Lateral Field Emission Diodes Research Articles

The effect of emitter geometry on lateral field emission diodes fabricated by AFM-based electrochemical nanolithography

Lateral field emission diodes were successfully fabricated using atomic force microscopy (AFM)-based electrochemical nanolithography and tetramethyl ammonium hydroxide (TMAH) wet etching method. Field emission (FE) current of the silicon emitter cathode was measured as a function of the applied anode voltage under vacuum environment. For narrowed nanogaps from 55 to 35 nm, the turn-on voltage was decreased from 21 to 16 V. The turn-on voltage of the 35 nm gap was reduced from 16 to 8 V by changing the curvature radius of the cathode tip. The sharper emitter had the lowest turn-on voltage, largest field-enhancement factor, and good stability, which were attributed to the small emitter radius at the cathode tip and very slight changes in the local field factor. These results indicate that the diodes fabricated using this technique had the lowest value of turn-on voltage ever reported for lateral silicon FE devices.

Fabrication and implementation of nanodiamond lateral field emission diode for logic OR function

This article reports successful fabrication and characterization of vacuum microelectronic OR gate logic using nanodiamond lateral diode structures. Two identical sets of four nanodiamond lateral diodes with different numbers of emitters, viz., 125, 325, 2340 and 9360, and with equal anode–cathode spacing of ~3.5-μm were fabricated on silicon-on-insulator (SOI) wafers. First the fabricated lateral emitters were characterized for emission current scaling to examine the scaling effect of different structures with respect to the forward emission current. Then, two identical diodes were connected in a circuit using diode–resister logic to realize the logic OR function with a square wave as an input signal. The current scaling behavior, demonstrating 1μA current at 18, 15, 7 and 2.2V for 125-, 325-, 2340- and 9360-fingered emitter structures respectively, directly affects the logic OR response. These nanodiamond vacuum logic gates are promising for application in harsh environments.

Field emission in lateral silicon diode fabricated by atomic force microscopy lithography

A novel vacuum lateral silicon diode was fabricated using atomic force microscopy (AFM) lithography to characterise field emission. The silicon diode was approximately 100 nm thick, with an exceptionally smooth surface, and included a finger-like emitter with a gap width of 35 nm. From the Fowler-Nordheim, equation, the field enhancement factor (β) and the field emitting area (A) were assessed to ascertain the high emission current and the low turn-on voltage. The very small emitting area was obtained due to the extremely sharp cathode and very small radius of the anode tip curvature. The turn-on voltage of the diode was 8 V, the smallest value ever reported for lateral silicon field emission diodes.

Nanodiamond lateral field emission vacuum logic OR gate

Reported are fabrication and characterisation of a novel vacuum logic OR gate using two identical nanodiamond lateral field emission diodes fabricated on silicon-on-insulator wafers. Each diode consists of 9000 finger-like emitters with 4 µm interelectrode spacing. High and stable emission current with low turn-on field have been observed and verified by a Fowler-Nordheim plot for each structure. Diode-resistor logic is used to realise the logic OR function. This nanodiamond vacuum logic gate is very promising for application in harsh environments.

Half-wave rectification and envelope detection utilising monolithic nanodiamond lateral field emission diode

Successful fabrication and characterisation of a vacuum microelectronic half-wave rectifier and envelope detector using a 2000-fingered nanodiamond lateral field emitter diode with 4 µm inter-electrode spacing is reported. The electrical characterisation demonstrates low turn-on field (∼1.4 V/µm) and high emission current, verified by the Flower-Nordheim plot. The diode is then connected in appropriate circuits to realise half-wave rectification and envelope detection. This approach demonstrates a new way of developing temperature- and radiation-tolerant integrated microelectronics.

A diamond in the making

Vacuum logic OR gates based on nanodiamond emission devices have been demonstrated by researchers at Vanderbilt University in the US. By fabricating two identical nanodiamond lateral field emission diodes on a silicon-on-insulator wafer, and using diode-resistor logic, they have been able to realise logic devices that have the potential to be used in extreme environment applications.

Nanodiamod lateral device field emission diode fabricated by electron beam lithography

Nitrogen incorporated nanodiamond film is known to aid in promoting enhanced electron emission via the induced graphitic behavior both in the bulk material and also the surface of the film. Since electron emission current is inversely proportional to the cathode to anode inter-electrode distance; it is necessary to implement electron beam lithography (EBL) to obtain a small emission gap. To achieve high resolution from EBL, a thinner nanodiamond film is required. In this work, we fabricated lateral field emitters on a 0.65 µm nanodiamond film. The nanodiamond film was deposited onto a silicon-on-insulator (SOI) substrate in CH 4/H 2/N 2 plasma ambient by microwave chemical vapor deposition. The SOI was prepared for diamond nucleation using mechanical abrasion and ultrasonication in nanodiamond powder. Electron beam lithography (EBL) was used to delineate a 10 emitter tipped diode with a 2 µm anode-to- anode emission gap.

Surface potential of functionalised nanodiamond layers

AbstractCarbon nanomaterials especially ultrananocrystalline diamond and nanocrystalline diamond films have attracted more and more interest due to their unique electrical, optical and mechanical properties, which make them widely used for different applications (e.g. MEMS devices, lateral field emission diodes, biosensors and thermoelectrics). Nanocrystalline diamond can also offer novel advantages for drug delivery development. Recent studies have begun to use nanocrystalline diamond for in-vivo molecular imaging and bio-labeling. To enable grafting of complex bio-molecules (e.g. DNA) the surface of ND requires specific fictionalization (e.g. H, OH, COOH & NH2). Due to the surface dipoles of functionalised nanodiamond band bending at the surface can be easily induced and from the measured band bending we can deduce the type of the fictionalization on the surface. The surface potential of H-terminated and OH terminated nanodiamond layers was investigated by Kelvin probe microscope. From the change of the surface potential value (as the departure of the material surface from the state of electrical neutrality is reflected in the energy band bending) the work function of the H-terminated nanodiamond layer was established to be lower than OH-terminated nanodiamond layer. The surface potential difference can be explained by the surface dipole induced by the electro-negativity difference between the termination atoms.

Forms and behaviour of vacuum emission electronic devices comprising diamond or other carbon cold cathode emitters

Nanocarbon-derived electron emission devices, specifically nanodiamond lateral field emission (FE) diodes and gated carbon nanotube (CNT) triodes, are new configurations for robust nanoelectronic devices. These novel micro/nanostructures provide an alternative and efficient means of accomplishing electronics that are impervious to temperature and radiation. For example, nitrogen-incorporated nanocrystalline diamond has been lithographically micropatterned to use the material as an electron field emitter. Arrays of laterally arranged 'finger-like' nanodiamond emitters constitute the cathode in a versatile diode configuration with a small interelectrode separation. A low diode turn-on voltage of 7V and a high emission current of 90 microA at an anode voltage of 70V (electric field of approx. 7V microm(-1)) are reported for the nanodiamond lateral device. Also, a FE triode amplifier based on aligned CNTs with a low turn-on voltage and a small gate leakage current has been developed.

Field emission devices for advanced electronics comprised of lateral nanodiamond or carbon nanotube emitters

Nanocarbon-derived electron emission devices, specifically, nanodiamond lateral field emission diodes and gated carbon nanotube triodes are new configurations for robust nanoelectronic devices. These novel micro/nanostructures provide an alternative and efficient means of accomplishing electronics that are impervious to temperature and radiation. Nitrogen-incorporated nanocrystalline diamond has been lithographically micropatterned to utilize the material as an electron field emitter. Arrays of laterally arranged “finger-like” nanodiamond emitters constitute the cathode in a versatile diode configuration with small interelectrode separation. Nanodiamond lateral tip conditioning techniques are employed to improve emission and the subsequent device performance discussed. A low diode turn-on voltage of 7 V and a high emission current of 90 μA at an anode voltage of 70 V (electric field of ∼ 7 V/μm) is reported for the nanodiamond lateral device. Also, the development of a field emission triode amplifier based on aligned carbon nanotubes (CNTs) with low turn-on voltage and small gate leakage current, utilizing a dual-mask microfabrication process is reported. The2 × 20 μm CNT triode array displays a gate turn-on voltage of ∼ 44 V, and low gate currents less than 3% of the anode currents. The low gate leakage currents observed confirmed the effectiveness of the convex-shaped gated CNT emitter in alleviating the cathode-gate leakage problem that compromises the operation of a field emission triode.

Nanocrystalline diamond lateral field emission diode fabrication by dual micropatterning technique

A dual-mask micropatterning process has been developed to fabricate nanocrystalline diamond lateral field emission diode with reduced reversed leakage current. In contrast to the all-diamond lateral device reported previously, this vacuum microelectronic device integrates a 6-finger lateral nanodiamond emitter cathode with a nickel metal anode on a SiO2 underlying substrate serving as the spacer material. In this configuration, the nitrogen-incorporated nanodiamond cathode has higher field enhancement factor, geometrically as well as materially, resulting in high rectification and excellent diode behavior. This lateral device processing further illustrates the viability of nanocrystalline diamond for device integration.

Nanodiamond lateral comb array field emission diode for high current applications

Nanodiamond comb-shaped lateral field emitter arrays in diode configuration were fabricated and characterized for high current field emission. Nitrogen-incorporated nanocrystalline diamond with grain size of 5–10 nm was micropatterned using RIE to realize interconnected arrays of comb structures equipped with uniformly spaced high aspect ratio lateral emitter fingers. A 9000-fingered nanodiamond lateral comb array diode with an inter-electrode spacing of 8 μm demonstrated a high emission current of ∼ 25 mA at an anode voltage of 260 V (electric field ∼ 32 V/μm) in 10 − 7 Torr vacuum. The lateral emitter configuration shows potential for higher power with no emission current saturation observed. These vacuum micro/nanoelectronic devices comprised of nanodiamond lateral field emission diodes are attractive for low-voltage operating high current electron sources, high-power and high-speed switches, and other extreme demand/extreme environment electronics.

Nanocarbon field emission devices

AbstractWe are fabricating and examining nanocarbon derived electron emission devices, specifically, nanodiamond lateral field emission diodes and gated carbon nanotube triodes. These novel microstructures provide interesting means of accomplishing electronics that are unaffected by temperature and radiation. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Single-mask multiple lateral nanodiamond field emission devices fabrication technique

We report an efficient microfabrication process technique developed to realize multiple lateral diamond field emitter structures on the same wafer using a single mask. Nanodiamond films with grain size of 5–10nm deposited by CH4∕H2∕N2 microwave plasma enhanced chemical vapor deposition were selectively micropatterned using reactive ion etching at an etch rate of 0.5μm∕min. Several nanodiamond lateral field emission diodes and triodes of different emitter geometries and electrode configurations have been batch fabricated on a silicon-on-insulator wafer. Interelectrode spacing down to 2μm was achieved in arrays of devices on a SiO2 dielectric layer. This fabrication process technique, with its single-mask utility, high manufacturability, combined with its reproducibility, is an efficient and cost-effective approach to realize various configurations of field emission structures in wafer process technology. These nanodiamond vacuum nanoelectronic lateral devices hold high-speed and high-frequency operation potential.

Nanodiamond planar lateral field emission diode

We report the fabrication and field emission characteristics of the nanodiamond planar lateral field emission diode. Nanodiamond films with grain size as small as 5–10 nm have been realized through the process of CH 4/H 2/N 2 microwave plasma enhanced chemical vapor deposition (MPECVD) by employing an effective growth rate reduction technique. Well-controlled processes have been developed; including reactive ion etch (RIE) to pattern the nanodiamond films to fabricate lateral field emission devices with planar lateral fingers. An anode–cathode spacing of 2 μm between the nanodiamond anode and cathode has been achieved. A nanodiamond lateral diode equipped with 6 fingers and an inter-electrode separation of 3 μm exhibits a turn-on voltage of 5.9 V (threshold electric field of 1.9 V/μm), one of the lowest reported for lateral field emission devices, and a high emission current of 1.1 mA (∼ 183 μA current per finger) at an anode voltage of 100 V (∼ 30 V/μm). The emission current is found to be stable with ∼ 4% fluctuation at 1 mA over 10 h. The nanodiamond lateral device is very promising for applications in vacuum nanoelectronics, sensors, and nanoelectromechanical systems.

Diamond vacuum field emission devices

This article reports the development of (a) vertical and (b) lateral diamond vacuum field emission devices with excellent field emission characteristics. These diamond field emission devices, diode and triode, were fabricated using a self-aligning gate formation technique from silicon-on-insulator wafers using conventional silicon micropatterning and etching techniques. High emission current >0.1 A was achieved from the vertical diamond field emission diode with an indented anode design. The gated diamond triode in vertical configuration displayed excellent transistor characteristics with high DC gain of ∼800 and large AC output voltage of ∼100 V p–p. Lateral diamond field emission diodes with cathode–anode spacing less than 2 μm were fabricated. The lateral diamond emitter exhibited a low turn-on voltage of ∼5 V and a high emission current of 6 μA. The low turn-on voltage (field ∼3 V/μm) and high emission characteristics are the best of reported lateral field emitter structures.

Deep reactive ion etching for lateral field emission devices

The authors describe the design, fabrication and testing of lateral field emission diodes utilizing the deep reactive ion etch (DRIE). Devices were fabricated on silicon-on-insulator (SOI) wafers of varied thickness, by etching the device silicon in the STS DRIE system in a single mask process. After subsequent oxidation sharpening and oxide removal, diodes were tested on a probing station under vacuum. A typical diode exhibited very high currents on the order of /spl sim/100 /spl mu/A at 60 V, and turn-on voltage between 35 V and 40 V. The high electron current is emitted in such a diode by multiple sharp tips vertically spaced by 450 nm along the etched sidewall due to the pulsed nature of the DRIE process.

Lateral field emission diode with wedge-type tip and nanogap on separation by implantation of oxygen silicon

A field emission diode array with a novel nanometer scale silicon gap in a separation by implantation oxygen structure was fabricated using the thin film stress that had been generated during high-temperature annealing and cooling. In this work, an interelectrode gap ranging from 20 to 100 nm was obtained depending on the width of the pattern when the patterned wafer was cooled after annealing at 1050 °C for 1 h in N2 ambient. The parameters for determining the gap size were identified, and the crystal orientation dependency in forming the gaps was clarified. The proposed nanogap formation technique is very simple and applicable to a field emission (FEA) with a short interelectrode distance. The fabricated FEA exhibited a turn on voltage of 25 V and an emission current of 6 μA per tip at 35 V.

Lateral field emission diodes using SIMOX wafer

Lateral field emission diodes were fabricated by using separation by implantation of oxygen (SIMOX) wafer and their current-voltage characteristics (I-V) were analyzed. Applying conventional photolithography and local oxidation of silicon (LOGOS) process, we fabricated single-crystalline lateral silicon field emitters with very sharp cathode and anode tips and very short cathode to anode spacing ranging from 0.3 to 0.8 /spl mu/m as well. Two different types of tips, tapered and wedge-shaped emitters, were typically formed according to oxidation time. The turn-on voltages for both types of diodes were as low as 22/spl sim/25 V and the emission currents were as high as 6 /spl mu/A/tip at voltages of 35/spl sim/38 V. From the Fowler-Nordheim (FN) equation, field emitting area (A) and field enhancement factor (/spl beta/) for both types of diodes were estimated to explain the low turn-on voltages and the high emission currents.