Yukihiro Kanechika

Electron Spin Resonance of Defects Related to Thermal Conductivity in AlN Ceramics

Defects of AlN ceramics with a thermal conductivity from 102 to 216 W m-1 K-1 are investigated using electron spin resonance (ESR). Two ESR signals at g=2.006 and 1.999 are related to thermal conductivity. The g=1.999 signal intensity increases with a decrease in thermal conductivity, an increase in oxygen concentration, and an increase in Mg concentration. The g=1.999 signal is tentatively supposed to be caused by an electron-trapped center. The g=2.006 signal intensity is increased with an increase in thermal conductivity, a decrease in oxygen concentration, and an increase in Ca concentration. A defect responsible for the g=2.006 signal is assigned as a hole trapped in an ON–VAl complex.

Thermal Conductivity and Cathodoluminescence of AlN Ceramics Sintered with Ca3Al2O6 as Sintering Additive

Aluminum nitride (AlN) ceramics with various amounts of Ca3Al2O6 (C3A) as a sintering additive were sintered at 1880°C for 50 h in N2 atmosphere. The thermal conductivity of AlN ceramics increased with increasing amount of C3A in the range from 0.5 to 4.8 mass%. Cathodoluminescence (CL) intensity attributed to oxygen-induced defects decreased with increasing amount of C3A. From the results, the increase of the thermal conductivity was considered to relate to the decrease of the oxygen-induced defects by increasing amount of C3A.

Coloration and thermoluminescence of translucent AlN ceramics sintered with Ca3Al2O6 as sintering additive

Coloration of translucent AlN ceramics sintered with Ca3Al2O6 as a sintering additive occurs by exposure to ultraviolet light. The trap related to this coloration was investigated by thermoluminescence (TL) measurements. With increasing oxygen content, the TL intensity increased, reflecting an increase in the trap concentration in the samples. The thermal activation energy of the trap also decreased with decreasing defect density. The trap is considered to be an oxygen-induced defect.

In Situ High Resolution Transmission Electron Microscopy Studies of High Temperature Behavior of Surface Al2O3 Thin Layer on an AlN Particle

A high temperature HRTEM holder equipped with a W-coil heater was used to make insitu observation of high temperature behavior of Al2O3 very thin (about 1 nm in thickness) protective film on AlN particles. The film was used to prevent AlN particles from damages by moisture. Rapid melting and rapid solidification of very small Al2O3 particles of about 2 nm in diameter were found within about 0.2 seconds. Therefore we concluded that the Al2O3 protective film worked as the sintering additives in the high temperature heating process. In the present study, very small Al2O3 particles were identified by the space between observed lattice fringe images. It was found that a tilt boundary was instantaneously formed and annihilated in an Al2O3 particle. There was also evidence that showed the formation and annihilation of edge dislocations within seven seconds during sintering.

Temperature Dependence of Cathodoluminescence for AlN Ceramics Sintered with Ca3Al2O6

Aluminum nitride ceramics were sintered with 1.0 and 4.8 mass% Ca3Al2O6 (C3A) as a sintering additive. Temperature dependence of cathodoluminescence (CL) for the ceramics was investigated in order to obtain information on lattice defects. The CL peak intensity at 3.5 eV in the ceramics sintered with 1.0 mass% C3A decreased with increasing temperature, so called thermal quenching. The maximum CL peak intensity of the ceramics sintered with 4.8 mass% C3A was much lower than that with 1.0 mass% C3A, reflecting that the oxygen-induced defect density dramatically decreased with increasing amount of C3A. In case of the ceramics sintered with 4.8 mass% C3A, the CL peak intensity at 3.4 eV showed the thermal quenching in the range of 130 - 350 K, whereas in the range of 80 - 130 K and 350 - 475 K, it increased with increasing temperature, so called “negative” thermal quenching. From the results, we suggest a presence of at least two trapping levels in the ceramics sintered with C3A.