Microstructure and dielectric response of SrTiO3/NdGaO3 interdigitated capacitors

Epitaxial strontium titanate (SrTiO₃ or STO) thin films were prepared by an off-axis pulsed laser deposition technique on neodymium gallate (NdGaO₃ or NGO) substrates held at temperature of 820 °C. This technique allows different film growth rates in a deposition. Coplanar capacitors were fabricated and dielectric responses were measured at 1 MHz and at 2 GHz, and from 300 K to 4 K. The electric field tunability of the dielectric constant and loss tangent were taken with a range of electric field. The structure and morphology of the films were analyzed using high-resolution X-ray diffractometry and atomic force microscopy, respectively. The results showed that the films are crystalline with (1 0 0) orientation and the grains are columnar. Increased in-plane grain size and reduced surface to volume ratio were found to play a major role in improved performance of the film coplanar capacitors. The film with the growth rate of approximate 40 Å/min showed the highest change in the dielectric constant with an electric field of 4 V/μm. The film also showed the largest in-plane grain size of about 3000 Å.     

钛宝石的晶体生长与性能

本文采用提拉法生长出了高光学质量的Ti:Al2O3单晶,讨论了生长和退火工艺对晶体质量的影响。在室温条件下,14.8mm长的TiAl2O3激光棒,以35mJ的Nd:YAG倍频激光泵浦,在带有色散元件的激光腔中,获得了6.4mJ(780nm)激光输出,激光效率为18%。     

MgO-Y_2O_3对热压烧结Al_2O_3性能的影响

以高纯的硫酸铝氨分解的无定形Al2O3为原料,MgO-Y2O3为烧结助剂,在N2气氛下热压烧结制备Al2O3陶瓷。研究了烧结助剂掺量对Al2O3材料的相组成、显微结构、烧结性能、力学性能、热导率和介电性能的影响。结果表明:所制Al2O3陶瓷具有细晶的显微结构特征和超高的抗弯强度。随着MgO-Y2O3掺量的增加,晶粒尺寸、抗弯强度和热导率先增大后减小,而介电损耗则呈现先减小后增大的变化规律。当MgO和Y2O3掺量均为质量分数2%时,Al2O3陶瓷呈现为较佳的综合性能:抗弯强度达最大值为603 MPa,热导率为36.47 W.m–1.K–1,介电损耗低至6.32×10–4。     

Optical properties and tunable laser action of Verneuil-grownsingle crystals of Al2O3:Ti3+

Using the Verneuil technique, the authors have grown large single crystals of Al₂O₃:Ti³⁺ having concentrations up to 0.15%. Laser action was observed in this material, tunable over the range 700-810 nm. Losses in the 800-nm region are less than 0.03 cm^-1 (below the detection limit in the measurements)     

BHA:Cr~(3+)(BeO·3Al_2O_3:Cr~(3+))晶体的荧光特性

本文对新晶体BHA:Cr~(3+)(BeO·3Al_2O_3:Cr~(3+))的荧光谱进行了仔细辨认,发现晶体中存在着几种不同的发光中心。提出了不同Cr离子中心之间的能量传递模型。     

Residual infrared absorption in as-grown and annealed crystals ofTi:Al2O3

Data for as-grown and partially oxidized samples of Ti:Al₂ O₃ grown by the vertical-gradient-freeze technique show that the residual infrared absorption in these samples is largely due to Ti³⁺-Ti⁴⁺ pairs. In agreement with this pair model, the residual absorption in as-grown samples has been substantially decreased by annealing in a reducing atmosphere. Data for an as-grown crystal grown by the heat exchanger method indicate the presence of a second mechanism for residual absorption that may set a lower limit on the ratio of this absorption to the Ti⁺³ absorption used to pump laser emission     

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.     

Improved electrical properties using SrTiO3/Y2O3 bilayer dielectrics for MIM capacitor applications

In this paper, we show that the capacitance–voltage linearity of MIM structures can be enhanced using SrTiO₃ (STO)/Y₂O₃ dielectric bilayers. The C(V) linearity is significantly improved by combining two dielectric materials with opposite permittivity-voltage responses. Three STO/Y₂O₃ stacks with different thicknesses were realized and compared to a 20 nm STO single layer structure. We observed that an increase in the Y₂O₃ thickness leads to an improvement in the voltage linearity, while maintaining an overall capacitance density greater than 10 fF/μm².     

Layered Al2O3-TiO2 compositedielectric resonators

Aluminium oxide displays a very low tanδ at microwave frequencies. It also possesses a remarkably high thermal conductivity, ideal for heat dissipation in high power satellite filters. However, its temperature coefficient of the resonant frequency (τ_f) is approximately 60 ppm/K. It is shown that the application of a film of titanium oxide which has a T_f of opposite sign (45O ppm/K) produces a composite in which the τ_f can be tuned to be zero over a wide temperature range. The tanδ of the composite at zero T_f is 3.3×10⁵ (Q=30000) at room temperature and at 10 GHz     

Electrical and interfacial characteristics of nanolaminate (Al2O3/ZrO2/Al2O3) gate stack on fully depleted SiGe-on-insulator

The structural and electrical characteristics of a novel nanolaminate Al₂O₃/ZrO₂/Al₂O₃ high-k gate stack together with the interfacial layer (IL) formed on SiGe-on-insulator (SGOI) substrate have been investigated. A clear layered Al₂O₃ (2.5 nm)/ZrO₂ (4.5 nm)/Al₂O₃ (2.5 nm) structure and an IL (2.5 nm) are observed by high-resolution transmission electron microscopy. X-ray photoelectron spectroscopy measurements indicate that the IL contains Al-silicate without Ge atom incorporation. A well-behaved C–V behavior with no hysteresis shows the absence of Ge pileup or Ge segregation at the gate stack/SiGe interface.     

Dielectric thinning model applied to metal insulator metal capacitors with Al2O3 dielectric

The extrinsic fails of metal insulator metal capacitors (MIMCAPs) with Al₂O₃ dielectric are modeled by a thinning model that is based on the intrinsic reliability model and the assumption that the extrinsic fails behave like an intrinsic dielectric with a reduced thickness. The intrinsic reliability model is developed from voltage acceleration experiments at four temperatures and four dielectric thicknesses. Voltage and thickness dependence of the logarithm of the intrinsic lifetime scales with the electric field and the temperature dependence is described by an Arrhenius factor. The voltage acceleration is not temperature dependent. The thinning model is shown to consistently describe acceleration experiments with random extrinsic fails of unknown root cause at low defect density (0.1 cm⁻²) as well as a systematic extrinsic failure mechanism caused by process induced plasma damage. It is also shown that the random extrinsic fails that were investigated on large area teststructures can be extrapolated to much smaller product typical capacitors. A criteria based on the stored energy is derived that allows to decide, whether an extrinsic fail will cause product failure. These results allow a quantitative prediction of early product fails due to the MIMCAP.     

Single-frequency Ti:Al2O3 ring laser

Over 500 mW of single-frequency power has been obtained from a Ti:Al₂O₃ ring laser pumped by 10 W (all lines) from an argon ion laser. The ring laser can be tuned from 750 to 850 nm while maintaining more than 100 mW in single-frequency operation without realignment or a change of optics. The free-running frequency stability of the laser is 3 MHz. Thermal effects cause changes in the ring cavity parameters, limiting the output power. This ring laser has also been operated with an acoustooptic mode locker to obtain 200-ps mode-locked pulses at 250 MHz with nearly the same average power as in single-mode operation     

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     

Magnetic properties of Co- and Mn-implanted BaTiO3, SrTiO3 and KTaO3

Implantation of Co or Mn into single-crystal BaTiO₃(K), SrTiO₃ or KTaO₃(Ca), followed by annealing at 700 °C, produced ferromagnetic behavior over a broad range of transition metal concentrations. For BaTiO₃, both Co and Mn implantation produced magnetic ordering temperatures near 300 K with coercivities 70 Oe. The M–T plots showed either a near-linear decrease of magnetization with increasing temperature for Co and a non-Brillouin shaped curve for Mn. No secondary phases were detected by high-resolution X-ray diffraction. The same basic trends were observed for both SrTiO₃ and KTaO₃, with the exception that at high Mn concentrations (5 at.%) the SrTiO₃ was no longer ferromagnetic. Our results are consistent with recent reports of room temperature ferromagnetism in other perovskite systems (e.g. LaBaMnO₃) and theoretical predictions for transition metal doping of BaTiO₃ [Nakayama et al., Jap. J. Appl. Phys. 40 (2001) L1355].     

A Ti:Al2O3 master-oscillator/power-amplifiersystem

The authors have constructed a multistage Ti:Al₂O₃ master-oscillator/power-amplifier system which generates 115-ns, 0.38-J pulses at 800 nm. The system is tunable from 760 to 825 nm and has a repetition rate of 10 Hz. Measurements of the output pulse demonstrate near-diffraction-limited performance and a Fourier-transform-limited bandwidth of ~4 MHz     

Electrical properties of CuInSe2 single crystals

Various bulk electrical properties and device characteristics have been measured. It has been shown that the majority carrier type is dependent on crystal stoichiometry. Mobilities of 660 cm²/V sec and 30 cm²/V sec have been measured for n-and p-type samples, respectively. Rectifying contacts and p-n junctions have been investigated by small signal analysis and the associated doping levels and equilibrium band diagrams have been determined. Photovoltage measurements on rectifying contacts have shown that the band-gap has a value of 0.95 ± 0.01eV.     

Co_2O_3掺杂对0.965MgTiO_3-0.035SrTiO_3微波介质陶瓷性能的影响

采用传统电子陶瓷制备方法研究了Co2O3(1.5%～5.0%,质量分数)掺杂的0.965MgTiO3-0.035SrTiO3(MST0.035)微波介质陶瓷,分析了Co2O3含量对MST0.035陶瓷的烧结性能、晶相结构、显微形貌以及微波介电性能的影响。结果表明:Co2O3的掺杂促进了MST0.035陶瓷的烧结。随着Co2O3掺杂量的增加,陶瓷介电常数略有下降,谐振频率温度系数以及品质因数增加,同时中间相MgTi2O5逐渐减少直至完全消失。当Co2O3掺杂量为质量分数3.0%时,MST0.035陶瓷的烧结温度由1 380℃降低到1 290℃,其烧结所得的样品具有优良的微波介电性能:谐振频率温度系数τf=–2.53×10–6/℃,高的品质因数Q·f=19 006 GHz和介电常数εr=20.5。     

Laser micromachining of SrTiO3 single crystal

Laser micromachining of piezoelectric materials has many advantages over other etching techniques for the fabrication of ultrasound transducer linear arrays for medical imaging. It can achieve high aspect ratios and high etch rates without the use of complicated photolithography techniques. We have investigated a laser projection etch technique to make linear arrays in single crystal (0 0 1) SrTiO₃ substrates as a model of epitaxial piezoelectric thick film heterostructure. Feature sizes of 17.5 μm were obtained with depth to width aspect ratios of 4:1. The effect of laser fluence on etching was studied and it was found that straighter sidewalls and flatter trench floors were achieved as laser fluence increases. On the other hand, higher laser fluence caused increase in heat affected zone by post-pulse plasma and made the top surfaces rougher because of the accumulation of evaporated materials. Clean top surfaces of the features were achieved by deposition and subsequent lift off of a YBa₂Cu₃O₇ sacrificial layer. In addition, the phases of recast layers on the sidewalls were characterized by four-circle X-ray diffraction with 2-D area detector before and after removed with a wet chemical etch solution. It was found that the use of the wet etchant could remove the thin polycrystalline recast layers.     

Distribution and generation of traps in SiO2/Al2O3 gate stacks

In this work we combine charge-pumping measurements with positive constant voltage stress to investigate trap generation in SiO₂/Al₂O₃ n-MOSFET. Trap density has been scanned either in energy or in position based on charge-pumping (CP) measurements performed under different operating conditions in terms of amplitude and frequency of the gate pulse. Our results have revealed that the traps are meanly localized shallow in energy level, deeper in spatial position and they are mostly generated near the Si/SiO₂ interface.