Of all applications for which field emitter arrays (FEAs) are being designed, RF vacuum microelectronics is the most technically challenging application. The current density is typically three orders of magnitude larger than that required for displays (which require < 0.1 A/cm2). Due to their high current density capabilities and instant turn-on, FEAs may be a promising alternative to thermionic emitters for use in Inductive Output Amplifiers (IOAs). An analytical model of a field emitter is used to estimate Fowler Nordheim A and B parameters, effective resistance and capacitance of the array under several GHz modulation, signal propogation lengths, total current and current density, and effects of emitter non-uniformity on the basis of array geometry and materials. Estimates of inductance, resistance, and capacitance are made to estimate the drive power required to produce a bunched electron beam for Inductive Output Amplifier applications. An electronic efficiency of 32% with 15 dB gain may be possible from an array producing 260 mA peak, 71 mA average, current at 10 GHz using a TWT helix 1.51 cm long.

A triode structure of chimney-shaped field emitter arrays is proposed in this article. This triode structure includes the chimney-shaped emitter, thermal oxidation dioxide, and the plateau-shaped singlecrystalline silicon gate electrode. For the application of the matrix-addressable and large area flat panel display, the uniform structure of the emitters and the yield become critical manufacturing issues when attempting to control nano-meter size features. The uniformity and yield of the chimney-shaped emitters are very well controlled. The nano-sized gate-to-emitter separations can be created by the changing thickness of the insulator. The uniformity of the insulator and emitter material can be controlled within 3% which can be obtained by most large area thin film deposition tools, not by photolithography.

Over the past few years, Motorola, as well as several other companies around the world, have been developing a new type of flat panel display, called the field emission display (FED). The FED combines many of the advantages of its cousin, the cathode ray tube (CRT), including high brightness and contrast, wide angle viewability, and speed in a flat package that is only a few millimeters thick. A 14 cm diagonal FED prototype built at Motorola Flat Panel Display Division is shown below, in Figure 1.

We propose a novel lateral field emission triode, which does not require any additional vacuum sealing process and exhibits superb field emitter triode performance. The purpose of this paper is to compare titanium polycide tip with polycrystalline silicon tip. A new experimental results of the device, such as variation of tip material, device stability experiment, measurement of the novel device in vacuum chamber in order to verify the proposed vacuum sealing process, and transconductance characteristics at each current level.

The minimum turn-on anode to cathode voltage of titanium polycide tip is considerably decreased compared with polysilicon tip. The anode current measured in 10−8 Torr vacuum chamber is similar to the anode current measured in atmospheric pressure, which shows that the proposed vacuum sealing process is reliable. The stable current of 300μΑ is maintained during 60 h.

Wide bandgap semiconductors such as diamond and the III-V nitrides of GaN and AIN exhibit small or even negative electron affinities. Recent results have shown that surface treatments will modify the electron affinity of diamond to cause a negative electron affinity (NEA). Results are presented which correlate the field emission from single crystal p-type (boron doped) diamond with the electron affinity of the surfaces. The field emission is explored for nitrogen doped polycrystalline films. The threshold for field emission is significantly higher than from p-type diamond, and in fact, most surfaces are severely damaged during the emission measurement. High resolution photo-electron emission microscopy (PEEM) and field emission electron microscopy (FEEM) are employed to determine the relation of the emission to the surface morphology. PEEM results presented for diamond indicate relatively uniform emission with increased intensity at protruding crystallite edges. Results are presented for cold cathodes fabricated from epitaxial nitrides grown on 6H-SiC.

Carbon thin film cathodes have been produced with an emission site density of 2 × 105/cm2 and with current density higher than 40 mA/cm2at 10 V/μm extraction field. Characterization of the film bonding structure by UV Raman spectroscopy and emission sites by Atomic Force Microscopy (AFM) are presented and discussed in detail. A hypothesis of the nature of emission sites in these films is proposed in accordance with the analyses.

Strong and sustained electron emission at low electric fields has been observed in undoped, nano-structured diamond. The cold cathode emitters consist of a layer of nanometer-size diamond particulates coated on a silicon substrate which is subsequently heat treated in a hydrogen plasma for activation. Electron emission for a current density of 10 mA/cm2is observed at an applied field of 3-5 V/μm. We attribute this excellent emission property to the high defect density in the nano-structured diamond particles and the low electron affinity associated with the diamond surface. The emitters are useful for applications such as flat panel displays as, in addition to the very low fields required, they can easily be deposited on large area substrates by low-cost coating techniques and do not require complicated microtip fabrication processes.

The kinetic energy and spatial distribution of field electron emission from nitrogen (urea) doped, chemical vapor deposited (CVD) diamond films have been examined with simultaneous field emission and photoemission. A linear Fowler-Nordheim characteristic was measured over a wide range of currents. The field emission electrons originate from distinct areas of the flat sample. The dominant origin of field emission is due to electrons tunneling from near the valence band maximum. A time dependent fluctuation in the kinetic energy and spatial distribution of the emission is observed when the applied electric field (and hence emission current density) is increased well above the emission threshold.

Extreme Devices has fabricated and tested gated CVD diamond microtip arrays for use as cold cathodes in a variety of high power, high temperature, and high radiation applications. The uses for these devices include direct replacement of hot filament cathodes, microwave amplifiers, spaceborne sensors, and other areas requiring devices that provide high current output and that will function in harsh environments. The basic architecture of the device including an overview of the method for obtaining the self-aligned gated diamond microtip array is presented. Key developments for these robust devices include low electron extraction fields (3 V/μm), high current density output (>75A/cm2), stable operation for long periods of time, and operation in severe (high pressure) conditions. The gated cathodes offer low turn-on voltages (22 V) and appear to be well suited to a number of applications.

A novel processing sequence for the formation of gated diamond field emitter arrays (triode system) is proposed and the feasibility is tested by investigating the field emission property. The processing scheme is based on the selective deposition of diamond using the well established nucleation enhanced process on silicon substrate, so called bias enhanced nucleation (BEN). Selective deposition of diamond using the same process was also demonstrated on titanium nitride (TIN) electrode layer. Our preliminary results show that the diamond field emitter is turned on at around 97 V/μm with the current level of about several μA.

It is shown that the facile electron field emission from diamond and diamond-like carbon occurs because surface groups such as C-H can produce large changes in electron affinity, so that electric fields from the anode can be focused towards unhydrogenated surface areas of high affinity, the fields ending on negative charges in an underlying depletion layer. The resulting downwards band bending creates very large fields which cause Fowler-Nordheim emission, while not exceeding the breakdown field, which is the highest for any solid.

Field emission from silicon tips with carbon coatings deposited by VHF CVD at low temperature, Ts=225°C, has been studied. Emission was measured from both single tips and tip arrays. Structure and electronic properties of the films have been characterized. Significant effects due to pregrowth plasma treatment of the sample surface were observed on microstructure and emission characteristics. Optimized carbon coatings on silicon tips increased emission current by about two orders and reduced the threshold field to 0.1 V/μm.

This study explores the field emission properties of nitrogen doped diamond grown by microwave plasma CVD. Several diamond samples were grown on silicon under varying conditions. With certain process parameters, films can be grown which exhibit photoluminescence bands at 1.945eV and 2.154eV that are attributed to single substitutional nitrogen. Field emission characteristics were measured in ultrahigh vacuum with a position variable anode. For samples grown with gas phase [N]/[C] ratios less than 16, damage from micro-arcs occurred during the field emission measurements. Samples grown at higher [N]/[C] content could be measured without damage. These measurements indicate relatively high threshold fields (>100V/νm) for electron emission. From the data, two possible field emission mechanisms are presented. Conducting defect states in the bandgap of diamond may provide a source of electrons to the emitting diamond surface.

A combination of classical I-V characterization and voltage-dependent field emission energy distribution (V-FEED) analysis was employed to investigate the mechanisms that dominate field emission from tip-shaped Mo emitters electrophoretically coated with nominally intrinsic, cubic boron nitride (c-BN) powders. I-V characterization of Mo emitters before and after coating showed that the c-BN coating enhanced the field emission current by 2 orders of magnitude. V-FEED analysis revealed a voltage drop proportional to the applied voltage across the c-BN coating due to field penetration. This voltage drop was typically in the order of several Volts for applied voltages of several 100 Volts, and a cathode-to-anode distance of 500 μm. Extrapolation of V-FEED data to flat band condition identified the conduction band minimum of c-BN as the origin of field emitted electrons. At larger field emission currents, an additional voltage drop was observed and was found to be proportional to the emission current. This observation was interpreted in terms of an ohmic resistance at the Mo/c-BN interface and was estimated to be in the order of 10 MΩ.

A vacuum microelectronic device containing carbon nanotube electron field-emitters was developed and tested. The gated cathode was fabricated using conventional microelectronics fabrication techniques and a final, self-aligned, in situ carbon nanotube growth step. To our knowledge, this is the first vacuum microelectronics device with carbon nanotube field-emitters grown in situ with a catalytic growth process. The turn-on voltage of the cathode was less than 20 volts and the emission current density at 50 volts was as high as 9 mA-cm−2. The fabrication process, device performance, manufacturing issues and cathode applications will be discussed.

New observations are presented on the emission of electrons from n-type boron nitride (BN) cold cathode films. These carbon-doped BN films demonstrate a significant improvement in the electron emission current, on the order of 1 to 3 orders of magnitude, as a function of the extraction field for many different materials and morphologies.

These BN cold cathodes have yielded stable DC currents in excess of 4 mA at an extraction field of approximately 30 V/μm.

We report the results of junction capacitance measurements on thin tetrahedral amorphous carbon (ta-C) films to deduce their defect densities. We find defect densities in the range 3 - 7 × 1017 cm−3 in the undoped ta-C films, and roughly an order of magnitude larger in the nitrogen doped (n-type) films. In some cases fairly uniform defect profiles were obtained covering a thickness of a couple of hundreds angstroems. We also observed a thermal activation process of carriers from defect states at the ta-C/c-Si interface with an activation energy in the range of 0.4eV to 0.5eV.

Secondary electron emission spectroscopy is used to examine the emission characteristics of diamond films as a function of the bulk and surface properties. We find significant variation in the secondary electron yields measured from diamond surfaces even when energy distribution measurements indicate that a low or negative electron affinity is present. In particular, we observe that the material properties, such as bulk and surface uniformity, surface composition, and impurity and defect concentrations, have a strong affect on the secondary electron yield measurements. Furthermore, the energy distribution of the emitted electrons is found to vary with adsorbate species. In certain cases, the energy distribution changes with adsorbate coverage even though the measured electron intensity remains unchanged. From an analysis of the data, we identify bulk and surface properties needed to optimize the emission characteristics.

Field emission from wide bandgap materials was investigated through voltage dependent field emission energy distribution (V-FEED) analysis. As compared to classical I-V characterization, V-FEED analysis can provide additional, detailed information about the origin of and the mechanism responsible for the field emission of electrons. The V-FEED technique consists of measuring the energy distribution of field emitted electrons collected at various extraction voltages. By measuring changes in the energy of the field emission peak at different voltages, data can be extrapolated to flat-band condition to determine the energy of the band from which the electron emission originated. In this study, field emission from cubic boron nitride (c-BN) coated and diamond coated tip-shaped Mo emitters was examined. For the nominally intrinsic wide bandgap coating materials studied, a linear voltage drop across the wide bandgap material, usually on the order of 1% of extraction voltage was observed and explained by field induced band-bending. For the intrinsic c-BN and diamond samples studied, the electron emission originated from the conduction band minimum at the wide bandgap material/vacuum interface.