A new concept for using a ferroelectric field effect transistor in a memory configuration is presented without the requirement of a negative voltage or an erase operation. The transistor is designed so that the accumulation sets in at a lower gate source voltage making it possible to reverse the polarization without applying a negative pulse to the gate.

The properties of nanoparticle aerosols of size ranging from 4.9 nm to 13 nm, generated by laser ablation of solid surfaces are described. The experimental system consisted of a pulsed excimer laser, which irradiated a rotating target mounted in a cylindrical chamber 4 cm in diameter and 18-cm long. Aerosols of oxides of aluminum, titanium, iron, niobium, tungsten and silicon were generated in an oxygen carrier gas as a result of a reactive laser ablation process. Gold and carbon aerosols were generated in nitrogen by non-reactive laser ablation. The aerosols were produced in the form of aggregates of primary particles in the nanometer size range. The aggregates were characterized using a differential mobility analyzer and electron microscopy. Aggregate mass and number concentration, electrical mobility size distribution, primary particle size distribution and fractal dimension were measured. System operating parameters including laser power (100 mJ/pulse) and frequency (2 Hz), and carrier gas flow rate (1 l/min) were held constant. A striking result was the similarity in the properties of the aerosols. Primary particle size ranged between 4.9 and 13 nm for the eight substances studied. The previous studies with flame reactors produced a wider spread in primary particle size, but the order of increasing primary particle size follows the same trend. While the solid-state diffusion coefficient probably influences the size of the aerosol in flame reactors, its effect is reduced for aerosols generated by laser ablation. It is hypothesized that the reduced effect can be explained by the collision-coalescence mechanism and the very fast quenching of the laser generated aerosol.

Conventional AND and NOR non-volatile memory array circuits utilizing a single ferroelectric memory field effect transistor (FEMFET) cell structure were simulated by using a BSIM3v3 based FEMFET compact model. It is shown that the use of the common V-pp/2 and V-pp/3 rules for programming a transistor in a FEMFET cell-array may cause the loss of stored information in adjacent memory cells due to disturb pulses.To overcome this problem we propose to back-bias the substrate during the write cycle, which extends the depletion region of the FEMFET to higher gate-source voltages, and thus reduces the influence of a disturb pulse on the polarization of the gate ferroelectric.In addition we discuss device improvements which reduce the susceptibility to data loss without back-biasing the substrate in order to minimize cell area.

The nanoparticle microreactor (NPMR) is a new concept that we have introduced to describe a very small-scale system capable of converting an aerosol precursor to solid particles. The liquid precursor of about 1 µl is injected by a syringe through a septum into a tubular evaporator of 1.0 cm 3 in volume with stopcocks at both ends. The evaporator has been preheated by a heating tape to a temperature sufficiently high for vaporization to occur in half a minute. By opening the stopcocks, the vaporized precursor is transported by a carrier gas stream into a quartz tube which is mounted along the axis of a tubular furnace. The nanoparticle aggregates produced in the reactor are sampled by deposition on an electron micrograph grid at the reactor exit. The NPMR was applied first to the synthesis of TiO 2 particles by thermal decomposition of titanium tetraisopropoxide (TTIP) in a nitrogen carrier gas, with TTIP concentrations varying from 1.0 to 7.0 mol% or 2.35×10 −6 to 1.65×10 −5 in TiO 2 volume loading, and decomposition temperatures from 300°C to 1000°C. Studies were made with a 2 mm reaction tube and a 4 mm tube with sheath gas. With the 2 mm tube, a considerable fraction of the TTIP precursor was consumed at the wall by surface reaction, resulting in very small particles. With the 4 mm tube, the primary particle size was comparable to that reported in the literature for steady flow experiments using a 22.2 mm tube. Primary particle sizes ranged from 200 to 400 nm. Depending on TTIP concentration and reactor temperature, the particles exhibited a bimodal size distribution, probably due to a two-stage nucleation. A fourfold increase in the gas flow rate had little effect on particle size, indicating that particle growth ended early, within one-fourth the tube length. Residence time in the reactor was between 0.35 and 1.4 s, and total run time about 1 min. The NPMR has potential for rapid assembly of large databases and is adaptable to combinatorial discovery of nanoparticles with novel properties. Design requirements for an ‘ideal’ aerosol microreactor are discussed briefly.

Nanoparticle chain aggregates (NCA) of inorganic oxides have elastic properties. The NCA of titania, alumina and iron oxide generated by laser ablation were deposited on an electron microscope grid. Expanding holes in the films on the grid produced by the electron beam caused the chains to stretch up to about twice their original length before snapping back. The NCA were several tenths of a micron long and were composed of 5–10 nm primary particles. Mechanisms for NCA elasticity are proposed. The application of these concepts to improving the properties of composites of NCA and molecular polymers (e.g., rubber) and to NCA coatings with special optical properties is discussed. The need to develop methods for the synthesis of NCA with prescribed primary particle size, chain length and other properties follows from these applications.

Chain aggregates of similar to7 nm titania particles exhibit elastic behavior when observed in the transmission electron microscope (TEM);(1,2) under tension produced by an expanding hole in the film, these nanoparticle chain aggregates (NCAs) stretch, and when the tension is relaxed, they contract. The film that coats the TEM grid on which the NCAs are deposited has an amorphous carbon side and a Formvar side. When the NCAs are deposited on the carbon side, the strained NCAs detach easily from the carbon layer and stretching does not occur. On the other hand, NCAs deposited on the Formvar side exhibit stretching and contraction probably because of the adhesion of the Formvar (poly(vinyl formal), mol wt 70 000-150 000) molecules to the ends of the particle chains. A similar phenomenon may explain the reinforcement of rubbery polymers by particulate fillers. Earlier observations of NCA behavior were made by using a conventional video camera with a speed of 30 frames/s (FPS). This was fast enough to follow the stretching but not the contraction process. An attempt was made to follow contraction using a high-speed camera (9000 FPS). The titania NCA stretched by about 10% and then contracted to 78% of the initial length. Inspection of the aggregate gate shape showed that chain segments folded after contraction. The length of the NCA oscillated in the direction of motion during stretching (similar to2 kHz) and contraction (similar to1 kHz).

A novel AND-type ferroelectric field effect transistor memory concept for solid state mass storage applications is described. Disturbance problems caused by disturbance pulses between adjacent memory cells are prevented by device improvements and by choosing appropriate programming and read voltages.The memory array presented here uses global source lines each of which is connected to its own sense amplifier. Disturbance free and fully functional operation of the memory concept has been demonstrated by circuit simulations. The results of the simulations yield a data access time comparable to DRAMs.

Previous studies have shown that nanoparticle chain aggregates (NCA) of titania are elastic [S. K. Friedlander, H. D. Jang and K. H. Ryu, Appl. Phys. Lett. 72, 1 (1998)]. The NCA were a few tenths of a micron long and composed of (approximately) 7 nm primary particles. They were produced by thermal decomposition of titanium tetraisopropoxide vapor in nitrogen. The goal of this study was to see whether the elastic behavior depends on (a) the material properties, (b) primary particle size, and (c) method of NCA formation. For this purpose, titania, alumina, and iron oxide NCA were generated by laser ablation. Rotating metal foil targets were mounted in a small cylindrical chamber and exposed to an excimer laser beam. The resulting aerosol was swept out by an oxygen stream. The generator was operated to produce NCA with similar mobility diameter and primary particle size. The NCA were deposited on the carbon or formvar films of an electron micrograph grid. Under the electron beam a hole develops in the carbon film in the neighborhood of the deposited NCA. The NCA then stretch and contract as described in our earlier study [S. K. Friedlander, H. D. Jang and K. H. Ryu, Appl. Phys. Lett. 72, 1 (1998)]. The titania, alumina, and iron oxide NCA generated by laser ablation all showed elastic behavior for primary particles smaller than about 10 nm. However, titania NCA composed of 36 nm primary particles did not exhibit elastic behavior indicating that very small primary nanoparticles are needed for this phenomenon to occur. The small scale stretching and contraction of chain segments were studied by measuring changes in the bond angles between adjoining particles and in the lengths of the segments studied. The elastic behavior is probably associated with local folding of chain segments due to van der Waals forces. Under tension, folded chains straighten but when the tension is relaxed, folds tend to reform but not reversibly. Rotation and sliding probably occur at the boundaries between particles during stretching. We hypothesize that elastic behavior is a general property of NCA composed of transition metal oxides with primary particles smaller than 10–15 nm; the phenomenon has now been observed for NCA produced in two ways, thermal decomposition and laser ablation. These phenomena may play a role in the action of nanoparticle additives such as fumed silica and carbon black used to improve the properties of rubber. NCA elasticity may also contribute to the ductile properties of nanoparticle compacts.

Electron microscopy studies in our laboratory have shown that nanoparticle chain aggregates (NCAs) of inorganic oxides have elastic properties. Measurements were made with titania, alumina, and iron oxide NCAs generated by laser ablation. Primary particles were 5–10 nm in diameter, and the mobility diameters of the NCAs studied were about 0.5 μm. NCA stretching appeared to begin with the rotation and/or sliding of adjacent nanocrystals. This led to a small change in the NCA length but allowed for chain straightening. Most of the NCA lengthening resulted from the separation of kinked chain segments held together by weak, probably van der Waals (vdw), forces. NCA strains up to 90% were observed. Calculated values for NCA deformation energies per unit volume were compared with those for conventional polymers; under certain conditions, the two deformation energies were of the same order of magnitude. These results may help explain the remarkable effects that nanoparticle reinforcing fillers such as carbon black and silica have on commercial rubber. It may be possible to improve the properties of composites of molecular polymers and NCAs through the use of NCAs with prescribed primary particle sizes, vdw-bond numbers, chain lengths, and morphological properties. Synthesizing such NCAs will require the use of modern concepts of aerosol aggregate formation. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2658–2665, 2000