Vacuum Microelectronic Devices Research Articles

Synthesis, characterization, photoluminescence and field emission properties of novel durian-like gallium nitride microstructures

Durian-like gallium nitride (GaN) microstructures were successfully synthesized on Si substrate by pre-treating Ga metal with aqueous NH3 via catalyst assisted chemical vapor deposition (CVD) method at 1200°C. The as-synthesized product was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). XRD and EDX analysis revealed that durian-like GaN is pure and single phase. SEM results showed that the size of the durian-like GaN structures was 20–25μm. GaN microstructures exhibited reasonable field emission properties with the turn-on field of 8.24Vμm−1 (0.01mAcm−2) and threshold field of 10.18Vμm−1 (1mAcm−2) which is sufficient for applications of electron emission devices, field emission displays and vacuum micro-electronic devices. Photoluminescence (PL) properties of durian-like GaN studied at room temperature showed a strong near-band-edge emission at 369.4nm (3.36eV) whereas at low temperature it showed near-band-edge emission at 364.2nm (3.4eV) without yellow band emissions. The photoluminescence properties showed that it has also potential application in light-emitting devices.

Synthesis of Al4C3 nanowalls via thermal evaporation and potential application in vacuum microelectronic devices as cold electron emitters

Ceramic Al4C3 nanowalls were fabricated through a VS mechanism via a chemical vapor deposition (CVD) method. XRD (X-ray diffraction), Raman spectra, SEM (scanning electron micrograph) and TEM (transmission electron micrograph) methods were employed to characterize the product. The synthesized 2-D nanostructures are confirmed to be polycrystalline R-Al4C3 with a Al2O3 sheath outside the nanosheet. Field emission (FE) measurements show that the turn-on field (where the emission current reaches 10 μA cm−2) of the as-prepared sample is 6.0–7.0 V μm−1. According to several comparative experiments, we propose an atmosphere-controlled nanowall growth mechanism from self-assembling templates under a low-pressure environment to explain the growth process.

Analytical Solution of Vibration Analysis on Fixed-Free Single-Walled Carbon Nanotube-Based Mass Sensor

Fixed-free single-walled carbon nanotubes (SWCNTs) have attracted a lot of interest in recent years due to their suitability for a wide range of applications, such as field emission and vacuum microelectronic devices, nanosensors, and nanoactuators. Based on a cantilever beam-bending model with a rigid mass at the free end and mode analysis, an analytical solution is developed in the present study to deal with the resonant frequency and mode shapes of a SWCNT- based mass sensor. The resonant frequency shift and mode shape of the fixed-free SWCNTs caused by the addition of a nanoscale particle to the beam tip are examined in order to explore the suitability of SWCNTs as a mass detector device. The simulation results reveal that the volume of the added particle has little effect on the first resonant frequency. In contrast, the second resonant frequency decreases with increasing the volume of the added particle. Furthermore, the resonant frequency shift of the first mode is very obvious for the amount of added mass, and the second resonant frequency decreases rapidly with increasing volume of added particle. Therefore, the first and second resonant frequencies can be used in the measurement of the mass of added particle and its volume, respectively.

Preface: Phys. Status Solidi C 1/2012

AbstractThe 8th International Vacuum Electron Sources Conference (IVESC 2010) and NANOcarbon 2010 was held in Nanjing, China from Oct. 14–16 in 2010. This international conference was organized by Southeast University, the Engineering Department of the University of Cambridge, IEEE Electron Devices Society, the National Key Laboratory of Science and Technology on Vacuum Electronics (China) and Jiangsu Vacuum Society of China.IVESC 2010 included numerous sessions on the fundamentals of electron emission, cathode technology, and the applications of electron sources in vacuum electronic devices and vacuum microelectronic and other novel devices. IVESC provides a unique international forum for the presentation of achievements, breakthroughs and developments in electron source technology since electron sources form the heart of vacuum electron devices.The aims of NANOcarbon 2010 were: 1. to establish an international forum for the discussion and promotion of the science and applications of nanomaterials, 2. to maintain awareness of the current developments in the field and 3. to encourage and foster collaborations and networks between researchers in both academia and industry from Europe, Asia and America. The symposium featured talks by distinguished speakers presenting the latest advances in the field, and contributed papers which had also been solicited including poster presentations. Topics covered had included nanomaterial synthesis, processing, characterization, properties and applications. The NANOcarbon 2010 Proceedings will thus provide an excellent opportunity for audience to read about the latest cutting edge research results in carbon nanotube, graphene and nanowire synthesis, development and applications.The conference also reinforced the commitment of IVESC and NANOcarbon to promote international collaboration and facilitate the open exchange of state‐of‐the‐art and state‐of‐the‐practice research findings.

A Bipolar Vacuum Microelectronic Device

This report provides the first demonstration of a vacuum microelectronic device that utilizes both positive and negative charge states (i.e., a bipolar vacuum microelectronic device), thus enabling the possibility of device designs that are not previously possible in traditional vacuum microelectronics. In the same way that complimentary metal-oxide-semiconductor (complimentary n-channel MOS and p-channel MOS) were required in solid-state electronics before digital logic applications could be addressed, vacuum microelectronic devices benefit from a second charge state to realize many applications. This advance could enable integrated circuits for radiation-intensive environments (nuclear power facilities and space-based communications such as satellites) and high-temperature applications (engines and materials processing). A microelectromechanical systems platform was used to construct pentode structures with integrated carbon nanotube field emitters for electron emission and bias electrodes for separate electron- and ion-current modulation. Ions were generated via electron impact in an argon ambient, and devices were tested in both voltage sweep and pulsed modes. Current that is greater than 2 mA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> was modulated at the anode between ion and electron collection, demonstrating that this novel platform has the potential to foster a new class of bipolar vacuum microelectronics.

Preparation of grass-like GaN nanostructures: Its PL and excellent field emission properties

We here report highly pure and single crystalline grass-like gallium nitride (GaN) nanostructures obtained on silicon substrate via catalyst-assisted CVD route under NH 3 atmosphere inside horizontal tube furnace (HTF) by pre-treating the precursors with aqueous NH 3. The as-obtained GaN nanostructures were characterized by XRD, SEM, EDS, HRTEM and SAED. The field emission (FE) characteristics of grass-like GaN nanostructures exhibited a turn-on field of 7.82 V μm − 1 and a threshold field of 8.96 V μm − 1 which are quite reasonable for applications in electron emission devices, field emission displays and vacuum microelectronic devices. Room temperature photoluminescence (PL) measurements of grass-like GaN nanostructures exhibited a strong near-band-edge emission at 368.8 nm (3.36 eV) without any defects related emissions which shows its potential applications in optoelectronics.

A review of recent results on diamond vacuum lateral field emission device operation in radiation environments

This paper describes the electrical characteristics of lateral field emission vacuum microelectronic devices comprised of nanodiamond in two terminal (diode) and three terminal (transistor) cathode–gate–anode configuration and their resistance to failure in severe radiation conditions that would shut down conventional solid state electronics. This is the first published data on radiation tolerance of three terminal diamond vacuum lateral field emission devices. No changes in device structure or electrical behavior were observed after exposure to high levels of X-ray or neutron radiation.

Electron field emission enhanced by geometric and quantum effects from nanostructured AlGaN/GaN quantum wells

Electron field emitters that provide intense and stable currents are important to vacuum microelectronic devices. In this work, we demonstrate high-performance electron field emission (FE) from nanostructured AlGaN/GaN quantum wells by coupling the quantum and geometric effects. Pulsed laser deposition is utilized to fabricate the FE cathode. The field emitter exhibits a low threshold field of only 1.1 V/μm and yields a stable emission current of 5 mA/cm2 at 1.8 V/μm, making it suitable for FE-based applications.

Microelectromechanical system-based vacuum gauge for measuring pressure and outgassing rates in miniaturized vacuum microelectronic devices

Cr/Au meander-shaped resistors were fabricated on 0.2 μm thick square-shaped silicon nitride diaphragms with diaphragm dimensions ranging from 0.775 to 2.275 mm. The performance of these sensors was measured in a vacuum chamber as a function of resistor powers from 0.5 to 3 mW at pressures ranging from 2×10−4 to 760 Torr. The lengths of the meander-shaped resistors increase from 5.5 mm for the 0.775 mm diaphragm to 33.6 mm for the 2.275 mm diaphragm devices. It is shown that the pressure dependence of the devices is governed by the kinetic gas theory and that the devices can measure pressures from about 10 to 1×10−3 Torr. At a resistor power of 2 mW at 760 Torr, the 2.275 mm diaphragm device, which has the largest sensing area, exhibits the highest sensitivity.

Carbon-in-Al4C3 Nanowire Superstructures for Field Emitters

As a kind of ionic (or salt-like) carbide, for Al(4)C(3), hardly any active functions have been found except for structure material purposes. However, considering the unique characteristic features of its crystal structure, we think Al(4)C(3) in fact might have huge potential for exhibiting active functionality on field-emission applications. Herein, we report the feasibility to approach such emitters by creating Al(4)C(3)-based nanowire superstructures. The conductive amorphous carbon (a-C) nanolayers are embedded quasi-periodically in Al(4)C(3) nanowire and generate essential electrical contact to the insulating Al(4)C(3). The superstructures acting as cold electron emitters display excellent field emission performance with the turn-on field as low as 0.65-1.3 V/μm and the threshold field down to 2.1-2.6 V/μm. We speculate that the emission characteristics, which are ever better than carbon nanotubes, are attributed to the unique crystal structure of Al(4)C(3) and the enhanced electrons transport in the nanowires due to the existence of a-C nanolayers. Such emitters are technologically useful, because they can be easily fabricated on large substrates, and the synthesis process is simple and broadly applicable. The findings conceptually provide new opportunities for the application of Al(4)C(3) ceramic material in vacuum microelectronic devices.

Field nanoemitter: One-dimension Al4C3 ceramics

As a kind of ionic (or salt-like) carbide, Al(4)C(3) hardly any active functions have been found except for structure material purposes. However, considering the unique characteristic features of its crystal structure, we think Al(4)C(3) in fact might have huge potential for exhibiting active functionality on field-emission application. Herein, we report for the first time the catalyst-free synthesis and excellent field emission properties of Al(4)C(3) one-dimension (1-D) nanostructures. The 1-D nanostructures acting as cold electron emitters display excellent field emission performance with the turn-on field as low as 1.4-2.0 V μm(-1) and the threshold field down to 4.2-4.4 V μm(-1). Such emitters are technologically useful, because they can be easily fabricated on large substrates, and the synthesis process is simple and broadly applicable. The findings conceptually provide new opportunities for the application of Al(4)C(3) ceramic material in vacuum microelectronic devices.

Fabrication and field emission performance of arrays of vacuum microdiodes containing CuO nanowire emitters grown directly on glass without a catalyst

Arrays of vacuum microelectronic sources are fabricated on a glass substrate using cupric oxide (CuO) nanowire emitters. The arrays of electron sources possess a microdiode structure, which can effectively induce field emission and control the delivery of emitted electrons to the anode in a triode-type device operation. A technique for precisely growing CuO nanowires at the centre of microcavities in an array without using a catalyst and at temperatures as low as 400°C is presented. Such a simplified fabrication procedure results in improved field emission performance from the array compared with previous vacuum microelectronic devices. Typical prototype devices have turn-on gate voltages as low as 169 V to give emission current densities of 10 μA/cm2 at the anode. The ratio of anode current to cathode current reaches ∼0.85, and the maximum change in emission current density per volt is 1 μA/cm2. Electron emission from the arrays is stable and reproducible under either pulsed or direct current fields. These characteristics indicate that microgate-controlled CuO nanowire emitters may find application in practical devices.

Titanium buffer layer for improved field emission of CNT based cold cathode

Carbon nanotube (CNT) based cold cathodes are considered to be the most promising material for fabrication of next generation high-performance flat panel displays and vacuum microelectronic devices. Adhesion of CNTs with the substrate and the contact resistance between them are two of the important issues to be addressed in CNT based field emission (FE) devices. Here in this work, a buffer layer of titanium (Ti) is deposited prior to the catalyst deposition and the growth was carried out using chemical vapor deposition (CVD) technique. There was significant increase in emission current density from 10 mA/cm 2 to 30 mA/cm 2 at the field of 4 V/μm by the use of titanium buffer layer due to much less dense growth of CNTs of smaller diameter. Field emission results suggest that the adhesion of the CNTs to the substrate has improved. The titanium buffer layer has also lowered the contact resistance between the CNTs and the substrate because of which a stable emission of 30 mA for a longer duration was obtained.

Ti5Si4 Nanobats with Excellent Field Emission Properties

Bat-shaped nanorods (nanobats) of Ti5Si4 were grown on titanium foil by a vapor and condensation method without catalysts. The average diameter of the heads and the tails of the nanobats as well as the length of the nanobats are 25, 15, and 350 nm, respectively. The resistivity of the Ti5Si4 nanobat was measured to be 348 Ωμ·cm. Excellent field emission properties were found with the turn-on voltage of the Ti5Si4 nanobats at the current density of 1 μA/cm2 being 1.47 V/μm and field amplification factor being as high as 1350. The possession of remarkable field emission properties indicates that the Ti5Si4 nanobats may be applicable as emitters in flat panel display and vacuum microelectronic devices.

Field emission characteristics of single crystal LaB6 field emitters fabricated by electrochemical etching method

Single crystal lanthanum hexaboride (LaB6) field emission arrays with uniform tip structures have been achieved using the electrochemical etching method and the field emission characteristics are evaluated. A direct current voltage source is introduced in the etching process and phosphoric acid is used as the electrolyte solution. The SEM observation of the emitters reflects the feasibility of the electrochemical etching method for the fabrication of single crystal LaB6 FEA. The turn-on field of LaB6 FEA is low at 3.2 Vµm−1 and the emission current exhibits high stability during the 20-minute operation. Furthermore, even at low vacuum (>1.5 × 10−5 Torr) it still exhibits good emission properties and a strong ability to withstand the ion bombardment, which is useful for low operation vacuum microelectronic devices.

이중층 탄소나노튜브 전계전자 방출원의 신뢰성 있는 전계방출 특성

촉매 화학기상증착법을 이용하여 합성된 이중층 탄소나노튜브를 가지고 전계전자 방출원을 제작하여 이들의 신뢰성 있는 전계전자 방출특성을 조사하였다. 합성된 탄소 필라멘트들은 TEM, TGA, 그리고 Raman 분석을 통하여 결함이 없고 순도가 높은 이중층 탄소나노튜브가 합성이 되었음을 확인하였다. 이들 이중층 탄소나노튜브 전계전자 방출원은 이전극 구조에서 낮은 턴-온 전계와 높은 전류밀도의 전계전자 방출 특성을 보여주었고, 균질한 전계방출 패턴과 좋은 전계방출 안정성을 나타내었다. We investigated the field emission characteristics from the planar field emitters made of double-walled carbon nanotubes (DWCNTs) synthesized by a catalytic chemical vapor deposition (CCVD) method. Transmission electron microscopy, Thermogravimetric and Raman analysis showed that the carbon materials have a low defect level in their atomic carbon structure, pointing to the synthesis of high-purity DWCNTs. For field emission properties of DWCNTs, the turn-on field of DWCNTs was <TEX>$1.9\;V/{\mu}m$</TEX> and the current density was about <TEX>$74\;mA/cm^2$</TEX> at <TEX>$8.1\;V/{\mu}m$</TEX>, which is sufficient for the applications of field emission displays and vacuum microelectronic devices. The DWCNT field emitters also exhibited a uniform field emission pattern and good field emission stability in a diode configuration.

Electron field emission from amorphous carbon with N-doped nanostructures pyrolyzed from polyaniline

Carbon-based materials have been of great interest due to their potential application in cold cathodes for field emission displays and other vacuum microelectronic devices. Pyrolyzed polyaniline (PPANI) with N-doped nanostructures was prepared by pyrolysis of polyaniline at high temperature of 900 °C. The morphologies and microstructures were investigated by scanning electron microscopy, transmission electron microscopy, AFM, Raman spectroscopy, and X-ray photoelectron spectroscopy. It was found that there were sp 2C–N and sp 3C–N bonds between the nitrogen and the carbon atoms in the nanostructures of the PPANI obtained. The electron field emission investigations showed that the turn-on field and effective work function ϕ e of PPANI were 1.7 V/μm and 0.010 eV which were lower than N-doped amorphous carbon films obtained by other methods.

THz vacuum microelectronic devices

Compact vacuum devices of output power even at 1W and at terahertz (THz) frequencies above 100GHz offer enormous applications for wide band communication, imaging radars, and spectroscopy. These active vacuum devices are also required in many more unexplored areas of scientific, industrial and medical applications. Such vacuum devices at frequency above 100GHz are very small in dimension and microelectronic technology is needed for their fabrication. Successful development of THz vacuum microelectronic devices therefore needs fusion of vacuum tube technology with the semi-conductor technology. Significant efforts are being carried out worldwide to develop successfully such compact vacuum devices using available LIGA and DRIE semiconductor technologies. This paper presents some details on THz vacuum microelectronic devices.

Uniform and enhanced field emission from chromium oxide coated carbon nanosheets

Carbon nanosheets, a two-dimensional carbon nanostructure, are promising electron cathode materials for applications in vacuum microelectronic devices. This letter demonstrates a simple approach to improve the spatial emission uniformity of carbon nanosheets by coating them with a chromium oxide thin film. Photoelectron emission microscopy observations and in situ field emission tests revealed that chromium oxide coated carbon nanosheets not only have spatial uniformity but also have coating thickness dependent field emission properties. For example, a coating thickness of ∼1.5nm gave a substantially greater field emission than as-grown nanosheets or other thickness coatings.

Growth and field emission of tungsten oxide nanotip arrays on ITO glass substrate

High-density and uniformly aligned tungsten oxide nanotip arrays have been deposited by a conventional thermal evaporation on ITO glass substrates without any catalysts or additives. The temperature of substrate was 450–500 °C. It was shown that the tungsten oxide nanotips are single-crystal grown along [0 1 0] direction. For commercial applications, field emission of the tungsten oxide nanotip arrays was characterized in a poor vacuum at room temperature. The field emission behaviors are in agreement with Fowler–Nordheim theory. The turn-on field is 2.8 V μm −1 as d is 0.3 mm. The excellent field emission performances indicated that the tungsten oxide nanotip arrays grown by the present approach are a good candidate for application in vacuum microelectronic devices.