Takehiro Dan

Preparation of new PTCR material by particle electrification processing

The purpose of the present work is to develop the materials with new functions by combining two kinds of particles electrified reciprocally. This paper reports a preparation method and the positive temperature coefficient of resistivity (PTCR) properties of complex particles consisting of semiconductive BaTiO3 granules and metallic indium powder particles. The conclusion obtained by the present experiment are as follows. (1) Vibrating cylindrical electrode can forced-electrify metal, semiconductor and insulator particles positively or negatively. (2) When the particles electrified reciprocally are mixed in the same region at the same time, complex particles can be created by the electrostatically attractive force working between the two kinds of particles. (3) Indium-semiconductive BaTiO3 complex particles made by this processing offer the new PTCR material which can be used in arbitrary shapes by filling and packing or drawing and painting.

Application of Forced Electrification for Preparation of Complex Particles

The purposes of the present work are to describe the importance of the application of forced electrification on complex particle preparation and to develop new materials with multiple functions by combining two kinds of particles electrified reciprocally. This paper reports a preparation method and the positive temperature coefficient of resistivity (PTCR) characteristics of composites consisting of semiconductive BaTiO3 particles and metallic indium powder. The forced electrification technique was applied to a complex particle preparation process and confirmed to be effective as follows: 1. A vibrating cylindrical electrode can force-electrify metal, semiconductor and insulator particles with positive or negative charges. 2. When two kinds of particles electrified reciprocally are mixed in the same region at the same time, complex particles can be produced by the electrostatically attractive force working between them. 3. Indium-semiconductive BaTiO3 complex particles made with this processing offer a new PTCR material which can be used in arbitrary shapes by simple packing. This behavior cannot be accomplished by the conventionally sintered PTCR materials.

Fabrication of microstructures and microdevices by the particle assemblage

We aim to fabricate microstructure and microdevices by integrating and arranging powder particles, i.e., the particle assemblage. We have developed three assembling techniques of the particles. The details of the assembling techniques and samples of the assembled microstructures are introduced. A manipulator is developed to manipulate and to weld metal particles by using a tungsten probe. Nickel alloy particles of 50 micrometers were piled on a gold substrate by the manipulator, and a leaning tower of the particles is fabricated. The array of the leaning tower is considered to act as an actuator. For the integration of a great number of particles, we developed another method based on the principle with the xerography. An electron beam or an ion beam is irradiated on an insulating substrate. An electrified pattern is formed on the substrate by the doped electron or doped ion. Fine particles are attracted to the pattern by the electrostatic force. Thus, we can arrange particles by immersing the substrate in the suspension of particles. The third is a productive method of ordered mixture by the electrostatic force. A self- thermostatic heater is made from the composite particles of BaTiO3 and In produced by the method.

Dispersive coating on electroceramic particles for fabrication of flexible sheet

Particles dispersively coated with other material is a kind of composite particles, i.e., core particles are dotted with other material. Two methods have been developed for such the composite particles. One is a forced electrification method and the other a rotating drum method. The former utilizes the electrostatic force, i.e., positively electrified core particles and negatively electrified child particles are mixed. The latter is a mechanical method as follows. Core particles and child particles are charged into a cylindrical vessel, and mixed by rotating the vessel for several hours. We prepared composite particles of PTCR (Positive Temperature Coefficient of Resistivity) barium titanate and the junction metal such as indium and solder. When the composite particles are filled, the junction metal always exists between the neighboring core particles. The PTCR property of the filling is almost the same with that of the sintered barium titanate. We fabricated a PTCR thin sheet by packing the composite particles between two sheet electrodes. If the composite particles are electrically connected but fixed not firmly, the sheet shows PTCR property and can bend by rearrangement of the particles. Thin ceramics sheet is practically impossible because of the brittleness. However, flexibility can be given to the sheet of the PTCR-junction metal composite particles. The composite particles are fixed by enveloping in an evacuated bag or by embedding in a heat resistant resin. Advantages and disadvantages of the preparation methods and fabrication methods are discussed. Preliminary experiments for a new approach to the PTCR sheet are introduced.

Application of composite particles to electronic devices

Electroceramic particles with electrodes of solder are prepared y a low cost and high productivity process. The electroceramic particles can be used as single particle devices, and moreover as multi-functional devices by their assembling. PTCR material is one of the electroceramics, having a positive temperature coefficient of resistivity. We prepare the PTCR particles with electrodes of solder as follows. Semiconducting barium titanate (BaTiO3) particles, a typical PTCR material, and solder particles are charged into a cylindrical vessel, and the vessel is rotated for several hours. The product is semiconducting BaTiO3 coated by solder particles. The solder particles are flattened out at the surface of the core particle. The solder forms small dot-like islands, and they are isolated each other. Several applications of such kind of composite particles are described. Single particle device is a PTC thermistor, which consists of one composite particle of semiconducting BaTiO3. Flexible and self-thermostatic sheets can be produced by packing the composite particles between two thin electrodes. Using NTC particles instead of the semiconducting BaTiO3 single particle devices of NTC thermistor and flexible NTC sheets can be produced. Twin particles device is a combination of a single particle PTC thermistor and a single particle NTC thermistor in series, and will be a V-type thermistor, having both PTC and NTC properties. The V-type thermistor can be obtained also by stacking the layer of PTC composite particles and that of NTC composite particles in series. It can be applied to a protective device.

I-V characteristics of the contact interface in a semiconductive BaTiO3-In composite particle

Abstract The authors previously fabricated semiconductive BaTiO 3 -In composite particles. The aggregate could be used as a new positive temperature coefficients (PTC) material, which could be used in arbitrary shapes, differing from the conventional rigid PTC materials. In the composite particle, the interface between the semiconductive BaTiO 3 particles and indium particles plays an important role. In this work I-V characteristics of the interface are investigated in detail. The conclusions obtained in this research are as follows. (1) The existence of indium particles at the interface between two semiconductive BaTiO 3 particles lowered the electric resistance markedly. This effect was ascribed to the good plasticity and a low value of the work function of indium. (2) In-Ga eutectic liquid alloy and physically vapor-deposited indium film satisfied Ohms law and did not form a Schottky barrier at the interface with the semiconductive BaTiO 3 material. (3) Physically vapor-deposited gold film formed a high electric resistance at the interface with the semiconductive BaTiO 3 material. This high resistance might be caused by a Schottky barrier.