**◆ Project Research Report: "Introduction to the Joint Research Project for the Development of High-Functionality Materials through Fusion of Unique Structure Metals and Inorganics in University Collaboration" ◆**

Activity Status of Electronics Materials Development Group

Hiroshi Kawarada and Toshio Kamiya

(Graduate School of Advanced Science and Engineering, Waseda University, Tokyo. Materials & Structures Laboratory, Tokyo Institute of Technology, Tokyo)
Keywords: piezoelectric materials, carbon nanotube (CNT), bio-sensing, a-IGZO TFT, topological insulator
Received March 2, 2015 [doi:10.2320/materia.54.232]

**Microelectromechanical System Devices Using Lead-Free Piezoelectric Ceramic Thin Films**

Regulations regarding the use of materials containing hazardous elements are progressing, mainly in Europe. Since currently commercialized piezoelectric ceramic materials are mainly lead-based oxide Pb(Zr, Ti)O3 (PZT) systems, the development of lead-free piezoelectric materials is an urgent issue. Among various lead-free materials, (K, Na)NbO3 (KNN) is attracting attention as a compound with a relatively high Curie temperature and excellent piezoelectric characteristics. The EcoTopia Science Institute at Nagoya University is thinning KNN-based compounds using a chemical process with a metal-organic compound precursor solution, which allows for high homogeneity, precise composition control, and low-temperature synthesis. To control the characteristics of KNN thin films to obtain desired properties, hetero elements are substituted or doped into KNN. Doping with the multivalent ion Mn solves the major problem of decreased electrical insulation. The mechanism is that Mn ions present in the thin film in the Mn2+ or Mn3+ state trap carriers in the thin film, resulting in improved insulation (1). Currently, we are conducting evaluations of the characteristics and examining the device application of thin films in collaboration with the Waseda University Organization for University Research Initiatives.

Figure 1: Electron micrograph of a cantilever-type (K, Na)NbO3-based thin film after microfabrication.

**Micro-Joining Technology Utilizing Nanoporous Structures**

In order to increase the efficiency of electrical energy and the ratio of renewable energy, power modules and energy modules are attracting attention. Power modules control current during operation, and the amount of heat generated increases as the current being controlled increases. In addition, miniaturization and weight reduction of modules cause temperature increases due to high-density mounting of components, raising concerns about performance degradation of semiconductor devices in such high-temperature environments. Advancement of each elemental technology within the device, including bonding technology, is also essential. Currently, high-melting-point solders containing harmful substances such as Pb (Pb-5Sn, etc.) are mainly used for such joints, but due to increasing environmental awareness, establishing alternative materials that do not contain harmful substances and their joining processes is an urgent issue. Therefore, the Joining and Welding Research Institute at Osaka University is working on the construction of a new micro-joining technology utilizing nanoporous structures in joint research with the Waseda University Organization for University Research Initiatives, with the aim of establishing alternative materials for high-lead-containing solders (Pb-5Sn, Pb-10Sn solders, etc.) used in power devices, and alternative joining processes for them. By controlling the joining process using Au nanoporous materials made from Au-Ag alloys (Figure 2), Cu/Cu joining and Au plating/Au plating joining are possible, and it has been clarified that a joining strength of 20 MPa or more, equivalent to that of high-lead-containing solder, can be obtained (2)(3).

We are promoting the development of cantilever-type actuators (Figure 3) that combine material technology and device processing technology, as well as the development of measurement of conversion of natural energy such as vibration into electrical energy, regarding the analysis of various electrical characteristics including strain sensitivity and the effect of microfabrication on those characteristics.

**Electrode for SiC Power Semiconductor Using Carbon Nanotubes**

The EcoTopia Science Institute at Nagoya University developed SiC surface

Project Report