Ultralow-voltage boron-doped diamond field emitter vacuum diode

A boron-doped diamond field emitter diode with ultralow turn-on voltage and high emission current is reported. The diamond field emitter diode structure with a built-in cap was fabricated using molds and electrostatic bonding techniques. The emission current versus anode voltage of the capped diamond emitter diode with boron doping, sp² content, and vacuum thermal electric (VTE) treatment shows a very low turn-on voltage of 2 V. A high emission current of 1 μA at an anode voltage of less than 10 V can be obtained from a single diamond tip. The turn-on voltage is significantly lower than comparable silicon field emitters     

Emission characteristics of silicon vacuum triodes with fourdifferent gate geometries

Arrays of 10×10, 30×30, and 50×50 phosphorus-doped 0.005-0.025 Ω-cm, monocrystalline silicon field emitters have been fabricated with an emitter height of approximately 4.5 μm, a cone angle of 110°, and four gate openings ranging from 1.8 to 5.3 μm. The placement of the rims of the gates range from coplanar with the apexes of the emitters for the 1.8-μm devices to fully recessed for the 5.3-μm devices. The devices have been characterized in terms of geometry-dependent β factors, scaling of emission currents with array size, temperature dependency from room temperature to 48 K, pressure dependency from 2.5×10^-9 to 0.8×10^-5 torr, current fluctuations at room temperature and at 48 K, and image formation. All of the measurements have been performed by operating the devices in the gate-induced field emission mode     

Diamond grit-based field emission cathodes

This letter describes the fabrication and operation of diamond grit gated cathodes. The structure is similar to Spindt-type cathode, but the field emission cone is replaced with a more planar diamond grit layer 50 to 200 nm thick. Although the minimum lithographic dimension of these cathodes is from 1 to 5 μm, these devices have exceptionally low turn-on voltages, 5 to 7 V. Cathode current noise is less than 2.5% rms with a maximum absolute current variation of 6.7% over a 6 h period. These devices can operate in pressures of nitrogen above 133 Pa (1 Torr). Although operation in 6.6×10^-2 Pa (5×10 ^-4 Torr) with more reactive gasses, O₂ or H₂ S, degrades performance, the cathodes recover when the pressure is reduced to ⩽1.3×10^-4 Pa (1×10^-6 Torr). Gate current varies from 0.2 to 100 times the emitted current and depends on the technique used to deposit the diamond grit. High current densities (>10 A cm^-2), low gate voltages (<50 V), low emission noise, excellent longevity, temporal uniformity, and ease of fabrication make these devices potential cathodes for flat panel displays. However, excessive gate current and unsatisfactory processing reproducibility at present limit their general application     

High performance poly-Si TFTs fabricated using pulsed laserannealing and remote plasma CVD with low temperature processing

Key technologies for fabricating polycrystalline silicon thin film transistors (poly-Si TFTs) at a low temperature are discussed. Hydrogenated amorphous silicon films were crystallized by irradiation of a 30 ns-pulsed XeCl excimer laser. Crystalline grains were smaller than 100 nm. The density of localized trap states in poly-Si films was reduced to 4×10¹⁶ cm^-3 by plasma hydrogenation only for 30 seconds. Remote plasma chemical vapor deposition (CVD) using mesh electrodes realized a good interface of SiO ₂/Si with the interface trap density of 2.0×10¹⁰ cm^-2 eV^-1 at 270°C. Poly-Si TFTs were fabricated at 270°C using laser crystallization, plasma hydrogenation and remote plasma CVD. The carrier mobility was 640 cm²/Vs for n-channel TFTs and 400 cm²/Vs for p-channel TFTs. The threshold voltage was 0.8 V for n-channel TFTs and -1.5 V for p-channel TFTs. The leakage current of n-channel poly-Si TFTs was reduced from 2×10^-10 A/μm to 3×10^-13 A/μm at the gate voltage of -5 V using an offset gate electrode with an offset length of 1 μm     

Poly-diamond gated field-emitter display cells

A microchip containing gated field-emitter display (FED) cells is designed and fabricated using vapor-deposited p-type polycrystalline diamond films and employing an integrated circuit (IC)-compatible diamond film technology on oxidized 4-in Si wafers. Current-voltage (I-V) data, measured in a diode configuration at 10^-6 torr, show Fowler-Nordheim (F-N) field emission behavior. A 1×4 pixel diamond gated display cell is demonstrated for the first time using phosphor-coated glass as an anode     

Arrayed silicon avalanche cathodes

Silicon avalanche cathodes (SACs) consisting of a heavily doped shallow (less than 300 A) p-n junctions were fabricated, characterized, and used as electron sources in Si-based microvacuum diodes. The emission current was investigated as a function of diode reverse-biased voltage and external field. The field was provided by an anode placed approximately 1 mm above the cathode to simulate the field which would be obtained with a built-on-chip anode. Eighteen different shapes and sizes of SACs were tested. An emission current of 0.24 μA and an emission efficiency (emission current/total diode current) of 2.1×10^-5 were observed from the single bare Si p-n junction cold cathode     

Low frequency noise in 6H-SiC MOSFET's

The noise spectra for n-channel, depletion-mode MOSFETs fabricated in 6H-SiC material were measured from 1-10⁵ Hz at room temperature. Devices were biased in the linear regime, where the noise spectra was found to be dependent upon the drain-to-source bias current density. At a drain-to-source current of 50 μA for MOSFETs with a W/L of 400 μm/4 μm, the measured drain-to-source noise power spectral density was found to be A/(f^λ), with A being 2.6×10^-12 V², and λ being between 0.73 and 0.85, indicating a nonuniform spatial trap density skewed towards the oxide-semiconductor interface. The measured Hooge parameter (α_H) was 2×10^-5. This letter represents the first reported noise characterization of 6H-SiC MOSFET's     

Electroptic diffraction modulation in ZnO film on sapphire

An electrooptic Bragg diffraction modulator with high diffraction efficiency which utilizes a low-loss epitaxial ZnO optical waveguide on a sapphire substrate is discussed. An interdigital electrode with a spatial period of 20 μm and an aperture of 3 mm was fabricated directly on the film surface using a photolithographic technique. For the TE₀ mode at 6328 Å, a maximum diffraction efficiency of 98% has been obtained from DC to 100 kHz with an applied voltage of about 31 V. The unclamped electrooptic coefficient r ₃₃ is estimated to be 5.8×10^-12 m/V which is much larger than the clamped value of 2.6×10^-12 m/V in the literature     

A novel fabrication process of a silicon field emitter array withthermal oxide as a gate insulator

We have successfully developed a fabrication process of a silicon field emitter array with a gate insulator formed by Si₃N₄ sidewall formation and subsequent thermal oxidation. This process overcomes some problems in the conventional fabrication, such as high etch rate, low breakdown field, and gate hole expansion arising from evaporation of gate oxide. Therefore, we could improve process stability and emission performance, and also reduce gate leakage current. The optimum process conditions were determined by process simulations using SUPREM-4. The turn-on voltage of the fabricated field emitters was approximately 38 V. An anode current of 0.1 μA (1 μA) per tip was measured for a 625-tip array at the gate bias of 80 V (100 V), and the gate current was less than 0.3% of the anode current at those emission levels     

GaAs planar-doped barrier vacuum microelectronic electron emitters

A novel vacuum microelectronic electron emitter has been demonstrated in GaAs by using a planar-doped-barrier (PDB) structure. Emitted electrons are collected in high vacuum by a tantalum anode placed ~1 mm away from the emitter surface. Surface passivation with (NH ₄)₂S_x followed by in situ heating in vacuum has been used to obtain an atomically clean surface. An emission current density of 0.42 A-cm^-2 and an efficiency of 0.3% have been obtained from a 60 μm×60 μm emission region with an anode bias of 100 V     

Arrays of microdischarge devices having 50-100 μm squarepyramidal Si anodes and screen cathodes

Microdischarge devices having (50-100 μm)² pyramidal Si anodes and metal screen cathodes have been operated continuously at Ne gas pressures up to 1350 Torr and voltages below 95 V. More than 34 μW of output power is produced by a single device in a solid angle of ~5×10^-2 sr for a Ne pressure of 500 Torr. 3×3 arrays of these devices have been fabricated     

Nitrogen-implanted SiC diodes using high-temperature implantation

6H-SiC diodes fabricated using high-temperature nitrogen implantation up to 1000°C are reported. Diodes were formed by RIE etching a 0.8-μm-deep mesa across the N⁺/P junction using NF₃/O₂ with an aluminum transfer mask. The junction was passivated with a deposited SiO₂ layer 0.6 μm thick. Contacts were made to N⁺ and P regions with thin nickel and aluminum layers, respectively, followed by a short anneal between 900 and 1000°C. These diodes have reverse-bias leakage at 25°C as low as 5×10^-11 A/cm² at 10 V     

Low temperature polycrystalline silicon thin film transistor withsilicon nitride ion stopper

The authors have fabricated a new low temperature polycrystalline silicon (poly-Si) thin film transistor (TFT) with silicon nitride (SiN _x) ion-stopper and laser annealed poly-Si. The fabricated poly-Si TFT using SiN_x as the ion-stopper as well as the gate insulator exhibited a field effect mobility of 110 cm²/Vs, subthreshold voltage of 5.5 V, subthreshold slope of 0.48 V/dec., and on/off current ratio of ~10⁶. Low off-state leakage current of 2.4×10^-2 A/μm at the drain voltage of 5 V and the gate voltage of -5 V was achieved     

Ohmic contacts on diamond by B ion implantation and Ti-Aumetallization

Low-resistance ohmic contacts have been fabricated on a natural IIb semiconducting diamond crystal and on undoped polycrystalline diamond films by B ion implantation and subsequent metallization with a Ti-Au bilayer metallization. A high B concentration of ~7×10²⁰ cm^-3 at the surface was obtained by ion implantation, a post-implant anneal, and a subsequent chemical removal of the graphite layer that resulted from the radiation damage. A bilayer metallization of Ti followed by Au annealed at 850°C yielded a specific contact resistance value on the order of 10^-6 Ω-cm² for chemical-vapor-deposition-grown polycrystalline films and on the order of 10^-5 Ω-cm² for the semiconducting natural crystal     

A novel self-aligned polycrystalline silicon thin-film transistorusing silicide layers

A novel self-aligned polycrystalline silicon (poly-Si) thin-film transistor (TFT) was fabricated using the three layers of poly-Si, silicon-nitride, and thin amorphous silicon. Gate and source/drain silicide formation was carried out simultaneously following silicon nitride and amorphous silicon patterning, enabling the use of only two mask steps for the TFT. The fabricated poly-Si TFT using laser annealed poly-Si exhibited a field-effect mobility of 30.6 cm²/Vs, threshold voltage of 0.5 V, subthreshold slope of 1.9 V/dec., on/off current ratio of ~10⁶, and off-state leakage current of 7.88×10^-12 A/μm at the drain voltage of 5 V and gate voltage of -10 V     

Ultra-sensitive autocorrelation of 1.5 μm light with singlephoton counting silicon avalanche photodiode

1.5 μm two-photon absorption in a single photon counting silicon avalanche photodiode at record continuous-wave levels below 100 μW is reported. Autocorrelation of a 10 GHz, 1.67 picosecond pulse-train using this device demonstrates 1.5 × 10^-3 (mW)² peak-power times average-power sensitivity without the use of lock-in detection     

Submicrometer poly-Si CMOS fabrication with low-temperature laserdoping

The laser doping process for submicrometer CMOS devices with leakage currents as low as 10^-12 A/μm for both n-channel and p-channel devices is discussed. The I-V characteristics are comparable to those of poly-Si devices fabricated using ion implantation and high-temperature annealing processes. The laser-induced melting of predeposited impurity doping (LIMPID) process was used to fabricate submicrometer polycrystalline-Si CMOS devices. This process uses a very low temperature, so no dopant atom can diffuse along the grain boundaries in the solid region. The use of stacked Al/SiO₂ films as a protection layer made it possible to reduce the leakage current from several tens of picoamperes per micrometer to 1 pA/μm     

Tensile-strained GaAsP-AlGaAs laser diodes for reliable 1.2-Wcontinuous-wave operation at 735 nm

Tensile-strained GaAsP quantum wells embedded in AlGaAs large optical cavity structure were investigated at an emission wavelength of 735 nm. 1.2-W continuous-wave operation for 100-μm stripe width diode lasers over 1000 h is reported. Experiments with different stripe widths showed a high stability at an output power of 12-mW/μm stripe widths with degradation rates below 5·10^-5 h^-1, i.e., lifetimes larger than 5000 h could be expected     

Emission cross sections and spectroscopy of Ho3+ laserchannels in KGd(WO4)2 single crystal

The spectroscopic properties of Ho³⁺ laser channels in KGd(WO₄)₂ crystals have been investigated using optical absorption, photoluminescence, and lifetime measurements. The radiative lifetimes of Ho³⁺ have been calculated through a Judd-Ofelt (JO) formalism using 300-K optical absorption results. The JO parameters obtained were Ω₂=15.35×10^-20 cm², Ω ₄=3.79×10^-20 cm², Ω₆ =1.69×10^-20 cm². The 7-300-K lifetimes obtained in diluted (8·10¹⁸ cm^-3) KGW:0.1% Ho samples are: τ(⁵F₃)≈0.9 μs, τ( ⁵S₂)=19-3.6 μs, and τ(⁵F₅ )≈1.1 μs. For Ho concentrations below 1.5×10²⁰ cm^-3, multiphonon emission is the main source of non radiative losses, and the temperature independent multiphonon probability in KGW is found to follow the energy gap law τ_ph ^-1(0)=βexp(-αΔE), where β=1.4×10^-7 s^-1, and α=1.4×10³ cm. Above this holmium concentration, energy transfer between Ho impurities also contributes to the losses. The spectral distributions of the Ho³⁺ emission cross section σ_EM for several laser channels are calculated in σ- and π-polarized configurations. The peak a σ_EM values achieved for transitions to the ⁵I₈ level are ≈2×10^-20 cm² in the σ-polarized configuration, and three main lasing peaks at 2.02, 2.05, and 2.07 μm are envisaged inside the ⁵I₇→⁵I₈ channel     

Fabrication and characterization of lateral field-emitter triodes

The author fabricated a field-emitter triode with tungsten electrodes arranged laterally on a quartz glass substrate by using the photolithography and dry etching techniques. The device consists of an array of 170 field-emitter tips with a 10-μm pitch, a columnar gate, and an anode. The emission characteristics followed the Fowler-Nordheim tunneling theory. The mutual conductance was about 0.02 μS at an anode voltage of 300 V. The authors improved the fabrication process to obtain an emitter with an operating voltage of about 100 V