Platinum alloys and iridium bottom electrodes for perovskite based capacitors in dram applications

Abstract

Two types of potential bottom electrode structures for integration of ferroelectric materials in DRAM technology have been investigated: one based on iridium, the other based on platinum alloyed with oxygen gettering elements, such as B and Ti. The electrode structures, deposited on Si substrates, have been annealed in oxygen at 650°C for 30 min and characterized by RBS and AES. It was found that alloying the Pt with 3% of alloying elements had no beneficial effect and did not improve the properties of Pt as a barrier to oxygen diffusion. At the investigated annealing conditions, oxygen diffuses through Pt or its alloys and oxidizes the underlaying material. On the other hand, a thickness of 1100 Å of Ir was found to provide a barrier to oxygen diffusion under the same conditions. A layer of Ta in contact with Pt or Ir was found to deteriorate the barrier properties of both metals at the investigated annealing conditions.     

Dielectric properties, of metallized paper-film capacitors

A capacitor formed of fluid-impregnated paper metalized on one side and a polymer film results in a relaxation peak caused by the much more rapid polarization of the dielectric fluid impregnated paper relative to the polymer film. This results in the capacitance being a function of frequency, with a substantial increase in capacitance at very low frequencies. A theory for such a capacitor is developed and compared with measurements on actual capacitors with relatively good agreement. The implications of the theory for discharge current and discharge efficiency are discussed.     

电化学电容器用多孔炭的性能调节

提出了电化学电容器所用多孔炭材料的“六高”性能指标的大致范围,即:①高比表面积,>1 500 m2/g;②高堆积密度,比孔容<1.0 ml/g;③高中孔率,孔径12~40 nm的孔容量≥0.4 ml/g,孔径40 nm以上的中孔容量<0.05 ml/g;④高电导率,>1.0 S/cm;⑤高纯度,灰分<0.1%;⑥高性价比。分析了这些性能指标的必要性,论述了影响“六高”性能的因素及相互关系,总结了调节“六高”性能的经验。     

Fabrication and properties of one-mask-patterned ferroelectric integrated capacitors

A one-mask-patterned ferroelectric capacitor test structure designed with a 0.5-μm feature size was fabricated. Oxygen plasma treatment after dry etching decreased the leakage current to as low as that of as-deposited film. These one-mask-patterned ferroelectric capacitors, with switching charge almost equal to as-deposited film, were successfully fabricated. Ferroelectric memories as dense as dynamic random access memories will become possible with this technology. However, the leakage current density for micron-sized capacitors is 2 to 10 times that of large capacitors. The leakage current in small capacitors is increased due to perimeter leakage that runs through the damaged region on the capacitor sidewall. © Scripta Technica, Inc. Electr Eng Jpn, 121(1): 43–50, 1997     

Reliability properties of low-voltage ferroelectric capacitors and memory arrays

We report on the reliability properties of ferroelectric capacitors and memory arrays embedded in a 130-nm CMOS logic process with 5LM Cu/FSG. Low voltage (<1.5 V) operation is enabled by the 70-nm thick MOCVD PZT ferroelectric films. Data loss resulting from high temperature bakes is primarily caused by the imprint effect, which shows /spl sim/1.5 eV time-to-fail activation energy. Excellent bit endurance properties are observed on fully packaged memory arrays, with no degradation up to 10/sup 13/ write/read polarization switching cycles. Retention measured after 10/sup 12/ switching cycles demonstrates no degradation relative to arrays with minimal cycling.     

Preparation and properties of sol-gel derived PZT thin films for decoupling capacitor applications

Abstract

The use of ceramic thin films as decoupling capacitors offers the possibility of capacitor integration within the integrated circuit (IC) package, and potentially, directly onto the IC itself. Since these configurations minimize series inductance, higher operational speeds are possible. In the present study we have investigated the dielectric and leakage characteristics of sol-gel PZT films. For compositions near the morphotropic phase boundary, dielectric constants of 1000, and loss tangents of about 0.02, were observed. The current-voltage behavior of the capacitors was characterized by a non-linear response, and significant asymmetry in both the leakage and breakdown characteristics as a function of bias sign was observed. Breakdown fields for PZT 53/47 thin films were typically ～800 kV/cm at 25°C. We have also studied the effects of La and Nb dopant additions and alternate firing strategies on film leakage characteristics. Donor doping at 2–5 mol% lowered leakage currents by a factor of 10³ For films prepared by a multilayering approach, firing each layer to crystallization resulted in leakage currents that were a factor of 10² lower than films prepared by the standard process.     

Preparation and properties of strontium barium niobate based glass-ceramics for energy storage capacitors

Na₂O–BaO–SrO–Nb₂O₅–B₂O₃–SiO₂ glass-ceramics were prepared by melt-casting followed by controlled crystallization. X-ray diffraction results show that Ba_0.27Sr_0.75Nb₂O_5.78 with tungsten bronze structure formed as the dielectric phases from the glass matrix at 800°C. However, a secondary phase NaSr_1.2Ba_0.8Nb₅O₁₅ occurs when crystallization temperature exceeds 850°C. The glass-ceramics exhibit excellent stability in permittivity values from room temperature to 200°C and low dielectric losses below 0.05. Electrical testing demonstrates that the breakdown strength increases with crystallization temperature. The P–E characteristics at room temperature do not show any clear ferroelectric behavior. The glass-ceramic material heated at 800°C/3 h + 950°C/3 h shows a breakdown strength of 1400 kV/cm and its energy storage density can reach up to 4.0 J/cm³, which may be a strong candidate for high energy density storage capacitors for portable or pulsed power applications.     

Dielectric properties and schottky barriers in silver tantalate-niobate thin film capacitors

Abstract

Submicron thick ferroelectric Ag(Ta,Nb)O₃ films have been pulsed laser deposited on the bulk Pt₈₀lr₂₀ polycrystalline substrates. They are ferroelectric at temperatures below 125 K with the remnant polarization of 0.4 μC/cm² @ 77K and paraelectric at higher temperatures with tanδ@ 100 kHz as low as 0.015. Extensive I-V characterization has been performed in a wide temperature range 77 K to 350 K for vertical Me/Ag(Ta,Nb)O₃/Pt₈₀Ir₂₀ capacitive cells, where the metals Me = Pd, Au, Cr, and Al have been used as a top electrode. The electronic transport in thin Me/Ag(Ta,Nb)O₃/Pt₈₀Ir₂₀ capacitors follows the Schottky emission mechanism with the barrier height for the Pd, Au, Cr, and Al of 0.85, 0.8, 0.74, and 0.69 eV, respectively.     

Measurement and simulation of partial switching in ferroelectric PZT thin-films

Abstract

In digital memory applications, metal ferroelectric metal (MFM) capacitors are typically fully switched from one polarization state to the other, with the difference in displacement current allowing determination of the cell state. However, by applying a pulse of insufficient amplitude and/or duration to fully switch the ferroelectric, such a device may be partially polarized. Here, the measurement of partial switching in sol-gel derived PZT MFM capacitors due to applied voltage pulses is reported. SPICE, a commonly used circuit simulation program, has been modified to incorporate a ferroelectric capacitor device model. The MFM device model added to SPICE is reviewed, and the simulation of partial switching is demonstrated. Simulation results modeling the PE hysteresis loops and switching transients due to applied voltage steps closely match those measured in the laboratory. We conclude with the modeling of incomplete switching due to applied pulses of insufficient amplitude to cause polarization saturation, which is attributed to the polycrystalline nature of the thin-films.     

Measuring, modeling, and decoupling of saturation-inducedsaliencies in carrier-signal injection-based sensorless AC drives

The focus of this paper is the measuring, modeling, and decoupling of saturation-induced saliencies in carrier-signal injection-based sensorless control. First, techniques for the measurement of saturation-induced saliencies are presented. The goal of these measurements is to provide useful information on the position and magnitude of the various saturation-induced saliencies. Using the results from several different experimental measurements, models are developed explaining the source and behavior of the saturation-induced saliencies. The paper concludes by presenting methods for decoupling the effects caused by the parasitic saturation-induced saliencies, eliminating the errors that they cause in rotor position or flux angle estimation     

Structure and electrochemical properties of titanate perovskite with in situ exsolution as a ceramic electrode material

Journal of Electroceramics - In this work, the structure and electrochemical properties of titanate ceramics with in situ Ni exsolution are investigated to identify the structure-performance...     

Maximum savings approach for location and sizing of capacitors in distribution systems

This paper proposes a computationally efficient methodology for the optimal location and sizing of static and switched shunt capacitors in radial distribution systems. The problem is formulated as the maximization of the savings produced by the reduction in energy losses and the avoided costs due to investment deferral in the expansion of the network. The proposed method selects the nodes to be compensated, as well as the optimal capacitor ratings and their operational characteristics, i.e. fixed or switched. After an appropriate linearization, the optimization problem was formulated as a mixed-integer linear problem, suitable for being solved by means of a widespread commercial package. Results of the proposed optimizing method are compared with another recent methodology reported in the literature using two test cases: a 15-bus and a 33-bus distribution network. For the both cases tested, the proposed methodology delivers better solutions indicated by higher loss savings, which are achieved with lower amounts of capacitive compensation. To calculate the energy savings and the deferral investment cost exactly, a load flow for radial distribution network is executed before and after the compensation. The proposed method has also been applied for compensating to an actual radial distribution network served by AES-Venezuela in the metropolitan area of Caracas. A convergence time of about 4 s after 22,298 iterations demonstrates the ability of the proposed methodology for efficiently handling compensation problems.     

Dielectric breakdown in high-ε films for ulsi DRAMs: III. Leakage current precursors and electrodes

Abstract

A somewhat qualitative review of leakage currents J(V,t) in perovskite oxides is presented. It is stressed that space-charge-limited currents (SCLCs) are not alternatives to ionic conduction, Schottky emission, Poole-Frenkel, or Fowler-Nordheim tunneling, but can occur whenever currents due to any of those mechanisms reach a certain threshold and are no longer limited by the details of the metal electrode-ferroelectric interface. Standard metal-semiconductor band models that exclude surface states fail qualitatively to account for the experimental dependences of leakage currents and breakdown voltages on electrode work function; the correct model is metal-n-p-n-metal, with surface donor-state trapping. A discussion of conduction properties in these materials is presented from an ionic conductor viewpoint.     

Selecting ratings for capacitors and reactors in applicationsinvolving multiple single-tuned filters

This paper focuses on the selection of ratings for capacitors and air-core reactors used in multiple single-tuned harmonic filter configurations. Digital transient simulations of an example power system demonstrate the exceptionally high voltage and current stresses placed upon filter components in these configurations. Design guidelines for increasing the component ratings to account for the extra stresses are described. A comparison between traditional rating methods and the proposed methods are presented for the example system