The electrical characteristics of a 4H-silicon carbide metal-insulator-semiconductor structure with Al2O3 as the gate dielectric

A 4H-silicon carbide metal-insulator-semiconductor structure with ultra-thin Al₂O₃ as the gate dielectric, deposited by atomic layer deposition on the epitaxial layer of a 4H-SiC (0001) 8⁰N-/N+ substrate, has been fabricated. The experimental results indicate that the prepared ultra-thin Al₂O₃ gate dielectric exhibits good physical and electrical characteristics, including a high breakdown electrical field of 25 MV/cm, excellent interface properties (1×10¹⁴ cm^-2) and low gate-leakage current (I_G = 1 × 10^-3 A/cm^-2@E_ox = 8 MV/cm). Analysis of the current conduction mechanism on the deposited Al₂O₃ gate dielectric was also systematically performed. The confirmed conduction mechanisms consisted of Fowler-Nordheim (FN) tunneling, the Frenkel-Poole mechanism, direct tunneling and Schottky emission, and the dominant current conduction mechanism depends on the applied electrical field. When the gate leakage current mechanism is dominated by FN tunneling, the barrier height of SiC/Al₂O₃ is 1.4 eV, which can meet the requirements of silicon carbide metal-insulator-semiconductor transistor devices.     

Triode field emitters with planar carbon-nanoparticle cathodes

We designed and fabricated three different types of triode field emitters with planar carbon-nanoparticle (CNP) cathodes such as a normal-gate structure, a double-gate structure, and a well-structure. A normal-gate structure CNP triode emitter showed good field emission properties. The field emission started at the gate-voltage of 45 V, and the anode current reached the level of 120 nA at the gate-voltage of 60 V. However, in general, normal-gate structure suffered from large gate current. Using the double-gate structure, we successfully reduced the gate current to the level less than 4% of anode currents up to the anode current of 250 nA. To simplify fabrication process while maintaining the gate current reduction effect of the double-gate structure, a triode emitter with a well-structure cathode was fabricated via reactive-ion etching of a heavily doped n-type silicon wafer. The triode emitter with a well-structure cathode and a recessed gate structure showed negligible gate current.     

Integration of ZnO nanowires in gated field emitter arrays for large-area vacuum microelectronics applications

Addressable field emitter arrays (FEAs) have important applications in vacuum electronic devices. However, it is important to integrate nanowire emitters into a gated structure without influencing the device structure and maintain the excellent field emission properties of nanowire emitters in the FEAs after the fabrication process. In this study, gate-structure ZnO nanowire FEAs were fabricated by a microfabrication process. The structure combines a planar gate and an under-gate, which is compatible with the preparation of ZnO nanowire emitters. The effect of electrode materials on the field emission properties of ZnO nanowires was studied using a diode structure, and it was found that ZnO nanowire pads on indium-tin-oxide (ITO) electrode showed better field emission performance compared with chromium (Cr) electrode. In addition, effective emission current modulation by the gate voltage was achieved and the addressing capability was demonstrated by integrating the ZnO nanowire FEAs in a vacuum-encapsulated field emission display. The reported technique could be a promising route to achieve large area addressable FEAs.     

电极布局对硅LED性能的影响

采用0.35μm双栅标准CMOS工艺设计和制备了叶型硅发光器件.叶型硅发光器件由3个楔型器件的组合而成,pn结结构为n阱/p+结.使用奥林巴斯IC显微镜测得了器件的显微图形,并对器件进行了电学特性测试.器件工作在雪崩击穿下,开启电压为8.8 V,能够发出黄色可见光;正向偏置下,器件开启电压为0.8 V.在与已经制备的楔...     

Field emission properties of nano-structured phosphorus-doped diamond

Nano-structured phosphorus-doped diamonds were fabricated for field emitters and their field emission properties were characterized. Two kinds of nano-structures were prepared; tip array structures and whiskers on tip structures. The tips, which have 100 nm radius and 10 μm height, are used in tip array structures; whiskers have tip radii of 5 nm and height of 500 nm. Following nano-structure formation, a reduction of threshold fields is observed compared to non-patterned flat surfaces. This is ascribed to field concentration at the tips. However, at higher electric fields, a saturation of the emission current is observed due to non-negligible bulk resistances in tips and whiskers.     

场发射栅孔阵列的制备

 采用硅的局部氧化技术以及湿法刻蚀技术,利用2.6 μm的光刻掩模板在n型硅片上形成了栅极孔径为1 μm的场发射阴极的栅极空腔阵列,实现了用大阵点尺寸的栅极掩模板制备较小尺寸栅孔阵列。硅的湿法刻蚀溶液采用各向同性的硝酸和氢氟酸混合溶液,刻蚀后空腔的深度和宽度均随刻蚀时间线性增加。同时,由于刻蚀溶液具有较高的Si/SiO₂ 刻蚀选择比,栅极孔径随刻蚀时间增大的速度远低于深度和宽度增大的速度,栅极孔径主要取决于掩模的尺寸和氧化层的厚度。通过选择掩模板的尺寸以及氧化层的厚度,采用局部氧化技术和湿法刻蚀技术能够制备出微米或亚微米的场发射阴极的栅极空腔阵列。     

类球状微米金刚石聚晶膜场发射的稳定性

在覆盖金属钛层的陶瓷上,利用微波等离子体化学气相沉积(MPCVD)法制备出类球状微米金刚石聚晶膜。通过二极管结构测试了聚晶膜的场致电子发射特性,利用扫描电子显微镜、拉曼光谱、XRD分析了场发射前后薄膜的结构和表面形貌的变化。发现在高场、大电流密度的场发射中,对类球状微米金刚石聚晶薄膜中的金刚石聚晶颗粒影响很小,而对金刚石聚晶颗粒间的非晶碳层影响很大。对类球状微米金刚石聚晶变化机理进行了研究。     

Growth and field emission properties of globe-like diamond microcrystalline-aggregate

The globe-like diamond microcrystalline-aggregates were fabricated by microwave plasma chemical vapor deposition (MPCVD) method. The ceramic with a Ti mental layer was used as substrate. The fabricated diamond was evaluated by Raman scattering spectroscopy, X-ray diffraction spectrum (XRD), and scanning electron microscope (SEM). The field emission properties were tested by using a diode structure in a vacuum. A phosphor-coated indium tin oxide (ITO) anode was used for observing and characterizing the field emission. It was found that the globe-like diamond microcrystalline-aggregates exhibited good electron emission properties. The turn-on field was only 0.55 V/μm, and emission current density as high as 11 mA/cm² was obtained under an applied field of 2.9 V/μm for the first operation. The growth mechanism and field emission properties of the globe-like diamond microcrystalline-aggregates are discussed relating to microstructure and electrical conductivity.     

Surface and electrical properties of organic-inorganic hybrid structure as gate insulator to organic thin film transistor

Carbon-based OTFT devices were fabricated using a plasma process for the gate electrode and gate insulators. A nanocrystalline carbon (nc-C) film was used as the gate electrode, and three different layers, cyclohexene, diamond-like carbon (DLC), and cyclohexene/DLC (hybrid insulator), were used as the gate insulator. The surface and electrical properties of the three different gate insulators on the nc-C gate electrode were investigated using the SPM method, and the leakage current density and dielectric constant of the metal-insulator-metal (MIM) structures with three different insulator layers were evaluated. The hybrid insulator layer had a very smooth surface, approximately 0.2 nm, a uniform surface without defects, and good adhesion between the layers. Overall, it is believed that the hybrid insulator lead to a decrease in the electrical leakage current and an improvement in the device performance.     

A Si nano–micro-wire array on a Si(111) substrate and field emission device applications

A large number of Si wires on Si(111) can be fabricated selectively by the vapor–liquid–solid growth method with a high aspect ratio greater than 100. The diameter of the wire can be controlled from less than a micron to a few hundred microns. We propose a novel smart field electron emission device using silicon nano-wires fabricated by this vapor–liquid–solid growth method, and demonstrate field electron emission with a quite low operation voltage from a gated silicon nano-wire. The threshold voltage is about 13 V, and the value is similar to those for gated carbon-nanotube field emitters. The emission current reaches 10 nA at 15 V gate voltage.     

Determining the work function of a carbon-cone cold-field emitter by in situ electron holography

Cold-field emission properties of carbon cone nanotips (CCnTs) have been studied in situ in the transmission electron microscope (TEM). The current as a function of voltage, i(V), was measured and analyzed using the Fowler–Nordheim (F–N) equation. Off-axis electron holography was employed to map the electric field around the tip at the nanometer scale, and combined with finite element modeling, a quantitative value of the electric field has been obtained. For a tip-anode separation distance of 680 nm (measured with TEM) and a field emission onset voltage of 80 V, the local electric field was 2.55 V/nm. With this knowledge together with recorded i(V) curves, a work function of 4.8 ± 0.3 eV for the CCnT was extracted using the F–N equation.     

Stable electron field emission from carbon nanotubes emitter transferred on graphene films

Carbon nanotubes (CNTs) arrays grown by microwave plasma enhanced chemical vapor deposition (MPCVD) method was transferred onto the substrate covered with graphene layer obtained by thermal chemical vapor deposition (CVD) technology. The graphene buffer layer provides good electrical and thermal contact to the CNTs. The field emission characteristics of this hybrid structure were investigated in this study. Compared with the CNTs arrays directly grown on the silicon substrate, the hybrid emitter shows better field emission performance, such as high emission current and long-term emission stability. The presence of this graphene layer was shown to improve the field emission behavior of CNTs. This work provides an effective way to realize stable field emission from CNTs emitter and similar hybrid structures.     

Characterization of heat-assisted magnetic probe recording on CoNi/Pt multilayers

A method of heat-assisted magnetic recording (HAMR) potentially suitable for probe-based storage systems is characterized. In this work, field emission current from a scanning tunneling microscope (STM) tip is used as the heating source. Pulse voltages of 2–7 V were applied to a CoNi/Pt multilayered film fabricated on either bare silicon or oxidized silicon substrates. Different types of Ir/Pt and W STM tips were used in the experiment. The results show that thermally recorded magnetic marks are formed with a nearly uniform mark size of 170 nm on the film fabricated on bare silicon substrate when the pulse voltage is above a threshold voltage. The mark size becomes 260 nm when they are written on the identical film fabricated on an oxidized silicon substrate. The threshold voltage depends on the material work function of the tip, with W having a threshold voltage about 1 V lower than Pt. A synthesized model, which contains the calculation of the emission current, the simulation of heat transfer during heating, and the study of magnetic domain formation, was introduced to explain experimental results. The simulation agrees well with the experiments.     

Charge storage and electron/light emission properties of silicon nanocrystals

Monodispersed silicon nanocrystals show novel electrical and optical characteristics of silicon quantum dots, such as single-electron tunneling, ballistic electron transport, visible photoluminescence and high-efficiency electron emission.Single-electron memory effects have been studied using a short-channel MOSFET incorporating Si quantum dots as a floating gate. Surface nitridation of Si nanocrystal memory nodes extends the charge-retention time significantly. Single-electron storage in individual Si dots has been evaluated by Kelvin probe force microscopy.Photoluminescence and electron emission are observed for surface-oxidized silicon nanocrystals. Efficiency of the no-phonon-assisted transition increases with decreasing core Si size. Electron emission efficiency as high as 5% has been achieved for the Si-nanocrystal-based cold electron emitter devices. The non-Maxwellian energy distribution of emitted electrons suggests that the mechanism of electron emission is due to ballistic transport through arrays of surface-oxidized Si nanocrystals. Combined with the ballistic electron emission, the quasi-direct light emission properties can be used for developing Si-based lasers.     

Electrodeposition of aligned ZnO sheet array on ITO substrate and their field emission characteristics

ZnO sheet array was fabricated by a simple electrodeposition method on the transparent ITO substrate at a temperature of about 60℃. The field emission properties of the ZnO sheet array were investigated. The fluctuation of the field emission current is less than 5% over several hours. The Fowler Nordheim curves with a roughly linear characteristic were obtained by analysing the current density and the intensity of the electrical field. The results prove that such a simple electrochemical method can potentially meet the demands on the production of cold cathodes for field emission display.[第一段]     

Photo-Fries-based photosensitive polymeric interlayers for patterned organic devices

This work reports on the investigation of the photosensitive polymer poly(diphenyl bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate) (PPNB), which undergoes the photo-Fries rearrangement upon illumination with UV-light, used as interfacial layers in organic electronic devices. Two cases were investigated: the use of a blend of PPNB with poly-vinylcarbazole (PVK) as an interlayer in para-sexiphenyl (PSP) based organic light emitting diodes (OLEDs) and the use of PPNB as gate dielectric layer in organic field effect transistors (OFETs). The photo-Fries rearrangement reaction causes a change of the polymer chemical structure resulting in a change of its physical and chemical properties. The electroluminescence spectra and emission of the PSP OLEDs are not affected when fabricated with a non-UV-illuminated PPNB:PVK blend. However, the electroluminescence is totally quenched in those OLEDs fabricated with UV-illuminated PPNB:PVK blend. Although the dielectric constant of PPNB increases upon UV-treatment, it is demonstrated that those OFETs built with UV-treated PPNB as gate dielectric have lower performance than those OFETs built with non-UV-treated PPNB. Furthermore, the effect of the UV-illumination of PPNB and PPNB:PVK blend on the growth of the small molecules C₆₀ and PSP has been studied by atomic force microscopy. Using photolithography, this kind of photochemistry can be performed to spatially control and tune the optical and electrical performance of organic electronic devices.     

Microwave plasma CVD-grown graphene–CNT hybrids for enhanced electron field emission applications

The growth and electron emission characteristics were investigated from a hybrid structure of multiwalled carbon nanotubes (MWCNTs) and multilayer layer graphene (MLG) deposited on silicon substrate coated with iron catalyst and an interlayer of aluminium. The hybrid structures were synthesized in a two-step process by microwave plasma-enhanced chemical vapour deposition technique. The formation of MWCNTs takes place by absorption and precipitation of carbon radicals into the catalyst particles. Thereafter, ample carbon forms MLG on tip of the MWCNTs resulting in a MLG-MWCNTs hybrid nanostructure. MLG was observed to grow branching out of the tips and sidewalls of the MWCNTs and is expected to attach by Van der Walls bonds. Transmission electron microscopy and micro-Raman spectroscopy confirmed the crystalline nature of the hybrid structures. Electron emission studies were carried out using a diode-type field emission setup. The enhancement factor was found to be ~3,500 for bare MWCNTs, ~4,070 to ~5,000 for hybrid structures and ~6,500 for N-doped MLG-MWCNTs hybrid structures. Modification in the defects structure and enhancement of emission sites are suggested to be responsible for the increase of the field emission characteristics.     

Emission properties of Ti-DLC films prepared by unbalanced magnetron sputtering

The field emission properties of Ti-DLC films in diode and coplanar device structures were studied. An emission current density of 1.14 A/cm² could be obtained at an applied field of 33 V/μm and the threshold field was 24 V/μm for the coplanar emission structure. The silicon substrate was found to limit the emission current in the diode structure because of its high resistivity.     

晶化时间及硅源对SAPO-5分子筛的结构及模板剂状态的影响

通过改变硅源和晶化时间的方法,采用水热法合成了系列SAPO-5分子筛材料,用X光衍射(XRD)和²⁷Al MAS NMR对产物的晶相结构进行表征,用¹³C CP MAS NMR研究了不同阶段的产物中模板剂的存在状态。结果可见:以SiO₂凝胶为硅源时;薄水铝石反应物有较高的活性,在48h的晶化时间内,延长晶化时间有助于SAPO-5分子筛的完整结晶,当晶化时间超过48h时,其中已形成的SAPO-5的结构部分被破坏,并转化为SAPO-34.且SAPO-34的量随晶化时间的延长而增多。当以Si(OEt)₄为硅源时,铝反应物的反应活性较低,在72h的晶化时间范围内,延长晶化时间有助于SAPO-5产物的形成,使其结构愈加完整,在SAPO-5分子筛的形成过程中,模板剂的状态随分子筛结构的变化而变化,由于三乙胺(Et₃N)模板剂中的甲基和亚甲基所处位置不同,其弛豫时间受分子筛结构的影响较大,可用其中甲基的¹³C MAS NMR诺线的强度及化学位移来表示分子筛结构的完整性。