Er3+ –Y3+-Codoped Al 2O3 for High-Temperature Sensing

Optical high-temperature sensing using the fluorescence intensity ratio (FIR) technique of green up-conversion emissions at 523 and 546 nm in Er³⁺-Y³⁺-codoped Al₂O₃ was studied in a wide temperature range of 295 K-973 K. The maximum sensitivity and the temperature resolution derived from the FIR technique are approximately 0.0035 K^-1 and 0.3 K, respectively, which indicated that Er³⁺-Y³⁺-codoped Al₂O₃ plays an important role for applications in the optical high-temperature sensing.     

LaNiO3: a promising material for contact with YBa2Cu3O7-x thin films

Epitaxial LaNiO₃ metallic oxide thin films have been grown on c-axis oriented YBa₂Cu₃O_7-δ thin films on LaAlO₃ substrates by pulsed laser deposition technique and the interface formed between the two films has been examined by measuring the contact conductance of the same. The specific contact conductance of the interface measured using a modified four probe method was found to be 1.4 to 6×10⁴ ohm^-1 cm^-2 at 77 K. There are indications that contact conductance can be brought closer to that obtained for noble metal-YBCO interface     

Electrical characterization of Al2O3n-channel MOSFETs with aluminum gates

High-effective mobilities are demonstrated in Al₂O₃ based n-channel MOSFETs with Al gates. The Al₂O₃ was grown in ultra-high vacuum using a reactive atomic beam deposition system. The mobility with maximum values at approximately 270 cm²/Vs, is found to approach that of SiO ₂ based MOSFETs at higher fields     

Improved gain performance in Yb3+-sensitized Er3+-doped alumina (Al2O3) channel opticalwaveguide amplifiers

Small-signal amplification in short, Yb³⁺-sensitized, Er³⁺-doped alumina (Al₂O₃) channel optical waveguides with high Er³⁺ concentrations is analyzed. Taking into account uniform up conversion, excited state absorption (ESA) from the Er³⁺ metastable level (⁴I_13/2 ), and Yb³⁺→Er³⁺ energy transfer by cross relaxation, the obtainable gain improvements compared to Yb³⁺ -free Er³⁺-doped Al₂O₃ optical waveguides are investigated. The amplifier model is based on propagation and population rate equations and is solved numerically by combining finite elements and the Runge-Kutta algorithm. The analysis predicts that 5-cm long Yb³⁺/Er³⁺ co-doped Al₂O ₃ waveguides show 13-dB net signal gain for 100 mW pump power at λ_p=980 nm     

End-pumped Nd:LaF3 and Nd:LaMgAl11O19 lasers

Nd:LaF₃ and Nd:LaMgAl₁₁O₁₉ (LMA) are promising candidates for pulsed diode-laser-pumped lasers because they have relatively long upper state lifetimes and large absorption bandwidths compared to other Nd³⁺ doped materials. Crystal growth of LMA and the spectroscopic properties of both materials are described. Continuous-wave (CW) end-pumped lasers have been demonstrated in these materials using a Ti:Al₂O₃ laser to simulate the diode-laser pump source. Slope efficiencies of 47% for Nd:LaF₃ and 32% for Nd:LMA were obtained. The results for Nd:LaF₃ are typical for end-pumped, CW, Nd³⁺ lasers; the lower slope efficiency for Nd:LMA is attributed to excited-state absorption     

Ga2O3(Gd2O3)/InGaAsenhancement-mode n-channel MOSFETs

We have demonstrated the first Ga₂O₃(Gd₂O₃) insulated gate n-channel enhancement-mode In_0.53Ga_0.47As MOSFET's on InP semi-insulating substrate. Ga₂O₃(Gd₂ O₃) was electron beam deposited from a high purity single crystal Ga₅Gd₃O₁₂ source. The source and drain regions of the device were selectively implanted with Si to produce low resistance ohmic contacts. A 0.75-μm gate length device exhibits an extrinsic transconductance of 190 mS/mm, which is an order of magnitude improvement over previously reported enhancement-mode InGaAs MISFETs. The current gain cutoff frequency, f_t, and the maximum frequency of oscillation, f_max, of 7 and 10 GHz were obtained, respectively, for a 0.75×100 μm² gate dimension device at a gate voltage of 3 V and drain voltage of 2 V     

磁控管用新型直热式稀土铪酸钆陶瓷阴极研究

为了提高大功率磁控管的输出功率,延长其使用寿命,采用难熔稀土氧化钆和过渡金属氧化铪制备大功率磁控管用新型直热式稀土铪酸钆陶瓷阴极,并对该阴极的热发射特性和寿命特性等进行了测试,热发射测试结果显示该阴极在1300℃ br即可提供0.1A/cm²发射电流密度,1600℃ br下可提供超过1.93A/cm²的发射电流密度.寿命实验结果显示,该阴极在1500℃ br,直流负载为0.5A/cm²的条件下,寿命已经超过4000h.最后,利用X射线衍射仪、扫描电镜、能谱分析仪、氩离子深度刻蚀俄歇电镜等设备分别对该阴极活性物质的分子结构,阴极表面微观形貌、元素成分及含量等进行了分析.结果表明,高温烧结合成了单一的铪酸钆物相,烧结过程中当一种Gd³⁺价稀土氧化钆掺入Hf⁴⁺价的过渡金属氧化铪时,会发生离子置换固溶,为了保持铪酸钆晶格的电中性,晶格中就会产生一个氧空位.当阴极在激活、老练、热发射测试时,会加速氧空位的生成,产生的氧空位越多,阴极表面导电性就会越好,这间接降低了逸出功,从而提高了阴极的热发射能力.     

Temporal stability of circulating current in thin film Tl2Ba2CaCu2O8 and YBa2Cu3O7

The temporal stability of trapped transport current in annular thin film Tl₂Ba₂CaCu₂O₈ (TBCCO) and YBa₂Cu₃O₇ (YBCO) wafers has been accurately measured and has been found to be of suitable quality for the stringent requirements of nuclear magnetic resonance (NMR) magnets. No detectable decay, to the limit of the experimental apparatus (2*10^-14 Ω), was detected in those wafers with transport current at or below the critical current density J_c. The critical current density, as previously determined from 12 μm meander lines, was confirmed in a wafer with a width of 1.9 cm. The profile of trapped magnetic field resulting from induced current was modeled in order to assess its effect on the uniformity of an NMR magnet     

Infrared cross-section measurements for crystals doped withEr3+, Tm3+, and Ho3+

The absorption and emission cross sections of the transition between the ground spin-orbit multiplet and the lowest excited multiplet were measured for Er³⁺, Tm³⁺, and Ho³⁺ ions in a variety of crystalline hosts. The materials that were investigated include LiYF₄, BaY₂F₈, Y ₃Al₅O₁₂, LaF₃, KCaF₃ , YAlO₃, and La₂Be₂O₅. The absolute magnitudes of the emission cross sections were determined from the absorption spectra, with the aid of the principle of reciprocity. The calculated radiative emission lifetimes derived from these measured cross sections agree well with the measured emission decay times for most materials. The potential use of these rare-earth-doped materials in pulsed laser applications requires that the ground state exhibit adequate splitting to minimize the detrimental effects of the ground state thermal population, and also that the emission cross section be sufficiently large to permit efficient extraction energy. The systems based on Ho³⁺ in the eightfold coordinated sites of LiYF₄, BaY₂F₈, and Y₃Al₅O₁₂ appear to be the most promising     

肖特基型β-Ga2O3日盲紫外光电探测器

本文制备并研究了肖特基型β-Ga₂O₃日盲紫外光电探测器.结果表明：通过脉冲激光沉积外延生长的β-Ga₂O₃的（-201）晶面 X射线衍射峰半高宽仅为36 arcsec,表现出了高的晶体质量;光暗条件下的I-V曲线显示所制备的器件具有明显的肖特基整流特性,在-5V偏压下暗电流保持在0.1nA量级,正向导通电压为1.5V;光电流谱显示器件在240nm处存在显著的峰值响应,并在260nm左右呈现陡峭的截止边,日盲紫外的带内带外抑制比达到1000.同时,也研究了不同掺杂对Ga₂O₃晶体质量的影响.     

原子层沉积方法制备低温多层Al2O3/TiO2复合封装薄膜的研究

原子层沉积(ALD)方法可以制备出高质量薄膜,被认为是可应用于柔性有机电致发光器件(OLED)最有发展前景的薄膜封装技术之一。本文采用原子层沉积(ALD)技术,在低温(80℃)下,研究了Al₂O₃及TiO₂薄膜的生长规律,通过钙膜水汽透过率(WVTR)、薄膜接触角测试等手段,研究了不同堆叠结构的多层Al₂O₃/TiO₂复合封装薄膜的水汽阻隔特性,其中5 nm/5 nm×8 dyads(重复堆叠次数)的Al₂O₃/TiO₂叠层结构薄膜的WVTR达到2.1×10^-5 g/m²/day。采用优化后的Al₂O₃/TiO₂叠层结构薄膜对OLED器件进行封装,实验发现封装后的OLED器件在高温高湿条件下展现了较好的寿命特性。     

Good High-Temperature Stability of TiN/ Al2O3/WN/TiN Capacitors

For the first time, good thermal stability up to an annealing temperature of 1000degC has been demonstrated for a new TiN/Al₂O₃/WN/TiN capacitor structure. Good electrical performance has been achieved for the proposed layer structure, including a high dielectric constant of ~ 10, low leakage current of 1.2times10^-7 A/cm² at 1 V, and excellent reliability. A thin WN layer was incorporated into the metal-insulator-metal capacitor between the bottom TiN electrode and the Al₂O₃ dielectric suppressing of interfacial-layer formation at Al₂ O₃/TiN interfaces and resulting in a smoother Al₂O₃/TiN interface. This new layer structure is very attractive for deep-trench capacitor applications in DRAM technologies beyond 50 nm.     

Fundamental characteristics of a magnetoresistive sensor using Y1Ba2Cu3O7-x ceramicsuperconducting films

The fundamental characteristics of a magnetic sensor fabricated from a Y₁Ba₂Cu₃O_7-x ceramic superconducting film are investigated. The operation principle of the sensor is based on the magnetoresistive properties of the material. The Y₁Ba₂Cu₃O_7-x ceramic film was prepared by the spray pyrolysis method. An element of the magnetic sensor consists of the film patterned to a meander shape. the sensitivity is discussed in connection with the noise measurement of the element. A magnetic field resolution of 2×10^-6 G/(Hz) ^1/2 at 100 Hz was obtained in the 0.1-100 G range. The sensitivity is much higher than that of a conventional semiconductor magnetic sensor. With an AC modulation provided by a magnetic field, phase detection of the magnetic field can be performed using a lock-in amplifier. An improvement in the low-frequency (<1 Hz) magnetic field resolution of about one order of magnitude was obtained using this method     

YBa2Cu3O7 superconductors forhigh-speed interconnects

The surface resistance of high-quality YBa₂Cu₃ O₇ superconducting films measured over a frequency range from 10 to 500 GHz using high-speed optoelectronic techniques is discussed. A direct comparison is made with the surface resistance of gold and superconducting niobium conductors. Using the measured surface resistance, the propagation characteristic of interconnects based on YBa ₂Cu₃O₇ superconductors at 77 K is simulated and compared to that of gold transmission lines at 77 K and superconducting niobium lines at 7.7 K     

Electrical characteristics of high quality La2O3 gate dielectric with equivalent oxide thickness of 5 Å

Electrical and reliability properties of ultrathin La₂O ₃ gate dielectric have been investigated. The measured capacitance of 33 Å La₂O₃ gate dielectric is 7.2 μF/cm² that gives an effective K value of 27 and an equivalent oxide thickness of 4.8 Å. Good dielectric integrity is evidenced from the low leakage current density of 0.06 A/cm² at -1 V, high effective breakdown field of 13.5 MV/cm, low interface-trap density of 3×10¹⁰ eV^-1/cm², and excellent reliability with more than 10 years lifetime even at 2 V bias. In addition to high K, these dielectric properties are very close to conventional thermal SiO₂      

High-performance polycrystalline SiGe thin-film transistors usingAl2O3 gate insulators

The use of aluminum oxide as the gate insulator for low temperature (600°C) polycrystalline SiGe thin-film transistors (TFTs) has been studied. The aluminum oxide was sputtered from a pure aluminum target using a reactive N₂O plasma. The composition of the deposited aluminum oxide was found to be almost stoichiometric (i.e., Al₂O₃), with a very small fraction of nitrogen incorporation. Even without any hydrogen passivation, good TFT performance was measured an devices with 50-nm-thick Al₂O₃ gate dielectric layers. Typically, a field effect mobility of 47 cm²/Vs, a threshold voltage of 3 V, a subthreshold slope of 0.44 V/decade, and an on/off ratio above 3×10⁵ at a drain voltage of 0.1 V can be obtained. These results indicate that the direct interface between the Al₂ O₃ and the SiGe channel layer is sufficiently passivated to make Al₂O₃ a better alternative to grown or deposited SiO₂ for SiGe field effect devices     

High-density MIM capacitors using Al2O3 andAlTiOx dielectrics

We have investigated the electrical characteristics of Al₂ O₃ and AlTiO_x MIM capacitors from the IF (100 KHz) to RF (20 GHz) frequency range. Record high capacitance density of 0.5 and 1.0 μF/cm² are obtained for Al₂ O₃ and AlTiO_x MIM capacitors, respectively, and the fabrication process is compatible to existing VLSI backend integration. However, the AlTiO_x MIM capacitor has very large capacitance reduction at increasing frequencies. In contrast, good device integrity has been obtained for the Al₂O₃ MIM capacitor as evidenced from the small frequency dependence, low leakage current, good reliability, small temperature coefficient, and low loss tangent     

Oxidized Ta2O5/Si3N4dielectric films on poly-crystalline Si for dRAMs

A dielectric film technology characterized by a novel multilayer structure formed by oxidation of Ta₂O₅/Si₃ N₄ films on polysilicon has been developed to realize high-density dRAMs. The dry oxidation of the Ta₂O₅/Si₃N₄ layers was performed at temperatures higher than 900°C. This film has a capacitance per unit area from 5.5 to 6.0 fF/ μm², which is equivalent to that of a 6.0- to 6.5-nm-thick SiO₂. The leakage current at an effective electric field of 5 MV/cm is less than 10^-9 A/cm². Under such an electric field, the extrapolated time to failure for 50% cumulative failure can be as high as 1000 years     

Submicrometer Inversion-Type Enhancement-Mode InGaAs MOSFET With Atomic-Layer-Deposited Al2O3 as Gate Dielectric

High-performance inversion-type enhancement-mode n-channel In_0.53Ga_0.47As MOSFETs with atomic-layer-deposited (ALD) Al₂O₃ as gate dielectric are demonstrated. The ALD process on III-V compound semiconductors enables the formation of high-quality gate oxides and unpinning of Fermi level on compound semiconductors in general. A 0.5-mum gate-length MOSFET with an Al₂O₃ gate oxide thickness of 8 nm shows a gate leakage current less than 10^-4 A/cm² at 3-V gate bias, a threshold voltage of 0.25 V, a maximum drain current of 367 mA/mm, and a transconductance of 130 mS/mm at drain voltage of 2 V. The midgap interface trap density of regrown Al₂O₃ on In_0.53Ga_0.47As is ~1.4 x 10¹²/cm² ldr eV which is determined by low-and high-frequency capacitance-voltage method. The peak effective mobility is ~1100 cm² / V ldr s from dc measurement, ~2200 cm²/ V ldr s after interface trap correction, and with about a factor of two to three higher than Si universal mobility in the range of 0.5-1.0-MV/cm effective electric field.     

Crystal growth, spectroscopy, and laser characteristics of Ti:Al2O3

The vertical-gradient-freeze technique has been used to grow laser-quality Ti:Al₂O₃ single crystals. Ti³⁺ -Ti⁴⁺ pairs have been shown to be responsible for the residual infrared absorption. Room-temperature oscillator and amplifier experiments are reviewed