Stephen A. Guerrera

Uniform High-Current Cathodes Using Massive Arrays of Si Field Emitters Individually Controlled by Vertical Si Ungated FETs—Part 2: Device Fabrication and Characterization

We report the demonstration of electron sources that achieve high-current and uniform emission using dense arrays of Si field emitters (FEs) that are individually ballasted by a current source. Each FE is fabricated on top of a vertical ungated field-effect transistor (FET), a two-terminal device based on a very-high-aspect-ratio Si column. The ungated FET takes advantage of the velocity saturation of electrons in silicon, the high aspect ratio of the ungated FET, and the doping concentration to achieve current-source-like behavior to obtain reliable uniform and high-current electron emission. Emitted currents in excess of 0.48 A were demonstrated.

Uniform High-Current Cathodes Using Massive Arrays of Si Field Emitters Individually Controlled by Vertical Si Ungated FETs—Part 1: Device Design and Simulation

In this paper, we report the design and simulation of electron sources composed of arrays of Si field emitters (FEs) that are individually ballasted by a current source. Each FE is fabricated on top of a vertical ungated field-effect transistor (FET), a two-terminal device based on a very-high-aspect-ratio Si column. The ungated FET takes advantage of the velocity saturation of electrons in silicon, the high aspect ratio of the ungated FET, and the doping concentration of the semiconductor to achieve current-source-like behavior. The proposed technology can be used to implement cathodes capable of reliable uniform and high current emission.

Toward Amp-Level Field Emission With Large-Area Arrays of Pt-Coated Self-Aligned Gated Nanoscale Tips

Design, fabrication, and characterization of Pt-coated, self-aligned, and gated Si field emission arrays are reported. Arrays of 320000 tips with 10 μm pitch are employed to emit currents as high as 0.35 A (current density of 1.1 A/cm2) at gate-emitter biases of 300 V. For reliability, the devices have a gate dielectric thicker than 2.5 μm maintaining the field inside gate insulator below 150 V/μm and a 5-nm-thick Pt-coating protecting the tips against sputtering by back-streaming ions. The Pt-coating also increases the capture cross section of electrons from the emitter cone, resulting in higher emission currents compared with uncoated Si tips when the supply of electrons is limited to the surface. The device failure at high currents is associated with plasma ignition due to local pressure rise caused by outgassing of the anode. At lower emission currents, the devices are capable of long-term emission (>3 h) at pressures as high as 10-5 Torr. Furthermore, a high-yield fabrication process is presented for large-area fabrication of highly-uniform gated tip arrays that could be expanded to active areas larger than 10 cm2 to increase the emission current.

Silicon Field Emitter Arrays With Current Densities Exceeding 100 A/cm 2 at Gate Voltages Below 75 V

We report silicon field emitter arrays (FEAs) that demonstrate current densities 100 A/cm2 at gate-emitter voltages <;75 V. These are the highest current densities reported for a semiconductor FEA, and approach the current densities of Spindt-type metal cathodes. We achieved these results using a new device structure that employs high-aspect-ratio silicon nanowire current limiters in series with each emitter tip to address the major failure mechanisms in FEAs. These current limiters mitigate emitter tip failure due to joule heating thus allowing for higher reliability. We employed a novel fabrication process to produce small gate apertures (≈350 nm) that are self-aligned to the field emitter tip enabling device operation at >100 A/cm2 with gate-to-emitter voltages that are less than 75 V. These FEAs demonstrate performance that has the potential to enable smaller, more efficient, and high-power vacuum electronics.

Self-aligned, gated field emitter arrays with integrated high-aspect-ratio current limiters

We report the fabrication of arrays of silicon field emitters with 1-micron pitch with integrated, self-aligned extractor gates and 10-micron tall high-aspect-ratio silicon vertical current limiters.

He channel NanoTransistors — Towards “vacuum-less” empty state electronics

We report the operation of a silicon field emitter array (FEA) in a helium ambient at pressures approaching 1 atmosphere (500 Torr). These devices demonstrate a new architecture with potential for high power amplification at high frequencies with small size, weight, and power.

High performance and reliable silicon field emission arrays enabled by silicon nanowire current limiters

We report a high current density (J > 100 A/cm2) cold cathode based on silicon field emitter arrays (FEAs) that operates at low voltage (VGE <; 60 V), and has long lifetime (T > 100 hours @ 100 A/cm2, > 300 hours @ 100 mA/cm2). The demonstrated current density is an increase of > 10x over state-of-the art (~10 A/cm2) for field emission cathodes operated in continuous wave (CW) mode. To achieve the record performance, we developed a unique device architecture that uses a high-aspect-ratio (~50:1) silicon nanowire current limiter to regulate electron flow to each field emitter tip in the array. High current, high current density, long lifetime cold cathodes that can be integrated with silicon ICs will enable new systems architectures for RF amplifiers, terahertz, IR, and x-ray sources.

Laser induced annealing dynamics of photo-electron spectra from silicon field emitter arrays

A marked increase in electron yield, an overall spectral red shift, and the formation of a higher energy peak from Si field emitter arrays (FEAs) are observed in photo-electron spectra throughout a laser annealing process.

Field emission from silicon tips embedded in a dielectric matrix

In this work, we present FEAs based on silicon field emitter tips on top of silicon nanowires with four different device structures: (a) buried tips, (b) buried tips with graphene, (c) released tips, and (d) released tips with graphene. Measured device parameters are used to characterize the performance of the devices. In general, we obtain low turn-on voltages when bFN is low. Additional studies of current variations are required.

High current density MEMS deuterium ionizers

In this work, we report a high current density MEMS ionizer for deuterium that is based on an array of high aspect ratio field emitter microstructures. The Si field emitter structure has a unique device architecture that uses a high-aspect-ratio (~50:1) silicon nanowire current limiter to regulate electron flow to each field emitter tip in the array. The nanowire diameter is 100-200 nm while the height is 10 μm. The gate electrode of the field emitter is supported by a 10 μm tall dielectric matrix while a 3-4 μm thick dielectric is under the contact pad and together they enable a bias of >300 V between the ionization tip and the gate without breakdown. Field emission characterization of field emitter arrays similar to this device show that the field factor, β, is > 1.2×106 cm-1, which is consistent with electrostatic simulations using COMSOL. Analytical and numerical modeling of the structure based on the measured tip radius statistics, suggest that it is possible demonstrate a D+ ion source with high current (500 μA) at high current density of 12 mA/cm2 in a compact volume while consuming less than 1 W.