Endurance Behavior Research Articles

Nanocrystal memories for FLASH device applications

Nanocrystals memory cells, in which the conventional polysilicon floating gate is replaced by an array of silicon nanocrystals, have been fabricated and characterized. Single cells and cell arrays of 1 Mb and 10 k have been realized by using a conventional 0.15 μm FLASH technology. Si nanocrystals are deposited on top of tunnel oxide by chemical vapor deposition. Properties of the memory cell have been investigated both for NAND and NOR applications in terms of program/erase window and programming times. Suitable program/erase threshold voltage window can be achieved with fast voltage pulses by adequate choice of tunnel and control dielectric. The feasibility of dual bit storage is also proven showing that the nanocrystals are separated and the inter-dot tunneling is inhibited. Good endurance and retention behaviors are demonstrated even after long cycling.

Nanocrystal memories for FLASH device applications

Nanocrystals memory cells, in which the conventional polysilicon floating gate is replaced by an array of silicon nanocrystals, have been fabricated and characterized. Single cells and cell arrays of 1 Mb and 10 k have been realized by using a conventional 0.15 μm FLASH technology. Si nanocrystals are deposited on top of tunnel oxide by chemical vapor deposition. Properties of the memory cell have been investigated both for NAND and NOR applications in terms of program/erase window and programming times. Suitable program/erase threshold voltage window can be achieved with fast voltage pulses by adequate choice of tunnel and control dielectric. The feasibility of dual bit storage is also proven showing that the nanocrystals are separated and the inter-dot tunneling is inhibited. Good endurance and retention behaviors are demonstrated even after long cycling.

Humidity and reflow resistance of flip chip on foil assemblies with conductive adhesive joints

The drive toward new first level interconnection technologies is running in parallel with the need to study their reliability as such, as well as in further processes such as second level reflow soldering. Both material properties and process settings have a significant effect on the reliability of adhesive interconnections of flip chips on flexible foil substrates. Integrated circuits (ICs) with pitches of 200 and 300 /spl mu/m bonded on two different foil types were subjected to various moisture preconditioning treatments, and subsequently reflow soldered. Measurements of the daisy chain resistance are used to monitor the yield before and after reflow testing, and to qualify the endurance behavior in the 85/spl deg/C/85% RH stress test. We address here the possible failure mechanisms.

Simultaneous hot-hole injection at drain and source for efficient erase and excellent endurance in SONOS flash EEPROM cells

An efficient erase technique is presented for SONOS EEPROM cells, using the concomitant hot-hole injection (HHI) at the drain and the source. Electrons trapped during the programming are thus fully eliminated throughout the entire channel, securing thereby a satisfactory cell endurance behavior. Additionally in the present HHI scheme the voltage applied at the common bulk terminal enables efficient erase in the entire erase sector. Also, HHI is quantitatively shown much more efficient for erase, compared with Fowler-Nordheim (F-N) tunneling. Finally, the elimination of trapped electrons throughout the entire channel is shown crucial for achieving a satisfactory cell endurance behavior.

Location of holes in silicon-rich oxide as memory states

The induced changes of the flatband voltage by the location of holes in a silicon-rich oxide (SRO) film sandwiched between two thin SiO2 layers [used as gate dielectric in a metal–oxide–semiconductor (MOS) capacitor] can be used as the two states of a memory cell. The principle of operation is based on holes permanently trapped in the SRO layer and reversibly moved up and down, close to the metal and the semiconductor, in order to obtain the two logic states of the memory. The concept has been verified by suitable experiments on MOS structures. The device exhibits an excellent endurance behavior and, due to the low mobility of the holes at low field in the SRO layer, a much longer refresh time compared to conventional dynamic random access memory cells.

Effects of ion implantation on microstructure, endurance and wear behavior of IBAD MoS 2

Thin MoS 2 coatings were prepared on steel and Si substrates via ion-beam assisted deposition using conditions known to produce dense, basal oriented microstructures. After deposition, the coated substrates were irradiated with 180 keV Ar 2+ ions at doses of 1×10 15, 1×10 16, and 5×10 16 ions/cm 2. Microstructures of as-deposited and ion irradiated MoS 2 coatings were examined using X-ray diffraction, high resolution transmission electron microscopy, and micro-Raman spectroscopy. Friction, wear and endurance were examined under both unidirectional and reciprocating sliding conditions in dry air. The lowest ion irradiation dose altered the initial microstructure, producing basal oriented, nearly defect-free crystalline domains of MoS 2 in an amorphous matrix; at the highest dose the coatings were nearly amorphous, but the remaining MoS 2 showed mixed orientation. Ion irradiation of the MoS 2 coatings did not significantly modify the friction behavior, and only at the highest dose was the endurance altered, decreasing by more than 75%. Two changes in wear behavior were observed in the highest dosed coatings: (1) accelerated wear of the coating and (2) elimination of solid lubricant reservoirs. Destruction of the solid lubricant replenishment process resulted in premature failure of the highest dosed coating.

Degradation of Ferroelectric Pb(Zr,Ti)O3 Under Reducing Conditions

AbstractThe degradation mechanism of Pb(Zr,Ti)O3 (PZT) under reducing conditions was revealed. In contrast to the significant decrease in the sample weight of SrBi2Ta2O9 due to decomposition, the weight of Pb(Zr,Ti)O3 samples change little during H2-annealing at typical process temperatures. Although no apparent changes were detected by thermogravimetric and x-ray diffraction measurements after annealing, the PZT material did actually change. The main mechanism of the degradation is introduction of oxygen defects into the materials. The oxygen defects produce a donor level within the band gap, and light absorption by this donor level accounts for the change in sample appearance from white to black. Different endurance behaviors of materials against reducing conditions were also found: PbZrO3 decomposes through oxygen dissociation more easily than PbTiO3. Oxygen atoms in PbZrO3 are more weakly bonded to Zr than to Ti in PbTiO3 because of a significant anti-bonding component in the hybridized orbitals.

NO/O 2 /NO plasma-grown oxynitride filmson strained-Si 1- x Ge x

The growth and electrical properties of high quality ultrathin oxide and oxynitride films on strained-Si/sub 0.74/Ge/sub 0.26/ layers using microwave O/sub 2/, NO and NO/O/sub 2//NO-plasma are reported. A significant improvement in the dielectric endurance and charge trapping behaviour under Fowler-Nordheim (F-N) constant current stressing is observed for NO/O/sub 2//NO grown oxynitride films.

Low-Temperature Synthesis of SrBi2Ta2O9 Ferroelectric Thin Films through the Complex Alkoxide Method: Effects of Functional Group, Hydrolysis and Water Vapor Treatment

SrBi2Ta2O9 (SBT) ferroelectric thin films were synthesized at lower temperatures by the sol–gel method using complex alkoxides. The effects of the complex alkoxide functional group, the amount of water used in hydrolysis, and a mixture of water vapor and oxygen flow during calcination, on the crystallization, the microstructural development, and the ferroelectric properties of the SBT thin films were addressed. The film which was deposited from complex alkoxide solutions and then calcined at 250°C in the mixture, contained a relatively smaller amount of the remaining alkoxy groups, and therefore, crystallized to SBT via rapid thermal annealing at temperatures below 500°C in an oxygen flow. Crystallinity improved significantly and the microstructure was able to develop up to 650°C. Remarkable grain growth was observed particularly in the SBT thin film deposited from the ethanolic solution of the complex ethoxide. Film annealed at 650°C exhibited the saturated P–E hysteresis loop and improved endurance behavior.

Chemical routes for low-temperature processing of layer-structured perovskite thin films

A complex alkoxide, Sr[BiTa(OC2H5)9]2, was prepared as the precursor for SrBi2Ta2O9 (SBT) thin films. The film deposited by using the ethanolic solution of the precursor crystallized to SBT below 500°C by rapid thermal annealing in an oxygen flow. The calcination at 250°C in a mixture of water vapor and oxygen following the rapid thermal annealing was found to be effective for improvement of the crystallinity and the development of the microstructure in the SBT films. The 650°C annealed film exhibited the saturated hysteresis loop at 5 V and improved endurance behavior.

Failure mechanisms during isothermal fatigue of SiC/Ti-24A1-11Nb composites

Failure mechanisms during isothermal fatigue of unidirectional SiC/Ti-24A1-11Nb (at.%) composites have been determined by microstructural analysis of samples from tests interrupted prior to the end of life and from tests conducted to failure. Specimens from three regions of life were examined based on the maximum strain from a fatigue life diagram: Region I (high strain), Region II (mid-strain) and Region III (low strain). Crack lenghts were also measured from interrupted samples and compared based on temperature (23–815 °C), region of life and numbers of cycles. Region I was controlled by fibre-dominated failure. A transition zone was observed between Regions I and II due to competition between failure mechanisms. Failure in Region II was generally described as surface-initiated cracking with varying amounts of fibre bridging. However, the specific descriptions of crack propagation through the fibres and matrix varied with strain and temperature over this broad region. Region III exhibited endurance behaviour at 23 °C with no cracking after 10 6 cycles. However at 425 °C, surface-initiated cracking was observed after 10 6 cycles with fractured fibres in the crack wake. If endurance behaviour exists for conditions of isothermal fatigue in air at temperatures of ⩾ 425 °C, it may only be found at very low strains and at greater than 10 6 cycles.

A new universal fatigue machine for plastics and composites

Polymers and composites are more and more involved as structural parts in industry, and so to help the designer we need specific data such as long term mechanical properties (creep, relaxation, fatigue). In this paper we present the fatigue test, by which we study the behavior under repeated loading. The failure process in fatigue can be always depicted as a sequence of two steps: 1. (1) Crack initiation 2. (2) Crack propagation A number of investigations were carried out on the crack propagation step, ignoring the initiation step, by working on precracked samples. This necessitates specialized equipment, methodologies and analysis. This paper is more devoted to ‘endurance behavior’, which is the result of the two previous mechanisms (initiation first and then propagation). After a short presentation of the specific definitions and means of fatigue testing, we present a new universal fatigue testing machine, on which we can run any kind of test under different conditions (temperature, environment, frequency, stress or strain control, alternate or ondulate bending, torsion, tensile, etc.).

Sputtering of Lead-Based Ferroelectrics

AbstractPbTiO3(PT), Pb1-xLaxTi1-x/4O3(PLT) and PbZrxTi1-xO3(PZT) thin films were prepared by rf magnetron sputtering. It was found that the thin films have remarkably large pyroelectric effect and high figures of merit for infrared sensors without poling treatment. High performance pyroelectric infrared sensors (single element and linear array) were fabricated by using the PLT(x=0.1) thin films with the new structures and the device process. This type of sensor is carried on the air conditioner to detect a thermal environment. The PZT thin films with x=0.9 showed a large remanent polarization of 46μC/cm2 and small coercive force of 28kV/cm. In addition, good endurance behavior (no degradation of Pr after 1011 cycles) was observed. Recent activities of ferroelectric thin film research in Japan is also reported.

Influences of Atmospheric‐Pressure Reoxidation on the Ultrathin Oxide Films Nitrided in Atmospheric NH 3 Ambient

Effects of thermal reoxidation on the time to dielectric breakdown of ultrathin nitrided oxides have been studied. At atmospheric pressure, it was found that a proper reoxidation processing is necessary for optimizing the charge‐to‐dielectric breakdown of an arbitrarily nitrided 100Å‐thick oxide. For the more heavily nitrided oxides, a higher‐temperature or longer‐time reoxidation is required to reduce the large quantity of electron traps in the nitrided films. A superior endurance behavior with a stress current of 100 mA/cm2 was achieved for the ultrathin oxides nitrided at 900°C for 30 min and subsequently reoxidized at 950°C for 30 min as the pure oxide exhibited a charge‐to‐breakdown of 27 C/cm2with the same current density. Positive fixed charges via the nitrogen radicals or defects were shown to be the main cause of the negative flatband shift of the nitrided or reoxidized oxides.

Metal-oxide-semiconductor characteristics of rapid thermal nitrided thin oxides

The electrical properties of thin nitrided oxide (∼100 Å) formed by rapid thermal nitridation (RTN) in pure NH3 have been studied. It is found that the current-voltage characteristic of RTN oxides follows a Fowler–Nordheim tunneling behavior with modifications caused by electron trapping processes at the oxide surface and interface. The trapping density is dependent on the RTN conditions. At the interface, both fixed charge (Nf) and interface state (Dit) densities exhibit turnaround phenomena when the RTN process proceeds. The maximum values of Nf and Dit at the turnaround points are lower for the higher temperature RTN, suggesting a viscous flow related strain relieving mechanism associated with RTN of thin oxides. Films with superior endurance behavior (QBD=20.4 C/cm2 compared with QBD=5.1 C/cm2 of thermal oxide under 10 mA/cm2 constant current stress) have been obtained by RTN at 1000 °C, 10 s.

Temperature and Water Velocity Effects on the Swimming Performances of Young-of-the-Year Striped Mullet (Mugil cephalus), Spot (Leiostomus xanthurus), and Pinfish (Lagodon rhomboides)

Swimming performances of young-of-the-year striped mullet (Mugil cephalus), spot (Leiostomus xanthurus), and pinfish (Lagodon rhomboides) were tested by examining the combination of physical endurance and swimming behavior to provide information on potential fish entrainment and impingement problems at industrial intakes. Tests were conducted at three temperatures (15–25 °C) and six water velocities (12–48 cm/s). Fish lengths ranged from 1.4 to 7.0 cm TL. Fish tested at higher temperatures exhibited increased time for steady swimming and for impingement avoidance. Temperature was also positively correlated with maximum swimming speeds and with the number of bursts performed during drift–burst activity (drifting with the current and returning upstream with a burst of swimming). Increased water velocities resulted in decreased times of steady swimming and impingement avoidance, and reduced drift–burst activity. Larger fish avoided impingement longer and had faster maximum swimming speeds; however, smaller fish showed stronger rheotaxis and swam steadily for longer periods at equal water velocities. Abnormally heavy mullet and spot had reduced capabilities for position maintenance (steady swimming) which may decrease their ability to avoid impingement. Key words: swimming speeds, temperature, water current, impingement, behavior, mullet, spot, pinfish