Flat Emitter Research Articles

SURFACE STRUCTURAL DESIGN OF SELECTIVE EMITTER FOR METHANE STEAM REFORMING

We performed structural optimization of a selective emitter with two-dimensional silicon based gratings coated by platinum as a thermal radiator to promote methane steam reforming reaction. The structural parameters were optimized by numerical calculation to radiate high thermal power in a vibrational absorption band of methane molecule at 3.3 μm. Optical property of the fabricated optimum selective emitter with periodicity Λ = 2.6 μm found that the emission peak was resonant with this absorption band. The amount of hydrogen produced by the methane steam reforming process using the optimized selective emitter became four times greater than that obtained by the flat emitter.

Model of Neutral-Beam Propagation in a Duct With Scrapers

A model of propagation of a neutral beam with geometric focusing and angular divergence in a duct is described. An algorithm is presented for calculation of a 2-D current-density profile at an arbitrary distance from a flat circular emitter with the account of multiple plane scrapers in the beam duct, which limit cross section of the beam. Numerical code is applied to calculation of current-density profiles and power loads on circular scrapers due to neutral particles.

A Field-Emission Display with an Asymmetric Electrostatic-Quadrupole Lens Structure

An asymmetric electrostatic-quadrupole lens (AEQL) system for high definition field emission displays (HD-FEDs) was proposed. It was applied to the double-gated structure where the emitters are a thick layer of carbon nanotube paste such as a flat surface emitter. The AEQL structure was designed with two opposing planar electrodes of noncircular apertures which generate the quadrupole electric field. Utilizing a design of field emitter arrays (FEAs) with AEQL, an optimized beam shape with horizontal reduction and vertical elongation was obtained. According to three-dimensional (3D) simulation results, this AEQL structure exhibited excellent focusing effects that satisfied the aspects of pixel size and shape in HD-FEDs.

Polysilicon metal-insulator-semiconductor electron emitter

The flat metal-insulator-semiconductor (MIS) electron emitter is a simple design, allowing easy manufacture. The emitters are relatively insensitive to environment, allowing them to operate in poorer vacuum conditions than are necessary for oxide thermionic or microtip field emitters. In most literature reports, MIS and metal-insulator-metal devices are limited in emission current (<0.001A∕cm2) by their low efficiencies (⪡0.1%). We have observed emission currents as high as 2–10A∕cm2 at efficiencies from 3%–10%. Our best results are from emitters comprised of 5–7.5nmgold∕15nm SiO2∕100nm polysilicon/n++ doped silicon substrate. The roles of each component of the flat emitter were investigated. The polysilicon serves a dual role: Bumps on its surface act as field-enhanced emission sites while the bulk of the film behaves as a self-adjusting ballast resistor preventing run away emission from any one emission site. The thin gold layer self-assembles into a nanomesh with >400pores∕μm2 through which electrons are emitted. Energy distribution and angular divergence of emitted electrons were measured. A coherent explanation of emission including the origination of the divergence is presented. Pros and cons of the MIS emitter and potential application are discussed.

Electron field emission from a patterned diamondlike carbon flat cathode

A 300-nm-thick diamondlike carbon (DLC) film was deposited on to a heavily doped n-type Si (111) wafer by filtered arc deposition. A flat thin film cylindrical emitter array was then fabricated by reactive-ion etching the DLC film. Its electron field emission properties were studied using a simple diode structure. A field emission current of 0.1 μA was detected under an electric field of 5.2 V/μm. As large as 64.1 mA/cm2 of field emission current density was achieved after an activation process under a 39 V/μm field. An image formed on the anode screen showed that electron field emission from the DLC flat emitter array is rather uniform. The field emission behavior is also consistent with Fowler–Nordheim theory. Hydrogen plasma surface treatments were found to enhance the field emission properties.

Highly-efficient flat electron emitter of single-crystalline CVD diamond

Abstract In the present work, using chemically-vapor-deposited single-crystalline diamond for the central layers of the cold cathode, highly-efficient electron emitters with a kind of MIS (metal–insulator–semiconductor) structure have successfully been fabricated. The attained cathode efficiency (defined as the emission current divided by the current injected into the emitter) has significantly been improved from 2% previously reported for a polycrystalline diamond MIS emitter to >10%, being almost independent of the amounts of the emission currents. The efficiency and the maximum currents obtained at 1100 V were sample-dependent and ranged from 14 to 100% and from 10−11 to 10−7 A, respectively. These clearly indicate that it is essential for an increase in the cathode efficiency of the diode-type diamond flat emitter to improve the crystalline quality of the central layers playing important roles in the electron injection and transportation processes. The emission mechanism is discussed on the basis of the emitter performance obtained.

DLTS and photoluminescence on wafer mapping analyses for AlGaAs/GaAs heterojunction bipolar transistors

The on-wafer mapping of the current gain in AlGaAs/GaAs heterojunction bipolar transistors (HBTs) has quite a close correlation with that of DLTS signals from the emitter/base junction region and with that of band-edge photoluminescence from the flat band emitter layer. It is found that the deep level with an activation energy around 0.6 eV, assigned as primarily ME6 or ME7, probably acts as an effective recombination center at the junction region and reduces the current gain of the transistors. It is also shown that the photoluminescence measurement is a promising method for nondestructive evaluation of the recombination centers in HBTs.

Optimisation of ‘radiator’ shelf design in order to achieve energy thrift

The traditional hot-water-filled ‘radiator’, i.e. a vertical, flat heat emitter, fitted below a window, can often lose > 10% of its heat output through the window (i.e. without making any useful direct contribution to heating the main body of the room in which it is placed). A reduction in this rate of heat loss can be achieved by replacing the single glazing by double glazing. However, a much lower capital-cost, energy-thrift option, which is considered here, merely requires installing a suitably designed horizontal shelf between the radiator and the window. By optimising the geometry of this shelf, placed between the two buoyancy-driven air flows, i.e. downwards from the window and upwards from the radiator, a reduction in the steady-state rate of heat loss through an experimental window of ∼14% of the radiator output has been achieved, resulting in a simple pay-back period for the installation of the shelf of ∼2 years. The wide variations in the dimensions of windows and radiators as well as their relative placements and surface temperatures preclude a simple optimal thermal design of the horizontal shelf, which is suitable for all occasions, being proposed. However, significant improvements in the system's energy performance (i.e. lower rates of heat loss through the window) will be achieved when the following are employed: either (1) a straight horizontal shelf, protruding from the wall by 84 mm; or (2) a horizontal shelf, with a curved underside of radius 98 mm, when the protrusion from the wall is 98 mm.

A vertically isolated self-aligned transistor—VIST

A vertically isolated self-aligned transistor (VIST) has been developed to make possible high-speed low-power dissipation bipolar devices suitable for LSI. This VIST consists of a bird's beak free oxide isolated structure and a high impurity density inactive base self-aligned to the polysilicon emitter. A flat emitter transistor with a self-aligned base is developed by forming an inactive high impurity density base region with an ion-implantation method using a polysilicon emitter as a mask. The transistors exhibit uniform current gain even to current levels as low as 10-8A. The f t value of this transistor is 6 GHz. The ring oscillators and counter are fabricated using the 13 × 6 µm2transistor cell. The power and delay product is 0.12 pJ.

Flat Emitter Transistor with Self-Aligned Base

A flat emitter transistor with a self-aligned base (FLET) has been developed to realize a high speed and low power dissipation bipolar LSI. This FLET has a flat bottom emitter and eliminates parasitic capacitance in the side wall. Accordingly, current gain (hFE) is almost independent of the emitter size and shape. Moreover, high cut-off frequency (fT) and high hFE can be obtained in low current region. The FLET also has an inactive base of high impurity density formed extremely near the emitter region. As a result, the base resistance can be lowered even though single line base structure is used. This base contact structure enables the reduction of CTC and CTS. The divider using FLET operated at frequencies up to 1.3 GHz. The power dissipation was 125 mW, being one fifth that of the conventional divider.

Energy Resolution of the Photoemission Analyzer

Resolution in the photoemission energy analyzer is investigated theoretically for the case of a finite emitter in a spherically symmetric retarding field with a magnetic field present. Resolution errors shift and broaden structure in measured energy distribution curves by an amount which is energy dependent. The analysis is applicable to the spherical capacitor analyzer, the screened emitted geometry, the multiscreened LEED system, and others. Electrolytic tank measurements show field distortions caused by a flat emitter, the emitter support, and the window aperture. Spherical symmetry is restored to a configuration with a large emitter or support structure by surrounding the emitter with a screened, field-free region. An explanation is given for the reasonable resolution obtained for any small emitter completely enclosed by a collector. Distortion of measured electron energy distributions caused by reverse photoemission, reflected electrons, and fringing fields at the emitter is also discussed.