Henry F. Gray

Structure and luminescence of annealed nanoparticles of ZnS:Mn

Structural and light-emitting properties of nanoparticles of ZnS:Mn annealed in vacuum at temperatures up to 525 °C are presented. Annealing the 3.5 nm particles at temperatures up to 350 °C caused growth of some particles without substantial change in the luminescence or ZnS lattice. After annealing at 400–525 °C, the high-temperature wurtzite phase of ZnS appeared, accompanied by an increase of the average particle diameter to approximately 100 nm and a rearrangement of the Mn ions. Dramatic increase in cathodoluminescence emission was also observed and is compared to the structural information obtained from electron microscopy, x-ray diffraction, x-ray absorption fine structure, and electron paramagnetic resonance measurements.

Analysis and design of microwave amplifiers employing field‐emitter arrays

An analysis of the microwave ( f≳1 GHz) properties of field‐emitter arrays (FEAs) and several representative medium power (10–100 W) microwave amplifiers employing FEAs is presented. The FEA analysis is limited to parallel‐plate structures having discrete pointlike vertical emitter tips and gate apertures aligned to each tip. A transmission line analysis of wave propagation in this structure is presented and used to evaluate the geometries and materials needed for microwave operation. This analysis is used to investigate the performance capabilities and emitter requirements of both modulated‐emission linear beam tubes and microdevices based on FEAs. Specific microtriode designs are used to investigate practical problems such as space charge and thermal effects. Competitive performance should be achievable in gated‐emission linear beam tubes by using FEAs that perform at levels previously reported by several laboratories. Existing FEA technology (currents of 10 μA per emitter, transconductances of 1 μS per...

Vacuum integrated circuits

There is a rebirth of interest in vacuum electronics for special purpose signal and data processing, based on specific advantages of the vacuum as a device medium, but also on the applicability of solid state fabrication technology to vacuum device and circuit concepts. Programs in this direction at several laboratories are reviewed. The prospects for vacuum ICs filling special application niches are discussed.

Effects of S, Ba, and C on impregnated cathode surfaces

Auger electron spectroscopy (AES) and scanning low‐energy electron probe (SLEEP) techniques have been used simultaneously for correlating electronic and surface chemical behavior of impregnated matrix cathodes. The role of S, Ba, and C has been related to emission poisoning, decay with life, and delayed response after cathode shutdown.

Linear theory of a field‐emitter‐array distributed amplifier

A small‐signal theory of a field‐emission‐array distributed amplifier consisting of two microstriplike transmission lines is developed to calculate the premodulation in the input channel and the gain in the output channel. A first‐order perturbation analysis is used to treat the beam‐wave coupling in this device within the framework of a cold fluid model. The dependence of the linear gain on frequency, beam voltage, beam current, and the circuit parameters is derived to determine the parameter range for operation of the device. It is found that the height of the circuit is restricted to lie between 80 and 120 μm to maintain high electronic gain and low loss arising from the finite conductivity of the metal surfaces. In an output line having a substrate with a relative dielectric constant, er=4, a net gain of 7 dB/cm is calculated with a beam voltage of 60 V and a beam current of 2.14 A/cm in each wedge of a seven‐wedge emitter array. As the beam voltage is increased in the range 60–100 V, the net gain dec...

Oxidation of Si surfaces

The oxide thickness for Si wafers of different doping species and densities has been measured from 30 to 1000 A for dry O2 oxidation at 900 °C. The transition from the linear to parabolic oxide growth rate occurs near 300 A with measured rate constants of 6 A/min and 2500 A2/min, respectively. Carbon in graphitic form was found on the surface of the wafers prior to oxidation. This changed to a carbide‐type form after oxidation and remained at the Si‐SiO2 interface.

A Silicon Field Emitter Array Planar Vacuum FET Fabricated with Microfabrication Techniques

In this paper we will discuss a new type of field effect transistor, a vacuum FET, where the usual channel material is the vacuum rather than a semiconductor. This new device is based on Field Emitter Arrays (FEA) which are inherently submicron structures. That is, the field emitters themselves must have dimensions less that 0.1 micrometers in order to generate the high electrostatic fields necessary for electron tunneling, and the control gate (or extraction electrode) must be very close to the field emitter tip in order to generate these high fields with reasonable voltages. Consequently, this new “FET” is the first of a new class of vaccum electronic switching devices based on microfabrication techniques, and susceptible to circuit integration.

Silicon field emission transistors and diodes

Uniform, sharp point, and wedge-type field emitter arrays (FEAs) have been fabricated by using orientation dependent etching (ODE) and reoxidation sharpening techniques. This fabrication process results in very sharp and reproducible silicon field emitters which have yielded electron emission currents exceeding 20 mu A per tip for the pointlike structures with under 90-V turn-on extraction voltages. Collected currents of 5 mu A were obtained on wedge arrays at 300 V. Arrays of up to 30000 pyramidal point-type emitters have been fabricated. A process has also been developed for sealing these microtriodes in a vacuum. In this configuration, these devices may be handled like a transistor in air. These devices possess potential applicability to high-temperature transistors and diodes with high kilowatt power at high frequencies >1 GHz and for high-brightness-high-resolution displays. >

Growth of low-dimensional structures on nonplanar patterned substrates

Si growth by molecular beam epitaxy on nonplanar patterned Si substrates is studied as a function of growth parameters. The substrates consist of a truncated pyramid template with {111} sides and (100) tops formed by anisotropic etching of Si(100). For growth temperatures ≤550°C no qualitative changes in the morphology of the template are observed. At growth temperatures between 650-700°C {113} facets begin to form on the (100) surface and reduce the lateral dimensions of the (100) facet to < 20 nm. At high temperatures (∼800°C) {113} facets remain stable and {111} facets no longer exist. The small (100) mesa formed at medium temperatures by facet reduction is exploited through the growth of Si/Si 1-x Ge x multiple quantum wells leading to low-dimensional structures. Observations are quantified by scanning electron and transmission electron microscopies.

Field-emitter displays (FEDs) for cockpit applications

Modern aircraft are incredibly complex machines. Although many, if not most, of the functions are automated, the pilot and other cockpit crew members must have access to large amounts ofinformation in a very small period oftime. And this information must be available to them in a format that is easily understood quickly. Today, this information is often provided by Cathode Ray Tube (CRT) screens. These CRTs have many advantages with respect to visualization. That is, color CRTs can have full color, high brightness, large viewing angle, high contrast, and high spatial resolution. The disadvantages lie, to a great extent, in the package. CRTs and their necessary electronics are large, heavy, and fragile. Furthermore, ifbroken accidentally, the resulting implosion can create disaster in the cockpit. Consequently, many display developers of cockpit displays believe that the ideal display should be full color, extremely thin, light weight, energy efficient, exhibit high brightness and high dynamic range, capable of being refreshed in real time without jitter, have high spatial resolution, display a large number of pixels, and be visible over a very wide range of angles (normal to grazing incidence both left-to-right and top-to-bottom). For military aircraft, the display should operate with the same characteristics over a very wide temperature range. This is particularly important in northern climates during the winter, or when the interior ofthe aircraft becomes very cold such as a result of damage to the aircraft body at high altitude (e.g. gunfire, missile attack). In cockpits, the display should also be available in a wide range of sizes include the possible use in head or helmet mounted configurations. There has also been the suggestion that virtual reality glasses might be beneficial in aircraft cockpits. The displays would be available not only for normal instrument readings but also for radar, mapping, computer monitors, and possible cockpit lighting. The ideal cockpit display should exhibit the same full color visual characteristics whether seen in direct sunlight during the day or in a darkened cockpit at night. Some cockpit applications are looking forward to wraparound displays. Todays best information-comprehensive displays for cockpit use are fast-refresh, high brightness cathode ray tubes (CRTs). Unfortunately, a single CRT takes up a lot of room since the depth ofthe CRT is often greater than the screen diagonal. The CRTs fragility impacts cockpit safety. Its brightness is limited by a scanning electron beam which comes from a low current density thermionic cathode. Its lifetime is often a problem because ofbarium evaporation from that same cathode. The CRT cathode needs its own power supply and a separate magnetic scanning circuitry. In fact, most of its energy is wasted on the cathode and scanning circuitry. The energy is not delivered to the user as useful, visible light. Nevertheless, the CRT is still the best display available for cockpit display applications because it creates its own full-color light by cathodoluminescence. Some flat-panel technologies are becoming feasible for cockpit applications, but the CRT is still projected to have a favorable cost-benefit ratio, and superior performance characteristics for some years to come.