Multilayer Actuator Products in Japan

It has been a decade since cofired multilayer piezoelectric ceramic actuators became a commercial item in Japan led by the effort at NEC. Tokin Corp. since then has purchased the license from NEC to produce the same type actuators. The PI spent six months Oct. 1991-March 1991 at Tokin Corp. R and D Lab in Sendai to study multilayer actuator development and reliability issues. Multilayer actuators can be divided largely into two categories one is a stack type, in which sintered disks are stacked with an alternate electrode in between each ceramic disk, and the other is a cofired type. There are various structures within the cofired multilayer actuators A ceramic multilayer capacitor MLC type, B plate-through with application of insulator at alternate electrodes, and C slits or gaps with MLC structure type. Each type has its own advantages and disadvantages, which are summarized in this report. A new structure actuator which does not belong to above categories, a three-dimensional interdigital electrode structure 3D-IDE, is being developed at Tokin Research Lab. The number of fine electrode lines controls the multiplication of piezoelectric effect, and multilayering is performed perpendicular to the displacement direction. Preliminary test results indicate that the 3D-IDE provides improved reliability compared with commercial plate-through type multilayer actuators.