Negative High Voltage Research Articles

The formation of polycrystalline-Si thin-film transistors by using large-angle-tilt-implantation of dopant through gate sidewall spacer

Formation of poly-Si thin-film transistor (TFT) by large-angle-tilt-implantation of dopant through gate sidewall spacer (LATITS) has been proposed. By this LATITS scheme, the lightly doped drain (LDD) region under the oxide spacer is formed by tilt implantation of dopant through spacer and then the n + source/drain region is formed via using the same mask layer while the CMOS integration. The resultant on-state currents are comparable for both the conventional LDD scheme and the LATITS scheme. In addition, the LATITS scheme can even cause a smaller leakage current than the LDD scheme at high negative gate voltage, due to less gate–drain overlap region. By the LATITS scheme with proper tilt implantation energy, dose and angle, poly-Si TFT devices with an on/off current ratio above eight orders may be achieved with fewer process steps, as compared to the conventional LDD scheme.

Luminescence from Liquid Helium Excited by Corona Discharges

Liquid helium (LHe) at 4.2 K was electronically excited using a corona discharge for both negative and positive high voltages. The experiments were carried out for different pressures in the range from 0.1 to 10 MPa at constant temperature. The light emitted from the zone close to the tip was spectroscopically analyzed showing features from atoms and excimer helium. The shifts and widths of the observed lines and bands were found to depend on the applied hydrostatic pressure and on the tip polarity. Our analysis showed that classic pressure broadening theory cannot account for the observed widths and shifts rather than the presence of bubbles which surround single excited atoms and molecules. For positive tip polarities red shifted features distinct from pure He and He <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> * were observed and tentatively assigned to "red satellites".

Effect of Discharge Electrode Parameters on the Flow Velocity Profile of the Wire-rod Type Electrohydrodynamic Gas Pump Exit

Experimental investigation has been conducted to study the effects of corona wire diameter, pipe length, and corona polarity on outlet flow velocity distribution profile of a wire-rod type electrohydrodynamic (EHD) gas pump. Upon applying negative or positive dc high voltage between a wire electrode (outer diameter (o.d.) 60 μm, 200 μm, or 300 μm) and a rod electrode (o.d. 3 mm) in atmospheric air, corona discharge occurs and EHD gas flow is generated in the direction from the wire electrode to the rod electrode through a cylindrical pipe (inner diameter (i.d.) 20 mm). For both polarities, the discharge current and average flow velocity increase monotonically on increasing the applied voltage before the onset of spark discharge. Using wire electrodes with a smaller diameter, stable corona discharge between corona onset and spark onset is generated in a wider voltage range, and the discharge current becomes larger, resulting in a higher flow velocity. The maximum average flow velocity of 2.0 m/s, corresponding to a flow rate of 38 l/min, was achieved with a wire of diameter 60 μm by applying a voltage of -16 kV.

Effect of Klein tunneling on conductance and shot noise in ballistic graphene

The conductance and the Fano factor in a graphene sheet in the ballistic regime are calculated. The electrostatic potential in the sheet is modeled by a trapezoid barrier, which allows one to use the exact solution of the Dirac equation in a uniform electric field in the slope areas (the two lateral sides of the trapezoid). Asymmetry with respect to the sign of the gate voltage manifests the difference between the Klein tunneling and the overbarrier transmission. The phase coherence between Klein-tunneling events in the slope areas ($p\text{\ensuremath{-}}n$ transitions) leads to conductance and Fano-factor oscillation at high negative gate voltages. The comparison of the developed theory with the experiment supports the conclusion that the Klein tunneling was revealed experimentally.

Spectroscopic investigation of liquid helium excited by a corona discharge: evidence for bubbles and “red satellites”

The establishment of corona discharges close to a point electrode under both negative and positive high voltage in normal liquid helium (LHe) at 4.2 K is reported. The experiments were carried out at constant temperature and pressures ranging from 0.1–10 MPa. Visible luminescence emitted from the zone close to the tip revealed lines due to excited He atoms and molecules. The molecular luminescence showed hot band emissions with vibrational levels populated up to v=2. Rotational temperatures of 800 K were estimated showing that the excitations do not thermalise. With increasing pressure the lines shifted to shorter wavelengths and became broader. The magnitude of the increase in width deviated from what is expected from the gas phase and from classical line broadening theory and rather showed similarities to the behavior of bubbles in LHe. The detailed analysis of the rotational line intensity distribution revealed the presence of an additional radiator at the long wavelength side of molecular bands that we tentatively assign to “red satellite” emission. For corona discharges with positive tip polarities both atomic and molecular lines showed “red satellite" bands with much larger intensity than for negative polarity. The origin of the red satellite and the polarity dependence is unclear yet.

Tunnel magnetoresistance for magnetic tunnel junctions with Co2FeAl0.5Si0.5 full Heusler electrodes fabricated by molecular beam epitaxy system

The authors fabricated Co2FeAl0.5Si0.5 full Heusler alloy thin films by using a molecular beam epitaxy system on Cr buffered MgO single crystal substrates and investigated their structural and magnetic properties. It was revealed that Co2FeAl0.5Si0.5 films formed ordered L21 and B2 structures after annealing above 500 °C and below 400 °C, respectively. Then magnetic tunnel junctions with these electrodes and Al-oxide or MgO barriers were also fabricated, and the bias voltage dependence of tunnel magnetoresistance ratio was investigated. It was found that the tunnel magnetoresistance ratio of the junction with Al-oxide barrier has a larger asymmetric bias voltage dependence compared with that with MgO barrier, and the negative tunnel magnetoresistance ratio at high negative bias voltage is observed for both junctions.

Investigation of plasma potential and pulsed discharge characteristics in enhanced glow discharge plasma immersion ion implantation and deposition

Enhanced glow discharge plasma immersion ion implantation and deposition (EGD-PII&D) does not require external plasma sources. In this technique, the plasma is produced by self-glow discharge when a high negative voltage is applied to the sample. The small-area, pointed-shape hollow anode and large area tabular cathode form an electron-focused electric field. Using a special electric field design, the electrons from either the plasma or target (secondary electrons) are focused to a special hollow anode. As a result of the special electron-focusing field, the self-glow discharge process can be enhanced to achieve effective ion implantation into the substrate. In this work, the plasma potential distribution is investigated in details and the possible pulse discharge mechanism is discussed. The unique characteristics of the pulsed plasma and plasma extinction are studied.

Intense pulsed neutron emission from a compact pyroelectric driven accelerator

Intense pulsed D–D neutron emission with rates of &amp;gt;1010 n/s during the pulse, pulse widths of approximately hundreds of nanoseconds and neutron yields of greater than 10 000 per pulse, are demonstrated in a compact pyroelectric accelerator. The accelerator consists of a small pyroelectric LiTaO3 crystal that provides the accelerating voltage and an independent compact spark plasma ion source. The crystal voltage versus temperature is characterized and compares well with theory. Results show neutron output per pulse that scales with voltage as V∼1.7. These neutron yields match a simple model of the system at low voltages but are lower than predicted at higher voltages due to charge losses not accounted for in the model. Interpretation of the data against modeling provides understanding of the accelerator and in general pyroelectric LiTaO3 crystals operated as charge limited negative high voltage targets. The findings overall serve as the proof of principle and basis for pyroelectric neutron generators that can be pulsed, giving peak neutron rates orders of magnitude greater than previous work and notably increase the potential applications of pyroelectric based neutron generators.

Influences of bias voltage on mechanical and tribological properties of Ti–Al–C films synthesized by magnetron sputtering

Ti–Al–C films were deposited on silicon (100) substrates using magnetron sputtering TiAl target and graphite target in argon atmosphere at various substrate negative bias voltages. The composition, surface morphology, hardness and friction coefficient of the resulting films were characterized using x-ray photoelectron spectroscope, energy dispersive spectrometry, atomic force microscopy, nanoindentation and tribological tester. Results show that the structure and properties of the deposited films strongly depend on the applied substrate negative bias voltage. The Ti–Al–C films deposited at high substrate negative bias voltage show high surface roughness, low hardness and short wear life. In contrast, the Ti–Al–C films deposited without negative bias voltage exhibit uniform and smooth surface, a high hardness of approximately 37 GPa and low friction coefficient and long wear life. Excellent friction and wear behaviors of the Ti–Al–C films deposited without negative bias may be attributed to the dense structure and high hardness.

Evaluation of the electron density and temperature in a sliding discharge

A sliding discharge using two electrodes on a dielectric layer (upper electrodes) and a third electrode on its reverse side, facing the upper inter-electrode gap (lower electrode) was generated in air at atmospheric pressure. Application of a high dc negative voltage to one of the upper electrodes and to the lower electrode, and a high ac voltage to the other upper electrode generates a stable and homogeneous surface plasma (plasma sheet) in the upper electrode's gap. In this work, the plasma sheet optical emission of the spectral bands corresponding to the 0–0 transition of the second positive system of N2 (λ=337.1 nm) and the first negative system of N2 + (λ=391.4 nm) has been measured and analysed. It was found that the plasma sheet consisted of a set of cathode-directed streamers. The streamer generation frequency and its transit time across the inter-electrode gap have been studied. On the basis of a reliable atomic model to interpret the line emission, the total electron number at the streamer head and the electron temperature have been derived.

The formation of polycrystalline-Si thin-film transistors with a thinned channel layer

Polycrystalline-Si thin-film transistors with a thinned channel layer have been examined. A thinner channel layer may yield a larger on-state current, due to better gate control over the entire channel region. In addition, a thinned channel layer can also reduce the source/drain bulk punch-through and thus the lateral electric field within the channel region. As a result, a 20 nm thick channel layer can significantly suppress the leakage current at relatively large negative gate voltages better than the 100 nm thick channel layer. However, a thinner channel layer would lead to more bending of the energy band at an applied gate voltage, thus enhancing the vertical electric field. Accordingly, when a channel length of 1 µm is examined, the 20 nm thick channel layer would resultantly cause a lowest leakage current (off-state current) value a half-order larger than the 100 nm thick channel layer. Hence, from the device aspect, a properly thinned channel layer, which is of 30 nm thickness here, can be employed to achieve a large on-state current without considerable degradation of the off-state leakage current, while suppressing the leakage current induced at relatively high negative gate voltages.

Measurements of the asymmetric dynamic sheath around a pulse biased sphere immersed in flowing metal plasma

A long-probe technique was utilized to record the expansion and retreat of the dynamic sheath around a spherical substrate immersed in pulsed cathode arc metal plasma. Positively biased, long cylindrical probes were placed on the side and downstream of a negatively pulsed biased stainless steel sphere of 1 in. (25.4 mm) diameter. The amplitude and width of the negative high voltage pulses (HVPs) were 2 kV, 5 kV, 10 kV, and 2 µs, 4 µs, 10 µs, respectively. The variation of the probe (electron) current during the HVP is a direct measure for the sheath expansion and retreat. Maximum sheath sizes were determined for the different parameters of the HVP. The expected rarefaction zone behind the biased sphere (wake) due to the fast plasma flow was clearly established and quantified.

Influence of Simulated LOCA on the Properties of Zircaloy Oxide Layers

Specimens of Zr1Nb and Zry-4W were pre-oxidized first for 360 days in steam at 425 °C and were then exposed for 3 min to 1200 °C in steam, simulating loss of coolant conditions. In this way, the oxide thickness was more than doubled. The I-V characteristics, measured up to 90 V at temperatures up to 180 °C, revealed the formation of double layers, consisting of dark monoclinic oxide with 1.3 eV activation energy near the metal, and of a whitish surface phase with only 0.5 eV, for both samples. The I-V characteristics of Zr1Nb showed normal behavior, whereas Zry-4W changed from an unusual sub-linear form at low temperatures and voltages to normal space-charge limited currents at higher temperatures and voltages. Observation of the injection and extraction currents in the Zry-4W sample showed abnormally high negative zero voltages produced by extraction after former injection.

Method of Fast Hydrogen Passivation to Solar Cell Made of Crystalline Silicon

AbstractPlasma immersion ion implantation (PIII) is a technique of material processing and surface modification, using controllable negative high voltage pulsed bias to attract the ion generated from the plasma. The method using PIII treatment quickly improves the performance of solar cell made of crystalline silicon, including monocrystalline, multicrystalline and polycrystalline silicon. Hydrogen ions are attracted and quickly implanted into solar cell under a predetermined negative pulse voltage, thus, the passivation of the crystal defects of the solar cell can be realized in a short period. Meanwhile, the properties of the antireflection layer can not be damaged as the proper operating conditions are used. Consequently, the series resistance can be significantly reduced and the filling factor increases as a result. Both the short-circuit and the open-circuit voltage can be increased. The efficiency can be enhanced.

A new approach to the preionization of flash lamps in power lasers

As long as neodymium amplifiers will be used in high-energy lasers, preionization problems will be present in firing the flash lamps. It is difficult to find papers describing technical solutions using preionization concept; only a few internal reports and proceedings from Pulsed Power conferences describe the usage of such circuits in power laser facilities. In all of them, a special negative high voltage power supply is used. A new simple solution, without any additional power supply, using only a small part of the energy gathered in the main capacitor bank for generating a preionization pulse is used. The firing order is split into two signals; the first one is triggering preionization circuit and the second one, after delaying, is triggering the main discharging circuit.

A direct current glow discharge plasma source for inner surface modification of metallic tube

A dc glow discharge plasma source was developed for inner surface modification of metallic tubes with an inner diameter of 10 mm. A tungsten wire of 30 μm thick was stretched inside the tube to form coaxial electrodes. DC glow discharge plasma was generated inside the tube by applying a negative high dc voltage to the tube. It was found that the length of the cylindrical plasma bulk depends linearly on the applied voltage. The electron excitation temperature of Ar plasma was measured as 12830 ± 550 K by optical emission spectroscopy method. As a preliminary application, diamond-like carbon (DLC) films were deposited onto the inner surface of stainless steel tube of 100 mm in length and 10 mm in inner diameter by using CH 4/Ar mixture with 40% CH 4 at 40 Pa pressure. The chemical structure of the DLC film deposited on the substrate was analyzed by Raman spectroscopy. The integrated intensity ratio ( I D: I G) was obtained as 1.62 from the Raman spectra. The thickness of the DLC film deposited on the substrate was estimated as 1.5 μm by scanning electron microscopy (SEM) observation.

Formation of High Flux Parallel Neutral Beam Using a Three Grid System of Ion Beam during Low Angle Forward Reflection of Ions

The energy and the flux of the ion gun with a three-grid system was compared with those of the ion gun with a two-grid system and the characteristics of the neutral beam sources composed of the ion guns with different grid systems and a reflector for the low angle reflection of the ions were investigated. By using the three-grid system instead of the two-grid system and by applying higher negative voltage to the 2nd grid, a higher ion flux without changing the ion energy could be obtained for the ion gun of the neutral beam source. The three-grid ion gun system generated higher neutral beam fluxes compared to the two-grid ion gun system. This result was confirmed by measuring the etch rates of Si and GaAs with Ar and fluorine neutral beam. Also, using the neutral beam source with the three-grid ion gun, 35nm-width Si patterns could be etched vertically by CF4 gas indicating the formation of a parallel neutral beam.

High‐field actively detuneable transverse electromagnetic (TEM) coil with low‐bias voltage for high‐power RF transmission

The design and construction of a 4T (170 MHz) transverse electromagnetic (TEM) actively detuneable quadrature head coil is described. Conventional schemes for active detuning require high negative bias voltages (>300 V) to prevent leakage of RF pulses with amplitudes of 1-2 kW. To extend the power handling capacity and avoid the use of high DC bias voltages, we developed an alternate method of detuning the volume coil. In this method the PIN diodes in the detuning circuits are shorted when the RF volume coil is tuned, and negatively biased with -12 V when the coil is detuned. To preserve the high Q(U)/Q(L) ratio of the TEM coil, we modified the method of Nabetani and Watkins (Proceedings of the 13th Annual Meeting of ISMRM, Kyoto, Japan, 2004, abstract 1574) by utilizing a high-impedance (approximately 200 Omega), lumped-element, quarter-wavelength transformer. A Q(U) of 500 was achieved for the detuneable TEM, such that incorporation of the detuning network had minimal effect (<1 dB) on the performance of the coil in vivo.

Preparation and properties of W-containing diamond-like carbon films by magnetron plasma source ion implantation

W-containing diamond-like carbon (DLC) films were prepared on silicon wafers by a process combining reactive magnetron sputtering with plasma source ion implantation (PSII). A tungsten disc was used as a target for the sputter source. Ar/C 2H 2 mixed gas was introduced into the discharge chamber. Superposed negative high voltage pulses (− 10 kV, 100 Hz, 100 μs and DC − 0.5 kV) were applied to the substrate holder. The chemical composition of the films was determined using X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). Surface morphology was observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The film structure was characterized by Raman spectroscopy, X-ray diffractometry and high resolution transmission electron microscopy (HREM). Sheet resistivity of the films was measured by a four-point probe method. Furthermore, a ball-on-disc test was employed to obtain information about the frictional properties and sliding wear resistance of the films. The structure of the films changed from metal-containing DLC to a composite of metal-containing DLC and metal carbides with increasing metal content in the films. WC 1− X carbides were observed for films composed of higher amounts of W than 20 at.%. Around 10 nm diameter nanocrystallites of WC 1− X were observed by HREM. The sheet resistivity of the films decreased drastically with increasing metal content in the films. The tribological properties of the films were improved by metal element doping. A low friction coefficient 0.09 was derived for 0.5 at.% W-containing DLC film.

Composition and chemical structure of ultra-thin a-C:F films deposited by RF magnetron sputtering with high pulsed bias

By applying a negative high pulsed voltage to Si (111) substrates, ultra-thin fluorine carbon films of about 3 nm thick are deposited and completely covered on the samples by RF magnetron sputtering with PTFE target. Angle resolved X-ray photoelectron spectroscopy analysis indicates that the surface of the deposited films is rich in fluorine, and C–F 2, CF–CF and C–F groups in the outmost surface layer are much more than those in the inner layer of the films. The reason for this forming fluorine-rich phenomenon is explained and a two-layer model is proposed.