Tungsten Probe Tip Research Articles

Performance Analysis of Forming Free Switching Dynamics of e-Beam Evaporated SnOx Based Resistive Switching Device

In this article, we have investigated the forming free bipolar resistive switching (RS) phenomena of <inline-formula> <tex-math notation="LaTeX">${e}$ </tex-math></inline-formula>-beam evaporated amorphous tin-oxide-based RS device with copper as a bottom electrode. To describe the impact of copper electrode over electrical response of tin-oxide-based RS device, we have used tungsten probe tip contact as a top electrode and copper as a bottom electrode. The crystal structure, energy bandgap, surface morphology, and device cross-sectional nanostructure view of deposited thin RS layer (tin-oxide) have been characterized by using X-ray diffraction (XRD), UV&#x2013;visible spectroscopy, and field-emission scanning electron microscopy (FESEM), respectively. The electrical behavior of fabricated switching device has been recorded by Keithley-4200 parametric analyzer with customized probe station. Reported switching device has capability to perform reversible RS phenomena for 500 cycles with low set/reset (&#x2212;0.52/0.39 V) voltage and good resistive window (&#x007E;15) without any considerable degradation. We have also discussed the primary reason for RS dynamics in the proposed device along with its conduction mechanism.

Resistive switching characteristics of UV-assisted room-temperature-fabricated top-electrode-free SnOx ReRAM

We investigated the resistive switching characteristics of a top-electrode-free SnOx-based resistive switching random access memory (ReRAM) which was fabricated at room temperature. The resistive switching layer was deposited by assistance of UV irradiation after two instances of spin coating of the Tin(II) acetylacetonate (Sn(AcAc)2) precursor. To minimize the coffee ring effect, the mixture of 2-methoxyethanol and ethanol was used as a solvent of the precursor. The resistive switching characteristics of the top-electrode-free device was measured by direct contact of a tungsten probe tip on the SnOx thin film in reference to the bottom ITO electrode. The device fabricated with 8 h of UV irradiation showed stable resistive switching characteristics even after repeating DC sweep switching cycles 200 times. The retention of the fabricated device was over 104 s. It was found that the Ohmic conduction is dominant in the low resistive state and the space charge limited conduction is dominant in the high resistive state. The resistive switching mechanism of this device was proposed as the tin ion-based filament-type ReRAM. The UV irradiation effects on the SnOx thin film were examined by x-ray photoelectron spectroscopy and the SnOx film thickness depending on the time of UV irradiation was measured by a field emission scanning electron microscope.

Research of quartz tuning fork tip length influence on the shear force imaging in liquids

In this article the use of sensors for shear force microscopy (SFM) is analysed. The sensor consists of a quartz tuning fork with an agglutined long tungsten probe tip for operation in liquid environments. The quartz tuning fork and a tip oscillation amplitude-frequency dependence in air and a tip in contact with surface were investigated using Finite Element Modeling and experimentally. The research results of our experimental research are valuable in the production of SFM sensors can be produced and used in nanotribology, nanolithography, nanometric acoustic spectroscopy and biological object research. DOI: http://dx.doi.org/10.5755/j01.mech.24.1.19059

Flame exposure time on Langmuir probe degradation, ion density, and thermionic emission for flame temperature.

The paper examines the effect of exposure time of Langmuir probes in an atmospheric premixed methane-air flame. The effects of probe size and material composition on current measurements were investigated, with molybdenum and tungsten probe tips ranging in diameter from 0.0508 to 0.1651 mm. Repeated prolonged exposures to the flame, with five runs of 60 s, resulted in gradual probe degradations (-6% to -62% area loss) which affected the measurements. Due to long flame exposures, two ion saturation currents were observed, resulting in significantly different ion densities ranging from 1.16 × 1016 to 2.71 × 1019 m-3. The difference between the saturation currents is caused by thermionic emissions from the probe tip. As thermionic emission is temperature dependent, the flame temperature could thus be estimated from the change in current. The flame temperatures calculated from the difference in saturation currents (1734-1887 K) were compared to those from a conventional thermocouple (1580-1908 K). Temperature measurements obtained from tungsten probes placed in rich flames yielded the highest percent error (9.66%-18.70%) due to smaller emission current densities at lower temperatures. The molybdenum probe yielded an accurate temperature value with only 1.29% error. Molybdenum also demonstrated very low probe degradation in comparison to the tungsten probe tips (area reductions of 6% vs. 58%, respectively). The results also show that very little exposure time (<5 s) is needed to obtain a valid ion density measurement and that prolonged flame exposures can yield the flame temperature but also risks damage to the Langmuir probe tip.

Blue and white light emission from zinc oxide nanoforests.

Blue and white light emission is observed when high voltage stress is applied using micrometer-separated tungsten probes across a nanoforest formed of ZnO nanorods. The optical spectrum of the emitted light consistently shows three fine peaks with very high amplitude in the 465–485 nm (blue) range, corresponding to atomic transitions of zinc. Additional peaks with smaller amplitudes in the 330–650 nm range and broad spectrum white light is observed depending on the excitation conditions. The spatial and spectral distribution of the emitted light, with pink–orange regions identifying percolation paths in some cases and high intensity blue and white light with center to edge variations in others, indicate that multiple mechanisms lead to light emission. Under certain conditions, the tungsten probe tips used to make electrical contact with the ZnO structures melt during the excitation, indicating that the local temperature can exceed 3422 °C, which is the melting temperature of tungsten. The distinct and narrow peaks in the optical spectra and the abrupt increase in current at high electric fields suggest that a plasma is formed by application of the electrical bias, giving rise to light emission via atomic transitions in gaseous zinc and oxygen. The broad spectrum, white light emission is possibly due to the free electron transitions in the plasma and blackbody radiation from molten silicon. The white light may also arise from the recombination through multiple defect levels in ZnO or due to the optical excitation from solid ZnO. The electrical measurements performed at different ambient pressures result in light emission with distinguishable differences in the emission properties and I–V curves, which also indicate that the dielectric breakdown of ZnO, sublimation, and plasma formation processes are the underlying mechanisms.

전기화학적 에칭법을 이용한 AFM용 텅스텐 탐침 제작에 관한 연구

As commercial atomic force microscopy (AFM) probes made of Si and <TEX>$Si_3N_4$</TEX> have low stiffness, it is difficult to induce sufficient elastic deformation on the surface of a specimen in a tapping mode. Therefore, high-guality phase contrast images can not obtained. On the other hand, a tungsten AFM probe has relatively higher stiffness than a commercial AFM probe. Accordingly, it is expected to provide an enhanced phase contrast image, which is an effective tool for achieving a better understanding of the micromechanical properties of worn surfaces and wear mechanisms. In this study, on electrochemical etching method was optimized to fabricate tungsten probe tips for an AFM. Electrochemical etching was performed by applying pulse waves with a 20% duty cycle at various voltages instead of only a DC voltage, which has been commonly used.

In situ plasma diagnostics study of a commercial high-power hollow cathode magnetron deposition tool

Using a newly designed and built plasma diagnostic system, the plasma parameters were investigated on a commercial 200mm high-power hollow cathode magnetron (HCM) physical vapor deposition tool using Ta target under argon plasma. A three dimensional (3D) scanning radio frequency (rf)-compensated Langmuir probe was constructed to measure the spatial distribution of the electron temperature (Te) and electron density (ne) in the substrate region of the HCM tool at various input powers (2–15kW) and pressures (10–70mTorr). The Te was in the range of 1–3eV, scaling with decreasing power and decreasing pressure. Meanwhile, ne was in the range of 4×1010–1×1012cm−3 scaling with increasing power and decreasing pressure. As metal deposits on the probe during the probe measurements, a self-cleaning plasma cup was designed and installed in the chamber to clean the tungsten probe tip. However, its effectiveness in recovering the measured plasma parameters was hindered by the metal layer deposited on the insulating probe tube which was accounted for the variation in the plasma measurements. Using a quartz crystal microbalance combined with electrostatic filters, the ionization fraction of the metal flux was measured at various input power of 2–16kW and pressure of 5–40mTorr. The metal ionization fraction reduced significantly with the increasing input power and decreasing gas pressure which were attributed to the corresponding variation in the ionization cross section and the residence time of the sputtered atoms in the plasma, respectively. Both the metal neutral and ion flux increased at higher power and lower pressure. The 3D measurements further showed that the ionization fraction decreased when moving up from the substrate to the cathode.

Electrical actuation and detection of mechanical oscillations in cantilevered multi-walled carbon nanotubes

A novel detection scheme, called the Harmonic Detection of Resonance (HDR) method, is described for measuring mechanical oscillations in nano-sized cantilevers under ambient conditions. HDR overcomes the problem of parasitic capacitance, which in the past has significantly limited the performance of capacitive sensors, by measuring resonances at higher harmonics (integer multiples) of the driving frequency. Individual multi-wall carbon nanotubes (MWNTs) were manipulated to serve as single-end clamped (diving board geometry) cantilevers and driven into resonance using a sharpened tungsten probe tip as the counter electrode. Two geometries between the MWNT and the probe tip were tested and HDR was found to work equally well for both geometries. Importantly, the HDR method has the advantage of being entirely electrical, both in actuation and detection, and thus is straightforward to integrate into standard CMOS technology.

Low Capacitance Electrical Probe for Nanoscale Devices and Circuits

An electrical probe is constructed of a small capacitor in contact with the circuit node under test so as not to load this circuit node and cause distortion of the input signal. The small capacitor is then placed in series with the small input resistance of a terminated coaxial signal line. The voltage signal at the output of the coaxial line will be approxi- mately the product of the small capacitance, the resistance of the coaxial line and the derivative with respect to time of the input signal. Tungsten probe tips can be sharpened to 100nm or less, enabling measurements of nanoscale devices.

Robust Ohmic contact junctions between metallic tips and multiwalled carbon nanotubes for scanned probe microscopy

We demonstrate a simple method that uses a scanning electron microscope for making a reliable low resistance contact between a single multiwalled carbon nanotube and a metallic tungsten probe tip or a Si cantilever. This method consists of using electron beam induced decomposition of background gases and voltage pulses to remove contaminants. The electrical quality of the contact is monitored in situ by measuring the current flow at constant bias or by observing the decay of current fluctuations. The quality of the contacts is confirmed via current-voltage spectroscopy. This method produces very stable, low resistance, mechanically robust contacts with high success rates approaching 100%.

Characterization of Electrical Properties and Gating Effect of Single Wall Carbon Nanotube Field Effect Transistor

We attempted to fabricate carbon nanotube field effect transistor (CNT-FET) using single walled carbon nanotube(SWNT) on the heavily doped Si substrate used as a bottom gate, source and drain electrode were fabricated bye-beam lithography on the 500 nm thick <TEX>$SiO_2$</TEX> gate dielectric layer. We investigated electrical and physical properties of this CNT-FET using Scanning Probe Microscope(SPM) and conventional method based on tungsten probe tip technique. The gate length of CNT-FET was 600 nm and the diameter of identified SWNT was about 4 nm. We could observed gating effect and typical p-MOS property from the obtained <TEX>$V_G-I_{DS}$</TEX> curve. The threshold voltage of CNT-FET is about -4.6V and transconductance is 47 nS. In the physical aspect, we could identified SWNT with phase mode of SPM which detecting phase shift by force gradient between cantilever tip and sample surface.

Surface Potential Measurement by Atomic Force Microscopy Using Quartz Resonator

Scanning Kelvin probe microscopy (SKPM) is demonstrated using a 1 MHz quartz length extension resonator as a force sensor. A tungsten probe tip glued onto the end of the quartz rod is electrically connected to the electrode of the resonator for the detection of Coulomb force between the tip and the surface. To detect Coulomb force, a frequency shift signal is used instead of the oscillation amplitude of the resonator. Surface potential mapping is measured on a Au(111) single crystal with nanoscale carbon dots. A potential difference of 100 mV is observed between the Au surface and the carbon dots. The resolution of surface potential mapping is discussed in terms of sharpness of tip, tip–sample separation and Kelvin probe measurement technique.

Electrophoretic drawing of continuous fibers of single-walled carbon nanotubes

Control over the current during electrophoretic drawing of continuous fibers of single-walled carbon nanotubes (SWCNTs) is shown to be critical in producing long fibers with specific diameters. In the process, as-produced SWCNTs are first dispersed in N,N-dimethylformamide (DMF) by sonication. A tungsten probe tip is then immersed in the SWCNT∕DMF solution, and a dc bias is applied between the tip and another electrode at the bottom of the beaker containing the solution. After a dark cloud several millimeters in diameter develops around the tip, the electrode is withdrawn to form continuous macroscopic fibers of SWCNTs. The resulting fiber length and diameter are found to be principally determined by the magnitude of the current. Under constant voltage conditions where the current is allowed to vary, the fibers are short (several millimeters long) and their diameters vary drastically along their lengths. Of significance is the fact that when the current is maintained at constant values, fibers several centimeters in length with uniform diameters ranging from 26to42μm are obtained at a withdrawal rate of 0.85μm∕s. For this withdrawal rate, long fibers (∼3cm and greater) are obtained at an optimum value of the current (400nA) using hybrid conditions where the voltage is maintained constant earlier in the process while the current is maintained constant later in the process. Control of the total current at low values during this process has the potential to produce long fibers with uniform submicron diameters.

Atomic resolution noncontact atomic force/scanning tunneling microscopy using a 1 MHz quartz resonator

A 1 MHz quartz length extension resonator is used as a force sensor for a noncontact atomic force/scanning tunneling microscope (AFM/STM). A tungsten probe tip glued onto the end of the quartz rod enables the detection of tunneling currents for STM observation. Au surface was observed in both AFM and STM modes. The resolution difference is discussed in terms of the insulating oxide layer on the tip. We also demonstrate the AFM/STM observation of the Si(111)-7×7 surface with atomic resolution in an ultrahigh vacuum.

Reproducible Electrochemical Etching of Tungsten Probe Tips

An electrochemical procedure in KOH electrolyte has been developed to reproducibly produce ∼5 nm radius tungsten probe tips. It has been found that a spurious electrochemical etching process, driven by the natural potential difference between an Ir electrode and the W tip, causes rapid tip blunting at the end of the electrochemical etching period. By electrically reversing this potential difference within 500 ns following tip separation, the blunting process is eliminated yielding sharp tips with varying cone angles.

Surface derivatization of nanoscale tungsten probes for interfacial force microscopy

Interfacial force microscopy is a novel technique for imaging and quantitative determination of the mechanical properties of a material such as elastic modulus, hardness, etc., with nm spatial resolution and nN force resolution. Due to the extreme pressures generated during probe-surface contact (many GPa), passivation of the chemical interactions, specifically adhesion, between the parabaloidal tungsten probe tips (radii 35&amp;lt;r&amp;lt;200 nm) and the substrate under investigation is often required. Convenient and effective protective monolayers are not generally available for many substrates, and it is necessary to develop a general procedure for passivation of the tip. We have derivatized tungsten(100) surfaces with the silane coupling agent (octadecyltrichlorosilane, OTS) and applied the same techniques to nm-scale tungsten tips. Force versus displacement (f–d) curves were recorded for the following tip–substrate interactions: underivatized tungsten tip against underivatized Au(111) surface, underivatized tungsten tip against derivatized Au(111) surface (C-18 thiol SAM), and derivatized tungsten tip (OTS) against underivatized Au(111). The data clearly show that the OTS derivatized tips were passivated against adhesive contact even at pressures of many GPa, thereby demonstrating the stability necessary for use in nanoindentation experiments.

Observations of Anisotropic Electron Scattering on Graphite with a Low-Temperature Scanning Tunneling Microscope

Low-temperature scanning tunneling microscopy was used to observe anisotropic (3-fold) scattering from point defects on a graphite surface. Such scattering from defects was theoretically predicted but is not typically apparent in room temperature scanning tunneling microscope images. This 3-fold scattering was previously observed only with C60-functionalized tips. The occupancy of the density of electronic states of the tungsten probe tip is sharpened sufficiently at cryogenic temperatures to enable the electron scattering to be imaged.

A BiCMOS active substrate probe-card technology for digital testing

An active substrate silicon probe card employs a polyimide membrane formed on a silicon substrate. The probe card combines tungsten probe tips and aluminum interconnects in the polyimide membrane with active test circuitry integrated in the silicon substrate. The card is potentially capable of providing more than 1000 probe tips in an array format. The choice of the active circuitry included in the substrate depends on the application of the probe card. If the probe card is intended for use with conventional digital testers, linear buffers can be integrated into the substrate to isolate the device under test (DUT) outputs from the 50/spl Omega/ transmission lines in the test system and drive those lines from matched impedances. Alternatively, by integrating the front-end circuits of a digital tester into the substrate, timing measurements can be made at distances less than 1cm from the probe tips, resulting in a significant improvement in testing accuracy. In this work, experimental circuits for both approaches are explored. An experimental prototype of an active substrate probe card employing linear buffers is integrated in a 2/spl mu/m BICMOS technology.

Scanning tunneling spectroscopy of Fe/W(110) using iron covered probe tips

We have used iron covered tungsten probe tips to study the electronic structure of thin films of Fe on a W(110) substrate by means of scanning tunneling spectroscopy. In contrast to earlier experiments which were performed with tungsten tips we have found a minimum in the differential conductivity dI/dV at submonolayer Fe coverage just above the Fermi level. At a coverage of 1.3 ML a pronounced peak is measured above Fe islands of the second layer approximately 0.9 eV above the Fermi level, i.e., in the empty sample states. This empty state peak was found to be extremely sensitive to contamination from the residual gas which is also known to influence the magnetic state of the second layer islands.

Polycrystalline tungsten and iridium probe tip preparation with a Ga+ focused ion beam

We have used a Ga+ focused ion beam (FIB) milling technique to produce sharp scanning‐probe microscope tips. The FIB procedure employs a roughly 0.2‐μm‐diam 20 keV Ga ion beam vector scanned in an annular pattern across the apex of an electrochemically etched wire. This method usually produces exceptionally sharp conical tips, but occasionally it generates a nearly cylindrical spike at the apex. In this paper, we show examples of the spikes, and we discuss possible mechanisms by which they are produced.