Prototype of Phase-Change Channel Transistor for Both Nonvolatile Memory and Current Control

We prototyped phase-change (PC) channel transistors and demonstrated two functions of nonvolatile memory and channel current control. We have developed prototype transistors that use a PC channel instead of a silicon channel. The PC material of a Ge₂Sb₂Te₅ thin film with a thickness of 50 nm was used. We demonstrated a memory function whereby we achieved a reversible change between the crystalline and amorphous phases by applying a source-drain (SD) voltage for Joule heating. In the experiment, the applied voltages for PC between amorphous and crystalline phases were from 5 to 8 V. Control of the channel current was realized by applying a gate bias. The SD current was suppressed to less than 1/20 of that at a gate bias of -3 V by applying a gate bias of 0-3 V     

Synthesis of Cobalt Nanoparticle and Fabrication of Magnetoresistance Devices by Ion-Assisted Aerosol Generation Method

The ionization chemical vapor deposition (ionization CVD) method, which is one of the ion-assisted aerosol generation methods, was used to synthesize Co nanoparticles and fabricate a magnetoresistance device using them. A cobalt tricarbonyl nitrosyl vapor is ionized by a high-pressure ionizer before being fed into the reactor. It reacts and forms nanoparticles by a thermal decomposition reaction in the furnace reactor. Particles deposit electrostatically on an insulator substrate that has two Au electrodes and fill the gap between the electrodes. This Co-nanoparticle device is then annealed under hydrogen gas to deoxidize the deposited particles. After annealing, two copper wires are attached to the two Au electrodes to connect with a DC voltage supplier and an ammeter. The magnetoresistance of the device was evaluated by measuring its electrical resistance using a superconducting quantum interference device (SQUID) magnetometer. The X-ray diffraction patterns of the nanoparticles before and after annealing revealed CoO and Co, respectively. Two fabricated devices with number densities of Co nanoparticles of 4.25 × 10¹⁰ and 1.16 × 10¹¹ cm^?2 showed magnetoresistance ratios of 73% and 1002%, respectively, at an applied voltage of 30 V, a measurement temperature of 5 K, and a magnetic field of ?1 ～ 1 T. It was found from the experimental results that the method developed in this article was useful to fabricate the Co-nanoparticle magnetoresistance device.     

New Pb-based 1212 Superconductor Containing Phosphorus, (Pb0.75P0.25)Sr2(Y1?xCax)Cu2Oz

New Pb-based 1212 compounds containing phosphorus have been discovered in the (Pb_1−y P _y )Sr₂(Y_1−x Ca _x )Cu₂O _z system; almost the single 1212 phase samples can be obtained for the composition range of 0.0≤x≤0.6 and y=0.25. The crystal structure for each sample has a tetragonal symmetry with the typical lattice parameters a=0.3828 nm and c=1.182 nm. Among them, the sample with x=0.6 and y=0.25 shows the onset of resistivity drop at about 39 K and zero-resistivity at about 17 K. Moreover, the sample shows a diamagnetic signal at about 38 K. These phenomena are found to originate from superconductivity with the bulk feature.     

Post-functionalization of poly(3-hexylthiophene) via anodic chlorination

Selective anodic chlorination of a poly(3-hexylthiophene) was successfully carried out by electrochemical polymer reaction. NMR and EDX analyses revealed the selective and sufficient substitution of chlorine atom at the 4-position of the repeating thiophene ring. GPC measurement of the polymer before and after electrolysis indicated that neither decomposition nor propagation of the polymer occurred even after passage of the excess charge. The optical and electrochemical properties of the obtained chlorinated polymer were investigated in detail.     

Lateral SbTeN based multi-layer phase change memory for multi-state storage

X-ray diffraction patterns and resistivity measurement indicate that as-deposited N-doped Sb₂Te₃ (STN) films become amorphous while the as-deposited Sb₂Te₃ film is crystalline. A lateral as-deposited STN-based multi-layer phase change memory was proposed for multi-state storage. The active region of the device consists of a top 30-nm TiN/180-nm STN/20-nm TiN/bottom 120-nm STN stacked multi-layer. Static switching properties of the device with STN initially starting from the amorphous state exhibit two apparent S-shaped switchings, which correspond to two marked device resistance drops by a factor of 2-5. The first and second threshold voltages are around 2.8-3.2 and 4.3-5.4 V, respectively. Finite element analysis of the device shows that the two switchings could sequentially occur at the electrode steps from the bottom 120-nm STN layer to the top thick 180-nm STN layer.     

Acetylacetoin synthase as a marker enzyme for detecting the 2,3-butanediol cycle

Acetylacetoin synthase (AACSase) and acetylacetoin reductase (AACRase) are representative enzymes of the 2,3-butanediol cycle. After examining their induction conditions in various bacteria, the former was induced by acetoin and the latter by glucose. All strains carrying AACSase also had AACRase, but the reverse was not true. Therefore, AACSase indicates the existence of the cycle. Acetylacetoin (AAC) accumulation or the ratio of 2,3-butanediol isomer formed also indicated the presence of the cycle in bacteria. This cycle is present in some strains and not in others even for those belonging to the same species. The cycle was not always associated with the representative 2,3-butanediol-producing bacteria or bacterial sporogenesis as reported previously.     

Scanning electron microscope for in situ study of crystallization of Ge2Sb2Te5 in phase-change memory

By introducing electrical connections into the chamber of a scanning electron microscope (SEM) via its holder assembly, it has become feasible to in situ observe and electrically characterize electronic devices. The in situ SEM was applied to investigate electric-pulse-induced behavior of Ge(2)Sb(2)Te(5) in a lateral phase-change memory cell. Randomly distributed nuclei with sizes from 20 to 80 nm were initiated at a low voltage pulse. Initially, grain growth depended strongly on pulse amplitude at around 60.3 nm/V and then a weak pulse amplitude dependence was observed at around 13.5 nm/V. Device resistance during crystallization dropped by two to three orders of magnitude with two falling steps, which probably resulted from amorphous to face-centered-cubic and subsequently to hexagonal transitions, respectively.     

Echo state networks for embodied evolution in robotic swarms

Artificial Life and Robotics - Embodied evolution is an evolutionary robotics approach that implements an evolutionary algorithm over a population of robots and evolves while the robots perform...     

Superconductivity and Ferromagnetism of the Ru-1232 Compounds in the (Ru1−x Nb x )Sr2(GdCe1.8Sr0.2)Cu2O z System

The Ru-1232 compounds have been synthesized in the (Ru_1?xNb _x )Sr₂(GdCe_1.8Sr_0.2)Cu₂O _z system, and effects of Nb substitution for Ru on superconductivity and ferromagnetism of the Ru-1232 compounds have been investigated. First, X-ray powder diffraction study shows that nearly the single 1232 phase samples can be obtained in the x composition range from 0.0 to 0.3. Then, from the electrical resistivity study, it is found that each of the samples shows resistivity dropping phenomenon at two temperatures of T _c ^l and T _c ^h, which originates from superconductivity of the Ru-1232 phase and the Ru-1222 one, respectively. Both of the starting temperatures are lowering with increasing Nb content x. Lastly, from the magnetic susceptibility study, it is found that superconducting transition temperature T _c is 20 K for the Ru-1232 sample with x = 0.0 and the ferromagnetic transition temperature T _m is about 90 K. This study also shows that both of the values of T _c and T _m become low with increasing x from 0.0 to 0.3.     

Repulsive delayed random walk

We studied a random walk with delayed feedback around an unstable fixed point. It was found that the random walker can be kept around the fixed point with longer delays. This is in contrast to the normal role of delay, which is generally thought to be a source of instability. We discuss the connection of our model to stick-balancing experiments, and propose new type of control paradigm called “delayed stochastic control.” This work was presented in part at the 9th International Symposium on Artificial Life and Robotics, Oita, Japan, January 28–30, 2004