M. Hajra

Effect of gases on the field emission properties of ultrananocrystalline diamond-coated silicon field emitter arrays

We performed studies of electron emission from ultrananocrystalline diamond (UNCD)-coated, ungated silicon field emitters as a function of in situ exposure to various gases during current versus voltage and current versus time measurements. The emitter arrays were fabricated by a subtractive tip fabrication process and coated with UNCD films using microwave plasma chemical vapor deposition with a CH4/Ar plasma chemistry. The emission characteristics of the coated tip arrays were studied in the diode configuration; using a 2 mm diameter anode with rounded edges to suppress arcing. Significant enhancement of the electron emission was observed, increasing from 35% to 100%, after the emitting surface was exposed to H2 at pressures in the 10−5 and 10−4 Torr range. Upon termination of the H2 exposure, the current decreased to the initial value of 2 μA. The emission current subsequently remained stable at 2 μA upon continued evacuation down to the base pressure below 10−9 Torr. The emission current variation is ...

Field emission characterization of silicon tip arrays coated with GaN and diamond nanoparticle clusters

Wide band-gap materials show promise for applications in coating of field emission tips. Recently nanocrystalline hexagonal GaN crystallites as small as 12 nm average diameter have been formed using reactive laser ablation of gallium metal in nitrogenating ambient [T. J. Goodwin et al., Appl. Phys. Lett. 70, 3122 (1997)]. In this article we investigated the performance of ungated emitters with and without surface coating. Silicon tip arrays are coated by dielectrophoresis of gallium nitride nanoparticles or nanocrystalline diamond clusters from an ethanol suspension. The emitters were evaluated and compared before and after the surface treatment using SEM image and I–V measurements in the diode configuration. The results suggest that the emitters benefit from coating the surface with nanocrystalline diamond clusters in terms of reduction in the turn on voltage by 100 V and increase uniformity in emission during low voltage operation. The long-term emission stability for both types of the coated cathodes w...

Fabrication and characterization of singly addressable arrays of polysilicon field-emission cathodes

Abstract Polysilicon is a viable candidate material for field-emission microelectronics devices. It can be competitive for large size, cost-sensitive applications such as flat-panel displays and micro electro-mechanical systems. Singly addressable arrays of field-emission cells were fabricated in a matrix configuration using a subtractive process on polysilicon-on-insulator substrates. Matrix rows were fabricated as insulated polycrystalline silicon stripes with sharp emission tips; and matrix columns were deposited as gold thin film electrodes with round gate openings. Ion implantation has been used to provide the required conductivity of the polysilicon layer. To reduce radius of curvature of the polysilicon tips, an oxidation sharpening process was used. The final device had polysilicon emission tips with end radii smaller than 15 nm, surrounded by gate apertures of 0.4 μm in diameter. Field emission properties of the cathodes were measured at a pressure of about 10−8 Torr, to emulate vacuum conditions available in sealed vacuum microelectronics devices. It was found that an emission current of 1 nA appears at a gate voltage of 25 V and can be increased up to 1 μA at 70 V. Over this range of current, no “semiconductor” deviation from the Fowler–Nordheim equation was observed. I–V characteristics measured in cells of a 10×10 matrix, with a cell spacing of 50 μm demonstrated reasonable uniformity and reproducibility.

Field-emission characterization of the 10×10 singly addressable double-gated polysilicon tip array

Polysilicon-on-insulator singly addressable arrays, consisting of double-gated field-emission cells, were fabricated and tested. The field-emission tips were formed by a subtractive technique, using an array of ten polysilicon stripes on the insulating substrate. The stripe structure was oxidized for dielectric isolation and coated with a second polysilicon layer as an extracting gate electrode. The polysilicon layer was then oxidized to provide a second isolation layer for separation from a top gold film, deposited as a focusing electrode. Finally, an 1.7 μm aperture was opened, using wet buffered etching of the silicon dioxide. The structure allows us to address electrically a single tip at the intersection of any cathode row and extracting gate column. A focusing voltage could be applied independently to the second gate of any tip during operation to focus the electron flux of an operating tip. The focused array may be suitable for multi-beam electron lithography application and new generation of data ...

Field emission characterization of the 10/spl times/10 singly-addressable double-gated polysilicon tip array

A conventional field-emission cell, which usually consists of an emission tip surrounded by a small aperture in an extracting electrode (grid), has very complicated electron-optical characteristics. Electron beam trajectories are influenced not only by the electric field formed between the emission tip and the gate, but also by the field in the proximity of the emission site. This problem can be effectively resolved by controlling the shape of the individual electron beams.

Field emission characterisation of silicon tip arrays coated with GaN and diamond nanoparticle cluster

Wide band gap materials show promise for applications in coating of field emission tips. Recently nanocrystalline hexagonal GaN crystallites as small as 5 nm average diameter have been formed using reactive laser ablation of gallium metal in a nitrogenating ambient. In this paper we have investigated the performance of ungated emitter. Silicon tip arrays coated by dielectrophoresis of gallium nitride nanoparticles or nanocrystalline diamond clusters from an ethanol suspension. The emitters were evaluated and compared before and after the surface treatment using SEM images and I-V measurements in the diode configuration. The phosphor screen, used as the anode was spaced nominally 70 /spl mu/m from the cathode. A field emission characteristics were measured in a high-vacuum chamber at a pressure range between 10/sup -5/ and 10/sup -8/ Torr. The results suggest that the emitters benefit from coating the surface with nanocrystalline diamond clusters in terms of reduction in the turn on voltage and increase in the uniformity of emission in low voltage operation. The long-term emission stability was studied over a period of 90 hrs.

Double-Gated Singly-Addressable Polysilicon Tip Array Fabrication and Characterization

Polysilicon-on-insulator singly-addressable arrays, consisting of double-gated field emission cells, were fabricated and tested. The field-emission tips were formed by a subtractive technique, using 2.5 µm thick polysilicon stripes on an insulating substrate. The tip structure was oxidized for dielectric isolation and coated with a 0.4 µm polysilicon layer as a first gate electrode. The polysilicon layer was then subsequently oxidized to provide a second isolation layer for separation from a 0.1 µm gold film, deposited as a second gate electrode. Finally, the 1.5 µm aperture was formed, combining wet etching of the silicon dioxide and dry etching of the polysilicon layers. The matrix allows addressing electrically any emission cell at the intersection of a cathode column and an extracting gate line. An independent voltage can be applied to the second gate during operation to focus the electron beam of an operating tip.

Field Emission Characteristic of Silicon Cathodes Coated with GaN Nanoparticles

Arrays of p-type silicon micro-emitters have been formed using a subtractive tip fabrication technique. Following fabrication, the emitter surface was coated with GaN nanoparticles and nanocrystalline diamond by a dielectrophoresis deposition technique. The emitters were evaluated and compared before and after the surface treatment using I-V measurements in the diode configuration. The phosphor screen, used as the anode, was spaced nominally about 70 µm from the cathode. The field emission characteristics were measured in a high vacuum chamber at a pressure range between 10 −5 and 10 −8 Torr. The results suggest that the emitters benefit from coating the surface with nanocrystalline diamond in terms of reduction in the turn on voltage, GaN coating increase the turn on voltage. Both diamond and GaN improved the emission uniformity in the region of the low voltage operation.

Surface Treatment on Silicon Field-Emission Cathodes

Arrays and single-tip p-type silicon micro-emitters have been formed using a subtractive tip fabrication technique. Following fabrication, several different surface treatments have been attempted for comparison. We utilized ion and electron bombardment at elevated pressures (with interrupted pumping), and also hydrogen seasoning during field emission operation. The objectives of these treatments include stabilization of the emission, lowering the effective workfunction, and reducing low-frequency noise. The tips were evaluated using I-V measurements in the diode configuration. A flat Si anode, spaced nominally 6 μm and 150 μm from the cathode, was used. For the purpose of treatment, the field emission characteristics are measured in a high vacuum chamber at a pressure range between 10 −5 and 10 −8 Torr. The results suggest that the emitters benefit from seasoning or conditioning, for optimal performance, low noise, minimum work function and maximum reproducibility and reliability over the lifetime of the cathode.