Planar Diode Configuration Research Articles

Some aspects of pulsed laser deposited nanocrystallineLaB6 film: atomic force microscopy, constant force current imaging and field emissioninvestigations

Nanocrystalline lanthanum hexaboride(LaB6) films have been deposited on molybdenum foil by the pulsed laser deposition(PLD) technique. The as-deposited films were characterized by x-raydiffraction (XRD), scanning electron microscopy (SEM) and atomic forcemicroscopy (AFM). The XRD pattern shows the cubic crystallinity of theLaB6 film. The AFM studies reveal that the conical shapedLaB6 nanostructures have height 60 nm, base 800 nm, and a typical radius of curvature∼20 nm. A comparison of force and in situ current imaging AFM studies revealsthat current contrast does not originate from the surface topography of theLaB6 film. Field emission studies have been performed in the planar diode configuration. A current densityof 4.4 × 10−2 A cm−2 is drawn from the actual emitting area. The Fowler–Nordheim plot is found to be linear,in accordance with the quantum mechanical tunneling phenomenon. The fieldenhancement factor is estimated to be 3585, indicating that the field emission is fromLaB6 nanocrystallites present on the emitter surface, as confirmed by the AFM. The emissioncurrent–time plots show current stability to the extent of 5% fluctuation about the averagecurrent over a period of 3 h.

Direct determination of electrical conductivity of oxide cathodes

The application range of oxide cathodes, e.g. in CRTs is limited by the critical dc current density (typically 1–3 A/cm 2) and hence by the electrical conduction mechanism. The electrical conductivity σ el of the oxide layer has now been determined directly in a new procedure in a close-spaced planar diode configuration in an UHV chamber, together with thermionic emission data. The cathode temperature measured as a function of continuous dc load is essentially the result of a superposition of electron emission cooling—proportional to the dc current—and ohmic heating proportional to the square of the dc current. At the compensation point between electron emission cooling and ohmic heating, σ el can be determined directly from the emission data. After activation a result of about 10 −2 (Ω cm) −1 at 780 °C true temperature is obtained for BaSr-oxide cathodes, which is consistent with literature. It is shown that electrical conductivity decreases with operating time in accordance with reduced Ba generation. σ el can be increased by oxide dopants like yttria or europia.

Etching behavior of an epoxy film in O2/CF4 plasmas

Epoxy polymers are commonly used in microelectronic packaging for printed circuit board fabrication. Exposure to plasma environments occurs during processing for purposes such as drill smear removal, surface modification, and decapsulation. In this investigation, epoxy films made from a brominated diglycidyl ether of bisphenol‐A, containing aliphatic and aromatic segments, were etched in a radio‐frequency plasma using a planar diode configuration. Etching rates were measured at various compositions of O2 and CF4 in the gas feed. Surface composition of etched and nonetched films were compared using x‐ray photoelectron spectroscopy. Comparison of etching behavior and fluorine surface coverage is made with polymers, which are either aliphatic or aromatic. Maxima in etching rates for polyimide, epoxy, and polyethylene films occurred at 22.5%, 35%, and 37.5% CF4 in O2, respectively. Fluorine atom surface coverage was 10%, 20%, and 2%, respectively, under these conditions. It is proposed that the low affinity for fluorine atoms of the aliphatic moieties in the epoxy drives the O2/CF4 gas feed mixture, which yields maximum etching rates toward higher CF4 concentrations, similar to observations made for fully saturated polymers like polyethylene. As a consequence, the aromatic epoxy segments become more heavily fluorinated as occurs for highly aromatic polymers, like polyimide, in fluorine‐rich plasmas.

A new correction to Schottky barrier lowering in cathodes

A new technique is developed for approximating cathode current-voltage (I-V) and current-temperature (I-T) characteristics in a planar diode configuration. For a uniform work function surface, this method allows both for space-charge effects and for Schottky barrier lowering. Using this method, we derive an explicit first correction to the Schottky effect: ΔΦnew =ΔΦ0[1−(Jnet/JC)]1/2, where ΔΦ0 is the standard Schottky barrier lowering (eV), Jnet is the net emission current density, and JC is the Child’s law current density. The following closed form expression then approximates the net emission current density: Jnet≂JC (JR>JC), and Jnet≂JR exp(ΔΦnew/kT) (JR<JC), where JR is the Richardson’s current density. This equation for Jnet connects the space-charge-limited (SCL) emission regime to the deep temperature-limited (TL) regime. The SCL-to-TL transition point is found to be JR, and the above equations for emission current are continuous with a continuous slope at the transition point.

Stability of a Magneto-plasma†

ABSTRACT The characteristic equation describing the stability of a magneto-plasma is elaborated for the planar diode configuration having an externally applied d.c. magnetic field parallel to the electrode system, ignoring the role of collisions. In the limits of either cold plasma or zero magnetic field, a somewhat modified analysis is required. These reduced cases are essential to the study, both to confirm the correctness of the more general solution and to arrive at more transparent situations which can be readily interpreted. Thus the familiar result secured earlier in the absence of the magnetic field is recovered with the additional feature that at. finite temperatures stable behaviour demands Jv0/p+≥2, where J is the current density, v0 the thermal velocity and p+ the mean plasma density. Behaviour of the cold magneto-plasma is delineated in terms of an elementary characteristic equation that reflects the stabilizing effect of the magnetic field for lower energy operation of a plasma diode. The re...