. For the demonstration, a 2D permittivity image of film of molybdenum oxide (MoO3), a kind of photoelectric material, was acquired. From the image, it could be found that the average values of permittivity of MoO3 film and of MoO3 film-doped NaCl were about 8.0 and 9.5, respectively. The experimental results were quantitatively consistent with other experimental results of the same material. The reported technique here could provide a novel method for imaging the relative permittivity with nanometer resolution and be helpful for the study of photoelectric materials.

Electrical Scanning Probe Microscopy Investigation of Schottky and Metal-Oxide Junctions on Hetero-Epitaxial 3C-SiС on Silicon

This paper presents a macro-and nanoscale electrical investigation of Schottky and metal-oxide junctions with hetero-epitaxial 3C-SiC layers grown on Si. Statistical current-density-voltage (J-V) characterization of Pt/3C-SiC Schottky diodes showed an increase of the reverse leakage current with increasing the devices diameters. Furthermore, C-V and J-V analyses of SiO2/3C-SiC capacitors revealed non-idealities of the thermal oxide, such as a high trapped positive charge (3×1012 cm−2) and a reduced breakdown field (EBD=6.5 MV/cm) compared to ideal SiO2. Nanoscale electrical characterizations by conductive atomic force microscopy (CAFM) and scanning capacitance microscopy (SCM) allowed to shed light on the origin of non-ideal behavior of Schottky and thermal oxide junctions, by correlating the morphological features associated to 3C-SiC crystalline defects with local current transport and carrier density.